study of astm c 1262 test variations and damage evaluation ... · study of astm c 1262 test...
TRANSCRIPT
National Concrete Masonry Association Foundation
STUDY OF ASTM C 1262 TEST VARIATIONS AND
DAMAGE EVALUATION
FINAL REPORT
Submitted by
Cornell University
FINAL February 5, 2009
February 5, 2009
FINAL REPORT ii
EXECUTIVE SUMMARY
In the spring of 2005 the National Concrete Masonry Association Foundation
(hereafter referred to as NCMA) provided funding to Cornell University (Cornell) to
support an experimental program to investigate sources of variability in the ASTM C
1262-98 test method. (ASTM C 1262-05 was released as this project was in progress.)
The NCMA project specifically addressed issues in the following categories:
1. ASTM C 1262 inherent test variability (significance of variations within the
test method)
2. Performance criteria assessment (i.e., what does “mass loss” as measured via
ASTM C 1262 represent in terms of other material properties?)
3. Between-freezer performance comparison of test specimens (when both
freezers meet ASTM C 1262 requirements)
To investigate Item 1, seven different Test Sets (identified from A to G) covering
variations in solution depth, specimen size and shape, and container size and shape
were tested in a Tenney freezer on loan from the NCMA. In addition, specimens
similar in size, shape and solution depth to those of a particular Test Set (Set A) were
tested in a walk-in environmental chamber meeting ASTM C 1262. These tests were
all conducted in saline solution (3% sodium chloride salt by mass of solution). For all
specimens in this study, freeze-thaw performance (Item 2) was evaluated through:
• ASTM C 1262 percent mass loss
• ASTM C 215 resonant frequency
• ASTM C 597 pulse velocity
• a modified ASTM C 672 visual scaling rating
• modulus of rupture (MoR)
February 5, 2009
FINAL REPORT iii
Each of these tests detected specific forms of specimen damage (i.e., internal damage
vs. external surface damage), and measuring these parameters for all specimens
enabled correlating these parameters to one another. The specimens tested in the
walk-in chamber were initially intended to yield data on MoR for mass loss less than
2%. This separate family of specimens however enabled a valuable comparison on
between-freezer variability (Item 3) as will be described ahead. Detailed discussions
on methods employed and test results are covered in this report. Immediately
following this Executive Summary is an overview of the research on SRW durability
conducted at Cornell University (in partnership with The University of Texas at
Austin) and how this NCMA study fits relative to other areas of study. A list of
references for work published or submitted for publication is also included.
One of the first steps prior to start of freeze-thaw testing was to survey the freezers for
their internal temperature spatial variability. Freezer surveys were essential to
understand patterns of internal temperature distribution in the freezers and to enable
better planning of test cycles through the development of R-curves (which relate the
proportion of specimen locations in the freezer compliant with ASTM C 1262
requirements to the length of cooling). One important finding from these surveys was
that using the Tenney freezer’s built-in temperature sensor to control cycle length can
lead to a large number of undercooled locations (i.e., locations not meeting the
minimum 4-hr cold soak required by C 1262). If the freezer were programmed for a –
18 ± 5°C (0 ± 10°F) cold soak for 4 hours based on this sensor, it is possible for all
specimen locations to be undercooled. For the freezers used in the NCMA study, a
cold soak of 4.6 hours in the Tenney freezer and 4.8 hrs in the walk-in freezer (based
on average internal temperature) were determined to maximize the number of
specimen locations in compliance with ASTM C 1262.
February 5, 2009
FINAL REPORT iv
Key findings from the NCMA study are presented below. The corresponding section
in the report where more detailed information can be found is shown in parentheses.
Effect of Variations in the ASTM C 1262 Test Method
1. Variations in solution depth, specimen and container sizes led to variations in
specimen performance in all measured parameters (mass loss, resonant frequency,
pulse velocity and scaling rating) (5.1, 6.1, 7.1, 8.1). With respect to mass loss,
these observed differences were determined to be statistically significant up to
approximately 1 to 1.5% mass loss (5.4). In particular, increasing the mass of
solution relative to the mass of specimen (i.e., ratio of msolution/mspecimen) increased
mass loss (5.2). For the specimens evaluated, this ratio was increased in any of the
following ways:
adding more solution to a test container (increasing solution depth), or
decreasing the specimen size for a given container size
These results indicate that specimen and container size must be specified in the test
method to minimize test variability. Specifically, specimen and container sizes
must be specified such that the ratio msolution/mspecimen is maintained approximately
constant. As reference, a 100 × 200 × 32 mm (4 × 8 × 1¼ in.) specimen
surrounded by 300 g of solution has a msolution/mspecimen equal to 0.20.
2. The relative performance ranking among Test Sets (based on any of the measured
parameters) up to 50 cycles (generally less than 0.25% mass loss) was not
representative of their rankings after 100 cycles (typically 0.5 to 1% mass loss)
(5.1, 6.1, 7.1, 8.1). While some general patterns have emerged for mass loss with
number of cycles, observed exceptions to these patterns advise caution when
making predictions of either mass loss at the 100th cycle, or the number of cycles
February 5, 2009
FINAL REPORT v
until 1% mass loss results is achieved, if such predictions are on the basis of early
test results.
Comparison of Specimen Evaluation Methods
3. The resonant (or fundamental) frequency is the lowest frequency at which a
specimen vibrates in a particular mode (e.g., flexural, torsional or longitudinal).
Progressive changes in the state of the specimen due to freeze-thaw damage can be
detected through changes in the resonant frequency of the specimen. These
changes are denoted by the Relative Dynamic Modulus (RDM), defined as
follows: RDM = (fn/fo)2×100%, where fn is the resonant frequency of the specimen
after n freeze-thaw cycles and fo is the initial (pre-freeze) resonant frequency.
Resonant frequency testing (based on ASTM C 215) was conveniently performed
on SRW specimens, and the sensitivity of this property to changes in structural
integrity of specimens makes this test valuable for evaluating freeze-thaw damage
of SRW specimens. For conventional concretes, an RDM of 60% is used as
threshold, and this value was adopted in this study as a reference value (3.4, 6.1).
4. Pulse velocity refers to the speed of compression pulse waves through concrete
and is also used to assess the internal state of specimens. Pulse velocity testing
(ASTM C 597) was also conveniently performed on SRW specimens in this study,
although this test was not as sensitive to internal damage as resonant frequency
tests (3.5, 7.1, 7.2, 7.3).
5. Visual scaling rating in the manner conducted in this study did not appear adequate
for detection of specimen cracking or loss of structural integrity until beyond 1%
mass loss, at which point spalling and pitting of specimen surfaces (which are
detected through scaling rating) accompanied cracking (detected from changes in
resonant frequency) (3.6, 8.1, 8.2).
February 5, 2009
FINAL REPORT vi
6. Overall, below mass loss of about 0.5%, mass loss was the most sensitive to
changing specimen condition (primarily due to loss of material from the sides of
specimens). Attention must be paid to isolated events such as popouts whose
significance to overall specimen condition can be better discerned by observing
actual rates of mass loss (5.3, 6.3, 7.2, 8.2).
7. Beyond about 0.5% mass loss however, once cracks started forming, resonant
frequency appeared to be more appropriate for evaluating specimen condition.
This is because resonant frequency is far more sensitive than mass loss to internal
damage and cracking (6.3).
8. Risky Specimens were defined as those with mass loss of 0.8 to 1.2% but with
RDM less than 60%. Approximately one-third of all specimens tested in the
Tenney freezer fell into this category. For these specimens, a 1% mass loss
(typically from the exterior surface) may not have been indicative of internal
damage, and at 1% mass loss, these specimens exhibited RDM of 3 to 76%. This
suggests that for some specimens and test conditions, acceptance based on a 1%
mass loss limit could result in acceptance of specimens that have been internally
damaged to a significant degree (6.3).
9. At mass loss of 0.8 to 1.2%, approximately 1/5 of all specimens tested in the
Tenney freezer exhibited pulse velocity values that were less than 90% of their
initial value (8.2).
10. Prior to shipment to Cornell, independent lab evaluation of the SRW units selected
for study indicated average absorption values of 5.6 to 5.9% (relative to the oven-
dried mass of the samples) when tested in accordance with ASTM C 140 (2.1.1,
Table 3). For the coupons shipped to Cornell for testing, the average1 moisture
1 For specimens tested at Cornell the term “average” moisture content reflects the fact that a specimen has a non-uniform distribution of internal absorbed moisture content, which is “averaged” over the specimen as a whole via standard test methods.
February 5, 2009
FINAL REPORT vii
content of representative samples obtained from ASTM C 642 (boiled absorption)
was about 7.0-7.4% (boiled immersion leads to a higher degree of saturation). For
dry coupons that were immersed for 24 hr immediately prior to freeze-thaw
cycling, average moisture content was measured as 4.7-4.9% (by mass). Over the
course of freeze-thaw cycling the mass of water absorbed in the coupons increased
with increasing freeze-thaw cycles beyond that amount absorbed over the first 24
hours. After 100 cycles of freeze-thaw testing, moisture contents had increased to
5.4-6.0% (approximately the same as obtained by C 140 testing), and after 150
cycles, moisture contents had increased slightly again to a range of 5.4 to 6.3% .
As discussed in this report, increased water absorption may be due to the tendency
of freeze-thaw cycles to pump additional water into pores, or to water absorption
into microcracks caused by freeze-thaw damage, or to both mechanisms. (5.5.2)
11. .When coupon performance as indicated by Relative Dynamic Modulus was
compared with the continuously increasing moisture content of the coupons, it was
observed that above moisture contents of 5.5-5.8% RDM values diminished
rapidly with increasing cycles. RDM changed little as long as moisture content
remained below this 5.5-5.8% range. Adopting a term from the portland cement
concrete durability literature, this moisture content threshold above which RDM
diminished rapidly is herein called the “critical moisture content.” This range of
critical moisture content was applicable over all seven Test Sets in the Tenney
freezer and for specimens tested in either of the two freezers, which indicates that
this parameter is likely to be a fundamental material property of the specific
masonry material evaluated in this test series.(6.4.1, 6.4.2).
12. Recall that for these specimens, average moisture content prior to freeze-thaw
testing per ASTM C 140 was 5.6 to 5.9% (2.1.1, Table 3), while the average
moisture content at saturation (obtained from ASTM C 642 boiled absorption) was
February 5, 2009
FINAL REPORT viii
about 7.0-7.4%. Thus, critical degree of saturation (calculated as critical moisture
content divided by moisture content at saturation) was 76 to 83% of the boiled
absorption, and about 95 to 100% of the ASTM C 140 absorption. As will be
documented, the critical degree of saturation for ordinary concretes has been
reported in the range of 75 to 90% of the boiled absorption values. Recall also that
the term “average” moisture content refers to an entire specimen for which it
would be expected that some pores (perhaps larger or closer to the exterior
surface) may be fully saturated while smaller pores at greater depth may be
relatively dry. It is therefore important to distinguish such values from the term
“critical saturation” as it is commonly applied in the portland cement concrete
freeze-thaw literature, in which an individual pore is “critically saturated” when it
is more than about 91% full, thus having insufficient free volume to accept the 9%
expansion of water as it turns to ice upon freezing. (6.4.1, 6.4.2).
13. Measured moisture contents were used to determine “moisture gain” which is the
additional moisture absorbed by the specimen after start of freeze-thaw cycling
(i.e., moisture absorbed by specimen beyond that absorbed during the initial 24-hr
immersion). Moisture gains typically were 0.6-1.1% after 100 cycles and 0.7-
1.5% after 150 cycles. At the critical moisture content of 5.5-5.8% mentioned in
Point 11, moisture gains were about 0.8-1.1% (6.4.1, 6.4.2). Moisture gain values
were found to be more repeatable among specimens in a Test Set in the Tenney
freezer and among all specimens in the walk-in chamber. This makes this
parameter valuable for inclusion in the ASTM C 1262 test method, considering
that the measurement of specimen moisture does not require significant changes to
current test procedures (11.10).
14. Modulus of rupture (MoR) (or flexural strength, ASTM C 78) of specimens
generally decreased with increasing mass loss. At less than 0.8% mass loss, MoR
February 5, 2009
FINAL REPORT ix
values ranged anywhere between approximately 4 to 100% of their initial,
undamaged value. At mass loss greater than 0.8% however, most MoR values
were below 40% of their initial, undamaged value (9.1).
Between-Freezer Performance Comparison of Specimens
15. Testing of specimens in separate freezers, both of which complied with ASTM C
1262 temperature-time requirements, resulted in dramatically different
performance of otherwise similar specimens. After 100 cycles, Test Set A
specimens in the Tenney freezer exhibited mass loss of 0.4% compared to 0.2%
for specimens in the walk-in freezer (factor of 2). After 200 cycles, Test Set A
specimens in the Tenney freezer exhibited mass loss of 4.4% compared to 0.8%
for specimens in the walk-in freezer (factor of 5.5). Substantial differences were
also observed in resonant frequency changes, pulse velocity changes and visual
scaling rating (10.1, 10.2, 10.3, 10.4).
16. Despite both freezers being compliant with ASTM C 1262 temperature-time
requirements, differences were measured in actual rates of temperature change
(cooling or warming) as follows (10.5):
The air inside the Tenney freezer was cooling about 3 times faster than the
air in the walk-in freezer at the onset of ice formation in the solution
surrounding the specimens.
The solution surrounding the specimens froze approximately 1.5 times
faster in the Tenney freezer than in the walk-in freezer.
The solutions reached different minimum temperatures during cold soak.
In the Tenney freezer, the solution temperature reached –18°C (0°F); while
in the walk-in freezer, the solution temperature reached –14°C (7°F).
February 5, 2009
FINAL REPORT x
Before ice melted, the peak warming rate of freezer air was 1.5 times faster
in the Tenney freezer than in the walk-in freezer. Moreover, the peak
warming rate of solution (i.e., the still frozen solution) was 2.5 times faster
in the Tenney freezer than in the walk-in freezer.
The above factors mean that specifying only the cold and warm soak lengths and
durations is not sufficient to ensure similar exposure of specimens. It is necessary
that a complete freeze-thaw cycle be specified which includes cooling rate, cold
soak length and duration (with tighter temperature tolerances), warming rate and
warm soak length and duration. Further research is needed to determine how each
of these parts of the freeze-thaw cycle affect overall specimen performance. For
example, studies could be conducted in which the warming (and thus thawing)
rates are varied (while maintaining the other parts of the cycle constant) to
determine the effect of variations in warming rate on specimen performance.
From the results and observations in this NCMA study, and the dissertation by Chan
(2006), modifications to the ASTM C 1262 test method have been suggested. These
revisions are targeted specifically for the freeze-thaw testing of SRW units and may or
may not apply to other manufactured concrete masonry products. Major modifications
are included in the following areas:
Specimen and container sizes
Although the results are scattered, it is clear that for the specimens and test
conditions used here test results are influenced by the selection of specimen
size and container size. As a corollary to this observation, variable results are
to be expected for tests performed on coupons cut from identical SRW units
when differing coupon sizes and differing containers are used. Based on this
study it appears that mass loss is increased when a small coupon with a high
February 5, 2009
FINAL REPORT xi
surface to volume ratio is placed in a container that is considerable larger than
the coupon. Alternatively, mass-loss is apparently decreased when a large
specimen with a low surface to volume ratio is placed in a container that is
only slightly larger than the coupon. For this reason it is recommended that the
range of specimen and container sizes currently permitted in ASTM C 1262 be
narrowed to reduce variability in results. It is recognized that the array of
available SRW unit geometries makes it difficult to precisely define a standard
coupon, which in turn makes it difficult to define a standard container. The
requisite and practical degree of flexibility thus called for nevertheless
contributes to variability in C1262 test results. The very highest quality
specimens and the lowest quality specimens may not be sensitive to such
factors—they are likely to pass or fail regardless of coupon or container size.
Specimens of an intermediate grade are the most likely to be influenced by
specimen and container size.
Specimen sampling and preconditioning
In previous studies it was observed that the material properties of coupons vary
depending on the locations from which they were extracted from the SRW unit
(perhaps due to compaction and curing). Thus the problem of reducing test
variability by narrowing the range of permitted coupon and container size is
compounded by the desire to standardize the location and orientation of
coupons relative to the SRW unit. If it were consistently practical to do so one
might recommend that specimens be sampled from the back face of the units
(i.e., the face parallel and opposite to the split face). Variability would also be
reduced by sampling such that the specimen primarily contains material from
the mid-height (relative to the casting direction) of the unit. In regard to
preconditioning of coupons, it is suggested that given the importance of
February 5, 2009
FINAL REPORT xii
specimen moisture content on behavior during freeze-thaw testing, variation in
pre-test moisture content may be one source of inter-laboratory variation in test
results (the higher the pre-test degree of saturation, the sooner freeze-thaw
damage may occur). For that reason it is suggested that in lieu of the current C
1262-mandated “less than 80%” humidity of the pre-test conditioning
environment, a more restrictive 45 to 55% range be required.
Freezer survey
As described in Appendix A, a survey should precede actual freeze-thaw
testing to evaluate the variability of temperature inside the freezing unit.
Calibrated temperature sensors should be placed at specimen locations in the
freezer (e.g., at each shelf and located in such manner that front-back and left-
right variations in the freezer are captured). The survey should also be done
using the same number, mass and arrangement of specimens that will be used
in actual testing. Decisions on cycle length for actual tests should then be
based on the survey results through the use of R-curves (mentioned earlier). A
key issue in surveying the freezer and defining the freeze-thaw cycle is
understanding the differences among:
♦ the temperature used to control the freezer (typically an air temperature
indicated by a sensor installed near the conditioned air entering the
chamber)
♦ the temperature of the air in the immediate vicinity of the containers
♦ the temperature of the air inside the containers,
♦ the temperature of the solution inside the containers,
♦ and the temperature within the coupons themselves.
The “control” temperature is often the most extreme of these values and thus is
often not the average value. The purpose of the freezer survey is to establish
February 5, 2009
FINAL REPORT xiii
these relationships so that a reliable, repeatable, and meaningful freeze-thaw
environment can be controlled for an acceptably high fraction of all specimens
over any given cycle, and for all specimens over the entire duration of the test.
Freeze-thaw cycle
Evaluation of the spatial variability and cooling capacity of the freezers used in
this study, in concert with the C1262 requirements, resulted in the specific
cooling rates, temperature and duration of cold soak, warming rates and
temperature and duration of warm soak reported here. Thus the detailed
characteristics of the freeze-thaw cycle were engineered to comply with C
1262 in this specific freezer unit loaded with 28 specimens of the coupon mass
and water volume described.
Resonant frequency and moisture content measurements
Given the sensitivity of resonant frequency to specimen geometry, pre-
conditioning, moisture content, and internal damage of specimens,
modifications are suggested for adapting ASTM C 215 (Standard Test Method
for Fundamental Transverse, Longitudinal, and Torsional Resonant
Frequencies of Concrete Specimens) for use with SRW unit freeze-thaw
coupons.
Through these studies, it was also evident that there are other areas requiring further
research. Of these, the major ones include:
Effect of freeze-thaw cycle on specimen performance
Future research should consider the effects of varying each parameter of the
freezer air cooling curve – cooling rate, cold soak length (4 hrs vs. 5 hrs), cold
soak temperature, warming rate and warm soak length (2.5 hrs vs. say 6 hrs) –
February 5, 2009
FINAL REPORT xiv
on ensuing specimen performance. This information will be valuable for
future revisions of the ASTM C 1262 test standard.
Investigating other SRW mixtures
While the behavior of resonant frequency and pulse velocity relative to mass
loss and moisture content were determined for one specific SRW mix in this
study, it is recommended that other mixtures be evaluated in the same manner
to determine if the trends observed in this study prevail with other mixtures.
Other mixtures may include mixtures of known lower and higher frost
durability than the one tested here as well as mixtures from other SRW unit
manufacturers.
Evaluating between-unit variability
Between-SRW unit variations (i.e., differences between units) even for units
produced within the same production run should also be investigated. The
reason for this proposition is based on variations observed even within Test
Sets (see for example mass loss for Test Set B and RDM vs. mass loss for Test
Set D). Variability of mix properties and performance should be evaluated for
units manufactured within the same day or on different days within the same
week. The effect of curing (i.e., temperature, relative humidity and length) and
storage conditions (e.g., weather and temperature) on SRW unit performance
should also be investigated further. Other production variables such as quality
of aggregates, mixture proportion and frequency and duration of compaction
may also be studied for their influence on between-unit variability.
February 5, 2009
FINAL REPORT ii
Overview of SRW Durability Research at Cornell University (in partnership with The University of Texas at Austin)
A. SRW MATERIAL CHARACTERIZATION • ASTM C 140 properties • ASTM C 457 microscopy • Within-unit variability of
properties • Significance of split surface
delaminations • Sampling procedures
B. DURABILITY UNDER NON-FROST CONDITIONS • Continuous immersion in
solutions of different types of deicing chemicals
• Rising damp of salt solutions
C. FROST DURABILITY • Freeze-thaw resistance of SRW units
from multiple manufacturers • Freeze-thaw resistance of SRW units
under different types of deicing chemicals
• Significance of paste and compaction void volume fraction on freeze-thaw resistance
• Frost Durability Indices
G. ASSESSMENT OF SPECIMEN CONDITION • Methods: mass loss,
resonant frequency, pulse velocity, visual scaling rating, modulus of rupture, moisture content
• significance of mass loss
F. SIGNIFICANCE OF VARIATIONS WITHIN ASTM C 1262 • Effect of solution depth,
specimen and container size and shape
• Between-freezer comparison of specimen performance
E. CHARACTERISTICS OF FREEZE-THAW CYCLE • Air vs. specimen cooling
curves • Water vs. saline:
- ice formation quantities and rates - ice formation mechanisms and damage
• Variations in cooling curves • Cooling and warming rates
D. FREEZE-THAW APPARATUS AND OTHER EQUIPMENT • Freezer characteristics:
- internal temperature distribution - cooling (and warming) capacity
• Freezer reliability (R-curves) • Temperature measuring devices
xivD
RA
FT REPO
RT
February 5, 2009
FINAL REPORT xv
These areas of study are covered in the following documents (shown with check
marks):
Study Area Hance (2005) a Chan (2006) b FHWA report c NCMA report
A
B
C
D
E
F
G a Hance, R.M., Studies of the Frost Resistance of Segmental Retaining Wall Units, Master’s Thesis, School of Civil and Environmental Engineering, Cornell University, May 2005.
b Chan, C., Freeze-Thaw Durability and ASTM C 1262 Testing of Segmental Retaining Wall (SRW) Units, Ph.D. Dissertation, School of Civil and Environmental Engineering, Cornell University, May 2006.
c FHWA, Durability of Segmental Retaining Wall Blocks, Federal Highway Administration Project No. DTFH61-02-R-00078, Final Report (in preparation, expected completion date Summer 2006).
In addition findings from these studies can also be found in technical publications that
have been published, submitted or in preparation as follows:
1. Chan, C., Hover, K.C., and Folliard, K.J., “Performance of Segmental Retaining
Wall (SRW) Units: from Laboratory to Field”, Construction Materials,
Proceedings of CONMAT 05 and Mindess Symposium (eds. N. Banthia, T.
Uomoto, A. Bentur and S.P. Shah), Vancouver, Canada, Aug. 21-24, 2005.
February 5, 2009
FINAL REPORT xvi
2. Chan, C., Hover, K.C. and Folliard, K.J., “Spatial Variations in Material Properties
of Segmental Retaining Wall (SRW) Units, Part I: Observed Variations”, Journal
of ASTM International, Civil Engineering and Building Materials, February 2005.
3. Chan, C., Hover, K.C. and Folliard, K.J., “Spatial Variations in Material Properties
of Segmental Retaining Wall (SRW) Units, Part II: Sampling Considerations for
Absorption Tests”, Journal of ASTM International, Civil Engineering and
Building Materials, February 2005.
4. Chan, C., Hover, K.C. and Folliard, K.J., “Comparison of Distribution of
Properties in Segmental Retaining Wall Units between Manufacturers” reviewed
and accepted for publication in the Journal of the Masonry Society, March, 2007.
5. Chan, C., Hover, K.C. and Folliard, K.J., “Segmental Retaining Wall (SRW) Split
Face Delaminations and Practical Implications”, Construction and Building
Materials, Edinburgh, Vol. 22, No. 8, August, 2008, pp 1749-1757.
6. Chan, C.T., Hover, K.C., Folliard, K., Trejo, D. “Frost Durability Indexes of
Segmental Retaining Wall Units,” ACI Materials Journal, Vol 104, No. 1., January
2007, pp. 23-32.
7. Chan, C., Hover, K.C. and Folliard, K.J., “Durability of Segmental Retaining Wall
(SRW) Concretes to Different Deicing Salt Types”, (in progress) 2008.
8. Chan, C.T., Carino, S.J., Durham, M., Hover, K.C., “Fundamental Frequency
Testing of Segmental Retaining Wall (SRW) Specimens: Test Considerations,”
Journal of ASTM International, Vol. 4, Issue 2, February, 2007, 14 pp., Published
Online, Paper ID: JAI100673.
February 5, 2009
FINAL REPORT xvii
TABLE OF CONTENTS
EXECUTIVE SUMMARY............................................................................... ii
TABLE OF CONTENTS.................................................................................. xvii
LIST OF FIGURES........................................................................................... xx
LIST OF TABLES............................................................................................. xxv
1.0 INTRODUCTION................................................................................. 1
1.1 Background...................................................................................... 1
1.2 Scope of work.................................................................................. 1
2.0 MATERIALS AND EQUIPMENT....................................................... 9
2.1 Materials.......................................................................................... 9
2.1.1 SRW units............................................................................... 9
2.1.2 Test containers........................................................................ 13
2.1.3 Saline solution........................................................................ 14
2.2 Freezers............................................................................................ 14
3.0 EXPERIMENTAL METHODS............................................................ 17
3.1 Test schedule................................................................................... 17
3.2 Freezer operation............................................................................. 18
3.3 Mass loss.......................................................................................... 22
3.4 Resonant frequency......................................................................... 26
3.5 Pulse velocity................................................................................... 35
3.6 Visual scaling rating........................................................................ 39
3.7 Modulus of rupture.......................................................................... 40
4.0 FREEZER SURVEY............................................................................. 42
4.1 Tenney freezer................................................................................. 42
4.1.1 Pre-test survey........................................................................ 42
4.1.2 Freezer performance during tests............................................ 48
4.2 Walk-in freezer................................................................................ 55
4.2.1 Pre-test survey........................................................................ 55
February 5, 2009
FINAL REPORT xviii
4.2.2 Freezer performance during tests............................................ 58
5.0 RESULTS AND DISCUSSION – ASTM C 1262 MASS LOSS......... 64
5.1 Mass loss results.............................................................................. 64
5.1.1 Mass Loss Results-Performance Criteria Series ......................... 64
5.1.2 Mass loss results-variability test series ....................................... 66
5.1.3 Overall performance evaluation of the variability and performance criteria test series specimens ...........................................
74
5.1.4 Effect of various specimen configurations-variability test series 75
5.1.4.1 Key observations from Figures 45a, b, and c. ........................ 82
5.1.4.2 Investigation of differences in specimen performance ............ 84
5.1.4.3. Summary of key observations from the variability series ...... 97
5.2 Rate of change of mass loss........................................................... 100
5.3 Other measured parameters............................................................. 106
5.3.1 Mass loss per surface area...................................................... 106
5.3.2 Moisture content changes....................................................... 115
5.3.3 Concentration of dissolved substances................................... 118
6.0 RESULTS AND DISCUSSION – RESONANT FREQUENCY......... 121
6.1 Relative dynamic modulus results................................................... 121
6.2 Rate of RDM change....................................................................... 132
6.3 Relationship to mass loss................................................................. 137
6.4 Relationship to moisture content..................................................... 141
6.4.1 Definitions.............................................................................. 141
6.4.2 Results..................................................................................... 144
7.0 RESULTS AND DISCUSSION – PULSE VELOCITY....................... 158
7.1 Pulse velocity results....................................................................... 158
7.2 Relationship to mass loss................................................................. 165
7.3 Comparison of methods................................................................... 167
8.0 RESULTS AND DISCUSSION – VISUAL SCALING RATING....... 171
8.1 Visual scaling rating results............................................................. 171
8.2 Relationship to mass loss................................................................. 171
February 5, 2009
FINAL REPORT xix
9.0 RESULTS AND DISCUSSION – MODULUS OF RUPTURE........... 182
9.1 Relationship to mass loss................................................................. 182
9.2 Relationships to RDM and PV........................................................ 185
10.0 BETWEEN-FREEZER COMPARISON OF SPECIMEN PERFORMANCE..................................................................................
188
10.1 Mass loss and rate of mass loss..................................................... 188
10.2 RDM (resonant frequency) and Rate of RDM change ................. 190
10.3 Pulse velocity................................................................................. 192
10.4 Visual scaling rating...................................................................... 193
10.5 Discrepancies in freeze-thaw cycles.............................................. 194
11.0 CONCLUSIONS AND RECOMMENDATIONS................................ 198
11.1 Freezer evaluation.......................................................................... 198
11.2 Effect of variations in the test method........................................... 199
11.3 Nature of mass loss evolution........................................................ 201
11.4 Damage assessment using resonant frequency.............................. 202
11.5 Damage assessment using pulse velocity...................................... 204
11.6 Damage assessment using visual scaling rating............................ 205
11.7 Relationship to modulus of rupture............................................... 206
11.8 Sources of variability..................................................................... 206
11.9 Comparison of specimen condition assessment methods.............. 207
11.10 Repeatability of results obtained using various test methods...... 209
11.11 Between-freezer comparison of specimen performance.............. 210
11.12 Recommendations for ASTM C 1262......................................... 212
11.13 Recommendations for future research......................................... 215
References........................................................................................................... 217
APPENDIX A--RECOMMENDED PROCEDURE FOR SURVEY OF INTERNAL TEMP.DISTRIBUTION OF FREEZE-THAW CHAMBER
A1
APPENDIX B--STATISTICAL ANALYSIS OF FACTORS AFFECTING MASS LOSS IN THE VARIABILITY TEST SERIES
B1
February 5, 2009
FINAL REPORT xx
LIST OF FIGURES
1 Sketches of the various test sets for ASTM C 1262 Variability Test
Series...................................................................................................... 6
2 Excerpts from Test Report on initial ASTM C 1262 testing of SRW units......................................................................................................
10
3 Timeline of events from SRW unit production to freeze-thaw testing at Cornell...............................................................................................
11
4 Freeze-thaw test specimen extraction from SRW units......................... 11
5 Containers used for NCMA study (a, b, c) (outer dimensions shown).. 14
6 Freezers used in NCMA study............................................................... 16
7 Schedule of tests for NCMA study........................................................ 17
8 Programmed freeze-thaw cycle in freezers............................................ 18
9 Typical freezer air temperature-time response (cooling curve)............. 21
10 Residue collection for mass loss determination..................................... 22
11 Resonant frequency test setup............................................................... 28
12 Example of different dominant peaks for 100 × 200 mm (4 × 8 in) specimen................................................................................................
29
13 Resonant frequency variations with moisture content........................... 34
14 Pulse velocity test setup......................................................................... 37
15 Relationship between transit times measured using different types of coupling media.......................................................................................
38
16 Pulse velocity measuring locations on specimen................................... 38
17 Modulus of rupture (MoR) testing of specimens................................... 41
18 View of thermocouple placement in cabinet freezer instrumented tests........................................................................................................
43
19 Typical cooling response of Tenney freezer as measured from survey. 45
20 Temperature mapping in Tenney freezer............................................... 46
21 R-curve obtained from survey of Tenney freezer loaded with 28 specimens...............................................................................................
48
22 Temperature-time response for first 10 cycles in Tenney freezer......... 50
23 R-curves for first 10 cycles in Tenney freezer....................................... 51
February 5, 2009
FINAL REPORT xxi
24 Temperature-time response Cycles 51 to 60 in Tenney freezer............ 52
25 R-curves for Cycles 51 to 60 in Tenney freezer.................................... 53
26 Times to reach –13°C for Tenney freezer............................................. 54
27 Schematic of thermocouple placement in walk-in freezer.................... 56
28 Typical cooling response of walk-in freezer as measured from survey 57
29 R-curve obtained from survey of walk-in freezer loaded with 16 specimens...............................................................................................
58
30 Temperature-time response for Cycles 11 to 20 in walk-in freezer...... 59
31 R-curves for Cycles 11 to 20 in walk-in freezer.................................... 60
32 Temperature-time response for Cycles 101 to 110 in walk-in freezer.. 62
33 R-curves for Cycles 101 to 110 in walk-in freezer................................ 63
34 Cumulative mass loss for PC Series specimens 65
35 Corner aggregate and mortar popouts resulting in mass loss jump 65
36 Cumulative mass loss for Variability Series (mass loss scale to 100%).....................................................................................................
67
37 Cumulative mass loss for Variability Series (mass loss scale to 3%)... 68
38 Test Set averages for Variability Series................................................. 69
39 Specimens with damage on test face after 100 cycles. 70
40 Damage on side surfaces, specimen D4................................................ 70
41 Extent of damage after 150 cycles......................................................... 71
42 Forms of cracking on specimens........................................................... 72
43 Example of continued crack growth leading to complete disintegration of specimen C1...............................................................
73
44 Predictions of most-probable mass loss to 200 cycles .......................... 78
45 Expected mass loss ............................................................................... 80
46 Range of values for characteristics of specimen configurations........... 85
47 Geometric basis for specimen characteristics ...................................... 86
48 Influence of specimen characteristics on mass loss ............................. 87
49 Relative values for characteristics of specimen configurations compared to those of specimen G.........................................................
90
50 Relative values of specimen characteristics, comparing E with G ….. 91
February 5, 2009
FINAL REPORT xxii
51 Relative values of specimen characteristics, comparing A with G ...... 93
52 Relative values of specimen characteristics, comparing B with A ...... 95
53 Relative values of specimen characteristics, comparing D with G ...... 96
54 Rates of mass loss for Variability Series............................................... 102
55 Rates of mass loss for Performance Criteria Series............................... 103
56 Popouts in Specimen E2 between 100 and 110 cycles.......................... 106
57a Mass loss per test face area as function of cycles for Variability Series......................................................................................................
110
57b Mass loss per wetted test area as function of cycles for Variability Series......................................................................................................
111
58 Mass loss per surface test area as function of cycles for PC Series...... 112
59a Relationship between ASTM C 1262 mass loss and mass loss per test face area................................................................................................
113
59b Relationship between ASTM C 1262 mass loss and mass loss per wetted area.............................................................................................
114
60 Moisture changes for Test Sets in Variability Series (control specimen also shown)............................................................................
116
61 Moisture changes for Test Sets in PC Series (control specimen also shown)....................................................................................................
119
62 Relationship between Mass Loss (from residue weighing) and Mass Gain (from specimen and residue weighing).........................................
120
63 Concentration of dissolved substances (S) in surrounding solution...... 120
64 RDM vs cycles for Variability Series – Sampling parameters: 20,000 Hz and 1,024 data points.......................................................................
122
65 RDM vs cycles for Variability Series – Sampling parameters: 102,400 Hz and 1,024 data points.........................................................
123
66 Damage evolution in specimen C1........................................................ 125
67 Examples of cracks on specimens with corresponding drops in RDM. 126
68 Average Test Set RDM vs cycles for Variability Series – Sampling parameters: 20,000 Hz and 1,024 data points........................................
127
69 Average Test Set RDM vs cycles for Variability Series – Sampling parameters: 102,400 Hz and 1,024 data points......................................
127
70 Comparison of RDM values obtained using two different sets of sampling parameters..............................................................................
130
February 5, 2009
FINAL REPORT xxiii
71 RDM vs cycles for PC specimens (sampling parameters 20,000 Hz and 1,024 data points)............................................................................
131
72 View of specimen C5L in PC Series after 160 cycles........................... 131
73 RDM vs cycles for PC average and control specimen (sampling parameters 20,000 Hz and 1,024 data points)........................................
132
74 Rates of RDM change for Variability Series......................................... 134
75 Rates of RDM change for Performance Criteria Series......................... 135
76 Rates of RDM change compared to rates of mass loss for Variability Series......................................................................................................
136
77 RDM vs mass loss relationship for Variability Series specimens......... 138
78 RDM vs mass loss relationship for PC Series specimens...................... 140
79 RDM vs mass loss at specified cycles................................................... 141
80 RDM vs moisture content relationship for Variability Series specimens...............................................................................................
145
81 Critical degree of saturation SCR of a certain concrete as function of concrete age (Fagerlund, 1999).............................................................
147
82 RDM vs moisture content relationship for PC Series specimens.......... 147
83 RDM vs moisture gain relationship for Variability Series specimens.. 149
84 RDM vs moisture gain relationship for all Variability Series specimens...............................................................................................
150
85 RDM vs moisture gain relationship for PC Series specimens............... 152
86 RDM vs. moisture gain relationship for control specimen.................... 153
87 “Uncorrected” and “corrected” RDM vs. moisture gain relationship for Variability Series specimens............................................................
154
88 “Uncorrected” and “corrected” RDM vs. moisture gain relationship for PC Series specimens........................................................................
155
89 Mass loss vs moisture gain relationship for all Variability Series specimens...............................................................................................
156
90 Example of relationship between cylinder compressive strength and pulse velocity (Naik et al., 2004)...........................................................
158
91 PV (as % of initial value) vs cycles for Variability Series.................... 160
92 Photos of specimens B3 and D2............................................................ 161
93 Average Test Set PV vs cycles for Variability Series........................... 162
February 5, 2009
FINAL REPORT xxiv
94 PV vs cycles for PC specimens............................................................. 164
95 PV vs cycles for PC average and control specimen.............................. 165
96 PV vs mass loss relationship for Variability Series specimens............. 166
97 PV vs mass loss relationship for PC Series specimens.......................... 167
98 Relationship between ∆RDMPV and ∆RDMRF...................................... 170
99 Scaling rating guide used in this study (based on ASTM C 672).......... 172
100 Visual Scaling Rating vs cycles for all Variability Series specimens... 173
101 Examples of crack formation accompanying surface scaling................ 174
102 Average Test Set Scaling Rating vs cycles for Variability Series......... 175
103 Scaling rating vs cycles for PC specimens............................................ 177
104 Comparison of immersed surface condition for selected PC Series specimens after 200 cycles....................................................................
178
105 Scaling rating vs mass loss relationship for Variability Series specimens...............................................................................................
179
106 View of various surfaces of specimen C2 after 160 cycles................... 181
107 Scaling rating vs mass loss relationship for PC Series specimens........ 181
108 MoR vs Mass Loss relationship for all specimens in study................... 183
109 Specimen C6L with MoR less than 1 MPa (145 psi) in the pre-0.8% mass loss region.....................................................................................
184
110 Best-fit relationship for MoR vs mass loss data.................................... 184
111 MoR vs RDM (from resonant frequency) relationship for all specimens in study.................................................................................
186
112 MoR vs PV relationship for all specimens in study.............................. 186
113 Best-fit relationship for MoR vs RDM (Res Freq) data........................ 187
114 Best-fit relationship for MoR vs PV data.............................................. 187
115 Mass loss comparison between specimens in Test Set A and PC Series......................................................................................................
189
116 Rate of mass loss comparison between specimens in Test Set A and PC Series................................................................................................
190
117 RDM comparison between specimens in Test Set A and PC Series..... 191
118 Rate of RDM comparison between specimens in Test Set A and PC Series......................................................................................................
191
February 5, 2009
FINAL REPORT xxv
119 PV comparison between specimens in Test Set A and PC Series......... 192
120 Visual scaling rating comparison between specimens in Test Set A and PC Series.........................................................................................
193
121 Cooling curves comparison for typical cycles in the two freezers........ 194
122 Rates of temperature change for curves in Figure 115.......................... 195
123 Coefficient of variation as function of cycles for various test methods 211
A.1 Freezer air cooling curve definitions A1
A.2 Examples of container and sensor placement on freezer shelf A3
A.3 Sample T-t, Tavg-t and σ-t graphs for Tenney freezer A4
A.4 Curve fits to Tavg-t and σ-t graphs of Figure A.3 for Tenney freezer A7
A.5 Curve fit to Tavg-t response of walk-in freezer (single curve). A8
A.6 Reliability (R) curve for the Tavg-t and σ-t graphs shown in Fig. A.3. A11
B.1 Simple example of Repeated Measures Analysis.................................. B2
B.2 Actual vs predicted mass loss based on data up to 50 cycles................ B8
B.3 Actual vs predicted mass loss based on data up to 100 cycles.............. B9
B.4 Actual vs predicted mass loss based on data up to 150 cycles.............. B10
B.5 Actual vs predicted mass loss based on data up to 200 cycles.............. B11
LIST OF TABLES
1 Test Sets in Variability Test Series........................................................ 3
2 Summary of variations investigated in the Test Sets of Table 1........... 5
3 ASTM C 140 tests on SRW units used for NCMA study..................... 12
4 Comparison of various types of containers........................................... 13
5 Area-based scaling rating of SRW specimens....................................... 39
6 Summary of cooling length parameters for Cycles 1 to 10 in Tenney freezer....................................................................................................
51
7 Summary of cooling length parameters for Cycles 51 to 60 in Tenney freezer....................................................................................................
53
8 Summary of cooling length parameters for Cycles 11 to 20 in walk-in freezer....................................................................................................
60
February 5, 2009
FINAL REPORT xxvi
9 Summary of cooling length parameters for Cycles 101 to 110 in walk-in freezer.......................................................................................
63
10 Cumulative mass loss for the Test Sets after specified number of cycles.....................................................................................................
77
11 Predicted Performance Based on Regression Equations ...................... 79
12 Incremental Mass Loss based on Prediction Models ........................... 80
13 Specimen Characteristics ..................................................................... 84
14 Discernable General Trends of the Influence of Specimen Characteristics on Mass Loss in the C 1262 Freeze-Thaw Test ..........
89
15 Mass loss prediction constant “a” for various Test Sets........................ 104
16 Number of cycles to 1% mass loss........................................................ 105
17 Ranking of Test Sets based on Mass Loss and RDM............................ 129
18 Summary of Risky Specimens............................................................... 139
19 ASTM C 642 test results........................................................................ 143
20 Ranking of Test Sets based on Mass Loss, RDM and PV..................... 163
21 Ranking of Test Sets based on Mass Loss, RDM, PV and scaling rating......................................................................................................
176
22 Comparison of cycle parameters between cabinet and walk-in freezers...................................................................................................
197
23 Sensitivity of tests to various forms of specimen damage..................... 209
A.1 R values for ttrial A11
B.1 Repeated Measures Analysis of various effects in mass loss vs cycle relationship............................................................................................
B5
B.2 Actual vs predicted number of cycle to 1% mass loss (using 50-cycle data).......................................................................................................
B12
February 5, 2009
FINAL REPORT 1
1.0 INTRODUCTION
1.1 Background
In the spring of 2005 the National Concrete Masonry Association (NCMA)
commissioned Cornell University (Cornell) to engage in an experimental program to
investigate sources of variability in the ASTM C 1262 test method. This study
followed directly from the FHWA-sponsored findings presented by Cornell at the
Manufactured Concrete Products Exposition (MCPX) 20052 and the work of Hance
(2005) which highlighted differences in the temperature response of a typical freeze-
thaw test specimen due to variations within the test method. Sources of variations
evaluated in these previous studies included specimen and container size, depth of
water surrounding specimen and specimen location in the freezer (Hance, 2005).
Overall, the NCMA funded project addressed the following general issues:
• ASTM C 1262 inherent test variability (significance of variations within the
test method)
• Performance criteria assessment (i.e., what does a 1% mass loss represent in
terms of other material properties?)
1.2 Scope of work
The NCMA research project was divided into two main parts: a) Variability Test
Series and b) Performance Criteria (PC) Test Series. These are described separately.
2 Manufactured Concrete Products Exposition MCPX 2005, NCMA Education Session 3: Highway Market Needs Why care about Freeze-Thaw?, Indianapolis, IN, February 11, 2005.
February 5, 2009
FINAL REPORT 2
Variability Test Series
This series was intended to evaluate the effect of variations within the ASTM C 1262
by varying specimen and container sizes to the extremes of ASTM C 1262 tolerances.
For example, the test method currently allows the exposed specimen area to vary
between 16,100 to 22,500 mm2 (25 to 35 in.2) with no mention of preferred specimen
geometry. Similarly, the water clearance around the specimens is permitted to vary
between 3 to 38 mm (1/8 to 1½ in.). In these tests, solution depth was also varied to
evaluate sensitivity to error in gauging the currently established 13 mm (½ in.) water
depth in the test method. In consultation with NCMA, seven Test Sets (labeled A to
G) were devised as summarized in Table 1 to evaluate the significance of each of the
following variations:
• Varying solution levels (Sets A, B and C)
These sets investigated the sensitivity of test results to solution depth which in
turn provided information on the significance of the volume of solution to be
frozen.
• Different specimen sizes for the same container size (Sets D, E and F)
For the same container size, variations in specimen size accordingly led to
variations in solution clearance between specimen and container. As such,
Sets D, E and F also addressed the significance of volume of solution to be
frozen. Sets D, E and F were tested at 13 mm (½ in.) deep solution. It is noted
that while the test face area of Set E specimens (11,250 mm2 (18 in.2)) was
outside the current ASTM C 1262 specimen size requirements, this test
provided useful information in the following manner: if the performance of
these specimens turned out to be similar to that of the compliant size
February 5, 2009
FINAL REPORT 3
Table 1 Test Sets in Variability Test Series
Set Size of container a
Dimensions of specimen, mm × mm (in. × in.)
Specimen area, mm2 (in.2)
Aspect ratio
Solution depth,
mm (in.)
Approx. solution
clearance b mm, mm (in., in.)
A Lg Rect 100 × 200 (4 × 8)
20,000 (32) 1:2 13
(1/2) 30 L, 30 W (1.2, 1.2)
B Lg Rect 100 × 200 (4 × 8)
20,000 (32) 1:2 10
(3/8) 30 L, 30 W (1.2, 1.2)
C Lg Rect 100 × 200 (4 × 8)
20,000 (32) 1:2 16
(5/8) 30 L, 30 W (1.2, 1.2)
D Sm Rect 100 × 200 (4 × 8)
20,000 (32) 1:2 13
(1/2) 5 L, 20 W (0.2, 0.8)
E Sm Rect 75 × 150 (3 × 6)
11,250 (18) 1:2 13
(1/2) 30 L, 33 W (1.2, 1.3)
F Sm Rect 113 × 150 (41/2 × 6)
16,950 (27) 1:1.3 13
(1/2) 30 L, 15 W (1.2, 0.6)
G Sq 133 × 150 (51/3 × 6)
20,000 (32) 1:1.1 13
(1/2) 25 L, 15 W (1.0, 0.6)
a Container sizes as follows (more information provided in Section 2.0): Lg Rect: inner dimensions of 260 × 160 mm (10.4 × 6.4 in.) at base of container Sm Rect: inner dimensions of 210 × 140 mm (8.4 × 5.6 in.) at base of container Sq: inner dimensions of 183 × 183 mm (7.3 × 7.3 in.) at base of container b L: in the long direction, W: in the wide direction
specimens, it implied that test area may not be a significant factor. However, if
a significant difference in performance is observed, it implied that test area and
possibly even water clearance may be influential.
• Different container sizes for the same specimen size (Sets A and D)
• Different specimen geometries (aspect ratios) (Sets A and G; Sets D, E and
F)
February 5, 2009
FINAL REPORT 4
Specimens from Test Sets A and G possessed similar mass of material (= 32
in.2 × specimen thickness) but different aspect ratios. Sets G was also tested at
13 mm (½ in.) deep solution. Specimens from Sets D, E and F, as described
earlier, also differed in their aspect ratios.
Table 2 provides a matrix summary of these various effects and Figure 1 provides
schematics to illustrate these variations. In each Test Set, four replicate specimens
were tested for a total of 28 specimens in the Variability Series. All specimens were
cut to the 32 ± 2 mm (1¼ ± 1/16 in.) thickness as per ASTM C 1262 and all tests were
conducted using 3% NaCl solution (30 g NaCl and 970 g water to make 1 kg of
solution). After every 10th cycle, the condition of the specimens was assessed by the
following methods:
• Mass loss percentage (from the collected residues)
• Mass loss per unit test face area
• Resonant frequency (ASTM C 215)
• Ultrasonic pulse velocity (ASTM C 597)
• Visual scaling rating (ASTM C 672)
These tests assess different forms of specimen damage. While mass loss and scaling
rating are sensitive to external forms of damage (i.e., loss of material from specimen
surfaces), resonant frequency and pulse velocity are more sensitive to changes in
specimen integrity (such as internal cracking). The evaluation of specimens using
these various techniques allows observing how different forms of damage evolve with
increasing freeze-thaw cycles and more importantly, enables comparing what certain
forms of damage such as mass loss mean in terms of other forms of damage, such as
specimen integrity, as measured from resonant frequency changes. A comparison
February 5, 2009
FINAL REPORT 5
between these various forms of damage detected by these methods is presented in the
Conclusions section, based on the data obtained in this study.
Table 2 Summary of variations investigated in the Test Sets of Table 1.
Test Set
Effect of solution
level
Effect of specimen
size
Effect of container
size
Effect of specimen geometry
A
B
C
D
E
F
G
Performance Criteria (PC) Test Series
Test specimens in this series were similar to those in Set A in the Variability Series,
i.e., 100 × 200 mm (4 × 8 in.) specimens in the Large Rectangular container. In
addition to assessing specimen condition using mass loss, resonant frequency,
ultrasonic pulse velocity and visual scaling rating, PC specimens were also tested for
their modulus of rupture (MoR). The MoR is a useful mechanical property which
characterizes the tensile capacity of the material. The primary objective of the PC
Series was to correlate MoR to the other measured properties listed earlier. For these
specimens, all measurements except for MoR were conducted after every 10th freeze-
thaw cycle. MoR tests were conducted on selected specimens at different mass loss
levels so as to obtain a spread of MoR values over the mass loss range of 0 to 2%. A
total of 16 specimens were tested in the PC Series, all in 13 mm (½ in.) deep solution.
February 5, 2009
FINAL REPORT 6
Figure 1 Sketches of the various test sets for ASTM C 1262 Variability Test Series
February 5, 2009
FINAL REPORT 7
a) Varying solution levels (all 100 × 200 mm (4 × 8 in.) specimens at 30 mm (1.2 in.)
of solution surrounding specimen)
b) Different specimen sizes for the same container size (all at 13 mm (½ in.) deep solution)
Figure 1 (Continued)
solution level at:
Set A 13 mm (½ in.)
Set B 10 mm (3/8 in.)
Set C 16 mm (5/8 in.)
Test Set D Test Set E Test Set F
20 mm (0.8 in)
100 × 200 mm (4 × 8 in.)
20,000 mm2
(32 in.2)
5 mm (0.2 in.)
33 mm (1.3 in)
30 mm (1.2 in.)
75 × 150 mm (3 × 6 in.)
11,250 mm2
(18 in.2)
15 mm (0.6 in)
30 mm (1.2 in.)
113 × 150 mm (4.5 × 6 in.)
16,950 mm2
(27 in.2)
February 5, 2009
FINAL REPORT 8
c) Different container sizes for the same specimen size (Sets A and D)
d) Different specimen geometries
Test Set A Test Set D
30 mm (1.2 in.)
30 mm (1.2 in.)
100 × 200 mm (4 × 8 in.)
20,000 mm2
(32 in.2)
20 mm (0.8 in.)
5 mm (0.2 in.)
100 × 200 mm (4 × 8 in.)
20,000 mm2
(32 in.2)
Test Set A Test Set G
30 mm (1.2 in.)
30 mm (1.2 in.)
100 × 200 mm (4 × 8 in.)
20,000 mm2
(32 in.2)
15 mm (0.6 in.)
25 mm (1 in.)
133 × 150 mm (5.3 × 6 in.)
20,000 mm2
(32 in.2)
February 5, 2009
FINAL REPORT 9
2.0 MATERIALS AND EQUIPMENT
2.1 Materials
2.1.1 SRW units
In this test program one single type of SRW unit was evaluated, which was selected
for this study by NCMA3. These units were 8 in. high of a typical “Retaining Wall
Block” (300 × 200 × 450 mm (12 × 8 × 18 in.)) configuration, obtained from a
commercial manufacturer. Units were selected on the basis of demonstrated good
performance, subsequently verified by lab tests at NCMA. It is understood that these
SRW units were manufactured in August 2004, at which point initial ASTM C 1262
tests were performed by an independent laboratory4. Key excerpts from that test
report are shown in Figure 2. Three pallets of these units were subsequently shipped
to the NCMA labs in Herndon, VA in May 2005 where the units were saw-cut
according to specifications provided by Cornell to obtain specimens of sizes shown in
Section 1. Following this, the saw-cut coupons were shipped to Cornell University
(Ithaca, New York) on July 2005, and freeze-thaw testing of these specimens for the
NCMA study was initiated in October 2005. A timeline of these events is shown in
Figure 3.
ASTM C 140 tests on SRW units from the three pallets (identified as A, B and C)
shipped to NCMA were carried out at the NCMA labs, and results of these tests are
shown in Table 3. Given the similarities in the properties of units from pallets A and
B, a decision was thus made to use units from these two pallets exclusively for
specimens in the Variability Test Series and units from pallet C exclusively for
3 Contact NCMA for details of SRW units that are not included in this report. 4 Contact NCMA for details of testing that are not included in this report.
February 5, 2009
FINAL REPORT 10
specimens in the PC Test Series. All freeze-thaw test specimens were extracted from
the back faces of the units as shown in Figure 4. Specimens that were 200 mm (8 in.)
long (i.e., Set A, B, C and D in Variability Series and all of PC Series) were typically
extracted by cutting through the height of the SRW unit as shown in Figure 4a.
Specimens that were 150 mm (6 in.) long (i.e., Set E, F and G) were extracted such
manner that the center of the specimens was at mid-height of the unit, as illustrated in
Figure 4b.
Report of Independent Testing Agency
Report date: November 3, 2004
Unit Description
8” Retaining Wall Block
Test specimen dimensions: 1.25 × 4 × 8 in.
Specimen sample location: Back molded vertical surface of the unit
Sampled by manufacturer
Figure 2 Excerpts from Test Report on initial ASTM C 1262 testing of SRW units.
0.00.51.01.52.02.53.03.54.04.55.0
0 10 20 30 40 50 60 70 80 90 100
Cycles
Per
cent
Los
s
February 5, 2009
FINAL REPORT 11
a from Test Report date and from communication with NCMA b from Test Report date
Figure 3 Timeline of events from SRW unit production to freeze-thaw testing at Cornell.
Figure 4 Freeze-thaw test specimen extraction from SRW units.
Aug 2004
Sep – Nov2004
May 2005
June 2005
July 2005
Oct – Mar2006
Manufacture of Rockwood SRW units a
ASTM C 1262 testing at Giles b
3 pallets of units shipped to
NCMA labs
- Saw-cutting of units as per Cornell specs
- ASTM C 140 tests
Saw-cut specimens shipped to Cornell
NCMA study at Cornell
all specimens 32 mm (1¼ in.) thick
split face
back face
test specimens
200 mm (8 in.)
100 mm (4 in.)
a) extraction of specimens from back face
b) 150 mm (6 in) specimens relative to 200 mm (8 in) specimens
150 mm (6 in.)
200 mm(8 in.)
75 mm (3 in.) 113 mm (4.5 in.) 133 mm (5.3 in.)
height of SRW unit
February 5, 2009
FINAL REPORT 12
Table 3 ASTM C 140 tests on SRW units used for NCMA study.
Pallet Unit No.
Compressive strength
MPa (psi)
Water absorption kg/m3 (pcf)
Oven-dry density
kg/m3 (pcf)
% Absorption
A 1 33.3 (4830) 127 (7.9) 2210 (137) 5.75% 2 35.4 (5130) 129 (8.0) 2210 (137) 5.84% 3 34.4 (4980) 130 (8.1) 2220 (138) 5.86%
Avg A 34.4 (4980) 129 (8.0) 2210 (137) 5.84% B 4 34.1 (4940) 125 (7.7) 2200 (137) 5.68% 5 36.2 (5250) 125 (7.8) 2210 (137) 5.66% 6 34.8 (5050) 126 (7.8) 2200 (137) 5.73%
Avg B 35.0 (5080) 125 (7.8) 2200 (137) 5.68% C 7 36.7 (5320) 130 (8.1) 2220 (138) 5.86% 8 37.8 (5480) 125 (7.8) 2230 (139) 5.61% 9 37.0 (5360) 125 (7.8) 2230 (139) 5.61%
Avg C 37.2 (5390) 127 (7.9) 2230 (139) 5.70%
February 5, 2009
FINAL REPORT 13
2.1.2 Test containers
Three types of test containers were used in this study as summarized in Table 1.
Details of these containers are shown in Table 4 and pictured in Figure 5. Also
included for comparison is a fourth container labeled “NCMA” container. This is a
container used for ASTM C 1262 testing in NCMA laboratories and is understood to
also be used in several other commercial laboratories. At the time of this study
however, this “NCMA” container was discontinued by the manufacturer, and in its
place, the Rubbermaid “Servin’ Saver Plus” rectangular (1.1 Gal / 4.0 L) (called “Lg
Rect: here) was used. Compared to the “NCMA” container (also manufactured by
Rubbermaid), this “Lg Rect” container has slightly larger overall dimensions (length,
width and height). However, as will be shown later, the volume of water required to
fill the containers to the 13 mm (½ in.) level is about the same (approximately 300
mL) for both “Lg Rect” and “NCMA” containers. As such, this “Lg Rect” container
was deemed suitable as replacement to the “NCMA” container.
Table 4 Comparison of various types of containers. Lg Rect Sm Rect Sq NCMA
Brand
Rubbermaid “Servin’ Saver
Plus” rectangular
Aero rectangular
Rubbermaid “Servin’
Saver Plus”
Rubbermaid Rectangle
#3861
Capacity 4.0 L / 1.1 Gal 3.6 L 3.0 L / 3.2 Qt 2-quart Length, mm (in.) a 310 (12.3) 273 (10.8) 225 (8.9) 292 (11.5)
Width, mm (in.) a 210 (8.3) 206 (8.1) 225 (8.9) 180 (7.1)
Height, mm (in.) a 108 (4.3) 111 (4.4) 105 (4.1) 67 (2.6)
a external dimensions
February 5, 2009
FINAL REPORT 14
a) Rubbermaid “Servin’ Saver Plus” 1.1 Gal / 4.0 L
b) Aero rectangular 3.6 L
c) Rubbermaid “Servin’ Saver Plus” 3.2 Qt / 3.0 L
d) Rubbermaid Rectangle #3861 2-quart (NCMA container)
Figure 5 Containers used for NCMA study (a, b, c) (outer dimensions shown)
2.1.3 Saline solution
Solutions of 3% NaCl concentration were used in all tests in this study. These
solutions were prepared by dissolving 30 g of salt into 970 g of water to make 1 kg of
solution. The salt used was a commercial grade NaCl obtained from the Chemistry
Stockroom at Cornell Olin Laboratories.
2.2 Freezers
Two freezers were used in this study. Specimens in the Variability Test Series were
tested in the Tenney Environmental (A Lunaire Company) chamber which was on
L: 292 mm (11.5 in.) W: 180 mm (7.1 in.) H: 67 mm (2.6 in.)
L: 310 mm (12.3 in.) W: 210 mm (8.3 in.) H: 108 mm (4.3 in.)
L: 273 mm (10.8 in.) W: 206 mm (8.1 in.) H: 111 mm (4.4 in.)
L: 225 mm (8.9 in.) W: 225 mm (8.9 in.) H: 105 mm (4.1 in.)
February 5, 2009
FINAL REPORT 15
loan to Cornell from NCMA (Model No. T20S-2.0, Serial No. 25919-02, labeled
Chamber #1). This freezer, shown in Figure 6a, is also equipped with cooling and
heating units which are programmable to allow uninterrupted freeze-thaw cycling.
Fans are also built into the unit to blast air through the cabin for better air temperature
distribution. This freezer operates at 5200 watts with a volume cooling capacity of 9.8
watts/L of freezer volume. This freezer was maintained in the Winter Laboratory at
Cornell.
Performance Criteria specimens were tested in a walk-in environmental chamber from
Environmental Structures Inc. (Colorado Springs, Co), housed at Cornell’s Mogami
Laboratory (Figure 6b). This freezer has ceiling mounted fan-driven cooling and
heating units to circulate air throughout the chamber thereby promoting more uniform
air temperature distribution. It operates at 2400 watts and has a cooling capacity of
0.13 watts/L of freezer volume. This freezer is also programmable and thus,
continuous freeze-thaw cycles can be run without human intervention.
Temperature data were obtained during the experiments using Type T thermocouples
(PR-T-24-SLE wire) from Omega Engineering Inc. These thermocouples, made from
copper and constantan, rely on the temperature difference between the sensing point
and the reference junction to produce a voltage which can be measured and converted
to a temperature measurement by calibration. The thermocouples were connected to
an Agilent 34970A high-resolution, multi-channel data acquisition/switch unit which
relayed the data over to a 128 Mb RAM, 550 MHz Pentium III PC unit with a
Microsoft Visual Basic interface setup to operate the data acquisition system and store
the collected measurements into data files.
February 5, 2009
FINAL REPORT 16
a) Tenney freezer (cabinet freezer) for Variability Test Series
b) Walk-in environmental chamber for Performance Criteria Test Series
Figure 6 Freezers used in NCMA study.
fan
air intake
1 m (39½ in.) deep × 0.76 m (30 in.) wide × 0.91 m (36 in.) high
February 5, 2009
FINAL REPORT 17
3.0 EXPERIMENTAL METHODS
3.1 Test schedule A weekly schedule was implemented to balance the concurrent testing programs in the
Variability and PC Series. This schedule is shown in Figure 7. Freeze-thaw tests were
typically run at 12-hr cycles (from a freezer performance standpoint, a 12-hour cycle
was optimal for the specific Tenney freezer unit used here, as will be described
ahead); and as such, 10 cycles stretched over a 5-day period. Mass loss, resonant
frequency and ultrasonic pulse velocity measurements were carried out in the
remaining 2 days in the week. This weekly routine was maintained for the duration of
the testing program starting from early October 2005. The only exceptions to this
routine were in late December 2005 at which point in time, the following alterations
from the routine were made: a) the length of the cycles between 110 and 120 cycles in
the Variability Series was extended to 24 hours (by lengthening the warm soak of each
cycle while maintaining the cold soak unchanged), and b) no measurements were
made after 120 cycles in the PC Series (i.e., 20 continuous cycles were run from 110
to 130 cycles).
Day of week Sun Mon Tue Wed Thu Fri Sat Freeze-thaw cycling VAR PC Measurements Daytime ML
VAR PV
VAR ML PC
Evening RF VAR
PV PC
RF PC
Legend VAR: Variability Series PC: Performance Criteria Series ML: ASTM C 1262 mass loss (incl. sample washing, residue collection, scaling rating) PV: Ultrasonic pulse velocity RF: Resonant frequency
Figure 7 Schedule of tests for NCMA study.
F/T cycling F/T cycling
February 5, 2009
FINAL REPORT 18
3.2 Freezer operation
The Tenney and walk-in freezers used in this study were of programmable type (i.e.,
user can define the temperature-time profiles), and the input parameters consisted of
the following portions of the cycle: a) ramp down, b) cold soak, c) ramp up, and d)
warm soak, as shown in Figure 8. For the Tenney freezer, the temperature-time
profile used during the tests was based on the profile used at NCMA laboratories
consisting of the following steps:
• Ramp down: 75 to 0°F in 15 min
• Cold soak: 4 hours
• Ramp up: 0 to 75°F in 15 min
• Warm soak: 3.5 hours
Figure 8 Programmed freeze-thaw cycle in freezers.
ramp down
ramp up
cold soak
warm soak
Temp.
time
February 5, 2009
FINAL REPORT 19
In the tests conducted at Cornell for the NCMA study, the Ramp Down and Ramp Up
rates were maintained as above, while the Cold and Warm Soak durations were
modified. The Cold Soak was modified from the 4 hours shown above to
approximately 4.5 hours to maximize the number of freezer internal locations
compliant with ASTM C 1262 (see Section 4 on Freezer Survey). On the other hand,
the Warm Soak was modified from the 3.5 hours shown above to 6.0 hours to enhance
freezer performance (see also Section 4 on Freezer Survey). As such, the programmed
temperature-time profile employed for the Tenney freezer at Cornell was as follows:
• Ramp down: 75 to 0°F in 15 min
• Cold soak: 4.5 hours
• Ramp up: 0 to 75°F in 15 min
• Warm soak: 4.5 hours (cycles 1 to 40)
6.0 hours (cycles 41 to 200)
The warm soak duration was extended from 4.5 to 6.0 hrs to improve freezer
performance, as will be discussed in detail. Using a 6-hr warm soak, this temperature-
time profile yielded actual freezer air temperature-time (cooling curves) as shown in
Figure 9a, where the curve represents the average of 23 measured locations inside the
freezer. It is seen that on average approximately 1.6 hours was required to reach –
13°C (10°F), and the overall cooling branch of the curve (ramp down + cold soak)
required about 6.1 hours. Hence, typical cold soak durations were approximately 4.5
hours. Using this profile, a full cycle length (from start of ramp down of one cycle to
start of ramp down of the next cycle) required about 12 to 12.5 hours, as shown in
Figure 9a
February 5, 2009
FINAL REPORT 20
The profile used for the walk-in freezer was similar to that used by Hance (2005) with
respect to Ramp Down and Ramp Up rates, but with modifications made accordingly
in the Cold and Warm soak durations to obtain Optimum Cold Soak conditions (see
Section 4 on Freezer Survey). As such, the temperature-time profile employed for this
freezer was as follows:
• Ramp down: from 75°F to –25°F at 10°F/min
• Cold soak: 6.2 to 6.3 hours
• Ramp up: from –25°F to 75°F at 10°F/min
• Warm soak: 5.4 to 5.5 hours
This profile yielded an actual freezer air cooling curve such as that shown in Figure
9b, where the curve shown also represents the average of 24 measured locations inside
the freezer. It is seen that, on average, approximately 1.7 hours was required to reach
–13°C (10°F), and the overall cooling branch of the curve (ramp down + cold soak)
required about 6.5 hours. Hence, typical cold soak durations were approximately 4.8
hours. Using this profile, a full cycle length required about 12 hours, as shown in
Figure 9b.
February 5, 2009
FINAL REPORT 21
a) Tenney freezer
b) Walk-in freezer Figure 9 Typical freezer air temperature-time response (cooling curve)
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hrs)
Tem
pera
ture
(°C
)
cool down ramp1.6 hrs
cold soak4.5 hrs
warm up ramp0.6 hrs
warm soak 5.4 hrs
0
20
40
60
Tem
pera
ture
(°F)
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hrs)
Tem
pera
ture
(°C
)
cool down ramp1.7 hrs
cold soak4.8 hrs
warm up ramp0.8 hrs
warm soak 4.7 hrs
0
20
40
60
Tem
pera
ture
(°F)
February 5, 2009
FINAL REPORT 22
3.3 Mass loss
At every 10th cycle, freeze-thaw test specimens were cleaned and their residues
collected for mass loss determination according to ASTM C 1262. Residue collection
was done by pouring the solution from the container along with the residues through a
filter paper fitted into a funnel. The material in the filter paper was subsequently
rinsed at least 3 times to wash off salts from the residues. This setup is shown in
Figure 10.
a) residue collection station b) funnels with filter paper
Figure 10 Residue collection for mass loss determination.
In addition to collecting residues, the following tasks were also carried out during
specimen washing and cleaning:
• Weighing the surface-dried (SD) mass of the specimens (routinely performed
for all specimens). This is equivalent to the parameter Wp (initial specimen SD
mass after 24-hr immersion and before any freezing) that is part of the test
method. Specimen mass is recorded in ASTM C 666 (ASTM C 666, 2004)
and has also been recorded in various other frost resistance studies on concrete
with the concept that water uptake increases with damage in the specimen
February 5, 2009
FINAL REPORT 23
(Janssen et al., 1999 and Setzer et al., 2002). Due to the continued loss of
material with increasing freeze-thaw cycles, the total SD mass of each
specimen after n cycles was estimated as follows:
1. Following thawing after each 10th cycle, specimens were removed from the
freezer.
2. Coupons were removed from the containers, and while being held directly
above the containers, were gently brushed and washed with saline solution (from
a plastic squeeze bottle) to remove all loosened material, taking care to retain all
rinse water and debris in the container.
3. Coupons were then rapidly patted with a paper towel on all surfaces to achieve
Surface Dry condition (i.e., no visible surface moisture film).
4. The mass of the Surface Dry coupons was measured.
5. All of the water and debris in the container was poured into a funnel lined with
pre-weighed filter paper. The container was gently washed-out with using a
plastic squeeze bottle to make sure all debris had been transferred to the filter-lined
funnel.
6. The filter paper was placed in a pre-weighed drying tin (such as that used for
soil samples) and dried overnight at 100-110oC (212-230oF). (It had been
observed previously that less than 1 hour in this environment was sufficient to dry
the debris, but it was convenient to leave samples in the oven overnight.)
7. The oven dry mass of the debris was subsequently determined after subtraction
of the mass of the drying tin and the filter paper.
8. For the current cycle, the total Surface Dry mass of the specimen was estimated
as the Surface Dry mass of the residual coupon from which all loose material had
been removed, plus the Oven Dry mass of the debris. A small error is introduced
by the fact that no attempt was made to measure the surface dry mass of the debris.
February 5, 2009
FINAL REPORT 24
This error is estimated to be less than 0.1% of the specimen mass and as such
considered negligible.
Thus, the total Surface Dry Mass of specimen (after n cycles) ≈ Measured
Surface Dry Mass of the residual coupon (at n cycles) + …
… + cumulative Oven Dry mass of residues from
cycle 0 to cycle n (1)
From this, and recalling that a Final Oven Dry mass of each coupon is recorded
at the conclusion of freeze-thaw testing (sum of residual coupon plus
cumulative debris), the Total Moisture Content (MC) after n cycles was
determined as follows:
Total MC (at n cycles) = (Total SD Mass at n cycles - Final Oven Dried Mass) 100%
Final Oven Dried Mass×
(2)
As pointed-out above, the value thus obtained will underestimate the Total MC
(at n cycles) by less than 1/10 of 1% for a typical specimen.
Note also that one can monitor mass gain as the test proceeds by comparing the
estimated surface dry mass of the residual coupon + debris with the initial
surface dry mass of the coupon obtained prior to freeze-thaw testing.
However, such data cannot be converted to moisture content relative to oven
dry mass until completion of freeze-thaw testing and establishment of oven dry
mass of the residual coupon.
February 5, 2009
FINAL REPORT 25
• Measuring concentration of dissolved substances in the solution (performed for
specimens A1, D1 and F1 only). This was performed by decanting the solution
surrounding specimens into aluminum pans (taking care to leave the insoluble
debris behind), weighing the total mass of pan and solution, drying the solution
overnight in an oven at 100 - 110°C and weighing the mass of pan and dried
salts. The concentration of dissolved substance (s) in the solution was then
expressed as follows:
s = %100pan) of (mass - solution) andpan of (masspan) of (mass - salts) dried andpan of (mass
× (3)
• Performing visual scaling rating. This is described in more detail ahead.
• Taking photographic documentation of specimen condition and noting
observations.
To maintain consistency in the manner in which solution was added to the test
containers, the mass of solution required to fill the containers to the 13 mm (½ in.)
solution level (or to other levels for Tests Sets B and C) was recorded during initial
filling (i.e., after the 24-hr soak period and prior to initiating freeze-thaw cycling).
This same mass of solution was subsequently added to the containers after each time
mass loss was collected. Due to the different container and specimen sizes, and the
intentionally varied depth of immersion, this mass of solution varied as follows: Test
Set A [300 g (0.66 lb)], B [225 g (0.50 lb)], C [365 g (0.80 lb)], D [185 g (0.41 lb)], E
[255 g (0.56 lb)], F [205 g (0.45 lb)] and G [175 g (0.39 lb)]. The 300 g solution
required in Test Set A was also the required amount to fill containers in the PC Series
February 5, 2009
FINAL REPORT 26
to this same level and was similar to the 300 g used by NCMA when using the
“NCMA container” (Figure 5d).
In addition to the 28 specimens in the Variability Series and the 16 specimens in PC
Series, a single control specimen also partially immersed in 13 mm (½ in.) saline
solution but not subjected to freeze-thaw cycles was monitored for mass changes,
resonant frequencies and pulse velocities. These measurements were taken weekly at
the same time measurements on the PC Series specimens were taken.
3.4 Resonant frequency
Resonant frequencies of all specimens were determined according to the methods of
ASTM C 215. The equipment used in this study consisted of an accelerometer (model
no. 352C33, sensitivity 99.4 mV/g [10.14 mV/m/s2] from PCB Piezotronics)
connected through a signal-conditioning unit to a 550 MHz, Pentium III desktop
computer (Figure 11). Labview 6.1 software was used to process the accelerometer
signal and convert it to the frequency domain. A thin layer of wax was smeared over
the base of the accelerometer to ensure good contact with the specimen surface, and
the accelerometer was held in place on the specimen using a rubber band. This
method of attaching the accelerometer to the specimen was also found by Janssen
(Janssen and Snyder, 1994) to be most effective for obtaining sharp and clear resonant
frequency peaks from the spectrum. As for impactor, the ASTM C 215 currently
recommends an impacting instrument with striking end of size 6 mm (1/4 in.).
Sansalone and Streett (1997) however provide a relationship between impacting
sphere diameter and maximum frequency of useful energy as follows:
fmax (Hz) = (m) D
291 (4)
February 5, 2009
FINAL REPORT 27
The maximum frequency of useful energies for a 6 mm (1/4 in.) impacting head is
thus about 48,000 Hz. Over this broad range of frequencies, the amplitudes of the
frequencies are however lower (Sansalone and Streett, 1997). For the test specimens
in this study, frequencies associated with vibration modes of interest (primarily those
associated with flexure about the transverse axis, see Figure 12a) were expected to be
less than 10,000 to 15,000 Hz (Chan et al., 2006) which results in a sphere diameters
in the range of 19 to 28 mm. The impactor thus used comprised a 19 mm (3/4 in.)
hardened steel ball attached onto the head of a steel rod (Figure 11). Soft rubber
February 5, 2009
FINAL REPORT 28
a) schematic of resonant frequency test setup
b) Pictures of equipment and setup at Cornell.
Figure 11 Resonant frequency test setup.
signal from accelerometer
frequency domain
× accelerometer
specimen A
ASignal
Amplifier
data acquisition and processing system soft rubber supports
impactor test sample
February 5, 2009
FINAL REPORT 29
a) accelerometer and impactor aligned
b) accelerometer and impactor misaligned
Figure 12 Example of different dominant peaks for 100 × 200 mm (4 × 8 in.) specimen.
accel. impact
×
accelerometer signal
frequency domain
impact
×
accel. accelerometer signal
frequency domain
note extra peak
February 5, 2009
FINAL REPORT 30
supports spaced apart at 0.552 × (length of specimen) were employed as required by
ASTM C 215.
From resonant frequencies, the Relative Dynamic Modulus (RDM) which is indicative
of material degradation is obtained as follows (from ASTM C 666 for ordinary
concretes):
RDM = 2
o
c
ff⎟⎟⎠
⎞⎜⎜⎝
⎛× 100 (5)
where fc = resonant frequency after c freeze-thaw cycles, and
fo = initial resonant frequency (at 0 freeze-thaw cycles)
This equation is based on the fact that the resonant transverse frequency of a concrete
specimen is related to its dynamic elastic modulus (Ed) as follows (ASTM C 215):
Ed = CMn2 (6)
where M = mass of specimen, kg
n = fundamental transverse frequency, Hz
C = constant dependent on specimen geometry and Poisson’s ratio
As such, for small changes in the geometry or Poisson’s ratio, changes in the dynamic
elastic modulus due to material degradation (Ed damaged / Ed undamaged) can be traced by
changes in its resonant frequency as per Equation 5. For reference, ASTM C 666
requires that the test be discontinued when RDM reaches 60%.
Prior to actual freeze-thaw testing of specimens, pre-test trials were carried out to
troubleshoot and identify possible sources of variations within this test method.
February 5, 2009
FINAL REPORT 31
Details of these pre-test trials are detailed in Chan et al. (2006) whose main findings
are summarized as follows:
1. Importance of correct identification of vibration mode
In the specimens tested, a number of different vibration modes can dominate
the signal resulting in resonant frequency peaks corresponding to different
modes appearing in the spectrum. An example of this is shown in Figure 12
for the 100 × 200 mm (4 × 8 in.) specimen. If the accelerometer and impactor
are neatly aligned along the centerline of the specimen (in the longitudinal
direction), a single resonant frequency peak appears in the spectrum,
corresponding to flexure about the transverse axis (Figure 12a). However,
misalignment of the accelerometer and impactor can induce a dominant
torsional mode whose corresponding resonant frequency peak also shows up in
the spectrum (Figure 12b). The concern here is that resonant frequencies for
different vibration modes could be recorded throughout the duration of the
freeze-thaw tests, thereby causing erroneous interpretations of specimen
damage condition. It is thus important to recognize the various possible modes
existent and to be able to consistently track frequencies corresponding to the
same vibrating mode during actual tests. Chan et al. (2006) provide guidelines
on how to detect the various modes and ensure consistency in their
identification.
2. Temperature effects
Resonant frequencies of laboratory air-dried SRW specimens were found to
vary by up to 20 Hz over a 5°C (10°F) change in temperature. ASTM C 1262
specifies a temperature tolerance of ± 5°C (± 10°F) during warm soak which
February 5, 2009
FINAL REPORT 32
implies that resonant frequencies could vary by up to 40 Hz depending on
actual warm soak temperature. For a 100 × 200 mm (4 × 8 in.) specimen
whose resonant frequency was determined to be in the range of 2200 to 3100
Hz, a 40 Hz variation yields accordingly a variation in RDM of 2 to 4%.
3. Moisture effects
Resonant frequencies of laboratory air-dried SRW specimens were found to
vary by up to ±5% with variations in ambient relative humidity. While actual
freeze-thaw test specimens are kept moist, variations due to humidity implied
possible variations with moisture content especially during resonant frequency
testing when specimens are removed from their containers and exposed to
laboratory air. This supposition was verified through tests in which the
frequencies of moist specimens (partially immersed in 13 mm (½ in.) water
and 3% NaCl solution for 24 hours) were tracked as the specimens dried in
laboratory air at ambient temperature of 29 to 32°C (85 to 90°F) and relative
humidity of 55 to 60%. These results are shown in Figure 13 which shows a
general decrease in frequencies as the specimens dried (i.e., decreasing
moisture content) with the measurements taken at 15 to 20 minute intervals.
The overall conclusion from these trials was that timing of resonant frequency
tests is critical, and specimens should not be allowed to remain exposed to
laboratory air for more than 15 min. nor should specimen surfaces become
visibly dry before frequencies are measured. (The recommended 15 minute
time limit corresponds to the first and second data points from right to left in
Figure 13.) These results were obtained for tests conducted at ambient
temperature in the range of 30 to 32°C (87 to 90°F) and relative humidity of 55
February 5, 2009
FINAL REPORT 33
to 63%. Drier laboratory environments are however expected to result in faster
specimen drying.
In this study, the resonant frequency of each specimen was measured at 2 different
rates of data sampling which are as follows:
1. Sampling of 1,024 points at 20,000 Hz, which are the standard ASTM C 215
sampling parameters.
2. Sampling of 1,024 points at 102,400 Hz. For the same total number of data
points (1,024), the higher sampling rate captured more closely-spaced points in
the vibration response of the specimen5. Trials were conducted in which this
approach appeared to produce more consistent resonant frequency results.
5 Communication with Prof. M. Sansalone, School Civil and Environmental Engineering at Cornell University.
February 5, 2009
FINAL REPORT 34
a) tests with plain water
b) tests with 3% NaCl solution
Figure 13 Resonant frequency variations with moisture content.
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
0.0 1.0 2.0 3.0 4.0
Moisture content, %
fn (H
z)
drying specimen
2000
2100
2200
2300
2400
2500
2600
2700
2800
2900
3000
0.0 1.0 2.0 3.0 4.0
Moisture content, %
fn (H
z)
drying specimen
February 5, 2009
FINAL REPORT 35
This set of sampling parameters is however accompanied by a coarser
frequency resolution which is defined as ∆f = (sampling rate / no. data pts) and
equal to 100 Hz for the current sampling parameters (compared to 19.5 Hz for
the standard ASTM C 215 sampling parameters). This means that frequencies
are measured at 100 Hz intervals (i.e., 2,200, 2,300, 2,400 Hz, etc), and each
measured frequency therefore has a ±50 Hz error range (equal to ½·∆f). This
frequency error range thus translates to an RDM error range as follows:
RDM = 2
21
ff f⎟⎠⎞
⎜⎝⎛ ∆± (7)
Hence, for an undamaged specimen with measured f = 2,500 Hz (typical of the
4 × 8 in. specimens), actual frequencies could be anywhere between 2,450 to
2,550 Hz. For this specimen then, its actual RDM could be anywhere between
96 to 104%.
For each set of sampling parameters, three resonant frequency measurements were
recorded. Results obtained using the two sets of sampling parameters are also
compared.
3.5 Pulse velocity
Pulse velocity (PV) measurements were performed in accordance with ASTM C 597
(ASTM C 597, 2004). In this test, the velocity of compression waves through
concrete samples is measured by placing two transducers (a transmitter and a receiver)
at opposite faces of a sample of known length and measuring the transit time taken for
these waves to travel from transmitter to receiver. Pulse velocity is then obtained by
February 5, 2009
FINAL REPORT 36
dividing the travel length by the travel time (Figure 14). In ordinary concretes, pulse
velocities are in the range of 4100 to 4500 m/s (13,500 to 14,800 ft/s) for concretes
with compressive strengths of 25 to 38 MPa (3,600 to 5,500 psi) (Naik et al., 2004).
The apparatus used in these tests consisted of a V-meter C-4902 (serial number:
25359) from James NDT Instruments, Chicago, IL, shown in Figure 14b. Generally, a
petroleum jelly is used as coupling material between the transducer and the concrete
surface to ensure good contact. The challenge with using grease for freeze-thaw test
specimens is that grease may contaminate the test solution, specimens and containers.
As such, rubber membranes (“Large Rubber Couplants”, V-24145-000 also distributed
by James Instruments.) were used as an alternate coupling medium. Coupling medium
consisting of rubber membranes in freeze-thaw test specimens has also been reported
in other works (Bager and Jacobsen, 1999). The use of rubber membranes however
required calibrating the “wave transit times measured using membranes” to the “wave
transit times measured using grease couplant” which was performed using specimens
of various sizes of the same SRW mix tested in this study. These specimens had been
previously immersed in 13 mm (½ in.) of 3% NaCl solution for 24 hours. The
relationship between transit times measured using the different coupling media is
shown in Figure 15. The measured transit times using rubber membranes were thus
corrected using the equation shown in Figure 15 to obtain equivalent transit times
using grease. This corrected value was then used in the computation of pulse velocity.
Pulse velocities were typically measured at four separate locations on the specimen, as
shown in Figure 16 and the average velocity of these four locations was taken as being
representative of the overall specimen. In addition, calibration checks of the
equipment using the manufacturer’s standard steel rod (at standard transit time of 26.0
February 5, 2009
FINAL REPORT 37
µs) were carried out after every 1 to 2 specimens to ensure all readings were being
taken on a consistent basis.
a) schematic of pulse velocity test
b) Pictures of equipment and setup at Cornell.
Figure 14 Pulse velocity test setup.
Pulse generator
Receiver amplifier Time
measuring unit
Transmitting transducer
Receiving transducer
L
V = L ∆t
L = travel distance ∆t = transit time
Pulse velocity:
February 5, 2009
FINAL REPORT 38
Figure 15 Relationship between transit times measured using different types of coupling media.
Figure 16 Pulse velocity measuring locations on specimen.
y = 1.02x + 1.76R2 = 1.00
0
10
20
30
40
50
60
0 10 20 30 40 50 60Transit time using rubber membranes (µs)
Tran
sit t
ime
usin
g gr
ease
(µs)
0.224L 0.224L 0.552L 0.33W
coincident with supports for resonant frequency test
February 5, 2009
FINAL REPORT 39
3.6 Visual scaling rating
The approach used in ASTM C 672 (ASTM C 672, 2004) for visually rating concrete
specimens was employed in this study. In this test method, specimens are rated on a
scale of 0 to 5, with 0 representing “No Scaling” and 5 representing “Severe Scaling
with coarse aggregate visible over entire surface”. The C 672 rating scale is however
rather subjective as it relies on qualitative descriptors such as “slight”, “moderate” and
“severe” scaling to discriminate between levels of scaling. Moreover, the rating guide
was developed primarily for ordinary concretes which may contain aggregate sizes
larger than those found in SRW concretes. For our purposes, this rating system was
modified to enable a more quantitative assessment of damage. The modified C 672
rating scale is based primarily on the percentage of area (on the test face of the
specimen) that is scaled as shown in Table 5 below.
Table 5 Area-based scaling rating of SRW specimens.
Rating % Area Scaled ASTM C 672 description (for reference)
0 < 10 No scaling
1 10 – 20 very slight scaling (3 mm [1/8 in.] depth, max) no coarse aggregate visible
2 20 – 30 slight to moderate scaling
3 30 – 60 moderate scaling (some coarse aggregate visible)
4 60 – 90 moderate to severe scaling
5 > 90 severe scaling (coarse aggregate visible over entire surface)
In this rating system the primary emphasis is on the area scaled based on the ASTM C
672 criterion for concrete, since scaled area relates to appearance and thus, in some
cases, to an owner’s subjective impression of performance. A secondary issue is the
depth of scaling which is nevertheless important although more difficult to assess. An
February 5, 2009
FINAL REPORT 40
approximate evaluation of depth of scaling could be obtained by dividing mass loss by
area scaled. Section 8 of this report discusses mass loss and visual scaling rating.
3.7 Modulus of rupture
Modulus of rupture (MoR) tests were conducted according to the methods of ASTM C
78 (ASTM C 78, 2004), which consists of a beam subjected to third-point loading.
For specimens that were 200 mm (8 in.) long, a 175 mm (7 in.) span was used with
supports equally spaced 59 mm (2.3 in.) apart; while for specimens that were 150 mm
(6 in.) long, a 125 mm (5 in.) span was used with supports spaced 42 mm (1.7 in.)
apart. These configurations are illustrated in Figure 17. All MoR tests were
performed in such manner that the face in tension corresponded to the test face of the
specimen (i.e., the molded face in the solution), as shown in Figure 17. In addition,
except for specimens tested prior to start of freeze-thaw cycling, all MoR test
specimens were wrapped in plastic film during testing to prevent drying of their
surfaces. These tests were all performed in a 60-kip Baldwin loading frame in Cornell
University’s Winter Laboratory.
Since one of the primary objectives of this study was to determine whether any
relationship existed between mass loss of ASTM C 1262 freeze-thaw specimens and
their MoR, specimens from the PC Series were selected for MoR testing at appropriate
times in such manner that mass loss values in the range of less than 2% were obtained
among all PC Series specimens. Once tested for MoR, these specimens were placed
back with the rest of the PC population for continued freeze-thaw cycling. In addition,
most specimens from the Variability Series were tested for their MoR at the
conclusion of 200 cycles, at which point mass loss for these specimens was generally
February 5, 2009
FINAL REPORT 41
greater than 2%. In the PC Series, 5 specimens were tested after 200 cycles and 6
specimens were tested between 200 and 300 cycles.
Figure 17 Modulus of rupture (MoR) testing of specimens.
P/2 P/2
P/2 P/2L
L/3 L/3 L/3 For 200 mm (8 in) specimens: L = 175 mm (7.0 in.) L/3 = 59 mm (2.3 in.) For 150 mm (6 in) specimens: L = 125 mm (5.0 in.) L/3 = 42 mm (1.7 in.)
portion of specimen under solution
February 5, 2009
FINAL REPORT 42
4.0 FREEZER SURVEY
Prior to initiating freeze-thaw testing, the freezers used in this study were surveyed for
their internal temperature characteristics as described in Appendix A. (See also Hance
(2005) and Chan (2006). These surveys served the following purposes:
• to determine the range of variability in the freezer as well as identify cold and
warm locations within the freezer, and
• to enable a more rational approach towards the selection of length of cycles.
Once freeze-thaw tests were initiated, temperature-time data from the freezers was
collected whenever possible for purposes of monitoring the overall performance of
freezers including cycle-to-cycle reproducibility. The results of the surveys for each
of the two freezers and overall freezer performance are described separately.
4.1 Tenney freezer
4.1.1 Pre-test survey
The Tenney freezer was surveyed using 23 thermocouples distributed throughout the
freezer cabin. Five thermocouples were placed in each of the four shelves in the
freezer and additional thermocouples were also placed near the cabin ceiling, the cabin
floor and the freezer internal temperature sensors. These placements are shown in
Figure 18. The freezer survey was carried out using the same number of specimens
(28) and the same arrangement (7 specimens per shelf) as that used in the actual tests.
In this manner, the actual test environments were simulated as close as possible during
the survey.
February 5, 2009
FINAL REPORT 43
Figure 18 View of thermocouple placement in Tenney freezer instrumented tests.
TC on ceiling
TC on floor
TC by sensors
freezer internal sensors
grate on
grate removed
5 TC’s on each shelf (4 at corners, 1 at center)
×
×
×
×
×
TC at about 25 mm (1 in.) above shelf
TC = thermocouple
February 5, 2009
FINAL REPORT 44
A typical cooling response for the surveyed locations, along with the overall average
freezer air temperature and standard deviation as function of time are shown in Figure
19. The coldest locations generally corresponded to those in the front part of the
freezer (i.e., near the door) and on the highest shelves (including the ceiling), while the
warmest locations corresponded to those towards the back of the freezer in the lowest
shelves (including the floor). The coldest overall spot was right at the location of the
freezer internal (built-in) temperature sensor, near the fan, whereas the warmest
overall location was at the back of the bottommost shelf. These spatial temperature
variations are shown in Figure 20a. This pattern of temperature distribution generally
coincided with the flow of air within the chamber, illustrated in Figure 20b where it is
seen that air coming out from the fan (the coldest air) reaches the top shelf and freezer
front locations first. On the other hand, the back locations in the lower shelves are
more or less “sheltered,” and as such, displayed the warmest temperatures.
One important conclusion from this survey is the fact that using the temperature
readout from the freezer built-in temperature sensor as the cycle-controlling
temperature may result in a significant number of specimen locations being
undercooled (i.e., receiving less than the ASTM C 1262 required 4-hr cold soak). This
is because as shown in Figure 19a, the built-in sensor was located at the coldest
overall location in the freezer. At the time the sensor temperature reached –13°C (1.7
hours), the average freezer internal temperature was –11.3°C (11.7°F) and the standard
deviation was 0.8°C (1.4°F). Thus, the sensor temperature was at about 2.1 × standard
deviation from the mean which implied that 98% of the total freezer locations were
still warmer than –13°C. For reference, the warmest measured location at this time
was at –9.7°C (14.5°F) corresponding to the back of the bottommost shelf, as
February 5, 2009
FINAL REPORT 45
a) Measured temperatures at various locations
b) Average and standard deviation of measured temperatures
Figure 19 Typical cooling response of Tenney freezer as measured from survey.
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11
Time (hr)
Tem
pera
ture
(ºC
)
freezer internal (built-in) temperature sensor
0
20
40
60
Tem
pera
ture
(°F)
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11
Time (hr)
Tem
pera
ture
(ºC
)
-5
-4
-3
-2
-1
0
1
2
3
4
5
Stan
dard
dev
iatio
n (°
C)
Average
St Dev
0
20
40
60
Tem
pera
ture
(°F)
February 5, 2009
FINAL REPORT 46
a) individual temperature locations (front view of freezer, plan view of each shelf)
b) side view of freezer cabin
Figure 20 Temperature mapping in Tenney freezer.
air flow
fan
air intake
door
front back
warmest spots
coldest spots
Temp. ranges: 1: –18.5 to –18.2°C 2: –17.7 to –18.0°C 3: –17.6 to –17.7°C 4: –17.1 to –17.5°C 5: –16.6 to –17.1°C 6: –16.0 to –16.4°C
fan
air intake
1ceiling
1
freezer internal sensor
5floor
4
2
3
13
4
3
5
23
5
4
6
46
6
2
5
26
front of freezer
back of freezer
February 5, 2009
FINAL REPORT 47
described above. This warmest location did not reach –13°C until 2.1 hours, or 0.4
hours after the sensor reached –13°C. The concern is that if this built-in sensor’s
temperature was used as the cycle-controlling temperature, depending on the selected
length of cold soak (4 to 5 hours), locations inside the freezer cabin may or may not be
compliant with ASTM C 1262. For instance, if the cold soak duration was selected as
being 4 hours long, based on the above analysis, 98% of the freezer locations would
not have received the minimum 4 hours cold soak before the warming branch of the
cycle started. The back of the bottommost shelf would only receive 3.6 hours of cold
soak. One solution to remedy this issue for this particular freezer (in which the built-
in sensor’s location was determined to be the coldest overall location) is to use the
sensor temperature as the cycle-controlling temperature and recognizing that this is the
coldest measured location in the freezer, run the cold soak for a longer period of time.
Alternatively, one could target a lower cold-soak temperature.
A rational approach is to evaluate the freezer through Reliability Curves (or R-curves)
which are obtained using the procedures outlined in Appendix A and explained in
more detail by Hance (2005) and Chan (2006). R-curves provide the proportion of
locations that are compliant with the ASTM C 1262 cold soak requirements as
function of the length of cooling branch (Figure 21). For the measured temperatures
and variability in the Tenney freezer loaded with 28 specimens (Figure 19a and b), its
R-curve is shown in Figure 21. Here, it is seen that for the particular shapes of
temperature-time curves and temperature distribution measured in this freezer, cooling
branches anywhere from 6.1 to 6.7 hours long yielded the maximum proportion of
compliant locations (> 95%). In this study, a cooling branch length of about 6.4 hours
was thus initially targeted which resulted in a cold soak of 4.6 hrs. This target
February 5, 2009
FINAL REPORT 48
Figure 21 R-curve obtained from survey of Tenney freezer loaded with 28 specimens.
temperature-time response was obtainable using the programmed profile shown earlier
in Section 3.2. As a related note, if the length of cold soak in the profile had been
entered as 4.0 hours instead of the currently used 4.5 hours, the length of cooling
branch would be about 5.9 hours (current 6.4 hours cooling branch minus 0.5 hours),
which yields a reliability of 42%, meaning that only 42% of the measured locations
would meet the cold soak requirements of ASTM C 1262. Depending on freezer
controls it may be possible to arrive at other settings that would produce an equivalent
probability that all specimens experience the specified micro-climate.
4.1.2 Freezer performance during tests
Frequent collection of temperature data during actual tests enabled monitoring the
performance of the freezer and implementation of changes if needed. Perhaps the
most notable finding in this respect concerns the length of warm soak and its effect on
overall freezer response. The first 40 cycles of testing in the Tenney were conducted
0102030405060708090
100
5.0 5.5 6.0 6.5 7.0 7.5 8.0Length of cooling branch (hr)
Rel
iabi
lity
(%)
-30
-20
-10
0
10
20
30
0 1 2 3 4 5 6 7 8 9 10
Time (hours)
Tem
p. (º
C)
-22
-13
-4
5
14
23
32
41
50
59
68
77
86
Tem
p. (°
F)
length of cooling branch
February 5, 2009
FINAL REPORT 49
using a programmed warm soak length of 4.5 hours. This produced consecutive
freeze-thaw cycles such as those shown in Figure 22 for the first 10 cycles of the test
program (average temperature shown). At first glance, all 10 cycles appeared similar
and reproducible. Analysis (including reliability analysis) of the each of these cycles
yielded the results summarized in Table 6. A closer inspection of the data revealed
that the rate of cooling decreased from each cycle to the next cycle, as noted from the
increasingly longer times to reach –13°C. This behavior was in turn reflected in the
R-curves for this set of 10 cycles, as shown in Figure 23, where the R-curves are seen
to gradually drift to the right with increasing cycles. This same trend was also
observed in Cycles 12 to 13, 25 to 30 and 31 to 40. Although the individual cycles
were optimized for maximum R, this overall behavior indicated an increasingly less
efficient freezer performance from cycle to cycle. It was hypothesized that the warm
soak duration was related to this phenomenon from the observation that the first cycle
in each set of 10 cycles required approximately similar times to reach –13°C but that
this time increased with consecutive cycles (note that there was a 2-day period of
freezer inactivity between sets of 10 cycles). It was thus suspected that longer warm
soak times enabled more thorough thawing of freezer components which render the
freezer more efficient in the following cycle. As such, the warm soak duration in each
cycle was prolonged to 6.0 hours. An example of results obtained with this modified
cycle length is shown for Cycles 51 to 60 in Figure 24 with corresponding cooling
length parameters summarized in Table 7 and the corresponding R-curves are shown
in Figure 25, where more uniformity is evident. Figure 26 shows a plot of “time to
reach –13°C” for most cycles from start to Cycle 85. It is seen that in each set of 10
cycles through the first 40 cycles the “time to reach –13°C” increased with increasing
cycles. Beyond 40 cycles (after switching warm soak parameters), the “time to reach
February 5, 2009
FINAL REPORT 50
–13°C” generally decreased or remained constant within each set of 10 cycles. Hence
a programmed warm soak duration of 6.0 hrs was employed from Cycle 41 onwards.
a) cycles 1 to 5
b) cycles 6 to 10
Figure 22 Temperature-time response for first 10 cycles in Tenney freezer.
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40 45 50 55
Time (hrs)
Tem
pera
ture
(ºC
)
Tsensor
Tavg
-25
-20
-15
-10
-5
0
5
10
15
20
25
55 60 65 70 75 80 85 90 95 100 105 110
Time (hrs)
Tem
pera
ture
(ºC
)
February 5, 2009
FINAL REPORT 51
Table 6 Summary of cooling length parameters for Cycles 1 to 10 in Tenney freezer.
Cycle Time to
reach –13°C (hrs)
Optimum range of cooling branch a
(hrs)
Optimum range of cold soak b
(hrs)
Actual duration of cold soak c
(hrs) 1 1.5 5.7 – 6.4 4.2 – 4.9 4.6 2 1.6 5.8 – 6.5 4.2 – 4.9 4.6 3 1.6 5.8 – 6.5 4.2 – 4.9 4.6 4 1.6 5.8 – 6.5 4.2 – 4.9 4.6 5 1.7 5.8 – 6.6 4.1 – 4.9 4.5 6 1.7 5.9 – 6.6 4.2 – 4.9 4.6 7 1.7 5.9 – 6.6 4.2 – 4.9 4.6 8 1.7 5.9 – 6.6 4.2 – 4.9 4.6 9 1.7 5.9 – 6.6 4.2 – 4.9 4.6
10 1.8 5.9 – 6.7 4.1 – 4.9 4.6 a for R > 95% b based on optimum range of cooling branch and time to reach –13°C c during tests
Figure 23 R-curves for first 10 cycles in Tenney freezer.
0102030405060708090
100
5.0 5.5 6.0 6.5 7.0 7.5 8.0Length of cooling period (hr)
Rel
iabi
lity
(%)
increasing cycles
February 5, 2009
FINAL REPORT 52
a) cycles 51 to 55
b) cycles 56 to 60
Figure 24 Temperature-time response Cycles 51 to 60 in Tenney freezer.
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (hrs)
Tem
pera
ture
(ºC
)
Tsensor
Tavg
-25
-20
-15
-10
-5
0
5
10
15
20
25
60 65 70 75 80 85 90 95 100 105 110 115 120 125
Time (hrs)
Tem
pera
ture
(ºC
)
February 5, 2009
FINAL REPORT 53
Table 7 Summary of cooling length parameters for Cycles 51 to 60 in Tenney freezer.
Cycle Time to
reach –13°C (hrs)
Optimum range of cooling branch a
(hrs)
Optimum range of cold soak b
(hrs)
Actual duration of cold soak c
(hrs) 51 1.7 5.9 – 6.5 4.2 – 4.8 4.7 52 1.6 5.8 – 6.5 4.2 – 4.9 4.6 53 1.6 5.8 – 6.5 4.2 – 4.9 4.7 54 1.6 5.8 – 6.5 4.2 – 4.9 4.6 55 1.6 5.8 – 6.5 4.2 – 4.9 4.6 56 1.6 5.8 – 6.5 4.2 – 4.9 4.6 57 1.6 5.8 – 6.5 4.2 – 4.9 4.6 58 1.7 5.8 – 6.5 4.1 – 4.8 4.6 59 1.7 5.8 – 6.5 4.1 – 4.8 4.6 60 1.7 5.8 – 6.5 4.1 – 4.8 4.6
a for R > 95% b based on optimum range of cooling branch and time to reach –13°C c during tests
Figure 25 R-curves for Cycles 51 to 60 in Tenney freezer.
0102030405060708090
100
5.0 5.5 6.0 6.5 7.0 7.5 8.0
Length of cooling period (hr)
Rel
iabi
lity
(%)
February 5, 2009
FINAL REPORT 54
Figure 26 Times to reach –13°C for Tenney freezer.
It is noted that as a result of these observations the warm-soak time was extended, thus
increasing the duration of not only a single cycle, but potentially increasing the
duration of the entire test. (“Down days” every ten cycles buffered that effect in this
case.) Whether the reliability and repeatability gained is worth the additional time
(and cost) depends on the degree to which the variability of the test results is reduced.
One might analyze the probability and associated cost of misjudging specimen
performance due to test variability to make a value judgment about extending test
duration, but such analysis has not been conducted here.
1.0
1.2
1.4
1.6
1.8
2.0
0 10 20 30 40 50 60 70 80 90 100
Cycle
Tim
e to
reac
h -1
3°C
(hrs
)
no data collection no data
collection
programmed warm soak: 4.5 hrs
programmed warm soak: 6.0 hrs
February 5, 2009
FINAL REPORT 55
4.2 Walk-in freezer
4.2.1 Pre-test survey
The walk-in freezer was surveyed using 24 thermocouples attached onto the cart
shelves holding the specimens. A schematic of this arrangement is shown in Figure 27
along with position references. As with the Tenney freezer, the survey was carried out
using the same number of specimens (16) and the same arrangement (4 specimens on
each of the 4 cart shelves) as that used in the actual tests. In this manner, the actual
test environments were simulated as close as possible during the survey.
A typical cooling response for the surveyed locations, along with the overall average
freezer air temperature and standard deviation as function of time are shown in Figure
28. In general, along the E-W direction (ref. Figure 27), the coldest locations
corresponded to those in the Center where the temperatures were generally about
0.5°C (0.9°F) colder than those in either East or West sides. The back side of the
freezer (opposite to the entrance) was also generally colder than the Front side of the
freezer by about 0.3°C (0.5°F). No significant variations were observed with respect
to Top or Bottom shelves.
February 5, 2009
FINAL REPORT 56
Figure 27 Schematic of thermocouple placement in walk-in freezer.
× thermocouple
× × × × ×
× × × × ×
specimen
TOP
BOTTOM
Elevation view
× × × × ×
× × × × ×
× ×
Plan view
EAST WEST CENTER
BACK
FRONT
entrance specimen
February 5, 2009
FINAL REPORT 57
a) Measured temperatures at various locations
b) Average and standard deviation of measured temperatures
Figure 28 Typical cooling response of walk-in freezer as measured from survey.
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10
Time (hr)
Tem
pera
ture
(ºC
)
0
20
40
60
Tem
pera
ture
(°F)
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10
Time (hr)
Tem
pera
ture
(ºC
)
-3
-2
-1
0
1
2
3
Stan
dard
dev
iatio
n (°
C)
Average
St Dev
0
20
40
60
Tem
pera
ture
(°F)
February 5, 2009
FINAL REPORT 58
For the measured temperatures and variability in the walk-in freezer loaded with 16
specimens (Figure 28a and b), its R-curve is shown in Figure 29. Here it is seen that
cooling branches anywhere from 5.9 to 6.6 hours long yielded the maximum
proportion of compliant locations (> 95%). In this study, a cooling branch length of
about 6.3 to 6.4 hours was thus initially targeted which resulted in a cold soak of about
4.5 hrs. Figure 29 R-curve obtained from survey of walk-in freezer loaded with 16 specimens.
4.2.2 Freezer performance during tests
Temperature-time data was obtained for Cycles 11 to 20 and from Cycle 80 to 180.
For Cycles 11 to 20, the train of consecutive cooling curves is shown in Figure 30,
their corresponding R-curves in Figure 31 and the cooling parameters in Table 8. It is
noted that this set of 10 curves slightly lagged those obtained during the survey by
about 0.1 to 0.2 hours. Note also that the optimum range of cooling branch length
measured for this set of 10 cycles was about 6.1 to 6.7 hours compared to the 5.9 to
0102030405060708090
100
5.0 5.5 6.0 6.5 7.0 7.5 8.0Length of cooling branch (hr)
Rel
iabi
lity
(%)
-30
-20
-10
0
10
20
30
0 1 2 3 4 5 6 7 8 9 10
Time (hours)
Tem
p. (º
C)
-22
-13
-4
5
14
23
32
41
50
59
68
77
86
Tem
p. (°
F)
length of cooling branch
February 5, 2009
FINAL REPORT 59
a) cycles 11 to 15
b) cycles 16 to 20
Figure 30 Temperature-time response for Cycles 11 to 20 in walk-in freezer.
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (hrs)
Tem
pera
ture
(ºC
)
-25
-20
-15
-10
-5
0
5
10
15
20
25
60 65 70 75 80 85 90 95 100 105 110 115 120
Time (hrs)
Tem
pera
ture
(ºC
)
February 5, 2009
FINAL REPORT 60
Table 8 Summary of cooling length parameters for Cycles 11 to 20 in walk-in freezer.
Cycle Time to
reach –13°C (hrs)
Optimum range of cooling branch a
(hrs)
Optimum range of cold soak b
(hrs)
Actual duration of cold soak c
(hrs) 11 2.1 6.1 – 6.7 4.0 – 4.6 4.3 12 2.1 6.1 – 6.7 4.0 – 4.6 4.3 13 2.1 6.1 – 6.7 4.0 – 4.6 4.3 14 2.1 6.1 – 6.7 4.0 – 4.6 4.2 15 2.0 6.1 – 6.7 4.1 – 4.7 4.3 16 2.0 6.1 – 6.7 4.1 – 4.7 4.3 17 2.0 6.1 – 6.7 4.1 – 4.7 4.2 18 2.0 6.1 – 6.7 4.1 – 4.7 4.3 19 2.0 6.0 – 6.7 4.0 – 4.7 4.3 20 2.1 6.1 – 6.7 4.1 – 4.6 4.3
a for R > 95% b based on optimum range of cooling branch and time to reach –13°C c during tests
Figure 31 R-curves for Cycles 11 to 20 in walk-in freezer.
0102030405060708090
100
5.0 5.5 6.0 6.5 7.0 7.5 8.0Length of cooling period (hr)
Rel
iabi
lity
(%)
February 5, 2009
FINAL REPORT 61
6.6 hours obtained from the survey. Hence, the programmed length of cold soak in
the freezer control unit was extended by 6 mins from 6.2 to 6.3 hours, as shown earlier
in Section 3.2. Overall, from the R-curves it is nevertheless seen that these 10 cycles
were consistent with one another and fully compliant with ASTM C 1262.
Results for Cycles 101 to 110 are shown in Figure 32 (train of consecutive cooling
curves), Figure 33 (their corresponding R-curves) and Table 9 (cooling parameters).
The response measured for this set of 10 cycles was similar and representative of that
measured for Cycles 80 to 180. It is now seen that the freezer appeared to have
become more efficient in terms of reaching cold soak faster (about 1.7 to 1.8 hrs to
reach –13°C, compared to 1.8 hrs in the survey and 2.0 to 2.1 hrs in Cycles 10 to 20).
As a consequence, the R-curves shifted to the left in Figure 33 with an optimum range
of cooling branch length of about 5.7 to 6.5 hrs, compared to 6.1 to 6.7 hrs for Cycles
11 to 20. For Cycles 101 to 110 shown, as was the case for most cycles from between
80 to 180, the actual cold soak duration was about 4.8 hrs. In reference to the R-
curves for this set of cycles, at 4.8 hrs cold soak, the reliability was still at 100%.
February 5, 2009
FINAL REPORT 62
a) cycles 101 to 105
b) cycles 106 to 110
Figure 32 Temperature-time response for Cycles 101 to 110 in walk-in freezer.
-30
-20
-10
0
10
20
30
0 5 10 15 20 25 30 35 40 45 50 55 60
Time (hrs)
Tem
pera
ture
(ºC
)
-30
-20
-10
0
10
20
30
60 65 70 75 80 85 90 95 100 105 110 115 120
Time (hrs)
Tem
pera
ture
(ºC
)
February 5, 2009
FINAL REPORT 63
Table 9 Summary of cooling length parameters for Cycles 101 to 110 in walk-in freezer.
Cycle Time to
reach –13°C (hrs)
Optimum range of cooling branch a
(hrs)
Optimum range of cold soak b
(hrs)
Actual duration of cold soak c
(hrs) 101 1.6 5.6 – 6.4 4.0 – 4.8 4.8 102 1.7 5.7 – 6.4 4.0 – 4.7 4.8 103 1.7 5.7 – 6.5 4.0 – 4.8 4.8 104 1.8 5.7 – 6.5 4.0 – 4.7 4.7 105 1.7 5.7 – 6.5 4.0 – 4.8 4.7 106 1.7 5.7 – 6.5 4.0 – 4.8 4.7 107 1.7 5.7 – 6.5 4.0 – 4.8 4.7 108 1.8 5.7 – 6.5 4.0 – 4.7 4.7 109 1.7 5.7 – 6.5 4.0 – 4.8 4.7 110 1.7 5.7 – 6.5 4.0 – 4.8 4.7
a for R > 95% b based on optimum range of cooling branch and time to reach –13°C c during tests
Figure 33 R-curves for Cycles 101 to 110 in walk-in freezer.
0102030405060708090
100
5.0 5.5 6.0 6.5 7.0 7.5 8.0Length of cooling period (hr)
Rel
iabi
lity
(%)
February 5, 2009
FINAL REPORT 64
5.0 RESULTS AND DISCUSSION – ASTM C 1262 Mass Loss
5.1 Mass loss results
ASTM C 1262 mass loss values are based on the mass of residues (after n number of
freeze-thaw cycles in saline) expressed as percentage of initial oven-dry mass of
specimen. In this study, measurements were made at 10-cycle intervals up to a total of
200 cycles for all specimens in the Variability Series, and 240 cycles for the
Performance Criteria Series.
5.1.1 Mass Loss Results-Performance Criteria Series
Figure 34 shows cumulative mass loss as function of number of cycles for all
specimens in the PC Series. The overall average of all 16 specimens was 0, 0.2, 0.4
and 0.8% after 50, 100, 150 and 200 cycles. While most specimens were banded
together and behaved similarly up to about 120 cycles, two specimens exhibited jumps
in mass loss. Specimen C2L exhibited a jump between 70 and 80 cycles, while
specimen C5L exhibited a jump between 90 to 100 cycles. In both cases, this jump
was caused by aggregate/mortar popouts which caused a corner of the specimens to
fall off as shown in Figure 35.
Given the increased vulnerability of edges and corners, mass losses occurring at these
locations may not be representative of overall specimen behavior and durability.
Refer to section 5.2 for one way to identify such non-representative mass loss.
February 5, 2009
FINAL REPORT 65
Figure 34 Cumulative mass loss for PC Series specimens.
C2L after 80 cycles C5L after 100 cycles
Figure 35 Corner aggregate and mortar popouts resulting in mass loss jump.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 40 80 120 160 200Cycles
Perc
ent m
ass
loss
February 5, 2009
FINAL REPORT 66
5.1.2 Mass loss results-variability test series
Figure 36 shows plots of cumulative mass loss (in a scale up to 100%) as function of
number of cycles for each individual Test Set, and Figure 37 shows these same plots
in a scale up to 3% mass loss. In each graph, curves for individual specimens as well
as for the average (bold curve) of the 4 specimens in the Test Set are shown. Figure
38 shows the Test Set average curves plotted together. The coarse resolution of the
vertical scale in Figure 36 suggests similar behavior of all specimens up to about 140
cycles, but the finer detail of Figure 37 (magnified by a factor of 33.3) shows that
specimen behavior began to be differentiated at about 50 cycles for different Test Sets.
For example, various specimens in Test Sets B and F exhibited rapid increases in mass
loss beyond 50 cycles, whereas specimens in Test Sets A and G showed steady
increases in their mass loss. Specimens in Test Sets C, D and E showed intermediate
increases in mass loss.
February 5, 2009
FINAL REPORT 67
Test Set A
0102030405060708090
100
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ssTest Set B
0102030405060708090
100
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Test Set C
0102030405060708090
100
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Test Set D
0102030405060708090
100
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Test Set E
0102030405060708090
100
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Test Set F
0102030405060708090
100
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Test Set G
0102030405060708090
100
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Figure 36 Cumulative mass loss for Variability Series (mass loss scale to 100%)
Individual specimens shown as light lines. Average of test set shown as bold line.
February 5, 2009
FINAL REPORT 68
Test Set A
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ssTest Set B
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Test Set C
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200
Cycles
Per
cent
mas
s lo
ss
Test Set D
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Test Set E
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200
Cycles
Per
cent
mas
s lo
ss
Test Set F
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Test Set G
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Per
cent
mas
s lo
ss
Figure 37 Cumulative mass loss for Variability Series (mass loss scale to 3%)
Individual specimens shown as light lines. Average of test set shown as bold line.
February 5, 2009
FINAL REPORT 69
Figure 38 Test Set averages for Variability Series.
As for forms of damage, up to about 100 cycles most specimens exhibited little loss of
material on their test faces. The exceptions were specimens B3, D1, E4 and F2 which
developed pockmarks and some scaling on this test face by 100 cycles, as shown in
Figure 39 after 100 cycles. Damage in most other specimens occurred primarily on
the side surfaces, as exemplified in Figure 40 for specimen D4. Beyond 100 cycles,
the forms and extent of deterioration varied among the various specimens. Examples
of damage after 150 cycles for specimens B4, D1 and F2 are shown in Figure 41, in
which extensive surface scaling can be seen on specimen F2. Also beyond 100 cycles,
cracking on the specimens became more prominent, either in the form of surface
cracks (Figure 42a) or through-cracks (from top to bottom surface, Figure 42b).
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Perc
ent m
ass
loss
A
C
D
E
F
G
B
February 5, 2009
FINAL REPORT 70
Figure 39 Specimens with damage on test face after 100 cycles in NaCl.
Figure 38 Damage on side surfaces, specimen D4.
Figure 40 Damage on side surfaces, specimen D4 after 100 cycles in NaCl.
B3: ML = 1.4% D1: ML = 0.6%
E4: ML = 0.8% F2: ML = 0.9%
localized loss of material
D4: ML= 0.5%
February 5, 2009
FINAL REPORT 71
Figure 41 Extent of damage after 150 cycles in NaCl.
B4: ML= 0.3%
D1: ML = 1.7%
F2: ML = 2.3%
February 5, 2009
FINAL REPORT 72
a) Cracks on top (non-submerged) surface of specimen (B3 after 140 cycles)
b) Through cracks on specimen D2
Figure 42 Forms of cracking on specimens.
February 5, 2009
FINAL REPORT 73
After 150 cycles, no evident cracking After 160 cycles, hairline crack
After 170 cycles, macrocrack noted After 180 cycles, break-up
Figure 43 Example of continued crack growth leading to complete disintegration of
specimen C1. (ML prior to 150 cycles = 1.7%)
As will be described in Section 6, the observation of cracking on specimens normally
coincided with the time when resonant frequencies declined. Typically, once cracks
were first observed on specimens, continuous crack propagation and new crack
formation were evident in subsequent cycles leading to break-up of some specimens
(see Figure 43 for example in specimen C1).
February 5, 2009
FINAL REPORT 74
5.1.3 Overall performance evaluation of the variability and performance criteria
test series specimens
As far as mass loss specification limits are concerned, ASTM C 1372, which specifies
material performance requirements for Segmental Retaining Wall Units (ASTM C
1372, 2003), currently contains only freeze-thaw durability specification for tests in
water, but not for saline. For tests in water, ASTM C 1372 requires that the mass loss
of all replicate test specimens (5 in a set) shall not exceed 1% after 100 cycles or that
the mass loss of 4 out of 5 replicate test specimens shall not exceed 1.5% after 150
cycles. For reference, the Minnesota Department of Transportation has different
criteria for passing or failing mixes based on testing in saline solution (MnDOT,
2001). These are stated as follows:
“The freeze/thaw durability of wall units tested in accordance with ASTM C 1262 in a
3% saline solution shall be the minimum of the following:
1) The weight loss of each of five test specimens at the conclusion of 90 cycles
shall not exceed 1% of its initial weight; or
2) The weight loss of 4 out of 5 specimens at the conclusion of 100 cycles
shall not exceed 1.5% of its initial weight, with the maximum allowable
weight loss for the 5th specimen to not exceed 10%.”
As such, all 28 specimens in Test Sets A to G complied with the requirements of both
these clauses. All specimens in the performance series complied as well.
February 5, 2009
FINAL REPORT 75
5.1.4 Effect of various specimen configurations-variability test series
The essence of the variability experiment was that seven test specimen/container
configurations were evaluated in head-to-head comparative testing as shown in Table
1 and Figure 1 below (both reprinted from Section 1.2 of this report.).
Table 1 Test Sets in Variability Test Series (From Section 1.1)
Set Size of container a
Dimensions of specimen, mm × mm (in. × in.)
Specimen area, mm2 (in.2)
Aspect ratio
Solution depth,
mm (in.)
Approx. solution
clearance b mm, mm (in., in.)
A Lg Rect 100 × 200 (4 × 8)
20,000 (32) 1:2 13
(1/2) 30 L, 30 W (1.2, 1.2)
B Lg Rect 100 × 200 (4 × 8)
20,000 (32) 1:2 10
(3/8) 30 L, 30 W (1.2, 1.2)
C Lg Rect 100 × 200 (4 × 8)
20,000 (32) 1:2 16
(5/8) 30 L, 30 W (1.2, 1.2)
D Sm Rect 100 × 200 (4 × 8)
20,000 (32) 1:2 13
(1/2) 5 L, 20 W (0.2, 0.8)
E Sm Rect 75 × 150 (3 × 6)
11,250 (18) 1:2 13
(1/2) 30 L, 33 W (1.2, 1.3)
F Sm Rect 113 × 150 (41/2 × 6)
16,950 (27) 1:1.3 13
(1/2) 30 L, 15 W (1.2, 0.6)
G Sq 133 × 150 (51/3 × 6)
20,000 (32) 1:1.1 13
(1/2) 25 L, 15 W (1.0, 0.6)
a Container sizes as follows (more information provided in Section 2.0): Lg Rect: inner dimensions of 260 × 160 mm (10.4 × 6.4 in.) at base of container Sm Rect: inner dimensions of 210 × 140 mm (8.4 × 5.6 in.) at base of container Sq: inner dimensions of 183 × 183 mm (7.3 × 7.3 in.) at base of container b L: in the long direction, W: in the wide direction
February 5, 2009
FINAL REPORT 76
Figure 1 Specimen and container dimensions (From Section 1.1)
Essential results of the test program are presented in Table 10, showing cumulative
mass loss as of 50, 100, 150, and 200 cycles of freezing and thawing in saline.
Statistical analyses were performed on these data, the details of which are included as
an appendix to this report). These analyses indicated that statistically significant
differences existed in freeze-thaw behavior among the specimen/container
configurations. Analysis also produced equations to predict mass loss as a function of
number of cycles for each specimen/container configuration, also shown in the
appendix.
Effect of Test Details
Test Set A Test Set B Test Set C
Test Set D Test Set E Test Set F Test Set G
0.8”
0.2”
1.3”
1.2”
0.6”
1.2”0.6”
1.0”
depths: 1/2” 3/8” 5/8”
Tenney
February 5, 2009
FINAL REPORT 77
Table 10 Cumulative mass loss (%) for the Test Sets after specified number of cycles.
Test Set Container Coupon mm (in) 50 cycles 100
cycles 150
cycles 200
cycles
A Lg Rect (Control)
100 × 200 (4 × 8) 0.1 0.5 1.0 4.6
B Lg Rect (Underfill)
100 × 200 (4 × 8) 0.1 0.7 2.6 37
C Lg Rect (Overfill)
100 × 200 (4 × 8) 0.2 0.7 1.6 26
D Sm Rect 100 × 200 (4 × 8) 0.2 0.5 1.3 51
E Sm Rect 75 × 150 (3 × 6) 0.1 0.7 1.8 7.0
F Sm Rect 113 × 150 (41/2 × 6) 0.2 0.6 1.8 28
G Sq 133 × 150 (51/3 × 6) 0.1 0.4 0.9 2.5
Using cumulative, observed behavior as of 50 cycles, 100 cycles, and 150 cycles it
was possible to make “most probable” estimates of 100 cycle behavior for each
specimen/container configuration. These predictions are shown graphically in Figures
44a-c below. It is important to recognize that these so-called “regression” equations
are predictors of average expected behavior based on the actual experimental results,
and the graphs that follow do not indicate the broad scatter or uncertainty
characterized by the actual test data.
February 5, 2009
FINAL REPORT 78
Figure 44a Predictions of most-probable mass loss to 200 cycles based on observations up to 50 cycles.
Figure 44b Predictions of most-probable mass loss to 200 cycles based on observations up to 100 cycles. Curve fit for “B” is obviously unrealistic for
low numbers of cycles.
Comparison of Testing VariablesBased on 50 Cycles
-0.500
0.000
0.500
1.000
1.500
2.000
0 50 100 150 200
Number of Cycles
Mas
s Lo
ssABCDEFG1% Loss100 Cycles
Comparison of Testing VariablesBased on 100 Cycles
-0.500
0.000
0.500
1.000
1.500
2.000
0 50 100 150 200
Number of Cycles
Mas
s Lo
ss
ABCDEFG1% Loss100 Cycles
February 5, 2009
FINAL REPORT 79
Figure 44c Predictions of most-probable mass loss to 200 cycles based on observations up to 150 cycles. Curve fit for “B” is obviously unrealistic for low
numbers of cycles. Using these generalized relationships the following tabulated expectations for
specimen performance were prepared.
Table 11 Predicted Performance Based on Regression Equations
Analysis based on 50 Cycles of Testing Specimen Configuration A B C D E F G Predicted Mass Loss as of 100 cycles (%) 0.46 0.38 0.36 0.70 0.70 0.84 0.31 Predicted number of cycles to 1% ML 147 184 233 136 119 109 206
Analysis Based on 100 Cycles of Testing Specimen Configuration A B C D E F G Predicted Mass Loss as of 100 cycles (%) 0.44 0.63 0.65 0.52 0.72 0.60 0.45 Predicted number of cycles to 1% ML 148 119 127 146 117 130 153
Analysis Based on 150 Cycles of Testing Specimen Configuration A B C D E F G Predicted Mass Loss as of 100 cycles (%) 0.45 0.80 0.69 0.55 0.77 0.69 0.44 Predicted Mass Loss as of 150 cycles (%) 1.03 2.78 1.62 1.29 1.81 1.79 0.92 Predicted number of cycles to 1% ML 148 106 119 133 113 117 157
Comparison of Testing VariablesBased on 150 Cycles
-0.500
0.000
0.500
1.000
1.500
2.000
0 50 100 150 200
Number of Cycles
Mas
s Lo
ss
ABCDEFG1% Loss100 Cycles
February 5, 2009
FINAL REPORT 80
Mass Loss to 50 Cycles
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
A B G E C F D
Specimen Configuration
Mas
s Lo
ss (p
erce
nt)
Table 12 Incremental Mass Loss based on Prediction Models
(% Mass Loss) Specimen Configuration A B C D E F G 0 to 50 (based on 50-cycles 0.11 0.11 0.16 0.19 0.15 0.18 0.11 50 to 100 (based on 100 cycles 0.34 0.53 0.49 0.33 0.57 0.42 0.33 Cumulative to 100 cycles 0.45 0.64 0.65 0.52 0.72 0.60 0.44 100 to 150 (based on 150 cycles 0.59 2.14 0.97 0.77 1.08 1.19 0.47 Total Mass Loss to 150 cycles 1.04 2.78 1.62 1.29 1.80 1.79 0.91
On the basis of these predictive relationships, mass loss for each specimen
configuration is plotted in comparative fashion in Figures 45a-c, below, shown as of
50, 100, and 150 cycles.
Figure 45a Expected mass loss as of 50 cycles, based on the 50-cycle
regression equations.
February 5, 2009
FINAL REPORT 81
Mass Loss to 100 Cycles
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
G A D F B C E
Specimen Configuration
Mas
s Lo
ss (p
erce
nt)
Figure 45b Expected mass loss at 100 cycles, based on 100-cycle regression equations. Note re-ordering of specimens as D and F cease to show greatest mass loss and E moves from “middle of the pack” to highest ML at 100 cycles.
Figure 45c Expected mass loss at 150 cycles, based on 150-cycle regression equations. Note further re-ordering as B ultimately shows greastest mass at 150 cycles (by a large margin), and C and E fall back
Mass Loss to 150 Cycles
0
0.5
1
1.5
2
2.5
3
G A D C F E B
Specimen Configuration
Mas
s Lo
ss (p
erce
nt)
February 5, 2009
FINAL REPORT 82
5.1.4.1 Key observations from Figures 45a, b, and c. a. General:
♦ Apparent uniformity of results is suggested by the fact that none of the
specimens tested had a mass loss in excess of 1% at 100 cycles, regardless of
specimen configuration. SRW units that are this freeze-thaw resistant will
perform well in the C 1262 test under the wide variety of specimen
configurations permitted by the current test specification.
♦ Apparent non-uniformity is suggested by the facts that for coupons all taken
from the same population of SRW units:
o As of 50 cycles the greatest mass loss was 1.7 times the least mass loss.
o As of 100 cycles the greatest mass loss was 1.6 times the least mass
loss.
o As of 150 cycles the greatest mass loss was 3 times the least mass loss.
♦ Specimen configuration has an obvious impact on C 1262 freeze-thaw test
performance.
b. As of 50 cycles (and less than 0.2% mass loss):
♦ Specimens A, B, and G exhibit the least mass loss.
♦ Specimens D and F exhibit the most mass loss.
February 5, 2009
FINAL REPORT 83
c. As of 100 cycles (and still less than 0.7% mass loss):
♦ Specimens A and G continue to exhibit the lowest mass loss.
♦ From 50 to 100 cycles Specimen E has moved from the “middle of the pack”
to exhibiting the greatest mass loss as of 100 cycles.
d. As of 150 cycles (with mass loss ranging from less than 1% to over 2.5%):
♦ Specimens A and G continue to exhibit the least mass loss (with A just
breaking over the 1% threshold at 150 cycles, and “bulletproof” G at less than
1% at 150 cycles).
♦ Specimen B shows the interesting trend of low mass loss at 50 cycles,
intermediate at 100 cycles, to having the highest mass (by a large margin) as of
150 cycles. Specimen B clearly “came from behind.”
♦ Specimen E remained high in total mass loss although overtaken by B from
100 to 150 cycles.
♦ While Specimen D exhibited the highest mass loss at 50 cycles, after this early
degradation, total mass loss at both 100 and 150 cycles was less than average
for all specimens.
e. Specimen configurations might be grouped as follows:
♦ A and G clearly represent overall damage resistance
♦ D represents damage vulnerability within the first 50 cycles
♦ E represents damage vulnerability from 50 to 100 cycles
♦ B represents damage vulnerability from 100 to 150 cycles
February 5, 2009
FINAL REPORT 84
5.1.4.2 Investigation of differences in specimen performance
To identify reasons for the differences in performance among the specimen
configurations, 11 quantitative specimen characteristics were defined as shown in the
following table and Fig. 46.
Table 13a Specimen Characteristics (US Units)
Specimen Characteristic Units A B C D E F G Vol coupon in3 40.0 40.0 40.0 40.0 22.5 33.8 40.0 Wetted depth of immersion in 0.41 0.28 0.53 0.41 0.41 0.41 0.41 Wetted coupon volume in3 13.0 9.0 17.0 13.0 7.3 11.0 13.0 Net saline volume in3 20.3 16.0 24.6 10.5 16.2 12.6 13.6 Vol. saline/ Vol. coupon ratio 0.51 0.40 0.62 0.26 0.72 0.37 0.34 Area of horizontal face of coupon in2 32.0 32.0 32.0 32.0 18.0 27.0 32.0 Total side area of coupon in2 30.0 30.0 30.0 30.0 22.5 26.3 28.3 Surface area of coupon / Vol. coupon 1/in 2.4 2.4 2.4 2.4 2.6 2.4 2.0 Wetted surface area of coupon in2 41.8 38.8 44.8 41.8 25.3 35.5 41.2 Wetted surf. area coupon / Vol. coupon 1/in 1.04 0.97 1.12 1.04 1.13 1.05 1.03 Average Clearance to wall of container in 1.2 1.2 1.2 0.4 1.2 1.2 0.8
Table 13b Specimen Characteristics (SI Units)
Specimen Characteristic Units A B C D E F G Vol coupon ml 656 656 656 656 369 554 656Wetted depth of immersion mm 10.4 7.1 13.5 10.4 10.4 10.4 10.4Wetted coupon volume ml 213 148 279 213 120 180 213Net saline volume ml 333 262 403 172 266 207 223Vol. saline/ Vol. coupon ratio 0.51 0.40 0.62 0.26 0.72 0.37 0.34Area of horizontal face of coupon mm2 20650 20650 20650 20650 11600 17400 20650Total side area of coupon mm2 19350 19350 19350 19350 14520 17000 18300Surface area of coupon / Vol. coupon 1/mm 0.093 0.093 0.093 0.093 0.102 0.094 0.091Wetted surface area of coupon mm2 27000 25000 29000 27000 16300 22900 26600Wetted surf. area coupon / Vol. coupon 1/mm 0.041 0.038 0.044 0.041 0.044 0.041 0.041Average Clearance to wall of container mm 30.5 30.5 30.5 10.2 30.5 30.5 20.3
February 5, 2009
FINAL REPORT 85
Figure 46 Range of values for characteristics of specimen configurations.
Characteristics of Specimen Configurations
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
A B C D E F G
Vol couponWetted depth of immersionWetted coupon volumeNet saline volumeVol. saline/ Vol. couponArea of horizontal face of couponTotal edge area of couponSurface area of coupon / Volume of couponWetted surface area of couponWetted surface area coupon / Vol couponAverage Clearance to wall of container
February 5, 2009
FINAL REPORT 86
Figure 47 Geometric basis for specimen characteristics
To discover general trends among specimen characteristics and freeze-thaw test
performance, predicted mass loss was plotted as a function of the characteristics
shown in the table above. To identify those factors which may have an effect over the
duration of the 150 test cycles Figures 48a-k separately indicate mass loss over 0 to 50
Side areas
Side areas in contact with solution
Horizontal face area of specimen
Total wetted area = total side areas in contact with solution + test face area of specimen
February 5, 2009
FINAL REPORT 87
cycles, 50 to 100 cycles, and 100 to 150 cycles. Table 14 summarizes discernable
trends.
a) Coupon volume (in3) b) Wetted depth (in)
c) Wetted coupon volume (in3) d) Net saline volume (in3)
e) Vol. saline / vol. coupon f) Coupon face area (in2)
Figure 48 Influence of specimen characteristics on mass loss
Incremental Mass Loss -- Impact of Specimen Volume
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35 40 45
Volume of Specimen
Pre
dict
ed M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
Incremental Mass Loss--Impact of Wetted Depth
0
0.5
1
1.5
2
2.5
0 0.1 0.2 0.3 0.4 0.5 0.6
Wetted Depth
Pre
dict
ed M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
Incremental Mass Loss -- Effect of Wetted Specimen Volume
0
0.5
1
1.5
2
2.5
0 2 4 6 8 10 12 14 16 18
Wetted Specimen Volume
Pre
dict
ed M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
Incremental Mass Loss -- Effect of Net Saline Volume
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30
Net Saline Volume
Pred
icte
d M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
Incremental Mass Loss -- Effect of (Vol. Solultion / Vol. Coupon)
0
0.5
1
1.5
2
2.5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Volume Solution/Volume Coupon
Pred
icte
d M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
Incremental Mass Loss -- Effect of Test Coupon Face Area
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35
Test Face Area
Pred
icte
d M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
February 5, 2009
FINAL REPORT 88
g) Coupon side area (in2) h) Surface area coupon / vol. coupon
(in2/in3)
i) Wetted surface area (in2) j) Wetted surface area / vol. coupon (in2/in3)
k) Average coupon-to-container clearance (in)
Figure 48 Influence of specimen characteristics on mass loss (continued)
Incremental Mass Loss -- Effect of Average Clearance
0
0.5
1
1.5
2
2.5
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Average Clearance
Pre
dict
ed M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
Incremental Mass Loss -- Effect of Wetted Surface Area of Coupon
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35 40 45 50
Wetted Surface Area of Coupon
Pre
dict
ed M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
Effect of Wetted Surface Area Coupon / Vol. of Coupon
0
0.5
1
1.5
2
2.5
3
0.96 0.98 1 1.02 1.04 1.06 1.08 1.1 1.12 1.14
Wetted Surface / Volume of Coupon
Pred
icte
d M
ass
Loss
(Per
cent
)
100 / 50100 / 100100 / 150150 / 150
Incremental Mass Loss -- Effect of Side Area
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30 35
Side Area
Pred
icte
d M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
Incremental Mass Loss -- Effect of Surface Area Coupon / Vol. Coupon
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5 3
Surface Area / Volume
Pred
icte
d M
ass
Loss
(Per
cent
)
0 to 5050 to 100100 to 150
February 5, 2009
FINAL REPORT 89
Table 14 Discernable General Trends of the Influence of Specimen Characteristics
on Mass Loss in the C 1262 Freeze-Thaw Test
Factor Mass Loss from 0 to 50 Cycles
Mass Loss from 50 to 100 Cycles
Mass Loss from 100 to 150
Cycles Increasing specimen volume --- --- --- Increasing coupon surface area / coupon vol Increases ML Increases ML
May significantly increase ML
Increasing wetted depth Increases ML --- May significantly
decrease ML Increasing saline solution vol./ coupon vol. --- Increases ML Increasing average clearance to container wall. --- Increases ML
May significantly increase ML
Alternatively, Figure 49 compares all specimen characteristics to those of specimen G,
which consistently exhibited resistance to freeze-thaw damage.
February 5, 2009
FINAL REPORT 90
Figure 49 Relative values for characteristics of specimen configurations compared to those of specimen G.
Characteristics Relative to Configuration G
0.0
0.5
1.0
1.5
2.0
2.5
A B C D E F G
Vol couponWetted depth of immersionWetted coupon volumeNet saline volumeVol. saline/ Vol. couponArea of horizontal face of couponTotal edge area of couponSurface area of coupon / Volume of couponWetted surface area of couponWetted surface area coupon / Vol couponAverage Clearance to wall of container
February 5, 2009
FINAL REPORT 91
One factor that stands out in Figure 49 is the [volume of saline / volume of coupon].
Specimens C and E have the highest values, and are likewise the two most vulnerable
specimens as of 100 cycles. This confirms the general trends identified above. Other
relationships are more obscure.
Additional insight may be obtained by comparing Specimen G (least vulnerable to
freeze-thaw damage) with Specimen E (most vulnerable to freeze-thaw damage at 100
cycles) as shown in Figure 50.
Figure 50 Relative values of specimen characteristics, comparing E with G.
Observations from the comparison of specimen configurations E and G displayed in
Figure 50 include the following:
a. Referring to the dimensions shown on Table 1 and Figure 1, Specimen G
(5-1/3 x 6in.) can be generally described as a “large coupon in a small
Sorted Relative comparison of Specimens E to G
0.00
0.50
1.00
1.50
2.00
2.50
E G
Wetted surface area coupon / Vol couponVol couponWetted coupon volumeArea of horizontal face of couponWetted surface area of couponTotal edge area of couponWetted depth of immersionNet saline volumeSurface area of coupon / Volume of couponAverage Clearance to wall of containerVol. saline/ Vol. coupon
February 5, 2009
FINAL REPORT 92
container,” and specimen E (3 x 6in.) is just the opposite: a “small specimen in
a large container.”
b. Looking at Figure 50 one sees that for characteristics that relate to specimen
geometry (leftmost 6 bars in the graph) Specimen E characteristics are less
than for Specimen G. These are all a function of coupon E being smaller than
coupon G. This suggests in this case that smaller coupons are more vulnerable
to freeze-thaw damage as measured by C 1262. The general trend, however is
that coupon volume alone is not a key factor.
c. A consequence of the selection of coupon dimensions and aspect ratio is the
ratio of the coupon surface area to coupon volume. This ratio for the more
vulnerable Specimen E is 1.33 times greater than for Specimen G. This agrees
with the general trend.
d. Since wetted depth is the same for both specimens, this factor evidently
does not directly influence performance.
e. While specimen E has a nominal increase in saline volume compared to G,
more significantly, specimen E has more than twice the [volume of saline
relative to the volume of the coupon] than the less-vulnerable specimen G, in
agreement with the general trend.
f. Similar to observation e, Specimen E has 1.5 times the average clearance
from the coupon to the edge of the container, in agreement with the general
trend.
February 5, 2009
FINAL REPORT 93
Whereas the previous analysis compared two specimens that behaved very differently,
Figure 51 compares A with G, two specimens that performed very similarly.
Figure 51 Relative values of specimen characteristics, comparing A with G.
Key observations from Figure 51 include the following:
a. Referring to the dimensions shown in Table 1 and Figure 1, specimens A (4
x 8 in) and G (5-1/3 x 6in.) had the same coupon volume, but A had the
slightly larger container.
b. As a result of the larger container Specimen A had a clearance to container
wall, saline volume, and ratio of saline volume to coupon volume almost 1.5
times greater than Specimen G . Although these appeared to be important
factors when comparing the very different behavior of E and G, these same
factors do not appear significant when comparing the very similar behavior of
Relative Comparison of Specimens A with G
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
A G
Wetted surface area coupon / Vol couponVol couponWetted depth of immersionWetted coupon volumeArea of horizontal face of couponWetted surface area of couponTotal edge area of couponSurface area of coupon / Volume of couponAverage Clearance to wall of containerNet saline volumeVol. saline/ Vol. coupon
February 5, 2009
FINAL REPORT 94
A and G. This is in contrast to the general trend observed among all
specimens.
It is also instructive to compare specimens A and B (Figure 52), due to the fact that the
only difference between the two was a reduced depth of saline for B. Even though A
and B performed almost identically up to 50 cycles, Specimen B was the one that
“came from behind” and ultimately showed the greatest mass loss at 150 cycles.
February 5, 2009
FINAL REPORT 95
Figure 52 Relative values of specimen characteristics, comparing B,
the most vulnerable as of 150 cycles, with A, one of the least vulnerable. A and B performed almost identically at 50 cycles.
Since depth of immersion is the only recorded difference between Specimens A and B,
and since A and B performed similarly through 50 cycles, it suggests that depth of
immersion is not a significant factor in early-cycle test behavior. However, since
Specimen B pulled away to show considerably more mass loss than Specimen A by
150 cycles, it suggests that reduced depth of immersion may in fact expose a greater
area of the coupon to cold air during the later-cycle time period in which considerable
absorption of saline solution has already taken place. This agrees with the general
trend.
Concentrating on only the first 50 cycles of testing, Specimen D exhibited the greatest
mass loss while A, B and G were nearly identical in exhibiting the least mass loss.
Sorted Comparison of Specimens A and B
0
0.2
0.4
0.6
0.8
1
1.2
B A
Wetted depth of immersionWetted coupon volumeNet saline volumeVol. saline/ Vol. couponWetted surface area of couponWetted surface area coupon / Vol couponVol couponArea of horizontal face of couponTotal edge area of couponSurface area of coupon / Volume of couponAverage Clearance to wall of container
February 5, 2009
FINAL REPORT 96
After this early-cycle mass loss Specimen D did not remain the most vulnerable, but
instead exhibited less mass loss than all but Specimens A and G by 100 and 150
cycles. Thus any key differences between D and G (the standard of comparison) may
primarily affect early-cycle damage, as shown in Figure 53.
Figure 53 Relative values of specimen characteristics, comparing D,
the most vulnerable as of 50 cycles, with G, among the least vulnerable.
Key observations from Figure 53 include the following:
a. Reduced clearance from the coupon to the wall of the container and reduced
saline volume and [vol. saline / vol coupon] appear to increase severity of mass
loss in the first 50 cycles. This was not generally observed for all specimens.
b. Increased [surface area of coupon / volume of coupon] likewise appears to
increase mass loss in the first 50 cycles. This was generally observed for all
specimens.
Sorted Comparison of Specimens D with G
0
0.2
0.4
0.6
0.8
1
1.2
1.4
D G
Average Clearance to wall of containerNet saline volumeVol. saline/ Vol. couponVol couponWetted depth of immersionWetted coupon volumeArea of horizontal face of couponWetted surface area coupon / Vol couponWetted surface area of couponTotal edge area of couponSurface area of coupon / Volume of coupon
February 5, 2009
FINAL REPORT 97
5.1.4.3. Summary of key observations from the variability series
a. Seven test specimen/container configurations were evaluated in head-to-
head comparative testing, all originating with the same population of SRW
units.
b. Statistical analyses were performed on the data collected for mass loss as a
function of numbers of freeze-thaw cycles. These analyses indicated that
statistically significant differences existed in freeze-thaw behavior among the
specimen/container configurations.
c. For the purposes of comparative analysis, the actual mass loss data were
replaced by mass loss predictions obtained from statistically-based regression
equations.
d. Apparent uniformity of results is suggested by the fact that none of the
specimens tested had a mass loss in excess of 1% at 100 cycles, regardless of
specimen configuration. SRW units that are this freeze-thaw resistant will
perform well in the C 1262 test under the wide variety of specimen
configurations that are permitted by the current test specification.
e. Apparent non-uniformity is suggested by the facts that for coupons all taken
from the same population of SRW units:
♦ As of 50 cycles the greatest mass loss was 1.7 times the least mass
loss.
February 5, 2009
FINAL REPORT 98
♦ As of 100 cycles the greatest mass loss was 1.6 times the least mass
loss.
♦ As of 150 cycles the greatest mass loss was 3 times the least mass
loss.
f. Specimen configuration has an obvious impact on C 1262 freeze-thaw test
performance.
As of 50 cycles (and less than 0.2% mass loss):
♦ Specimens A, B, and G exhibit the least mass loss.
♦ Specimens D and F exhibit the most mass loss.
As of 100 cycles (and still less than 0.7% mass loss):
♦ Specimens A and G continue to exhibit the lowest mass loss.
♦ From 50 to 100 cycles Specimen E has moved from the “middle of
the pack” to exhibiting the greatest mass loss as of 100 cycles.
As of 150 cycles (with mass loss ranging from less than 1% to over 2.5%):
♦ Specimens A and G continue to exhibit the least mass loss (with A
just breaking over the 1% threshold at 150 cycles, and “bulletproof”
G at less than 1% at 150 cycles).
♦ Specimen B shows the interesting trend of low mass loss at 50
cycles, intermediate at 100 cycles, to having the highest mass (by a
large margin) as of 150 cycles. Specimen B clearly “came from
behind.”
February 5, 2009
FINAL REPORT 99
♦ Specimen E remained high in total mass loss although overtaken by
B from 100 to 150 cycles.
♦ While Specimen D exhibited the highest mass loss at 50 cycles,
after this early degradation, total mass loss at both 100 and 150
cycles was less than average for all specimens.
g. Specimen configurations might be grouped as follows:
♦ A and G clearly represent overall damage resistance
♦ D represents damage vulnerability within the first 50 cycles
♦ E represents damage vulnerability from 50 to 100 cycles
♦ B represents damage vulnerability from 100 to 150 cycles.
h. Within the population of specimens tested here, there are some contradictions
to the general trends described. It is thus obvious that cause-and-effect
relationships between specimen characteristics and specimen performance are not
yet fully understood
i. The behavior monitored and analyzed here is to an unknown extent dependent
on the unique material properties of this particular SRW unit population.
February 5, 2009
FINAL REPORT 100
5.2 Rate of change of mass loss
Aside from considering mass loss alone, another interesting and perhaps useful index
of specimen performance is the rate at which mass loss increases over the duration of
the test. For example, the familiar “Hockey Stick” pattern of mass loss is the result of
an increasing rate of deterioration that shows up as an increasingly large cumulative
mass loss as the number of cycles increase. Rate of Mass Loss can be numerically
evaluated as the slope of the Mass Loss vs. cycles curve as follows (for example,
between 90 to 100 cycles):
(Rate of mass loss)90-100 = K 90-100 = cycles 90100
)Loss MassLoss (Mass 90cycles100cycles
−
− (8)
The units of this parameter are thus [% / cycle]. This parameter was evaluated
through 200 cycles for the Variability Series specimens and through 210 cycles for the
PC Series specimens, and plotted in Figures 54 and 55, respectively. As before, each
curve in the graphs in these figures represents the results for each specimen and the
bold line represents the average response for all specimens in a given Test Set.
Rate of Mass Loss is another way to describe the overall trend in mass loss evolution.
For instance, it is seen from Figures 54 and 55 that specimens generally exhibited a
linearly increasing rate of mass loss with increasing cycles through at least 100 cycles
in the Variability Series (except Test Set B) and up to 170 cycles in the PC Series.
This linearity is illustrated in Test Set A in Figure 54, where a straight line has been
fitted through data over the first 160 cycles. The linearity in the Rate of Mass Loss
implies that the incremental mass loss with each freeze-thaw cycle is increasing or
February 5, 2009
FINAL REPORT 101
“accelerating” by a fixed amount per cycle. In mathematical terms, this also means
that when the mass loss rate is increasing linearly, the mass loss curve itself is a
parabola that is concave up, and given that the parabola starts at zero mass loss at zero
cycles, the equation of the mass loss curve is given by:
ML = a×cycle2 (9)
where a = K/2.
Example Calculation for Test Set A:
Rate of Mass Loss, ∆(ML%) / ∆(cycle) = 0.00009×cycle
hence, Mass Loss, ML% = (0.00009)/2×cycle2
ML% = 0.000045×cycle2
Thus, a = 0.000045
Predicted mass loss at 100 cycles = 0.000045(100)2 = 0.45%
February 5, 2009
FINAL REPORT 102
Test Set A
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
Test Set B
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
Test Set C
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
Test Set D
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
Test Set E
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
Test Set F
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
Test Set G
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
Figure 54 Rates of mass loss for Variability Series. Note that the vertical axis shows
the rate of mass loss in % per cycle.
straight line slope = 0.00009%/cycle2
February 5, 2009
FINAL REPORT 103
Figure 55 Rates of mass loss for Performance Criteria Series. Note that the vertical axis shows rate of mass loss in units of % mass loss per cycle.
Equation 9 is the same form of relationship observed by Hance (2005) in his study
using laboratory-prepared SRW mixes. In that study, eight mixes of varying
composition were evaluated for their frost durability, and through a series of curve-
fitting operations on the Mass Loss vs. cycles data for each mix, Hance determined
that the parabolic (2nd order) equation best modeled his freeze-thaw mass loss results.
Hance’s mass-loss prediction constant “a” was determined for the other Test Sets with
the results shown in Table 15. Also shown in this table is the maximum number of
cycles through which the rate of mass loss continued to increase in a linear manner
(referred to as the Mass Loss Linear Threshold Point), and the corresponding range of
specimen mass loss at this Threshold Point. These results implied that overall, Test
Sets C, E and F which displayed the highest values of “a” would also be the ones
deteriorating the fastest of all Test Sets, while Sets A and G which displayed lower
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200 220
Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
C2LC5L
February 5, 2009
FINAL REPORT 104
values of “a” would also be the ones deteriorating the slowest of all Test Sets. Set B,
despite displaying low “a” value, was only evaluated up to 80 cycles. For comparison,
for the low strength, low durability mixes evaluated by Hance, the mass loss
prediction constant “a” was in the range of 0.006 for the best performing mix to 0.35
for the worst performing mix. It is also interesting to note here that, except for Set B,
the range of mass loss at the Mass Loss Linear Threshold Point straddled 1%,
indicating that this method of characterizing and predicting specimen behavior works
well up to a mass loss of about 1%, the utility of these indices breaks down.
Table 15 Mass loss prediction constant “a” for various Test Sets
Test Set K (% / cycle2)
Hance’s “a” (% / cycle2)
Mass Loss Linear Threshold Point a
Mass Loss range (%)
A 0.00009 0.000045 160 0.8 – 1.3 B 0.00006 0.000030 80 0.1 – 0.3 C 0.00013 0.000063 130 0.7 – 1.4 D 0.00009 0.000047 130 0.6 – 1.1 E 0.00014 0.000070 140 1.2 – 1.7 F 0.00012 0.000061 130 0.8 – 1.7 G 0.000076 0.000038 150 0.5 – 1.0 PC 0.000038 0.000019 170 0.2 – 1.8
a Maximum number of cycles at which approximate linearity still existed for the Rates of Mass Loss
From the parabolic Mass-Loss vs. cycles relationship, it was also possible to calculate
the number of cycles required for 1% mass loss as follows:
Cycle to 1% mass loss = √ (1 / a) (10)
For the values of “a” shown in Table 15, this number of cycles is shown in Table 16
and compared to the actual average number of cycles from the test data. In most
February 5, 2009
FINAL REPORT 105
cases, the predicted and actual values were quite similar (except for Test Set B in
which 2 specimens showed substantially greater increases in mass loss.
Table 16 Number of cycles to 1% mass loss.
Test Set Predicted Observed Average Error, %
A 149 148 1 B 183 114 61 C 126 123 2 D 146 137 7 E 120 109 10 F 128 123 4 G 162 154 5 PC 229 212 8
Another benefit in considering Rates of Mass Loss was that individual mass loss
occurrences may be better discerned. For instance, in specimen E2, a spike in the Rate
of Mass Loss occurred between 100 and 110 cycles, which was associated with a
couple of aggregate/mortar popouts in the specimen (one at a corner and one at an
edge, as shown in Figure 56). After 110 cycles however, the Rate of Mass Loss in
specimen E2 was comparable to other specimens. Similarly, as mentioned earlier for
the PC Series, specimens C2L and C5L exhibited jumps in mass loss between 70 and
80 cycles (C2L) and 90 to 100 cycles (C5L). An inspection of the Rates of Mass Loss
curves for these 2 specimens (Figure 55) revealed spikes at these times followed by
two distinct behaviors: a) for C2L, after the spike, its rate of mass loss dropped back
down to the approximately the same level before the spike and similar to most other
specimens, while b) for C5L, after the spike, its rate of mass loss dropped back down
but then started increasing again. The overall conclusion from these observations was
February 5, 2009
FINAL REPORT 106
the fact that jumps in mass loss per se may not necessarily indicate a genuinely
representative increase in specimen deterioration (e.g., C2L) since the jump may have
been caused by a local event such the corner damage seen here. However, when such
jumps in mass loss occur, it is prudent to continue to cycle the specimens to observe
subsequent behavior. In a case like specimen C5L, where increasing rates of mass
loss followed the spike in the rate, it is indicative of a genuinely rapid deterioration of
the specimen.
corner damage edge damage
Figure 56 Aggregate and mortar popouts in Specimen E2 between 100 and 110 cycles.
5.3 Other measured parameters
5.3.1 Mass loss per surface area
Mass loss was also calculated in terms of “mass loss per unit surface test area (kg/m2
(lb/ft2))”. The surface test area for the specimens in this study was defined in two
different ways (Figure 47):
February 5, 2009
FINAL REPORT 107
• Test face area of the specimen, i.e., 100 × 200 mm2 (4 × 8 in.2), 75 × 150 mm2
(3 × 6 in.2), 113 × 150 mm2 (4½ × 6 in.2) or 133 × 150 mm2 (5-1/3 × 6 in.2),
and
• Wetted area which is the total surface area of specimen under the solution.
Results of mass loss expressed in terms of these areas are shown in Figure 57a for
mass loss per test face area and Figure 57b for mass loss per wetted area for Test Sets
in the Variability Series. In each of Figures 57a and b, graphs with vertical scale up to
40 kg/m2 (8.2 lbs/ft2) and 5 kg/m2 (1.0 lbs/ft2) are shown. The corresponding graphs
for the average of all PC specimens are shown in Figures 58a and b. Generally,
average mass loss per test face area for Test Sets in the Variability Series were about
0.1 kg/m2 (0.03 lbs/ft2) after 50 cycles, 0.3 to 0.5 kg/m2 (0.07 to 0.11 lbs/ft2) after 100
cycles, 0.7 to 2.0 kg/m2 (0.1 to 0.4 lbs/ft2) after 150 cycles and 1.8 to 37 kg/m2 (0.4 to
8 lbs/ ft2) after 200 cycles. Values of mass loss per wetted area were generally about
75 to 80% of the value of mass loss per test face area, except Test Set B whose mass
loss per wetted area were about 85% of the value of mass loss per test face area.
For reference, the Canadian test standard CSA A231.1-99 for Precast Concrete Paving
Slabs specifies maximum limits for mass loss of concrete pavers subjected to freezing
and thawing in the presence of a 3% NaCl solution (CSA A231.1, 1999). These limits
are as follows (here, the test area is the surface area that is ponded by the saline
solution):
• 0.3 kg/m2 (0.06 lbs/ft2) after 28 freeze-thaw cycles (or 0.5 kg/m2 (0.1 lbs/ft2)
for specimens with an architectural finish), or
February 5, 2009
FINAL REPORT 108
• 0.8 kg/m2 (0.16 lbs/ft2) after 49 freeze-thaw cycles (or 1.2 kg/m2 (0.25 lbs/ft2)
for specimens with an architectural finish)
It must be recognized however that the limits shown above pertain to tests in which
the concrete specimens are surface-ponded with saline solution, unlike the partial
immersion as in ASTM C 1262, and these values are provided for reference purposes
only. In general, Variability Series specimens reached mass loss per test face area of
0.8 kg/m2 (0.16 lbs/ft2) after 110 to 160 cycles, and mass loss per wetted area of 0.8
kg/m2 (0.16 lbs/ft2) after 130 to 180 cycles. Recall from Section 5.1, mass loss (as
defined by ASTM C 1262) reached about 1% in the range of 109 to 154 cycles. Mass
loss per test face area and mass loss per wetted area are plotted as function of ASTM
C 1262 mass loss in Figures 59a and 59b respectively. In each of these figures, graphs
based on 100 and 150-cycle data are shown. It generally appears that for the particular
specimens in this study, a 1% mass loss based on ASTM C 1262 definitions translated
to a mass loss per test face area of approximately 0.7 to 0.8 kg/m2 (0.14 to 0.16
lb/ft2). This correspondence between mass loss defined in these two manners was
valid regardless of the data set used (100 cycle or 150 cycle data). On the other hand,
a 1% mass loss based on ASTM C 1262 definitions translated to mass loss per wetted
area of approximately 0.6 kg/m2 (0.12 lb/ft2) . In either case, the linearity displayed in
Figures 59a and b suggests that mass loss could be reported either in the conventional
terms of mass loss relative to the initial coupon mass, or in terms of mass loss relative
to some predefined fraction of surface area given that one can readily and reliably
convert from one measure to the other . In retrospect this is not surprising given that
for the case of the “test face area” the conversion factor is a function of only the
density of the material and the thickness of the coupon, which were about constant for
all specimens tested. On the basis of the measured oven-dry density of about 2210
February 5, 2009
FINAL REPORT 109
kg/m3 (129 lb/ft3) and a thickness of 32 mm (1.25 in) one would compute that mass
loss expressed in kg/m2 of test face area would be 0.70 times the mass loss as a
percent of initial coupon mass. The conversion factor for the wetted surface area
would be influenced by both length and width of a coupon as well, and thus more
scatter is seen in Figure 59b since coupon length and width varied among specimens.
Pigeon and Pleau (1995) also cite a limit of 1 kg/m2 (0.20 lb/ft2) after 50 freeze-thaw
cycles, below which concrete is considered to have adequate scaling resistance.
Variability Series specimens generally reached mass loss per test face area of 1 kg/m2
(0.20 lb/ft2) after 130 to 170 cycles. In contrast, PC Series specimens reached this
value after approximately 240 cycles.
February 5, 2009
FINAL REPORT 110
i) vertical scale up to 40 kg/m2 (8.2 lbs/ft2)
ii) vertical scale up to 5 kg/m2 (1.0 lbs/ft2)
Figure 57a Mass loss per test face area as function of cycles for Variability Series.
0
5
10
15
20
25
30
35
40
0 20 40 60 80 100 120 140 160 180 200
Cycles
Mas
s lo
ss (k
g/m
2 )
0.0
1.0
2.0
3.1
4.1
5.1
6.1
7.1
8.2
Mas
s lo
ss (l
bs/ft
2 )
A
G
E
D
B
F
C
0
1
2
3
4
5
0 20 40 60 80 100 120 140 160 180 200
Cycles
Mas
s lo
ss (k
g/m
2 )
0.0
0.2
0.4
0.6
0.8
1.0
Mas
s lo
ss (l
bs/ft
2 )
A
G
E
B
F
C
D
February 5, 2009
FINAL REPORT 111
i) vertical scale up to 40 kg/m2 (8.2 lbs/ft2)
ii) vertical scale up to 5 kg/m2 (1.0 lbs/ft2) Figure 57b Mass loss per wetted test area as function of cycles for Variability Series.
0
5
10
15
20
25
30
35
40
0 20 40 60 80 100 120 140 160 180 200
Cycles
Mas
s lo
ss (k
g/m
2 )
0.0
1.0
2.0
3.1
4.1
5.1
6.1
7.1
8.2
Mas
s lo
ss (l
bs/ft
2 )
A G
E
D
B
F
C
0
1
2
3
4
5
0 20 40 60 80 100 120 140 160 180 200
Cycles
Mas
s lo
ss (k
g/m
2 )
0.0
0.2
0.4
0.6
0.8
1.0
Mas
s lo
ss (l
bs/ft
2 )
A
G
E
B
F
C
D
February 5, 2009
FINAL REPORT 112
a) Mass loss per test face area
b) Mass loss per wetted test area
Figure 58 Mass loss per surface test area as function of cycles for average of all PC Series specimens.
0
1
2
3
4
5
0 20 40 60 80 100 120 140 160 180 200
Cycles
Mas
s lo
ss (k
g/m
2 )
0.0
0.2
0.4
0.6
0.8
1.0
Mas
s lo
ss (l
bs/ft
2 )
0
1
2
3
4
5
0 20 40 60 80 100 120 140 160 180 200
Cycles
Mas
s lo
ss (k
g/m
2 )
0.0
0.2
0.4
0.6
0.8
1.0
Mas
s lo
ss (l
bs/ft
2 )
February 5, 2009
FINAL REPORT 113
i) using data after 100 cycles
ii) using data after 150 cycles Figure 59a Relationship between ASTM C 1262 mass loss and mass loss per test face
area.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Mass loss (%)
Mas
s lo
ss (k
g/m
2 )
0.00.51.01.52.02.53.03.54.04.55.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Mass loss (%)
Mas
s lo
ss (k
g/m
2 )
February 5, 2009
FINAL REPORT 114
i) using data after 100 cycles
ii) using data after 150 cycles
Figure 59b Relationship between ASTM C 1262 mass loss and mass loss per wetted area for the variability series.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Mass loss (%)
Mas
s lo
ss (k
g/m
2)
0.00.51.01.52.02.53.03.54.04.55.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Mass loss (%)
Mas
s lo
ss (k
g/m
2)
February 5, 2009
FINAL REPORT 115
5.3.2 Moisture content changes
As described in Section 3.3, the total moisture content of all specimens was
determined each time mass loss measurements were made. At each residue collection
interval (after n cycles), the surface-dried mass (mSD,n) of each specimen was
measured (this is equivalent to measuring Wp in ASTM C 1262, i.e., Wp = mSD,n at 0
cycles). However, because of continued mass loss with increasing cycles, mSD,n
represents the surface-dried mass of only the remaining portion of the specimen.
Hence, to estimate the total surface-dried mass of the specimen, the cumulative mass
of residue up to n cycles needs to be added to mSD,n (Equation 1) (Note that this
calculation is similar to the one in ASTM C 1262 to determine the initial oven-dried
mass of the specimen. The only difference here is that the surface-dried mass is
obtained rather than the oven-dried mass). Once the total surface-dried mass of the
specimen is obtained at n cycles, the moisture content is determined from Equation 2.
Moreover, the difference between the total surface-dried mass of the specimen at n
cycles and Wp is the additional moisture absorbed from start of test to n cycles.
Moisture content results, for the average of each Test Set, are shown in Figure 60a,
where the moisture content of the control specimen is also shown. Curves for several
Test Sets were discontinued after about 170 cycles because at this point, specimens in
these particular Test Sets had broken (split) into several pieces. It is seen that in
general, freeze-thaw test specimens and the control specimen started at similar
moisture contents of about 4.7 to 4.9%. However, from about 20 cycles onwards, the
rates of moisture gain diverged. After 100 cycles, the moisture content of freeze-thaw
test specimens was in the range of 5.6 to 5.8% while the control specimen was at
5.5%; and after 200 cycles, freeze-thaw test specimens were in the range of 5.9 to
February 5, 2009
FINAL REPORT 116
a) Total moisture content
b) Total moisture gain after start of freezing and thawing Figure 60 Moisture changes for Test Sets in Variability Series (control specimen also
shown).
3.0
4.0
5.0
6.0
7.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Est.
M.C
. (%
)
Variability Series Test Sets
control
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Moi
stur
e ga
in (%
) Variability Series Test Sets
control
February 5, 2009
FINAL REPORT 117
6.3% while the control specimen was at 5.7%. Of all Test Sets, Set D had the largest
overall moisture contents, followed by Set G. Sets C and F exhibited the lowest
overall moisture contents.
For each specimen, moisture gain after start of freezing and thawing was also
computed as follows:
Moisture gain (at n cycles) = Total moisture content – Initial moisture content (11)
The initial moisture content refers to the value obtained after the initial 24-hr
immersion of specimens, when Wp (as defined in ASTM C 1262) was determined.
These results are shown in Figure 60b. For all specimens, moisture gains ranged from
0.6 to 1.5% after 100 cycles and 0.8 to 1.8% after 200 cycles. These values were
similar to those reported by Kasparek and Setzer (2002) for tests in which specimens
were subjected to unidirectional heat flow by placing only one face of the specimens
in contact with a cooling medium. Other studies have shown that moisture uptake
after freezing and thawing can be up to 2 times or more the initial capillary uptake
prior to freeze-thaw testing (Setzer et al, 1999). Of all Test Sets in this study, Set D
had the largest overall moisture gain, followed by Set F. Sets A and G exhibited the
lowest overall moisture gain. These trends correspond more or less to the mass loss
trends after 200 cycles, whereby Sets B, D and F exhibited largest mass loss, while
Sets A and G displayed lowest mass loss.
The corresponding total moisture content and moisture gain graphs for specimens in
the PC Series are shown in Figure 61a and b, respectively. On average, PC specimens
reached total moisture contents of 5.7% after 100 cycles (control at 5.5%) and 6.0%
February 5, 2009
FINAL REPORT 118
after 200 cycles (control at 5.7%). Moisture gains for these specimens were 0.8%
after 100 cycles (control at 0.6%) and 1.1% after 200 cycles (control at 0.8%).
From the above results, it appears that specimens subjected to freeze-thaw cycles
absorbed more moisture than a similarly immersed specimen not subjected to freezing
and thawing. As such, after each given number of cycles, there was a cumulative mass
loss (determined in the standard manner by residue weighing, as per ASTM C 1262)
as well as a cumulative moisture gain (determined in the manner described in this
section, based on specimen and residue weighing). These two parameters are related
to one another as shown in Figures 62a to d using data from 50, 100, 150 and 200
cycles. Overall, there seemed to be a consistent trend in regards to increases in these
two parameters. It has been suggested by other researchers that ice-induced
microcracking during freezing and thawing creates a more continuous crack system
with accompanying volume expansion which can accommodate more water in the
concrete (Bager and Jacobsen, 1999; Setzer et. al, 1999). This water uptake continues
until a critical saturation is reached at which point rapid volume expansion and
damage take place in the material.
5.3.3 Concentration of dissolved substances
The concentration of dissolved substances in the solution surrounding specimens was
measured for specimens A1, D1 and F1 in the Variability Series and specimens C1L
and C10L in the PC Series, using gravimetric methods. These results are shown in
Figure 63a for Variability specimens and 63b for PC specimens. Generally, this
concentration remained more or less constant at around 3.2 to 3.3% over the duration
of the test program in either Test Series. This value was slightly higher than the initial
3% NaCl concentration in the solution.
February 5, 2009
FINAL REPORT 119
a) Total moisture content
b) Total moisture gain after start of freezing and thawing Figure 61 Moisture changes for Test Sets in PC Series (control specimen also shown).
3.0
4.0
5.0
6.0
7.0
0 20 40 60 80 100 120 140 160 180 200
Cycles
Est.
M.C
. (%
)
control
PC average
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 20 40 60 80 100 120 140 160 180 200
Cycles
Moi
stur
e ga
in (%
)
control
PC average
February 5, 2009
FINAL REPORT 120
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.0 0.1 0.2 0.3 0.4 0.5
Percent mass loss
Perc
ent m
ass
gain
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Percent mass loss
Perc
ent m
ass
gain
a) after 50 cycles b) after 100 cycles
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.0 1.0 2.0 3.0 4.0 5.0
Percent mass loss
Perc
ent m
ass
gain
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.0 1.0 2.0 3.0 4.0 5.0
Percent mass loss
Perc
ent m
ass
gain
A4, B2, B3, C1, C3, C4, D1, D2, D4, E4,
F2 excluded
c) after 150 cycles d) after 200 cycles
Figure 62 Relationship between Mass Loss (from residue weighing) and Mass Gain
(from specimen and residue weighing)
0.0
1.0
2.0
3.0
4.0
5.0
0 50 100 150 200Cycle
S (%
)
0.0
1.0
2.0
3.0
4.0
5.0
0 50 100 150 200Cycle
S (%
)
a) Variability Series b) PC Series
Figure 63 Concentration of dissolved substances (s) in surrounding solution.
D1
F1 A1 C1L
C10L
February 5, 2009
FINAL REPORT 121
6.0 RESULTS AND DISCUSSION – RESONANT FREQUENCY
6.1 Relative dynamic modulus results
Variability Series
The relative dynamic modulus (RDM) calculated from resonant frequencies at every
10th cycle was used to detect damage state in specimens. Equation 5 was used to
calculate RDM and an RDM value of 60% was taken as reference, based on the limit
specified by ASTM C 666 and C 260 for ordinary concrete specimens (i.e., tests
discontinued when RDM reaches 60%). Results of RDM as function of cycles for
Variability Series specimens are shown in Figure 64 for tests using sampling
parameters of 20,000 Hz and 1,024 data points and Figure 65 for tests using sampling
parameters of 102,400 Hz and 1,024 data points. In the general case, the curves stayed
more or less flat (at RDM > 80%) up until about 100 to 120 cycles, at which point the
RDM values dropped rapidly. The only exception to this trend was specimen B3
which showed steadily decreasing RDM values with increasing cycles since start of
testing. After 100 cycles, most specimens exhibited RDM values greater than 80%,
with the exceptions of specimens B3 (40%) and D2 (70%). These results generally
implied that internal damage in most specimens progressed more or less steadily for
the first 100 cycles; but after 100 cycles, the rate of deterioration increased. In the
cases where RDM had reached 0% (beyond 150 cycles), the specimens were mostly
disintegrated.
With respect to correlating RDM results to actual observations of specimen condition,
specimen C1 is taken as an example to demonstrate the typical behavior observed in
February 5, 2009
FINAL REPORT 122
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set A
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set B
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set C
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set D
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set E
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set F
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set G
Figure 64 RDM vs. cycles for Variability Series – Sampling parameters: 20,000 Hz
and 1,024 data points.
B3
February 5, 2009
FINAL REPORT 123
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set A
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set B
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set C
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set D
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set E
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set F
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
Test Set G
Figure 65 RDM vs. cycles for Variability Series – Sampling parameters: 102,400 Hz
and 1,024 data points.
B3
February 5, 2009
FINAL REPORT 124
most specimens. The RDM vs. cycles plot for this specimen is shown in Figure 66
along with photos of specimen condition at various stages on the curve. Generally,
surface blemishes such as popouts or scaling on the sides of specimens (see Figure 38
for more examples of scaling on sides) were observed as the first visible signs of
damage on specimens. At this point, RDM values were still fairly high (~80%) (Point
A in Figure 66). However, without substantial changes in the visible damage on the
specimens, RDM values started declining (Point A to B). By the time other damage
forms such as cracking or streaking on the specimen surface were visible at 140
cycles, RDM values had reduced to 22% (Point C). For the case of specimen C1,
RDM values close to 0% were measured at 170 cycles, just prior to complete
disintegration of the specimen. These trends portrayed by specimen C1 were
generally observed in most other specimens. Figure 67 shows photos of specimens B3
and D2 when cracks were first observed on these specimens. By the time these cracks
were observed, RDM values were measured at 40% for B3 and 54% for D2.
As far as sorting behavior among the various Test Sets in the Variability Series is
concerned, Figure 68 shows average RDM vs. cycles plots for tests using sampling
parameters of 20,000 Hz and 1,024 data points and Figure 69 for tests using sampling
parameters of 102,400 Hz and 1,024 data points. The following trends were
discerned:
• Within Test Sets A, B and C, Sets A and C performed similarly overall, while
Set B displayed lower RDM values from about 50 cycles onwards, which
suggested that underfilling of solution resulted in larger damage in the
specimens.
February 5, 2009
FINAL REPORT 125
Figure 66 Damage evolution in specimen C1 (mass loss values shown).
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
C1
A
B
C D
E
0.9%
1.2%
1.7%
2.9%>40%
February 5, 2009
FINAL REPORT 126
Figure 67 Examples of cracks on specimens with corresponding drops in RDM.
D2, after 120 cycles, mass loss = 0.6%, RDM = 54%
B3, after 100 cycles, mass loss = 1.5%, RDM = 40%
February 5, 2009
FINAL REPORT 127
Figure 68 Average Test Set RDM vs. cycles for Variability Series – Sampling parameters: 20,000 Hz and 1,024 data points.
Figure 69 Average Test Set RDM vs. cycles for Variability Series – Sampling parameters: 102,400 Hz and 1,024 data points.
0
10
20
30
40
50
60
70
80
90
100
110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
D
B
G
C
F
A E
0
10
20
30
40
50
60
70
80
90
100
110
0 20 40 60 80 100 120 140 160 180 200Cycles
RD
M, %
D
B
G C
F
A E
February 5, 2009
FINAL REPORT 128
• Within Test Sets D, E, F, Set E exhibited highest overall RDM values,
followed by Sets F and D, which suggested that for a given container size,
increasing the specimen size resulted in lower RDM values. The common
observation among Test Sets B and D was that these sets had the lowest ratio
of mass-of-solution-to-mass-of-specimen (msolution/mspecimen) among sets in their
respective comparison groups (i.e., Set B in A, B, C and Set D in D, E, F).
• Comparing Sets A and D, it is seen that for a specimen size, decreasing the
container size resulted in lower RDM values.
• Comparing Sets A and G, it appeared that geometrical effects were not
significant.
When comparing the ranking of the various Test Sets obtained from RDM testing to
those obtained from mass loss testing, the results in Table 17 were obtained. It is seen
that in general, the manner in which RDM and Mass Loss ranked the Test Sets relative
to one another was more or less similar at 150 cycles, except for Test Sets D and E.
Using RDM, the rankings after 100 cycles was also more or less similar to the
rankings after 50 cycles, which contrasts mass loss for which the rankings after 50
cycles did not assimilate the rankings after 100 cycles. In neither RDM nor mass loss
are the rankings after 50 cycles similar to the rankings after 150 or 200 cycles. This
observation pointed to the fact that the short term performance of these specimens
could not be reliably used to predict longer term performance.
Note also that the results obtained using either sampling method produced comparable
results, as shown from the similarities in the RDM vs. cycles plots in Figures 68 and
69. In general, the RDM values obtained using the two sampling methods had almost
direct 1:1 correspondence as shown in the graphs of Figure 70a for data after 100
February 5, 2009
FINAL REPORT 129
cycles and Figure 70b for data after 160 cycles, where the y = x line is also drawn.
Hence, for these tests, either set of resonant frequency sampling parameters would
have been adequate.
Table 17 Ranking of Test Sets based on Mass Loss and RDM.
50 cyc. 100 cyc. 150 cyc. 200 cyc. Mass
loss RDM Mass
loss RDM Mass
loss RDM Mass
loss RDM
Highest RDM and B C G C G G G E lowest Mass Loss A D A A A E A G G A D E D A E F E E F G C C C B F F C F F F F C
Lowest RDM and D G B D E B B A highest Mass Loss C B E B B D D D
Performance Criteria Series
Figure 71 shows RDM vs. cycles plots for all specimens in the PC Series. Only the
results using sampling parameters of 20,000 Hz and 1,024 points are shown here. The
overall average RDM of all 16 specimens was 100, 100, 95 and 79% after 50, 100,
150 and 200 cycles. Of all specimens, C5L in particular showed the earliest decline in
RDM. For this particular specimen, RDM of 60% was reached after about 150 cycles.
This specimen was also the one which had shown a jump in mass loss after 100 cycles,
followed by increasingly rapid rate of mass loss (see Figure 42). However, as seen in
Figure 72 taken after 160 cycles, no visible damage was apparent on the specimen
aside from the corner chip with minor blemishes on the surface. Figure 73 shows
RDM vs. cycles for the average RDM value of all PC specimens as well as the control
specimens (which was also partially immersed in 13 mm (½ in.)
February 5, 2009
FINAL REPORT 130
a) data after 100 cycles
b) data after 160 cycles
Figure 70 Comparison of RDM values obtained using two different sets of sampling parameters.
0102030405060708090
100110120
0 10 20 30 40 50 60 70 80 90 100 110 120
RDM using sampling rate of 20 kHz, 1,024 data pts
RD
M u
sing
sam
plin
g ra
te o
f 102
.4 k
Hz,
1,
024
data
pts
0102030405060708090
100110120
0 10 20 30 40 50 60 70 80 90 100 110 120
RDM using sampling rate of 20 kHz, 1,024 data pts
RD
M u
sing
sam
plin
g ra
te o
f 102
.4 k
Hz,
1,
024
data
pts
February 5, 2009
FINAL REPORT 131
saline solution, but not subjected to freezing and thawing). Here it is seen that after
about 120 cycles, RDM in the control specimen gradually increased. The implications
of this increase in RDM are described ahead.
Figure 71 RDM vs. cycles for PC specimens (sampling parameters 20,000 Hz and 1,024 data points)
Figure 72 View of specimen C5L in PC Series after 160 cycles.
0
10
20
30
40
50
60
70
80
90
100
110
0 20 40 60 80 100 120 140 160 180 200 220Cycles
RD
M, %
corner popout
February 5, 2009
FINAL REPORT 132
Figure 73 RDM vs. cycles for PC average and control specimen (sampling parameters 20,000 Hz and 1,024 data points)
6.2 Rate of RDM change
In the same manner in which rates of change were computed for mass loss, rates of
change were also computed for RDM values. Equation 12 was used for these
calculations which is similar in form to Equation 8 used for Rates of Mass Loss. This
is as follows (for example, between 90 to 100 cycles):
(Rate of RDM)90-100 = cycles 90100
)RDM (RDM 90cycles100cycles
−
− (12)
The units of this parameter are thus [% / cycle]. This parameter was evaluated
through 200 cycles for the Variability Series specimens and through 210 cycles for the
PC Series specimens, and plotted in Figures 74 and 75, respectively. As before, each
0102030405060708090
100110120
0 20 40 60 80 100 120 140 160 180 200 220Cycles
RD
M, %
control
Avg. PC
February 5, 2009
FINAL REPORT 133
graph in Figure 74 shows the results for each specimen and the bold line represents the
average response for all specimens in a given Test Set. It is observed that in most
cases, the rate of RDM steadily increased in an almost linear fashion (in the negative
range) with increasing cycles up to about 100 to 120 cycles, after which the rates
deviated from linearity and grew increasingly larger. This behavior is highlighted by
the dark line in Test Set A. The exception to this behavior was Set G which displayed
almost constant rate of RDM change over the first 120 cycles. Beyond 130 cycles
however, its rate of RDM change also became increasingly larger. This point at which
the RDM rate of change ceased its steady increase and grew increasingly faster is
referred to as the RDM Linear Threshold Point. Mass loss values for the specimens at
the RDM LinearThreshold Points were as follows: Set A: 0.4 to 0.7% (at 120 cycles),
Set B: 0.4 to 2.0% (at 120 cycles), Set C: 0.7 to 1.2% (at 120 cycles), Set D: 0.4 to
0.8% (at 110 cycles), Set E: 1.0 to 1.5% (at 130 cycles), Set F: 0.3 to 0.9% (at 100
cycles) and Set G: 0.4 to 0.8% (at 130 cycles). In Section 5.3, the Mass Loss Linear
Threshold Point was defined as the point at which the rate of mass loss ceased being
linear, and this occurred at mass loss values of around 1%. On the other hand, it is
seen here that the RDM Linear Threshold Points occurred mostly at mass loss values
below 1%. For the PC specimens, the rate of RDM change also stayed more or less
constant up until about 150 cycles, after which this rate became increasingly larger.
Figure 76 shows the rate of RDM change plotted together with the rate of mass loss
for each Test Set in the Variability Series. In these graphs, only the average rates in
each Test Set are shown, and the rates of RDM change from Figure 74 have been
multiplied by –1 to convert these values to positive for convenient comparison to the
mass loss rates. Overall, it is evident from all Test Sets that RDM values reached their
February 5, 2009
FINAL REPORT 134
Test Set A
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200
Cycles
Rat
e of
RD
M (%
/ cy
cle)
Test Set B
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200
Cycles
Rat
e of
RD
M (%
/ cy
cle)
Test Set C
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200
Cycles
Rat
e of
RD
M (%
/ cy
cle)
Test Set D
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200
Cycles
Rat
e of
RD
M (%
/ cy
cle)
Test Set E
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200
Cycles
Rat
e of
RD
M (%
/ cy
cle)
Test Set F
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200
Cycles
Rat
e of
RD
M (%
/ cy
cle)
Test Set G
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200
Cycles
Rat
e of
RD
M (%
/ cy
cle)
Figure 74 Rates of RDM change for Variability Series.
Threshold Point
February 5, 2009
FINAL REPORT 135
Figure 75 Rates of RDM change for Performance Criteria Series.
Threshold Points prior to mass loss values reaching their corresponding Threshold
Points. For example, in Test Set A, RDM values changed at an increasingly faster rate
after 120 cycles while mass loss changed increasingly faster after about 160 cycles.
This indicates that the rate of internal damage in the specimens increased prior to
increasing damage being detected in the form of mass loss from the specimens. These
measurements and analyses were supported by observations of the specimen
conditions as described in Section 6.1 and as illustrated in Figure 66 for specimen C1.
For this particular specimen, the RDM Linear Threshold Point was at 80 cycles but the
Mass Loss Linear Threshold Point was at 120 cycles. From 80 to 120 cycles, mass
loss increased from 0.6 to 1.2% while RDM dropped from 96 to 57%. Twenty cycles
later, at 140 cycles, mass loss had increased to 1.7% but RDM had dropped to 22%.
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200
Cycles
Rat
e of
RD
M (%
/ cy
cle)
February 5, 2009
FINAL REPORT 136
Test Set A
0.0
0.5
1.0
1.5
2.0
0 40 80 120 160 200Cycles
Rat
e of
RD
M (%
/ cy
cle)
0.00
0.10
0.20
0.30
Rat
e of
Mas
s lo
ss
(% /
cycl
e)
Test Set B
0.0
0.5
1.0
1.5
2.0
0 40 80 120 160 200Cycles
Rat
e of
RD
M (%
/ cy
cle)
0.00
0.10
0.20
0.30
Rat
e of
Mas
s lo
ss
(% /
cycl
e)
Test Set C
0.0
0.5
1.0
1.5
2.0
0 40 80 120 160 200Cycles
Rat
e of
RD
M (%
/ cy
cle)
0.00
0.10
0.20
0.30
Rat
e of
Mas
s lo
ss
(% /
cycl
e)
Test Set D
0.0
0.5
1.0
1.5
2.0
0 40 80 120 160 200Cycles
Rat
e of
RD
M (%
/ cy
cle)0.00
0.10
0.20
0.30
Rat
e of
Mas
s lo
ss
(% /
cycl
e)
Test Set E
0.0
0.5
1.0
1.5
2.0
0 40 80 120 160 200Cycles
Rat
e of
RD
M (%
/ cy
cle)
0.00
0.10
0.20
0.30
Rat
e of
Mas
s lo
ss
(% /
cycl
e)
Test Set F
0.0
0.5
1.0
1.5
2.0
0 40 80 120 160 200Cycles
Rat
e of
RD
M (%
/ cy
cle)
0.00
0.10
0.20
0.30
Rat
e of
Mas
s lo
ss
(% /
cycl
e)Test Set G
0.0
0.5
1.0
1.5
2.0
0 40 80 120 160 200Cycles
Rat
e of
RD
M (%
/ cy
cle)
0.00
0.10
0.20
0.30
Rat
e of
Mas
s lo
ss
(% /
cycl
e)
Figure 76 Rates of RDM change compared to rates of mass loss for Variability Series.
RDM
mass loss
February 5, 2009
FINAL REPORT 137
6.3 Relationship to mass loss
Besides examining changes in RDM and mass loss as function of freeze-thaw cycles,
the relationship between RDM and mass loss was also examined. This analysis was
possible since for every specimen tested, data was available for these parameters at
every 10th cycle. Hence, plots of RDM vs. mass loss were constructed as shown in
Figure 77 for each specimen in the Variability Series. Also shown in these graphs is
the 60% RDM reference line as well as the zone of mass loss in the vicinity of 1%.
This zone shown as a dashed rectangle in Figure 77 was arbitrarily set between mass
loss values of 0.8 to 1.2%. The data used to construct these graphs consisted of all
available data. In most cases, it is seen that RDM values remained fairly “flat” for
mass loss below about 0.5% followed by a decline, such as all specimens in Test Sets
A, C and E. For these specimens, this trend suggested that below 0.5% mass loss,
RDM was not as sensitive to damage in the material as mass loss was. If RDM was
indicative of internal damage in the specimens, little internal damage was probably
induced in the specimens at mass loss values below 0.5%. However, beyond a certain
mass loss which varied from specimen to specimen, RDM became increasingly
sensitive and thus the curves became steeper (i.e., d(RDM)/d(Mass Loss) increased
negatively). An example of such behavior was shown earlier in Figure 66
demonstrating the damage evolution in specimen C1. After 100 cycles, mass loss was
0.9% and RDM had dropped 21% from it is initial value. Between 100 and 140
cycles, for another 0.5% increase in mass loss, RDM dropped another 57%. There
were various however exceptions to this trend such as several specimens in Set B, D
and G, which showed a steady decline in RDM starting from the start.
February 5, 2009
FINAL REPORT 138
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
RD
M, %
Test Set A
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
RD
M, %
Test Set B
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
RD
M, %
Test Set C
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
RD
M, %
Test Set D
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
RD
M, %
Test Set E
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
RD
M, %
Test Set F
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
RD
M, %
Test Set G
Figure 77 RDM vs. mass loss relationship for Variability Series specimens.
February 5, 2009
FINAL REPORT 139
The graphs in Figure 77 also show another important result which was the possibility
of specimens exhibiting mass loss in the vicinity of 1% but whose RDM values were
below 60%. Specimens of this nature were termed Risky Specimens since their
acceptance at 1% mass loss did not necessarily imply internal structural soundness.
There were 11 out of 28 specimens in this category and are listed in Table 18, which
also shows the number of cycles to 1% mass loss and the Mass Loss Linear Threshold
Points. Overall, about half of these specimens reached 1% before reaching their
Threshold Points. Recall from the previous section, the RDM Threshold Points
always preceded the Mass Loss Threshold Points. As such, a mass loss of 1% was not
indicative of actual conditions in the specimens or pending damage in them. Below a
mass loss of 0.8%, 5 out of 28 specimens exhibited RDM less than 60%; and below a
mass loss of 0.6%, 3 out of 28 specimens exhibited RDM less than 60%.
Table 18 Summary of Risky Specimens
Spec. A2 A4 B1 B3 B4 C1 C4 D1 D2 D4 G1
Cycles to 1% ML 166 142 184 93 199 108 149 123 154 134 149
ML Threshold Pt 150 150 160 85 140 130 180 130 140 140 150
RDM @ ML=1% 65 57 23 44 26 69 76 54 3 36 62
Figure 78 shows the RDM and mass loss relationships for the PC Series specimens.
Here, all curves reached less than 2% mass loss since specimens were gradually
withdrawn throughout the test program for Modulus of Rupture testing. Nevertheless,
from the available data, it is seen that there were several Risky Specimens in this series
as well. For several of these specimens, RDM dropped below 60% even before mass
loss reached 1%.
February 5, 2009
FINAL REPORT 140
Figure 78 RDM vs. mass loss relationship for PC Series specimens.
From a practical standpoint, specimens are typically evaluated for their mass loss after
a prescribed number of cycles. Figure 79 shows plots of RDM and mass loss for all
specimens based on all data from the Variability and PC Series after 50, 100, 150 and
200 cycles. For the typical 100 cycle specification, it is seen that for these particular
specimens, none of the specimens below 1% mass loss displayed RDM values below
60%. However, after 150 cycles, 1 out of 22 (<5%) specimens with mass loss below
1% also had RDM less than 60%. At 200 cycles, 2 out of 11 (18%) specimens with
mass loss below 1% also had RDM less than 60%. These results showed that with
increasing cycles, there was a greater likelihood of having specimens with less than
1% mass loss (which would comply with specifications) but with RDM less than 60%.
This is because as shown previously, beyond a certain mass loss (which varied from
specimen to specimen), RDM dropped at an increasingly faster rate relative to mass
loss. When coupled with the observation that performance trends are unreliable in
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
RD
M, %
February 5, 2009
FINAL REPORT 141
fewer than 50 cycles (Section 5), this suggests that the appropriate duration for a mass-
loss based test is somewhere between 50 and 150 cycles.
0
20
40
60
80
100
120
0.0 0.1 0.2 0.3 0.4
Percent mass loss
RD
M, %
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Percent mass loss
RD
M, %
a) after 50 cycles b) after 100 cycles
0
20
40
60
80
100
120
0.0 1.0 2.0 3.0 4.0 5.0
Percent mass loss
RD
M, %
0
20
40
60
80
100
120
0.0 1.0 2.0 3.0 4.0 5.0
Percent mass loss
RD
M, %
c) after 150 cycles d) after 200 cycles
Figure 79 RDM vs. mass loss at specified cycles
6.4 Relationship to moisture content
6.4.1 Definitions
The preceding section demonstrated a general trend in the relationship between RDM
with mass loss (little change in RDM at mass loss below about 0.5% followed by
increasingly faster reductions in RDM). Section 5.3.2 also showed a correlation
between mass loss and moisture condition in the specimens. This section explores the
February 5, 2009
FINAL REPORT 142
relationship between RDM and moisture condition in the specimens. For clarification,
several parameters are first defined:
Parameters related to moisture condition of a specimen
• Moisture Content (MC):
MC = 100% specimen of mass dried Oven
)C105at drying hrs 24after removed water of (Mass×
° (13)
This is the same form of expression as Equation 2, which is shown again:
MC (at n cycles) =
100% MassDriedOven
Mass) DriedOven - cycles nat Mass DriedSurface (Total× (2)
Equation 2 calculates the Moisture Content of the specimen after n freeze-thaw
cycles.
• Moisture Gain (MG):
This parameter was defined in 5.5.2 and is shown again:
Moisture Gain (at n cycles) =
Moisture Content (at n cycles) – Initial Moisture Content (14)
Moisture Gain refers to the additional moisture absorbed by the specimen after
start of freeze-thaw cycles, and since it is computed from Moisture Content
(Equation 2), it can also be determined after n freeze-thaw cycles. For the
Moisture Content values shown above, Moisture Gains were 0% before freeze-
February 5, 2009
FINAL REPORT 143
thaw cycling, typically 0.6-1.1% after 100 cycles and 0.7-1.5% after 150
cycles.
• Degree of Saturation (S):
Degree of Saturation is defined as follows:
S = saturationat content Moisturecontent moisture Actual (15)
where actual Moisture Content is determined from Equation 2.
The “Moisture Content at Saturation” was determined from ASTM C 642
(boiled absorption and volume of permeable voids, ASTM C 642, 2002) tests
conducted on companion specimens of the same mix as the freeze-thaw
specimens used in this study. Two specimens from each of the three pallets of
SRW units (see Section 2.1.1) were tested and results are shown in Table 19.
Thus, “absorption after immersion and boiling” was used as the “Moisture
Content at Saturation” in Equation 15.
Table 19 ASTM C 642 test results Specimen Absorption
after Immersion (%)*
Absorption after Immersion and Boiling (%)
Volume of Permeable Voids (%)
A6L 5.1 7.4 16.8 A6R 4.9 7.3 16.6 B6L 5.0 7.3 16.6 B6R 5.0 7.4 16.8 C3L 4.7 7.0 16.1 C3R 4.8 7.2 16.3
Note: first letter in specimen label denotes source pallet. * Immersion refers to full immersion of specimens, not partial immersion as is the case in ASTM C 1262. Note that ASTM C 140 absorption varied from 5.7 to 5.9% with an average of 5.8%
February 5, 2009
FINAL REPORT 144
From the Moisture Content values of specimens in this study, the degree of
saturation, S, was approximately 0.64-0.67 after the initial 24-hr immersion
and before freeze-thaw cycling, 0.74-0.82 after 100 cycles and 0.74-0.86 after
150 cycles.
Parameters related to moisture condition and integrity of specimens
• Critical Moisture Content:
Moisture Content at which RDM begins to diminish rapidly with increasing
cycles (typically 5.5-5.8%).
• Critical Moisture Gain:
Moisture Gain at which RDM begins to diminish rapidly with increasing
cycles (typically 0.8-1.1%).
• Critical Degree of Saturation SCR:
Degree of Saturation at which RDM begins to diminish rapidly with increasing
cycles (typically 0.76-0.83, or 95 to 100% of the ASTM C 140 Absorption).
The origin of the values shown in parenthesis is presented ahead.
6.4.2 Results
Using the above definitions, RDM vs. moisture content plots were constructed using
data for each specimen at every 10th cycle up to 200 cycles for the Variability Series.
Figure 80 summarizes these results. It is seen that below moisture contents of 5.5%,
RDM values remained more or less unchanged (except for several specimens in Set C
which showed increases in RDM). However, once the moisture content in the
specimens exceeded 5.5%, RDM values dropped sharply and continued decreasing
February 5, 2009
FINAL REPORT 145
0
20
40
60
80
100
120
4.5 5.0 5.5 6.0 6.5 7.0
Moisture content, %
RD
M, %
Test Set A
0
20
40
60
80
100
120
4.5 5.0 5.5 6.0 6.5 7.0
Moisture content, %
RD
M, %
Test Set B
0
20
40
60
80
100
120
4.5 5.0 5.5 6.0 6.5 7.0
Moisture content, %
RD
M, %
Test Set C
0
20
40
60
80
100
120
4.5 5.0 5.5 6.0 6.5 7.0
Moisture content, %
RD
M, %
Test Set D
0
20
40
60
80
100
120
4.5 5.0 5.5 6.0 6.5 7.0
Moisture content, %
RD
M, %
Test Set E
0
20
40
60
80
100
120
4.5 5.0 5.5 6.0 6.5 7.0
Moisture content, %
RD
M, %
Test Set F
0
20
40
60
80
100
120
4.5 5.0 5.5 6.0 6.5 7.0
Moisture content, %
RD
M, %
Test Set G
Figure 80 RDM vs. moisture content relationship for Variability Series specimens.
February 5, 2009
FINAL REPORT 146
until 0%. In most cases, this critical moisture content was in the range of 5.6 to 5.8%,
(i.e., approximately the ASTM C 140 moisture content) although several specimens
exhibited slightly lower (5.5%) and higher (6.1%) critical moisture contents. This
observed behavior concurred with the concepts of Critical Degree of Saturation (SCR)
theory proposed by Fagerlund (1975) for ordinary concretes. Degree of Saturation, S,
and Critical Degree of Saturation, SCR, were defined in 6.4.1.
In Fagerlund’s theory, any particular material (with its unique combination of material
properties such as strength and pore properties) possesses a unique value of SCR, and
significant frost damage does not occur until the Degree of Saturation, S, in the
material exceeds SCR. This behavior is shown in Figure 81 (taken from Fagerlund,
1999) where the relative dynamic modulus after 3 freeze-thaw cycles (E3/Eo) has been
plotted as function of saturation level S for ordinary concrete of different ages. At S <
SCR, there is little change in E3/Eo, but once S reaches and exceeds SCR, E3/Eo drops
rapidly. For ordinary concretes, the normal range of SCR is 0.75 to 0.90 (Fagerlund,
1977), with the specific actual value affected by the volume and distribution of pores
(Fagerlund, 1999).
The relationship between RDM and moisture content for specimens in the PC Series is
shown in Figure 82. Trends comparable to those seen in the Variability Series were
also obtained for the PC specimens. Critical moisture contents were on average 5.8%.
By comparison, the moisture content of the control specimen, which had been
continuously immersed (per ASTM C 1262) but not subjected to freezing and thawing
was 5.7%, at the time the average moisture content in the freeze-thaw specimens
reached 6.0% (at 220 cycles).
February 5, 2009
FINAL REPORT 147
Figure 81 Critical degree of saturation SCR of a certain concrete as function of concrete
age (Fagerlund, 1999)
Figure 82 RDM vs. moisture content relationship for PC Series specimens.
0
20
40
60
80
100
120
4.5 5.0 5.5 6.0 6.5 7.0
Moisture content, %
RD
M, %
February 5, 2009
FINAL REPORT 148
For the specimens in this study, critical degrees of saturation were computed using
values of critical moisture content and Equation 15. For the range of measured
critical moisture contents (5.5 to 5.8%) and boiled absorptions (7.0 to 7.4%), the range
of critical degrees of saturation was 0.76 to 0.83, which is within the range of SCR
values for ordinary concretes mentioned earlier.
The moisture content represents an absolute moisture condition of the specimens
themselves (i.e., it accounts for total water removed after 24 hrs drying at 105°C
(220°F)). However, according to Fagerlund’s theory, freeze-thaw cycles gradually
increase the level of moisture in the specimen until it reaches a critical value. Thus
another relevant parameter is the change in moisture content, or moisture gain, as
defined in Section 6.4.1. Moisture gain was shown to be correlated to specimen mass
loss. Figure 83 shows RDM as function of moisture gain for all specimens in the
Variability Series through 200 cycles. More uniform trends were observed among all
specimens in this series, compared to the previously observed relationships for RDM-
Mass Loss or RDM-Moisture Content. In general, critical moisture gains were in the
range of 0.8% to 1.1%, with the exception of specimen F2.
Figure 84 shows RDM vs. Moisture Gain curves for all specimens in the Variability
Series. A curve was fitted through this data to get a mathematical relationship
between RDM and moisture gain. This is shown Figure 84a in which the curve-fit
was generated using the software TableCurve 2D (version 4, from AISN Software
Inc., copyright 1989-1996). The 3rd order polynomial shown below exhibited the
highest level of correlation to the actual data:
February 5, 2009
FINAL REPORT 149
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
Test Set A
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
Test Set B
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
Test Set C
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
Test Set D
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
Test Set E
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
Test Set F
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
Test Set G
Figure 83 RDM vs. moisture gain relationship for Variability Series specimens.
February 5, 2009
FINAL REPORT 150
a) TableCurve 2D software fit
b) straight line fits
Figure 84 RDM vs. moisture gain relationship for all Variability Series specimens.
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
RDM = 104 – 25(moisture gain)3
R2 = 0.61
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, % slow RDM drop
rapid RDM drop
0.9%
February 5, 2009
FINAL REPORT 151
RDM, % = 104 – 25×(moisture gain, %)3 R2 = 0.61 (16)
Using this equation, an RDM value of 60% was predicted at a moisture gain of 1.2%.
This equation also showed that 90% RDM was reached at about 0.8% moisture gain,
after which RDM values dropped rapidly. It is however noted that this correlation is
only an approximate one (note relatively low R2) intended to obtain a numerical
relationship between RDM and moisture gain. It is recognized that other forms of
expressions may be applicable such as logistic functions (to model the S-curve
behavior) which could be further explored. A second curve-fitting method consisting
of a simple bilinear function manually fitted through the data was also employed, as
shown in Figure 84b. The first line represented the region of slow RDM drop, while
the second line represented the region of rapid RDM drop. Using this straight-line fit,
the intersection of these two lines occurred at 0.9% moisture gain, and an RDM value
of 60% was reached also at moisture gain of 1.2%.
The relationship between RDM and moisture gain for specimens in the PC Series is
shown in Figure 85. Trends comparable to those existing in the Variability Series
were also obtained for the PC specimens. Critical moisture gains were generally
about 1.0 to 1.1%. In summary, it appears that for all specimens in this study
(Variability and PC Series), moisture gains of about 0.8 to 1.1% were the upper limit
before RDM started dropping rapidly. By contrast, the moisture gain of the control
specimen at the time PC specimens had reached 220 cycles was at 0.8%.
February 5, 2009
FINAL REPORT 152
Figure 85 RDM vs. moisture gain relationship for PC Series specimens.
In Section 6.1, it was pointed out that the RDM of the control specimen increased with
increased immersion time and increased moisture content (in the absence of freezing
and thawing). Thus for the actual freeze-thaw test specimens, the cycle-induced
increase in moisture content and accompanying increase in RDM could have been off-
setting part of the freeze-thaw-damage-induced decrease in RDM. One possible way
in which these effects can be separated out is to correct the measured RDM of test
specimens (at a given moisture gain) by the corresponding increase in RDM of the
control specimen (at the same moisture gain). For the control specimen, the RDM vs.
moisture gain relationship can be modeled by the following equation (also shown in
Figure 86):
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
February 5, 2009
FINAL REPORT 153
RDM = 26.5 exp ⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎠⎞
⎜⎝⎛
4.2
MG103.98- + 100 (17)
where RDM is in %
MG = moisture gain in %
Figure 86 RDM vs. moisture gain relationship for control specimen.
An example of how the RDM of freeze-thaw test specimens can be corrected is shown
for specimen A1. After 100 cycles, the moisture gain was 0.8% and the measured
RDM was 97%. From Equation 17, the RDM of the control specimen is calculated to
be 20%. Thus, for this specimen, the corrected RDM is 97 / (1+20/100) = 81%.
Performing this calculation for all other specimens using all available data led to the
RDM vs. moisture gain plots shown in Figure 87 for the specimens in the Variability
Series and Figure 88 for the PC Series specimens. In these figures, the dark lines
80
90
100
110
120
130
140
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Moisture gain, %
RD
M, %
RDM = 26.5 exp ⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎠⎞
⎜⎝⎛
4.2
MG103.98- + 100
February 5, 2009
FINAL REPORT 154
0102030405060708090
100110120130
0.0 0.5 1.0 1.5 2.0 2.5Moisture gain, %
RD
M, %
Test Set A
0102030405060708090
100110120130
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
RD
M, %
Test Set B
0102030405060708090
100110120130
0.0 0.5 1.0 1.5 2.0 2.5Moisture gain, %
RD
M, %
Test Set C
0102030405060708090
100110120130
0.0 0.5 1.0 1.5 2.0 2.5Moisture gain, %
RD
M, %
Test Set D
0102030405060708090
100110120130
0.0 0.5 1.0 1.5 2.0 2.5Moisture gain, %
RD
M, %
Test Set E
0102030405060708090
100110120130
0.0 0.5 1.0 1.5 2.0 2.5Moisture gain, %
RD
M, %
Test Set F
0102030405060708090
100110120130
0.0 0.5 1.0 1.5 2.0 2.5Moisture gain, %
RD
M, %
Test Set G
Figure 87 “Uncorrected” and “corrected” RDM vs. moisture gain relationship for
Variability Series specimens.
February 5, 2009
FINAL REPORT 155
Figure 88 “Uncorrected” and “corrected” RDM vs. moisture gain relationship for PC
Series specimens.
represent the “uncorrected” RDM values which are also those in Figure 84 for the
Variability Series and Figure 85 for the PC Series. It is seen here that a “knick point”
below which RDM values did not change significantly and above which RDM
dropped increasingly rapid existed at moisture gain of about 0.5% in all specimens.
The method shown here to separate the effects of moisture-induced changes in RDM
from the freeze-thaw-damage-induced changes in RDM is an approximate one.
Further studies should be conducted to confirm the actual changes in RDM of freeze-
thaw specimens due to their increased moisture content. This may be done by freezing
and thawing test specimens which are subsequently oven-dried and tested for their
frequency at predetermined cycles.
Now, since RDM values were observed to drop rapidly after a critical value of
moisture gain, it was instructive to also observe mass loss behavior relative to
0102030405060708090
100110120130
0.0 0.5 1.0 1.5 2.0 2.5Moisture gain, %
RD
M, %
February 5, 2009
FINAL REPORT 156
moisture gain. This relationship for all Variability Series specimens is shown in
Figure 89. Best-fit curves were also determined for this data using TableCurve 2D,
with the top three curve fit results shown as follows:
Figure 89 Mass loss vs. moisture gain relationship for all Variability Series specimens.
Mass loss, % = – 0.2 + 1.1×(moisture gain, %)2.5 R2 = 0.35 (18)
Mass loss, % = – 0.4 + 1.4×(moisture gain, %)2 R2 = 0.35 (19)
Mass loss, % = – 0.025 + 0.89×(moisture gain, %)3 R2 = 0.34 (20)
Using these imprecise and empirical relationships, a 1% mass loss was predicted to
occur when the average moisture content of freeze-thaw specimens increased by 1.0 to
1.1%. From the raw test data, 1% mass loss was reached at moisture content increases
of 0.8 to 1.3%, which is also the approximate range of critical moisture gains for
Variability Series specimens. These results provide another perspective on the
existence of Risky Specimens, since it is evident that there are specimens capable of
0.0
1.0
2.0
3.0
4.0
5.0
0.0 0.5 1.0 1.5 2.0 2.5
Moisture gain, %
Mas
s lo
ss, %
ML = –0.4 + 1.4(moisture gain)2
R2 = 0.35
February 5, 2009
FINAL REPORT 157
absorbing water beyond the critical 0.8 to 1.1% range, while exhibiting mass loss
about 1% or less. Once their moisture gain exceeds the critical value, however, their
RDM values drop rapidly.
February 5, 2009
FINAL REPORT 158
7.0 RESULTS AND DISCUSSION – PULSE VELOCITY
7.1 Pulse velocity results
Variability Series
Pulse velocity (PV) measurements were made on all specimens after every 10 freeze-
thaw cycles, and changes in the material condition were assessed by expressing PV as
percentage of its original value. Unlike RDM, no reference values relating changes in
PV to material condition were found in the literature. More commonly, plots of
cylinder compressive strength versus pulse velocities for estimating concrete strengths
are available in the literature. An example of one such plot is given in Figure 90 (Naik
et al., 2004), where it is seen that cylinders whose compressive strengths differed by
10% exhibited PV values which differed by about 3 to 4%; and for those whose
compressive strengths differed by 20%, PV values differed by about 6 to 8%.
Figure 90 Example of relationship between cylinder compressive strength and pulse
velocity (Naik et al., 2004)
February 5, 2009
FINAL REPORT 159
Results of PV as function of cycles for Variability Series specimens are shown in
Figure 91. As with RDM vs. cycles results, the curves stayed essentially flat (at PV of
about 100% of their initial value) up until about 120 cycles, at which point the PV
values dropped rapidly. After 100 cycles, specimens B3 and D2 exhibited lowest PV
values of all test specimens at 93 and 96% of their initial values, respectively. After
150 cycles, these two specimens were also lowest at 63 and 70% respectively. These
observations supported those from resonant frequency whereby after 100 and 150
cycles, these 2 specimens also exhibited the lowest RDM values of all test specimens
in the Variability Series. Figure 92 shows photos of these two specimens and the
cracked locations on them. In both cases, PV measurements taken in a direction
transverse to the crack direction displayed low values. After 200 cycles, PV values
ranged anywhere from 0 to 80% of their initial values, with most of them being in the
20 to 60% range.
Results of the Test Sets in the Variability Series are discussed below. Figure 93 shows
PV vs. cycles plots for average Test Set results. The following trends were discerned:
• Within Test Sets A, B and C, Sets A and C performed similarly overall, while
Set B displayed lower PV values from about 90 cycles onwards, which
suggested that underfilling of solution resulted in larger damage in the
specimens.
• Within Test Sets D, E, F, Set E exhibited highest overall PV values, followed
by Sets F and D, which suggested that for a given container size, increasing the
specimen size resulted in lower PV values. The common observation among
February 5, 2009
FINAL REPORT 160
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200
Cycles
UPV
, % o
f ini
tial
Test Set C
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
UPV
, % o
f ini
tial
Test Set A
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200
Cycles
UPV
, % o
f ini
tial
Test Set B
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200
Cycles
UPV
, % o
f ini
tial
Test Set D
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
UPV
, % o
f ini
tial
Test Set E
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200Cycles
UPV
, % o
f ini
tial
Test Set F
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200
Cycles
UPV
, % o
f ini
tial
Test Set G
Figure 91 PV (as % of initial value) vs. cycles for Variability Series
February 5, 2009
FINAL REPORT 161
a) specimen B3
b) specimen D2
Figure 92 Photos of specimens B3 and D2.
PV value in this direction low
PV value in this direction low
PV value in this direction low
February 5, 2009
FINAL REPORT 162
Test Sets B and D was that these sets had the lowest msolution/mspecimen ratio
among sets in their respective comparison groups (i.e., Set B in A, B, C and
Set D in D, E, F).
• Comparing Sets A and D, it is seen that for a specimen size, decreasing the
container size resulted in lower PV values.
• Comparing Sets A and G, it appeared that geometrical effects were not
significant.
Figure 93 Average Test Set PV vs. cycles for Variability Series.
When comparing the ranking of the various Test Sets obtained from PV testing to
those obtained from mass loss and RDM (from resonant frequency) testing, the results
in Table 20 were obtained. It was pointed out earlier that the short-term performance
of these specimens could not be reliably used to predict longer-term performance.
0
10
20
30
40
50
60
70
80
90
100
110
0 20 40 60 80 100 120 140 160 180 200Cycles
UPV
, % o
f ini
tial
D
B
G
C
F
A
E
February 5, 2009
FINAL REPORT 163
This fact still remains true when considering PV based rankings. However, it also is
observed that in general, after 100 cycles, PV ranked the Test Sets similarly to the
manner in which RDM ranked these Test Sets.
Table 20 Ranking of Test Sets based on Mass Loss, RDM and PV.
50 cyc. 100 cyc. Mass
loss RDM PV Mass
loss RDM PV
Highest RDM, PV and B C E G C E lowest Mass Loss A D C A A G G A F D E F E E G F G A F F D C F C
Lowest RDM and D G A B D D highest Mass Loss C B B E B B 150 cyc. 200 cyc. Mass
loss RDM PV Mass
loss RDM PV
Highest RDM, PV and G G E G E E lowest Mass Loss A E G A G G D A A E F F C C F C B C F F C F C A
Lowest RDM and E B D B A B highest Mass Loss B D B D D D
Performance Criteria Series
Figure 94 shows PV vs. cycles plots for all specimens in the PC Series. The overall
average PV of all 16 specimens was at 101, 101, 100 and 99% of their initial value
after 50, 100, 150 and 200 cycles. Of all specimens, C5L in particular showed the
earliest decline in PV. For this particular specimen, PV was at 99 and at 98% of its
initial value after 100 and 150 cycles. This observation matches that from RDM
February 5, 2009
FINAL REPORT 164
(resonant frequency) whereby specimen C5L was also the one showing earliest drops
in RDM among all specimens. Figure 95 shows PV vs. cycles for the average PV
value of all PC specimens as well as the control specimens (which was also partially
immersed in 13 mm (½ in.) saline solution, but not subjected to freezing and thawing).
Here it is seen that after about 120 cycles, PV in the control specimen gradually
increased. Previous Cornell data showed that PV values of air-dried specimens
increased after being immersed in water for 24 hrs. Thus, continuous water absorption
may increase PV value in the absence of any freeze-thaw damage. This could also
explain why PV was less sensitive to the number of cycles than RDM. The cycle-
induced increase in moisture content and accompanying increase in PV could have
been off-setting the freeze-damage-induced decrease in PV. Further studies are
required to separate the effects of increased moisture content and freeze-thaw damage
on PV values.
Figure 94 PV vs. cycles for PC specimens.
0
10
20
30
40
50
60
70
80
90
100
110
0 20 40 60 80 100 120 140 160 180 200 220Cycles
UPV
, % o
f ini
tial
February 5, 2009
FINAL REPORT 165
Figure 95 PV vs. cycles for PC average and control specimen.
7.2 Relationship to mass loss
In the same manner in which RDM-Mass loss relationships were examined, plots of
PV as function of mass loss were also developed, which are shown in Figure 96 for
each specimen in the Variability Series. Also shown in these graphs is the zone of
mass loss in the vicinity of 1%. As with RDM from resonant frequency tests, it is
seen that PV values remained fairly “flat” up to 0.8% mass loss and above in most
cases, followed by a decline. These trends suggest that from a pulse wave velocity
standpoint, there was probably little internal damage in most specimens up to about
0.8% mass loss. This means that pulse velocity was not as sensitive to internal
damage as RDM was. However, beyond a certain mass loss which varied from
specimen to specimen, damage accelerated. Of all specimens in the Variability Series,
0
10
20
30
40
50
60
70
80
90
100
110
0 20 40 60 80 100 120 140 160 180 200 220Cycles
UPV
, % o
f ini
tial
control
Avg PC
February 5, 2009
FINAL REPORT 166
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
PV,
% in
itial
val
ue
Test Set A
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
PV, %
initi
al v
alue
Test Set B
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
PV, %
initi
al v
alue
Test Set C
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
PV, %
initi
al v
alue
Test Set D
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
PV, %
initi
al v
alue
Test Set E
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
PV, %
initi
al v
alue
Test Set F
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
PV, %
initi
al v
alue
Test Set G
Figure 96 PV vs. mass loss relationship for Variability Series specimens.
February 5, 2009
FINAL REPORT 167
several exhibited comparatively larger decrease in PV. In the range of 0.8 to 1.2%
mass loss, PV values in specimens A2, B1, B4, D2, G1 and G4 dropped below 90% of
their initial values. Except for G4, the other specimens also corresponded to the Risky
Specimens summarized in Table 18. Risky Specimens were identified as those
specimens with RDM less than 60% (i.e., fair level of internal damage) despite
displaying mass loss of about 1%. Figure 97 shows the PV and mass loss relationship
for the PC Series specimens. From the available data, only specimen C13R exhibited
comparatively larger drops in PV at mass loss of about 1%. This specimen had also
shown an RDM of 54% at 1% mass loss.
Figure 97 PV vs. mass loss relationship for PC Series specimens.
7.3 Comparison of methods
From RDM (using resonant frequency) and PV results, it appears that both techniques
for internal damage detection were capable of identifying relative performance of
specimens in a similar manner. Both methods also exhibited similar trends with
0
20
40
60
80
100
120
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
PV, %
initi
al v
alue
%
February 5, 2009
FINAL REPORT 168
respect to mass loss and were similarly able to identify Risky Specimens. The velocity
of pulse waves through concrete is in fact also a measure of a dynamic property of the
concrete specimens. Compression wave velocity is related to the dynamic elastic
modulus (Ed) as follows (Naik et al., 2004):
V = ρ
KE (21)
where V = compression wave velocity
K = (1 – µ) / [(1 + µ) (1 – 2µ)]
E = dynamic modulus of elasticity
ρ = mass density
µ = dynamic Poisson’s’ ratio
As such, it was also possible to define a Relative Dynamic Modulus based on pulse
velocity measurements (RDMPV) by rearranging the above equation, as follows:
RDMPV = ⎟⎟⎠
⎞⎜⎜⎝
⎛
undamaged d
damaged d
EE
× 100% = 2
undamaged
damaged
PVPV
⎟⎟⎠
⎞⎜⎜⎝
⎛ × 100% (22)
where Ed damaged = dynamic elastic modulus in damaged specimen
Ed undamaged = dynamic elastic modulus in undamaged specimen
PV damaged = PV after n freeze-thaw cycles
PV undamaged = PV at 0 cycles (before freezing and thawing)
Damage assessment using this expression is actually employed in the CIF-Test in
European freeze-thaw test standards (Siebel, 1995)
February 5, 2009
FINAL REPORT 169
To compare RDM values obtained using both resonant frequency and pulse velocity
methods (i.e., RDMRF vs. RDMPV), the changes in RDM from their initial values
(∆RDM) were considered, as opposed to just the RDM values alone. Thus, at 0
freeze-thaw cycles, ∆RDMRF = ∆RDMPV = 0 for all specimens. As an example of
these calculations, take specimen C1 after 100 cycles as follows:
• RDMRF = 79%, and thus ∆RDMRF = 100 – 79 = 21%
• PV as percent of its initial PV value was 98%, and thus, RDMPV = (0.98)2 ×
100% = 96% and ∆RDMPV = 100 – 96 = 4%.
Performing these calculations for all available specimens enabled plots of ∆RDMPV
vs. ∆RDMRF to be generated each time measurements were made. Recall in Section
7.1, it was mentioned that rankings of Variability Test Sets based on RDM (using
resonant frequency) and PV were similar after 100 cycles. Hence, relationships
between ∆RDMPV and ∆RDMRF based on data after cycles 120 and 160 are shown in
Figure 95. The line corresponding to ∆RDMPV = ∆RDMRF is also shown in these
plots. Two main observations were drawn from these plots:
1. ∆RDMRF varied more rapidly than ∆RDMPV which indicated that resonant
frequency tests were probably more sensitive to internal damage of specimens
compared to pulse velocity tests.
2. At the reference value of RDMRF of 60%, ∆RDMRF was 40% which
corresponded more or less to ∆RDMPV of 10 to 20%, and thus to RDMPV of 80
to 90%. These RDMPV values equated to PV values that were about 90 to 95%
of their initial values (Equation 22), which is similar to the reference 90%
value shown earlier.
February 5, 2009
FINAL REPORT 170
In summary, both methods of internal damage detection, using either resonant
frequency or pulse velocity, sorted specimens and Test Sets in the Variability Series in
a comparable manner. PV methods appeared to be less sensitive to internal damage
compared to resonant frequency methods, especially before 100 cycles (i.e., below a
maximum mass loss of about 1% was reached for any given specimen). However, if
using PV to assess damage in specimens, a different acceptance criteria must be used.
It was demonstrated here that an RDM of 60% based on resonant frequency methods
corresponded more or less to PV values in the range of 90 to 95% of their initial
values. Thus an acceptance criterion based on PV would have to be much higher than
the 60% for RDM based on resonant frequency.
-10
0
10
20
30
40
50
60
70
80
-10 0 10 20 30 40 50 60 70 80
∆RDM (RF), %
∆R
DM
(PV)
, %
-10
0102030405060708090
100
-10 0 10 20 30 40 50 60 70 80 90 100
∆RDM (RF), %
∆R
DM
(PV)
, %
a) after 120 cycles b) after 160 cycles
Figure 98 Relationship between ∆RDMPV and ∆RDMRF.
∆RDMPV = ∆RDMRF ∆RDMPV = ∆RDMRF
February 5, 2009
FINAL REPORT 171
8.0 RESULTS AND DISCUSSION – VISUAL SCALING RATING
8.1 Visual scaling rating results
Variability Series
As described earlier in Section 3.6, visual scaling rating was performed using a
modified version of ASTM C 672’s approach for rating ordinary concretes subjected
to salt surface scaling tests. Modification was necessary because of the of the
typically smaller aggregate sizes used in SRW mixes compared to ordinary concretes
which rendered the ASTM C 672 guides inadequate for SRW specimens. An alternate
approach based on Percent Scaled Area was thus used as summarized in Table 5. This
guide correspondingly yielded ratings to specimens in the manner depicted in Figure
99.
Scaling rating was conducted on all specimens based in this modified guide, and the
results for the Variability Series specimens are shown in Figure 100. In general, it is
seen that under 100 cycles, less than 10% of the test face area (ref. Figure 44) was
scaled. Between 100 and 140 cycles most specimens exhibited increased scaling, and
by 200 cycles, various specimens had reached scaling of 5. These typically
corresponded to specimens that had not only scaled over almost all the test face area,
but had fully disintegrated. In most specimens, surface scaling was accompanied with
cracking in the specimens, as shown in Figure 101a for specimen D1 after 140 cycles
(scaling rating = 2) and in Figure 101b for specimen D4 after 140 cycles, (scaling
rating = 1). As such, at this time also, RDM (using resonant frequency) also exhibited
reductions (in accordance with the discussion in Section 6.1).
February 5, 2009
FINAL REPORT 172
0 1
2 3
4 – 5
Figure 99 Scaling rating guide used in this study (based on ASTM C 672).
February 5, 2009
FINAL REPORT 173
Test Set A
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Scal
ing
ratin
gTest Set B
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Scal
ing
ratin
g
Test Set C
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Scal
ing
ratin
g
Test Set D
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Scal
ing
ratin
g
Test Set E
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Scal
ing
ratin
g
Test Set F
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Scal
ing
ratin
g
Test Set G
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Scal
ing
ratin
g
Figure 100 Visual Scaling Rating vs. cycles for all Variability Series specimens.
February 5, 2009
FINAL REPORT 174
a) specimen D1 after 140 cycles (scaling rating = 2).
b) specimen D4 after 140 cycles (scaling rating = 1).
Figure 101 Examples of crack formation accompanying surface scaling.
February 5, 2009
FINAL REPORT 175
As for sorting behavior among the various Test Sets in the Variability Series, Figure
102 shows scaling rating vs. cycles plots for average Test Set results. The following
trends were discerned:
• Within Test Sets A, B and C, Set A exhibited lowest scaling overall, while Set
B displayed largest scaling from about 110 cycles onwards, which suggested
that underfilling of solution resulted in larger scaling damage in the specimens.
• Within Test Sets D, E, F, Set E exhibited lowest overall scaling, followed by
Sets F and D, which suggested that for a given container size, increasing the
specimen size resulted in higher scaling damage.
• Comparing Sets A and D, it is seen that for a specimen size, decreasing the
container size resulted in larger scaling damage.
• Comparing Sets A and G, it appeared that Set G with increasingly square
specimens exhibited lower scaling damage.
Figure 102 Average Test Set Scaling Rating vs. cycles for Variability Series.
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200Cycles
Scal
ing
ratin
g
E
C
F
A
B
G
D
February 5, 2009
FINAL REPORT 176
When comparing the ranking of the various Test Sets obtained from Visual Scaling
Rating to those obtained from mass loss, RDM (from resonant frequency) and PV
testing, the results in Table 21 were obtained. It was pointed out earlier that the 50-
cycle performance at of these specimens could not be reliably used to predict longer
term performance (after 100 and 150 cycles). This remains true when considering
Scaling Rating, since no scaling was observed even up to 100 cycles for these
specimens. After 150 cycles, there appeared to be slight correspondence in the
rankings based on scaling rating to the rankings based on other measured properties.
After 200 cycles, the ranking among all methods was approximately similar.
Table 21 Ranking of Test Sets based on Mass Loss, RDM, PV and scaling rating.
50 cyc. 100 cyc. Mass
loss RDM PV Scal.
Rat. Mass loss
RDM PV Scal. Rat.
Highest RDM, PV and B C E - G C E - lowest ML and Scal. A D C - A A G - G A F - D E F - E E G - F G A - F F D - C F C -
Lowest RDM and D G A - B D D - highest ML and Scal. C B B - E B B - 150 cyc. 200 cyc. Mass
loss RDM PV Scal.
Rat. Mass loss
RDM PV Scal. Rat.
Highest RDM, PV and G G E G G E E G lowest ML and Scal. A E G A A G G A D A A C E F F E C C F E C B C F F F C B F C A C
Lowest RDM and E B D D B A B B highest ML and Scal. B D B F D D D D
February 5, 2009
FINAL REPORT 177
Performance Criteria Series
Figure 103 shows Scaling Rating vs. cycles plots for all specimens in the PC Series.
Only two specimens, C2L and C5L, exhibited more than 10% scaled area after 200
cycles. Beyond 200 cycles, specimens C10R and C13R also showed increased
scaling. Figure 104 shows the condition of the immersed surface of several specimens
in this Series.
Figure 103 Scaling rating vs. cycles for PC specimens.
8.2 Relationship to mass loss
From the available data, plots of Scaling Rating as function of mass loss were also
developed to explore the possibility of any relationship between these two forms of
damage assessment. These graphs are shown in Figure 105 for each specimen in the
Variability Series. Also shown in these graphs is the zone of mass loss in the vicinity
0.0
1.0
2.0
3.0
4.0
5.0
0 40 80 120 160 200
Cycles
Scal
ing
ratin
g
February 5, 2009
FINAL REPORT 178
Figure 104 Comparison of immersed surface condition for selected PC Series specimens after 200 cycles (note: these specimens had been tested for Modulus of
Rupture earlier)
Scaling rating = 1
Scaling rating = 1
Scaling rating = 0
February 5, 2009
FINAL REPORT 179
0
1
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
Scal
ing
ratin
g
Test Set A
0
1
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
Scal
ing
ratin
g
Test Set B
0
1
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
Scal
ing
ratin
g
Test Set C
0
1
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
Scal
ing
ratin
g
Test Set D
0
1
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
Scal
ing
ratin
g
Test Set E
0
1
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
Scal
ing
ratin
g
Test Set F
0
1
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
Scal
ing
ratin
g
Test Set G
Figure 105 Scaling rating vs. mass loss relationship for Variability Series specimens.
February 5, 2009
FINAL REPORT 180
of 1%. Overall, it is seen that weak relationships existed between these two
parameters. In general, scaling rating increased with increasing mass loss, as expected
(actually, mass loss increased with increasing scaling rating). However, there was no
consistency in the way these parameters increased. For instance, for specimens
displaying non-zero scaling, their scaling rating took off at different mass loss levels
(at mass loss of 0.8% for the specimen in Test Set A, at mass loss of 1.1 to 1.4% for
Test Set B specimens, and so on). Moreover, it is also seen that a number of
specimens still exhibited scaling rating of zero, but with large mass loss values. The
reason for this discrepancy in mass loss and scaling rating results was probably related
to the different form of damage measured by these two methods. It was observed in
many cases that damage occurred on the sides of the specimens. This is shown by an
example in Figure 106 for specimen C2, where it is seen that while the test face area
was relatively undamaged, wearing and material loss had taken place in other surfaces.
It is further seen from Figure 105 that at 1% mass loss, scaling of specimens ranged
anywhere from 0 to 1. Figure 107 shows Scaling Rating vs. mass loss for the PC
Series specimens, where no relationships were discerned.
In summary, visual scaling rating of specimens in the manner employed in this study
(based on a modification of ASTM C 672) did not appear to be particularly sensitive
to internal damage of specimens especially below 100 cycles (and mass loss less than
1%). In general, for these particular specimens, the occurrence of surface scaling was
accompanied by the presence of cracks in the specimen, and this may be why Scaling
Rating and RDM (using resonant frequency) and PV methods ranked Test Sets in a
similar manner after 150 cycles. When compared to mass loss however, weak and
inconsistent relationships were observed, especially in the range of 1% mass loss, at
which point most specimens still exhibited Scaling Rating of 0.
February 5, 2009
FINAL REPORT 181
immersed surface
Figure 106 View of various surfaces of specimen C2 after 160 cycles.
Figure 107 Scaling rating vs. mass loss relationship for PC Series specimens.
0
1
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Mass loss, %
Scal
ing
ratin
g
February 5, 2009
FINAL REPORT 182
9.0 RESULTS AND DISCUSSION – MODULUS OF RUPTURE
9.1 Relationship to mass loss
One of the primary objectives of this study was to investigate the relationship between
mass loss of ASTM C 1262 freeze-thaw specimens and their modulus of rupture
(MoR). To do so, specimens from the PC Series were withdrawn from the population
for MoR testing at appropriate times so as to obtain a spread of mass loss values over
the range of less than 2%. All unbroken specimens from the Variability Series were
also tested for their MoR at the conclusion of 200 cycles. These specimens yielded
data points for mass loss values that were primarily greater than 2%. In addition, MoR
tests were conducted on four separate 200 mm (8 in.) long specimens prior to freezing.
These specimens had undergone initial immersion in 13 mm (½ in.) depth saline
solution together with the other test specimens and thus were tested in a moist
condition. Tests on these specimens established baseline MoR values corresponding
to immersed but otherwise undamaged specimens (i.e., no mass loss).
For all specimens tested in this study, the MoR vs. Mass Loss plot is shown in Figure
108, where the square data points represent specimens from the PC Series (walk-in
freezer) and the circular data points represent specimens from the Variability Series
(Tenney freezer). Also shown on this graph is the 1% mass loss specification limit.
Pre-freeze (i.e., undamaged) MoR values were in the range of 2.1 to 3.2 MPa (304 to
467 psi). In general, it is seen that MoR values dropped with increasing mass loss. At
less than 0.8% mass loss, MoR values ranged anywhere between 0.1 MPa (15 psi) to
3.1 MPa (455 psi), or in other words, from about 4% of their initial value up to their
full value in the undamaged state. Most of the specimens (8 out of 11) in this pre-
0.8% mass loss region displayed MoR values that were at least one-half of the
February 5, 2009
FINAL REPORT 183
undamaged value. Of the specimens with MoR lower than 1 MPa (145 psi) in the pre-
0.8% mass-loss region, cracks on the test face were observed on some specimens, as
shown in Figure 109 for specimens C6L. Above 0.8% mass loss however, most MoR
values were below 1 MPa (145 psi), or less than 40% of the undamaged value.
Figure 108 MoR vs. Mass Loss relationship for all specimens in study. (Square data points: PC Series specimens; Circular data points: Variability Series
specimens)
The data in Figure 108 also were modeled using best-fit curves to determine a
mathematical form of the relationship between MoR and mass loss. Using the
software TableCurve 2D to perform this analysis, the result is shown in Figure 110 in
which a relationship of the following form was found to best represent the data:
MoR (MPa) = 0.42 + 2.2 exp (– Mass loss, % / 0.8) R2 = 0.59 (23)
0.0
1.0
2.0
3.0
4.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0Mass loss (%)
Mod
ulus
of r
uptu
re (M
Pa)
145
290
435
580
Modulus of ruputre (psi)
C6L
February 5, 2009
FINAL REPORT 184
The rapid decrease in MoR is reflected in the exponential term. From this
relationship, MoR is predicted to be approximately 1.2 MPa (175 psi), or
approximately 50% of the undamaged value at 1% mass loss.
Figure 109 Specimen C6L with MoR less than 1 MPa (145 psi) in the pre-0.8% mass loss region.
Figure 110 Best-fit relationship for MoR vs. mass loss data.
0 2 4 6Mass loss (%)
0
1
2
3
4
Mod
ulus
of r
uptu
re (M
Pa)
MoR (MPa) = 0.42 + 2.2 exp (– Mass Loss, % / 0.8) R2 = 0.59, St. Err = 0.62
February 5, 2009
FINAL REPORT 185
9.2 Relationships to RDM and PV
In addition to the relationship between MoR and mass loss, relationships with other
measured parameters were also explored. Figures 111 and 112, respectively, show the
MoR vs. RDM (from resonant frequency) and MoR vs. PV plots. Also shown in these
graphs are the reference RDM (60%) and PV (90%) values from earlier discussions.
As expected, MoR decreased with decreasing RDM and PV (increasingly more
damage in the specimens). Here, however, it appeared that MoR correlated better to
RDM and PV than to mass loss by noting the lower scatter in the data points and
higher R2, compared to the MoR-Mass Loss relationship. Best-fit curves were also
determined for these relationships using TableCurve 2D with the following results
MoR (MPa) = 0.31 + 0.00042 (RDM, %)1.9 R2 = 0.84 (24)
MoR (MPa) = 0.34 + 0.00027 exp (PV, % / 11.4) R2 = 0.75 (25)
These relationships are also plotted in Figure 113 for MoR vs. RDM and Figure 114
for MoR vs. PV. From these relationships, MoR is predicted to be approximately 1.1
MPa (160 psi) at RDM of 60%, and approximately 1.2 MPa (160 psi) for PV of 90%
of initial value. Overall, however it is seen that at RDM values less than 60%, MoR
values were generally less than 40 to 50% of the undamaged value. At PV below 90%
of initial value, MoR values were generally lower than 40% of the undamaged value.
February 5, 2009
FINAL REPORT 186
Figure 111 MoR vs. RDM (from resonant frequency) relationship for all specimens in
study. (Square data points: PC Series specimens; Circular data points: Variability Series specimens)
Figure 112 MoR vs. PV relationship for all specimens in study. (Square data points:
PC Series specimens; Circular data points: Variability Series specimens)
0.0
1.0
2.0
3.0
4.0
0 10 20 30 40 50 60 70 80 90 100RDM (%)
Mod
ulus
of r
uptu
re (M
Pa)
145
290
435
580M
odulus of ruputre (psi)
0.0
1.0
2.0
3.0
4.0
0 10 20 30 40 50 60 70 80 90 100PV, (% initial value)
Mod
ulus
of r
uptu
re (M
Pa)
145
290
435
580
Modulus of ruputre (psi)
February 5, 2009
FINAL REPORT 187
Figure 113 Best-fit relationship for MoR vs. RDM (Res Freq) data.
Figure 114 Best-fit relationship for MoR vs. PV data.
0 20 40 60 80 100RDM, Res Freq (%)
0
1
2
3
4
Mod
ulus
of r
uptu
re (M
Pa)
MoR (MPa) = 0.31 + 0.00042 (RDM, %)1.9 R2 = 0.84, St. Err. = 0.38
0 20 40 60 80 100PV (% of initial value)
0
1
2
3
4
Mod
ulus
of r
uptu
re (M
Pa)
MoR (MPa) = 0.34 + 0.00027 exp (PV, % / 11.4) R2 = 0.75, St. Err. = 0.49
February 5, 2009
FINAL REPORT 188
10.0 BETWEEN-FREEZER COMPARISON OF SPECIMEN PERFORMANCE
An important outcome of this study was the comparison of freeze-thaw performance
between specimens tested in two separate freezer environments. As described in
2.1.1, specimens in this study were extracted from SRW units from a single
production run and were tested in the Tenney and walk-in chambers. When tested
according to ASTM C 140 (Table 3), properties of the specimens evaluated in these
two freezers differed by no more than 7% in their compressive strength (average 37
MPa (5390 psi) for specimens in walk-in chamber vs. average 35 MPa (5030 psi) for
specimens in Tenney freezer) and 1% in oven-dry density (2230 kg/m3 (139 pcf) in
walk-in vs. 2210 kg/m3 (137 pcf) in Tenney). Average 24-hr water absorption was
similar for specimens in the two freezers at 127 kg/m3 (7.9 pcf). Of the various Test
Sets in the Variability Series, Test Set A specimens were similar to those tested in the
walk-in freezer, which comprised nominal 200 × 100 × 32 mm (8 × 4 × 1¼ in.) size
SRW coupons placed in 13 mm (½ in.) deep saline solution inside plastic containers of
size 310 × 210 × 108 mm (12.3 × 8.3 × 4.3 in.). The following sections compare the
performance of Test Set A specimens to PC Series specimens for the various
parameters covered in the preceding sections.
10.1 Mass loss and rate of mass loss
Figure 115 shows percent mass loss through 200 cycles for sixteen PC series
specimens (lighter lines) and four Test Set A specimens (darker lines). The average
mass loss of all specimens in the walk-in freezer, including the two specimens
exhibiting sudden jumps in mass loss at about 80 and 100 cycles, was 0.2% after 100
cycles and 0.8% after 200 cycles. By contrast, the average mass loss of Test Set A
specimens in the Tenney freezer was 0.4% after 100 cycles and 4.4% after 200 cycles.
February 5, 2009
FINAL REPORT 189
Thus, mass loss between specimens in the two freezers differed by up to a factor of 2
after 100 cycles and a factor of 5.5 times after 200 cycles.
Figure 116 shows the rate of mass loss through 200 cycles for these same specimens.
Except for the spikes exhibited by the two specimens in the PC Series at about 60 and
100 cycles, specimens in the Test Set A demonstrated overall higher rates of mass loss
from the time the tests were started. As mentioned in Section 5.3, the mass loss
prediction constant “a” was 0.000045 %/cycle2 (equivalent to a “mass loss
acceleration”, K = 0.00009 %/cycle2) for Test Set A and 0.000019 %/cycle2
(equivalent to K= 0.000038 %/cycle2) for PC Series.
Figure 115 Mass loss comparison between specimens in Test Set A and PC Series.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80 100 120 140 160 180 200
Cycles
Mas
s lo
ss, %
Test Set A
PC Series
February 5, 2009
FINAL REPORT 190
Figure 116 Rate of mass loss comparison between specimens in Test Set A and PC Series.
10.2 RDM (resonant frequency) and rate of RDM change
Figure 117 shows RDM through 200 cycles for the Test Set A and PC Series
specimens. The average RDM for specimens in the walk-in freezer was about 100%
after 100 cycles and 79% after 200 cycles. By contrast, the average RDM of Test Set
A specimens in the Tenney freezer was about 93% after 100 cycles and 4% after 200
cycles. Figure 118 shows the rate of RDM change through 200 cycles for the four
specimens in Test Set A and the sixteen specimens in the walk-in freezer. In general,
the rates of RDM change in the PC Series were approximately 0 up to 110 cycles and
only started changing after this point. Rates of RDM change in Test Set A started
increasing at about 50 cycles. In Test Set A, the rates exhibited a sudden jump after
120 cycles (RDM Linear Threshold Point), whereas in the PC Series, a Threshold
Point was not apparent.
0.00
0.01
0.02
0.03
0.04
0.05
0 20 40 60 80 100 120 140 160 180 200 220
Cycles
Mas
s lo
ss ra
te (%
/ cy
cle)
Test Set A
PC Series
February 5, 2009
FINAL REPORT 191
Figure 117 RDM comparison between specimens in Test Set A and PC Series.
Figure 118 Rate of RDM comparison between specimens in Test Set A and PC Series.
-4
-3
-2
-1
0
1
2
0 20 40 60 80 100 120 140 160 180 200 220
Cycles
Rat
e of
RD
M (%
/ cy
cle)
Test Set A
PC Series
0102030405060708090
100110
0 20 40 60 80 100 120 140 160 180 200
Cycles
RD
M, %
Test Set A
PC Series
February 5, 2009
FINAL REPORT 192
10.3 Pulse velocity
Figure 119 compares the PV values, expressed as percentage of initial values, for Test
Set A and PC Series specimens. Here, more pronounced differences can be observed
among specimens tested in the two freezers. While the PV values for PC Series
specimens remained relatively unchanged even after 200 cycles, those of Test Set A
displayed substantial reductions starting from about 130 cycles. After 200 cycles, two
of the four specimens in Test Set A were at PV of 0. Most specimens in the PC Series
were at about 95% of their initial value.
Figure 119 PV comparison between specimens in Test Set A and PC Series.
010
2030
4050
6070
8090
100110
0 20 40 60 80 100 120 140 160 180 200
Cycles
UP
V, %
of i
nitia
l
Test Set A
PC Series
February 5, 2009
FINAL REPORT 193
10.4 Visual scaling rating
Figure 120 compares the visual scaling rating for Test Set A and PC Series specimens.
Here, differences in performance between specimens in the two groups were not as
pronounced. Except for one specimen in Test Set A which had a rating of up to 4 after
200 cycles and 2 specimens in the PC Series with rating of 1 after 200 cycles, all other
specimens had ratings of 0 after 200 cycles. This suggests that scaling rating
conducted in the manner done for this study may not be a useful indicator of
differences in performance among specimens.
Figure 120 Visual scaling rating comparison between specimens in Test Set A and PC
Series.
0.0
1.0
2.0
3.0
4.0
5.0
0 20 40 60 80 100 120 140 160 180 200
Cycles
Sca
ling
ratin
g
PC Series
Test Set A
February 5, 2009
FINAL REPORT 194
10.5 Discrepancies in freeze-thaw cycles
As for the test environments in these two freezers, Figure 121 shows freezer air
temperature-time (T-t) curves for typical cycles in the two freezers. Also shown are
T-t curves for the solution surrounding instrumented specimens in the two freezers.
Both freezer air cycles were fully compliant with ASTM C 1262 test method
requirements. Specimens in the walk-in freezer were subjected to a cold soak period
of 4.8 hrs, whereas specimens in the Tenney freezer were subjected to a cold soak
period of 4.5 hrs. Each freezer reached a different minimum air temperature at the end
of cold soak (walk-in: –16.9°C (1.6°F) and Tenney: –18.5°C (–1.3°F)). The curves in
Figure 121 are reproduced again in Figure 122 together with rates of change of freezer
air temperature and solution temperature. Differences can be discerned in the
following areas:
Figure 121 Cooling curves comparison for typical cycles in the two freezers.
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12
Time (hrs)
Tem
pera
ture
(°C
)
Fzr air – Tenney
Fzr air – walk-in
Solution – walk-in
Solution – Tenney
0
20
40
60
Tem
pera
ture
(°F)
February 5, 2009
FINAL REPORT 195
Figure 122 Rates of temperature change for curves in Figure 121.
-25-20-15-10-505
10152025
0 1 2 3 4 5 6 7
Time (hrs)
Tem
pera
ture
(°C
)
-100
-70
-40
-10
20
50
80
110
140
0 1 2 3 4 5 6 7
Time (hrs)
Free
zer
air
dT/d
t (°C
/hr)
-25-20-15-10-505
101520253035
0 1 2 3 4 5 6 7
Time (hrs)
Solu
tion
dT/d
t (°C
/hr)
Fzr air – Tenney
Fzr air – walk-in
Solution – walk-in
Solution – Tenney
Tenney
Walk-in
Tenney
Walk-in
0
20
40
60
Tem
pera
ture
(°F)
-100
0
100
200
Free
zer A
ir dT
/dt (°F
/hr)
-40
0
40S
olut
ion
dT/d
t (°F
/hr)
February 5, 2009
FINAL REPORT 196
• Between 1.5 and 2 hours, the freezer air cooled at a rate of approximately –9 to
–10°C/hr (–16 to –18°F/hr) in the cabinet freezer, compared to approximately
–3 to –4°C/hr (–5 to –7°F/hr) in the walk-in freezer, which was almost a 3-fold
difference. This was also the time period during which the solution
surrounding specimens in both freezers entered their freezing plateaus.
• Between 6 and 7 hours, the peak freezer air warming rate was 135°C/hr
(245°F/hr) in the cabinet freezer, compared to about 88°C/hr (160°F/hr) in the
walk-in freezer, which was a 50% difference. These peaks occurred
immediately after the end of cold soak as the warming branch started.
• Before 2 hours, the cooling rate of the salt solution surrounding specimens was
–18°C/hr (–32°F/hr) for the specimen in the walk-in freezer and –19°C/hr (–
34°F/hr) for the specimen in the cabinet freezer. However, between 3 and 6
hours, after their respective freezing plateaus, the solutions cooled at –8°C/hr
(–14°F/hr) in the cabinet freezer, compared to about –4°C/hr (–7°F/hr) in the
walk-in freezer, which was a two-fold difference.
• Between 6 and 7 hours, the peak solution warming rate was 33°C/hr (59°F/hr)
in the cabinet freezer, compared to 14°C/hr (25°F/hr) in the walk-in freezer,
which was almost a 2.5 times difference. These peaks also occurred
immediately after the end of cold soak as the warming branch started.
• Moreover, the lengths of solution freezing plateaus were different in the two
freezers. For the walk-in freezer, the freezing plateau was estimated to be
approximately 1.9 hours long, while for the cabinet freezer, this was about 1.2
hours long. If it is assumed that the same volume of solution is frozen during
this freezing plateau (a reasonable assumption for these tests), the solution
froze 50% faster in the cabinet freezer compared to in the walk-in freezer.
February 5, 2009
FINAL REPORT 197
A summary of the measured differences between the two freezers is provided in Table
22. Which one of these specific differences translated to differences in specimen
performance remains unclear. These results however point to the fact that complying
with ASTM C 1262 freezer air requirements does not necessarily guarantee similar
specimen performance. This points to the need to specify the full freeze-thaw cycle
consisting of the cooling rate, cold soak temperature and duration, warming rate and
warm soak temperature and duration to ensure that the specimens undergo similar
exposure. At the same time, these results indicate the need to investigate further the
impact that each of these parts of the freeze-thaw cycle has on specimen performance.
Table 22 Comparison of cycle parameters between cabinet and walk-in freezers. Parameter Walk-in Cabinet
Time to reach:
· 0°C (32°F) 0.5 hrs 0.8 hrs
· start of cold soak 1.7 1.6 Rate of air cooling at start of solution freezing plateau a
3 to 4°C/hr (5 to 7°F/hr) 11°C/hr (20°F/hr)
Minimum attained temperatures
· Freezer air –16.9°C (1.6°F) –18.5°C (–1.3°F)
· Solution –13.7 (7.3) –18.0 (–0.4)
Rate of solution freeze b 160 g/hr (5.6 oz/hr) 250 g/hr (8.8 oz/hr)
Peak warming rates:
· Freezer air c 88°C/hr (160°F/hr) 135°C/hr (245°F/hr)
· Solution c 14 (25) 33 (59) a obtained from the tangent to the curves at T = –13 °C b obtained by dividing (mass of solution) / (length of freeze plateau) c immediately after end of cold soak
February 5, 2009
FINAL REPORT 198
11.0 CONCLUSIONS AND RECOMMENDATIONS
An experimental program was conducted at Cornell University with the objective of
evaluating variability in the ASTM C 1262 test method in addition to assessing the
different forms of specimen damage employing techniques other than mass loss. From
the results, analysis and observations obtained throughout the test program,
conclusions in the following areas can be offered for the particular specimens
evaluated in this study.
11.1 Freezer evaluation
11.1.1 Survey of the freezers prior to initiating actual tests was essential not only
for characterizing the internal spatial distribution of temperature, but also to
enable a rational decision on the length of cycles to use during testing by
means of freezer reliability curves.
11.1.2 In the Tenney freezer, the coldest locations generally corresponded to those
in the front part of the freezer (i.e., near the door) and on the highest
shelves, while the warmest locations corresponded to those towards the
back of the freezer in the lowest shelves.
11.1.3 The coldest location overall was right at the location of the internal (built-
in) temperature sensor, near the fan exit. Thus, using the temperature from
the freezer internal sensor as the cycle-controlling temperature can result in
a significant number of undercooled specimens unless the cycle is
appropriately adjusted in compensation..
11.1.4 Frequent temperature monitoring during testing helps to identify variations
in freezer performance. In the Tenney freezer, an increase in the
programmed warm soak length from 4.5 to 6.0 hours improved overall
February 5, 2009
FINAL REPORT 199
freezer cooling efficiency by increasing rate of cooling and improving
repeatability (by stopping drift in the response of consecutive cycles). The
significance of this is not clear until the sensitivity to variations in the
freeze-thaw cycle is determined more precisely.
11.1.5 In the walk-in freezer, freezer cooling rates gradually increased as the tests
progressed, and this was detected by frequent monitoring of the freezer.
11.1.6 For the particular freezers used, cold soaks in the range of 4.2 to 4.8 hrs for
the Tenney freezer and 4.0 to 4.8 hrs in the walk-in freezer (based on the
average freezer internal temperature) yielded maximum compliance with
respect to ASTM C 1262 requirements. Other thermal cycles of equal
effectiveness may have been possible.
11.2 Effect of variations in the test method
11.2.1 Seven test specimen/container configurations were evaluated in head-to-
head comparative testing, all originating with the same population of SRW
units. Statistical analyses were performed on the data collected for mass
loss as a function of numbers of freeze-thaw cycles. These analyses
indicated that statistically significant differences existed in freeze-thaw
behavior among the specimen/container configurations up to 1% mass loss.
11.2.2 All specimens in the Variability Series complied with freeze-thaw
specifications from Minnesota Department of Transportation (which were
used as reference in this study because ASTM C 1372 currently does not
have a specification limit for freeze-thaw tests in saline).
11.2.3 Apparent uniformity of results is suggested by the fact that none of the
specimens tested had a mass loss in excess of 1% at 100 cycles, regardless
of specimen configuration. SRW units that are this freeze-thaw resistant
February 5, 2009
FINAL REPORT 200
will perform well in the C 1262 test under the wide variety of specimen
configurations that are permitted by the current test specification.
11.2.4 Apparent non-uniformity is suggested by the facts that for coupons all taken
from the same population of SRW units:
♦ As of 50 cycles, the greatest mass loss was 1.7 times the least mass
loss.
♦ As of 100 cycles the greatest mass loss was 1.6 times the least mass
loss.
♦ As of 150 cycles the greatest mass loss was 3 times the least mass
loss.
11.2.5 The performance-ranking among Test Sets in the Variability Series up to 50
cycles was not representative of their rankings after 100 cycles. Both the
mechanisms and rates of damage change over the duration of the test.
11.2.6 From 0 to 50 cycles, mass loss appeared to increase with an increase in the
coupon surface area relative to the coupon volume, and with an increase in
the wetted depth.
11.2.7 From 50 to 100 cycles, mass loss appeared to increase with an increase in
the coupon surface area relative to the coupon volume, and with an increase
in the volume of saline solution relative to the volume of the coupon, and
with an increase in the average clearance between the coupon and the
container wall.
11.2.8 From 100 to 150 cycles (when mass loss ranged between 0.5 to 2.5%), mass
loss appeared to increase significantly with an increase in the coupon
surface area relative to the coupon volume, and appeared to increase
significantly with an increase in the average clearance between the
coupon and the container wall. Mass loss appeared to decrease
February 5, 2009
FINAL REPORT 201
significantly with an increase in the wetted depth.
11.2.9 Recognizing the uncertainty in the trends, it is suggested that for an SRW
material similar to that tested here, a higher mass loss (at 100 or 150 cycles)
would result by placing a small coupon with a high surface to volume ratio
into a large container. A lower mass loss appears likely to result from
placing a larger coupon with a low surface to volume ratio into a smaller
container.
11.3 Nature of mass loss evolution
11.3.1 Damage in specimens typically started as mass loss from the specimen sides
and aggregate/mortar popouts, followed by development of cracks at
random locations and then, in most cases, surface scaling.
11.3.2 Mass loss generally followed a 2nd order polynomial form from start of the
freeze-thaw tests until the Mass Loss Linear Threshold Point, which varied
from specimen to specimen. Mass Loss Linear Threshold Points generally
were between 130 to 160 cycles, except for two specimens in Test Set B for
which this Threshold Point was around 80 cycles.
11.3.3 In most cases, the 2nd order behavior was maintained until a mass loss of 1%
or higher. Increasingly faster deterioration occurred after 1% mass loss.
Assumption of a parabolic mass-loss curve yielded accurate predictions of
the number of cycles to 1% mass loss.
11.3.4 Observing rates of mass loss rather than mass loss alone was useful to avoid
the non-representative influence of individual mass loss events such as
aggregate/mortar popouts in specimen evaluation.
11.3.5 Specimens exposed to freeze-thaw conditions exhibited an increase in
moisture content with the number of freeze-thaw cycles. This increase was
February 5, 2009
FINAL REPORT 202
greater than that experienced by unfrozen specimens.
11.3.6 A 1% mass loss based on ASTM C 1262 definitions translated to a mass
loss per test face area of approximately 0.7 to 0.8 kg/m2 and a mass loss per
wetted area of approximately 0.6 kg/m2.
11.3.7 The concentration of dissolved substances in the solution surrounding
specimens did not vary significantly throughout the test program.
11.4 Damage assessment using resonant frequency
11.4.1 Resonant frequency testing (based on ASTM C 215) was conveniently
performed on SRW specimens, and the sensitivity of resonant frequencies
to changes in specimen structural integrity makes this test valuable for
evaluation of freeze-thaw damage of SRW specimens.
11.4.2 The use of this test method required close attention to procedural details,
however, to avoid confusion in the recorded frequencies corresponding to
different modes of vibration and to avoid variations in the recorded
frequency due to drying of specimens as they are removed from their
containers during testing.
11.4.3 RDM results based on sampling parameters of 20,000 Hz and 1,024 data
points (standard ASTM C 215 parameters) and 102,400 Hz and 1,024 data
points yielded comparable results, and as such, either one of these methods
would have been adequate for these tests.
11.4.4 Using resonant frequency, the following results from test variations were
obtained:
• For similar specimens and containers, underfilling of solution in the
containers appeared to result in greater damage in the specimens (Sets
A, B and C)
February 5, 2009
FINAL REPORT 203
• For the same container size, larger specimens resulted in greater damage
in the specimens (Sets D, E and F)
• For the same specimen size, specimens in smaller containers exhibited
larger damage in the specimens (Sets A and D).
• There appeared to be little effect from specimen geometry (Sets A and
G).
These observations do not necessarily match the correlations suggested by
mass loss tests. This is understandable given that the mass loss test
evaluates surface damage while resonant frequency is sensitive to damage
in the interior of the coupon.
11.4.5 The performance ranking among Test Sets as measured using resonant
frequency testing differed from the performance ranking based on mass
loss measurements.
11.4.6 As with mass loss however, 50-cycle performance ranking of Test Sets
was not indicative of rankings after 100 cycles.
11.4.7 The RDM Linear Threshold Point (between 100 and 130 cycles) occurred
prior to the Mass Loss Linear Threshold Point in all Test Sets evaluated,
indicating that internal specimen damage accelerated prior to being
detected by mass loss alone.
11.4.8 At mass loss below about 0.5%, external damage of specimens was more
prevalent than internal damage, as evidenced by increasing mass loss
values while RDM values remained relatively unchanged. However, RDM
values changed increasingly faster compared to mass loss in the range of
mass loss greater than 0.5%, indicating an increased rate of internal
damage.
11.4.9 Risky Specimens were defined as those with mass loss of 0.8 to 1.2% but
February 5, 2009
FINAL REPORT 204
with RDM less than 60%. Approximately 1/3 of all Variability Series
specimens fell into this category. For these specimens, a 1% mass loss
was not indicative of actual internal conditions or pending damage in
them. At 1% mass loss, these specimens exhibited RDM of 3 to 76%.
This means that the acceptance of specimens based on a 1% mass loss
limit could result in acceptance of specimens that have been internally
damaged. Note also that in regard to the validity of an RDM threshold of
60%, coupons with an RDM less than 60% generally had a MoR less than
40 to 50% of their initial, undamaged value.
11.4.10 Specimens exhibited a critical moisture content of about 5.6 to 5.8% and a
critical moisture gain of about 0.8 to 1.1%, above the pre-condition
moisture content (i.e., after the initial 24-hr immersion). Below these
values, RDM changed little. Above these values RDM dropped
considerably, in most cases to RDM of 0%. The degree to which this
observation would pertain to other SRW mixtures and materials is not
known, but the overall concept of a critical moisture content is well
documented in the concrete literature.
11.4.11 Above a moisture gain of about 1.0 to 1.2%, mass loss in these specimens
also increased dramatically.
11.4.12 RDM appears to increase with time in an immersed specimen that is not
subjected to freezing and thawing. It may be necessary to account for this
increase in evaluating specimen performance.
11.5 Damage assessment using pulse velocity
11.5.1 Pulse velocity testing (ASTM C 597) was also conveniently performed on
SRW specimens in this study, although measurements from this test were
February 5, 2009
FINAL REPORT 205
not as sensitive to changes in specimen integrity as those from resonant
frequency tests.
11.5.2 In general, from 150 cycles onwards, PV ranked the Test Sets similarly to
the manner in which RDM ranked these Test Sets.
11.5.3 As with RDM and mass loss however, 50-cycle performance ranking of
Test Sets was not indicative of rankings after 100 cycles.
11.5.4 The behavior of PV relative to mass loss was similar to that exhibited by
RDM, whereby little changes in PV occurred below a certain mass loss (for
PV, this was 0.8%), followed by increased decline in the PV values.
11.5.5 For the specimens evaluated, a drop in RDM of 40% computed from
resonant frequency corresponded more or less to a drop in RDM of 10 to
20% computed from pulse velocity. A drop of 10 to 20% in RDM from
pulse velocity resulted from drops in pulse velocity readings of 5 to 10% of
their initial value (recall RDMPV, n cycles is equal to (PVn cycles /
PVinitial)×100%) Thus, in general, an RDM of 60% based on resonant
frequency methods corresponded more or less to PV values in the range of
90 to 95% of their initial values.
11.5.6 Pulse velocity appears to increase with time in an immersed specimen that
is not subjected to freezing and thawing. It may be necessary to account for
this increase in evaluating specimen performance.
11.6 Damage assessment using visual scaling rating
11.6.1 Specimens exhibiting a fair amount of surface scaling (i.e., scaling rating at
1 and above) typically were also cracked. These specimens therefore also
exhibited rapid drops in RDM (from resonant frequency).
11.6.2 In general, only after 200 cycles were the performance rankings among Test
February 5, 2009
FINAL REPORT 206
Sets based on scaling rating similar to the rankings obtained from resonant
frequency or pulse velocity methods after 200 cycles.
11.6.3 As with RDM, PV and mass loss however, 50-cycle performance rankings
of Test Sets was not indicative of rankings after 100 cycles.
11.6.4 Visual scaling rating of specimens in the manner employed in this study
(based on a modification of ASTM C 672) is not a good indicator of
specimen cracking or loss of integrity. It did not correlate well to other
forms of specimen condition assessment. At 1% mass loss, scaling ratings
of specimens were still around 0.
11.7 Relationship to modulus of rupture
11.7.1 MoR generally decreased with increasing mass loss. At less than 0.8%
mass loss, MoR values ranged anywhere between approximately 4 to 100%
of their initial, undamaged value. At values greater than 1% mass loss,
however, most MoR values were below 40% of their initial, undamaged
value.
11.7.2 Below RDM (from resonant frequency) of 60% and PV of 90% of their
initial value, MoR values were less than 40 to 50% of their initial,
undamaged value.
11.8 Sources of variability
11.8.1 There are clearly two sources of variability in the test results from this study
as follows:
• Test method variability which was evident from the disparity in measured
properties among the various Test Sets (due to varying container sizes,
varying volumes of surrounding volumes and varying specimen sizes).
February 5, 2009
FINAL REPORT 207
Test method variability was also observed from testing in different
freezer environments, both of which complied with ASTM C 1262
freezer air temperature-time requirements.
• Material variability which was evident from disparity in measured
properties for specimens within a Test Sets (e.g., mass loss in Set B, and
RDM in Sets B and D). Material variability was also observed among
specimens in the PC Series (e.g., specimen C5L).
11.9 Comparison of test methods for specimen performance evaluation
In this study, various forms of specimen damage were observed. Each of the tests
used to assess the condition of specimens exhibited different sensitivities to each of
these forms of damage. Table 23 summarizes the forms of damage together with the
different tests and their sensitivity. References are made to specific parts in this report
where the damage form is illustrated. As for sensitivity to damage, these are shown as
being either H = highly sensitive, M = moderately sensitive, L = little to no sensitivity.
11.9.1 Overall, below mass loss of about 0.5%, mass loss is the most sensitive to
changing specimen condition (primarily due to loss of material from the
sides of specimens). Attention must be paid to isolated events such as
popouts whose significance to overall specimen condition can be better
discerned by observing actual rates of mass loss.
11.9.2 Beyond about 0.5% mass loss, however, once cracks started forming,
resonant frequency appeared to be more appropriate for evaluating
specimen condition. This is because RDM is far more sensitive than mass
loss to internal damage and cracking.
February 5, 2009
FINAL REPORT 208
11.9.3 Pulse velocity, despite portraying similar trends to resonant frequency
testing, was not as sensitive to changes in specimen structural integrity as
resonant frequency tests were until mass loss values greater than about 1%
(or beyond 100 freeze-thaw cycles in these tests). Pulse velocity is
generally not as sensitive to the presence of cracks as either RDM or MoR.
11.9.4 Visual scaling rating in the manner conducted in this study is not adequate
for detection of specimen cracking or loss of structural integrity until
beyond 1% mass loss, at which point spalling and pitting of specimen
surfaces accompanied cracking. Mass loss of about 1% may produce
scaling ratings of 0 to 1.
11.9.5 For the specimens in this study, substantial loss of specimen integrity begins
at a mass loss of about 0.7%. In most cases, it was evident that specimens
had reached their critical moisture gains and were past their RDM Threshold
Points (beyond which RDM decreases at an accelerated rate) beyond mass
loss of 0.7%.
February 5, 2009
FINAL REPORT 209
Table 23 Sensitivity of tests to various forms of specimen damage.
Test Method
Form of Damage Observed
Mass loss
RDM (resonant
frequency)
PV
Visual scaling rating
MoR
Aggregate popouts (Fig. 48) H L L see c L
Loss of material in localized zone (Fig. 37, B3)
H M L see d M?
Spalling and pitting on specimen sides (Fig. 38)
H L L L L
Spalling and pitting of specimen immersed face (Fig. 39, D1 and F2)
H M – H b M H M
Hairline cracks on top face (opposite to immersed face) (Fig. 40, B3)
L H M L L
Hairline cracks on immersed face (Fig. 64, B3)
see a H M L H
Through-thickness cracks (Fig. 40, D2)
see a H H L H
a M if cracks occurred together with spalling, L if cracks occurred alone b spalling on immersed face typically occurred in conjunction with crack formation and drops in RDM
c M if popout occurred on immersed face, L if popout occurred elsewhere d H if material loss occurred on immersed face, L if material loss occurred elsewhere
11.10 Repeatability of results obtained using various test methods
For any given method of specimen condition assessment, the test not only needs to be
sensitive to changes in the condition of specimens (whether damage is external or
internal), but it also needs to be repeatable (i.e., low variation between specimens).
One way in which repeatability can be measured is by computing the Coefficient of
Variation (CoV, equal to Standard Deviation divided by the Mean Value) among
February 5, 2009
FINAL REPORT 210
specimens in a given group (e.g., Test Set in this case). Coefficient of variations for
mass loss, RDM, PV and moisture gain were calculated as function of cycle for each
Test Set in the Variability Series and for the population of PC specimens. These
results are shown in Figure 123. The overall lower moisture-gain CoV compared to
mass-loss CoV over the 200 freeze-thaw cycles is evident from these graphs. While
mass-loss, RDM (resonant frequency) and PV CoV fluctuated over the 200 cycles,
moisture gain CoV remained fairly steady and below 35%. Differences in moisture-
gain CoV vs. mass-loss CoV are particularly notable for PC Series specimens. The
repeatability of moisture gain measurements together with the tight range of RDM-
moisture gain results are attractive reasons for including moisture content and
moisture gain measurements in ASTM C 1262.
11.11 Between-freezer comparison of specimen performance
11.11.1 Testing of specimens in separate freezers, both of which may comply with
ASTM C 1262 temperature-time requirements, does not necessarily result
in similar performance of specimens tested in the two freezers. Extreme
differences in performance were observed in mass loss, resonant frequency
changes, pulse velocity changes and visual scaling rating.
January 31, 2009
FINAL REPORT 211
0
50
100
150
200
250
0 50 100 150 200 250Cycles
Mas
s Lo
ss C
oV (%
)
0
50
100
150
200
250
0 50 100 150 200 250Cycles
Moi
stur
e G
ain
CoV
(%)
a) ASTM C 1262 mass loss b) Moisture gain
0
50
100
150
200
250
0 50 100 150 200 250Cycles
RD
M (R
es F
req)
CoV
(%)
0
50
100
150
200
250
0 50 100 150 200 250Cycles
PV C
oV (%
)
c) RDM (from resonant frequency) d) Pulse velocity (% of initial values)
Figure 123 Coefficient of variation as function of cycles for various test methods.
Var. Series Test Sets
PC Series
Var. Series Test Sets
PC Series
Var. Series Test Sets
PC Series
Var. Series Test Sets
PC Series
198D
RA
FT REPO
RT
January 31, 2009
FINAL REPORT 212
11.11.2 Despite both freezers being compliant with ASTM C 1262 temperature-
time requirements, differences were measured in actual rates of
temperature change (cooling or warming) as follows:
• The Tenney freezer air cooled about 3 times faster than the walk-in
freezer air at the onset of ice formation in the solution surrounding
specimens.
• The solution surrounding specimens froze approximately 1.5 times
faster in the Tenney freezer than in the walk-in freezer.
• The solutions reached different minimum temperatures during cold
soak (–18°C (0°F) in the Tenney freezer vs. –14°C (7°F) in the walk-in
freezer).
• Before ice melted, the peak freezer air warming rate was 1.5 times
faster in the Tenney freezer than in the walk-in freezer. Moreover, the
peak solution (i.e., the still frozen solution) warming rate was 2.5 faster
in the Tenney freezer than in the walk-in freezer.
11.12 Recommendations for ASTM C 1262
11.12.1 Prior to actual freeze-thaw testing, freezers should be surveyed for their
internal temperature characteristics (shape of cooling curve and
distribution of temperatures) and to determine the relationship between the
freezer’s control temperature and the actual temperature at specimen
locations. This survey should also record the spatial variation of
temperature within the freezing cabinet and the cycle temperatures and
durations should be optimized for maximum compliance. This survey
shall be carried out using the same number of specimens and arrangement
to be used in actual tests. During testing, the freezers shall also be
January 31, 2009
FINAL REPORT 213
frequently monitored to detect possible fluctuations in freezer
performance. If fluctuations are measured, the programmed cycle shall
then be adjusted accordingly to ensure: a) repeatability of cycles, and b)
optimum compliance with ASTM C 1262 (maximum R). Dummy
specimens of the same thermal characteristics and masses as the actual
specimens should replace test specimens as they are permanently removed
during testing.
11.12.2 The specified freezer-air temperature-time cycle should be tightened by
fully specifying the cycle which includes cooling rate, cold soak
temperature and duration, warming rate, and warm soak temperature and
duration. While the currently specified cold soak at 0 ± 10°F (-18 ± 5°C))
for 4 to 5 h and warm soak at 75 ± 10°F (24 ± 5°C) for 2.5 to 96 h appear
adequate for inducing expansion damage in the specimens (see Chan,
2006), the rates of cooling and warming are left unspecified. At this time,
there is limited data on how each of these parts of the freeze-thaw cycle
affects overall specimen performance, which warrants further studies to
investigate these aspects. Results from such studies will assist developing
a more detailed freeze-thaw curve for inclusion in the test standard.
Another question that arises is whether most of the freezers currently used
in test laboratories for ASTM C 1262 testing will be able to reproduce the
specified freeze-thaw cycle. If not, it may be necessary for the test method
to specify the type of freeze-thaw equipment necessary to fulfill this
purpose.
11.12.3 Given the large variations in test results observed here, it is suggested that
less latitude be permitted in container and specimen sizes. The nature of
SRW units makes this difficult to achieve, but reduced variability in test
January 31, 2009
FINAL REPORT 214
results may be achieved. In particular it appears important to minimize
fluctuations in the ratio of volume of solution to volume of specimen. For
example, from the results of this study, specimens within Test Set A
appeared to show least variation within the Test Set, and hence, 200 × 100
× 32 mm (8 × 4 × 1¼ in.) specimens placed in the 310 × 210 × 108 mm
(12.3 × 8.3 × 4.3 in.) containers seem to be a viable choice. This yields a
mass-of-solution-to-mass-of-specimen ratio of 0.2.
11.12.4 Since test results indicated sensitivity to both the volume of solution and
the wetted depth, it may be necessary to specify both parameters for a less
variable test. However, doing so reduces the freedom of choice for
specimen and container sizes. For arbitrarily selected coupon and
container sizes, specifying one of these two parameters will dictate the
other. Once volume and depth have been determined, however, it has
been shown that adding a measured volume of solution is more reliable
that attempting to measure depth of solution.
11.12.5 It is also recommended that surface-dry specimen masses be also measured
in the ASTM C 1262 test method, whenever mass loss measurements are
made. This additional step does not require substantial effort, but these
data are valuable. As demonstrated in this study, RDM of most specimens
appeared to behave in a more consistent manner when expressed relative to
moisture content (or moisture gain) as opposed to mass loss.
11.12.6 For specimens in this study, internal damage as detected by RDM is
initiated prior to mass loss reaching 1% (which is used as limit for tests in
saline in Minnesota Department of Transportation). Thus, these data do
not support an increase in a 1% specification limit without further study
and a correlation to actual field performance.
January 31, 2009
FINAL REPORT 215
11.13 Recommendations for future research
11.13.1 Among the remaining fundamental questions is the degree to which any of
the findings reported here apply to coupons from other SRW units. It is
suggested that either highly durable or low quality units may not be overly
sensitive to the testing variations studied here; they are likely to perform
well or poorly regardless of testing details. The real importance of these
findings is with units that might be fully satisfactory in actual field
conditions, especially in the absence of deicing salts, but may have a
variable track record in laboratory tests due to the issues observed in this
study. Thus more research might be directed at establishing the properties
that correspond to acceptable field performance, in addition to exploring
the effect of testing variables on other types of SRW units than those
evaluated here.
11.13.2 The behavior of resonant frequencies and pulse velocities relative to mass
loss were determined for one particular SRW mix in this study. It is
recommended that other mixes be evaluated in the same manner to
determine if the trends observed in this study prevail.
11.13.3 Although beyond the scope of this present study, the possibility of
between-SRW unit variations (i.e., differences between units) even for
units produced within the same production run should also be investigated.
The reason for this proposition is based on variations observed even within
Test Sets (see for example mass loss for Test Set B and RDM vs. mass loss
for Test Set D). One possible study is to evaluate material properties such
as ASTM C 140 parameters (compressive strength, water absorption and
density) and ASTM C 1262 frost resistance for say sets of 5 consecutive
January 31, 2009
FINAL REPORT 216
blocks in the production sequence, with each set of 5 blocks being sampled
at different times during the production run such as within the first 20% of
the entire run, between the 20 and 40% of the run, 40 to 60%, 60 to 80%
and the final 20% of the run. More frequent sampling (say every 10% of
the production run) for increased number of blocks is also possible.
Results from these tests will indicate whether the quality and properties of
the units vary within a production run, and if systematic variations are
observed, how these variations occur within the run.
11.13.4 In addition to studying variability within a production run, variability in
performance of SRW units produced over different runs and different days
of the week should also be evaluated. Moreover, the effect of curing (i.e.,
temperature, relative humidity and length) and storage conditions (e.g.,
weather and temperature) SRW unit performance should be investigated
further.
January 31, 2009
FINAL REPORT 217
REFERENCES ASTM C 78-02, “Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)”, Annual Book of ASTM Standards 2004, Volume 04.02, ASTM International, West Conshohocken, PA, pp. 36-38, 2004. ASTM C 260-01, “Standard Specification for Air-Entraining Admixtures for Concrete”, Annual Book of ASTM Standards 2004, Volume 04.02, ASTM International, West Conshohocken, PA, pp. 165-167, 2004. ASTM C 597-02, “Standard Test Method for Pulse Velocity Through Concrete”, Annual Book of ASTM Standards 2004, Volume 04.02, ASTM International, West Conshohocken, PA, pp. 310-313, 2004. ASTM C 642-97, “Standard Test Method for Density, Absorption, and Voids in Hardened Concrete”, Annual Book of ASTM Standards 2002, Volume 04.02, ASTM International, West Conshohocken, PA, pp. 334-336, 2002. ASTM C 666-03, “Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing”, Annual Book of ASTM Standards 2004, Volume 04.02, ASTM International, West Conshohocken, PA, pp. 337-342, 2004. ASTM C 672 / C 672 M-03, “Standard Test Method for Scaling Resistance of Concrete Surface Exposed to Deicing Chemicals”, Annual Book of ASTM Standards 2004, Volume 04.02, ASTM International, West Conshohocken, PA, pp. 353-355, 2004. ASTM C 1372-01a, “Standard Specification for Segmental Retaining Wall Units”, Annual Book of ASTM Standards 2003, Volume 04.05, ASTM International, West Conshohocken, PA, pp. 898-900, 2003. Bager, D. H. and Jacobsen, S., “A Model for the Destructive Mechanism in Concrete Caused by Freeze/Thaw Action”, Frost Damage in Concrete (eds. D.J. Janssen, M.J. Setzer and M. B. Snyder), Proceedings of the International RILEM Workshop, RILEM Publication PRO 25, Minneapolis, MN, 28-30 June 1999, pp. 17-39. CSA A231.1-99, Precast Concrete Paving Slabs, Canadian Standards Association, ISSN 0317-5669, January 1999. Chan, C., Freeze-Thaw Durability and ASTM C 1262 Testing of Segmental Retaining Wall (SRW) Units, Ph.D. Dissertation, School of Civil and Environmental Engineering, Cornell University, May 2006.
January 31, 2009
FINAL REPORT 218
Chan, C.T., Carino, S.J., Durham, M., Hover, K.C., “Fundamental Frequency Testing of Segmental Retaining Wall (SRW) Specimens: Test Considerations,” Journal of ASTM International, Vol. 4, Issue 2, February, 2007, 14 pp., Published Online, Paper ID: JAI100673. Chan, C., Hover, K.C. and Folliard, K.J., “Spatial Variations in Material Properties of Segmental Retaining Wall (SRW) Units, Part I: Observed Variations”, Journal of ASTM International, Civil Engineering and Building Materials, February 2005. Chan, C., Hover, K.C. and Folliard, K.J., “Spatial Variations in Material Properties of Segmental Retaining Wall (SRW) Units, Part II: Sampling Considerations for Absorption Tests”, Journal of ASTM International, Civil Engineering and Building Materials, February 2005. Chan, C., Hover, K.C., and Folliard, K.J., “Performance of Segmental Retaining Wall (SRW) Units: from Laboratory to Field”, Construction Materials, Proceedings of CONMAT 05 and Mindess Symposium (eds. N. Banthia, T. Uomoto, A. Bentur and S.P. Shah), Vancouver, Canada, Aug. 21-24, 2005. Chan, C.T., Hover, K.C., Folliard, K., Trejo, D. “Frost Durability Indexes of Segmental Retaining Wall Units,” ACI Materials Journal, Vol 104, No. 1., January 2007, pp. 23-32. Fagerlund, G., “The Significance of Critical Degrees of Saturation at Freezing of Porous and Brittle Materials”, ACI Special Publication, SP-47, American Concrete Institute, Detroit, MI, pp. 13-65, 1975. Fagerlund, G., “An Introduction to RILEM Methods of Testing Resistance of Concrete to Freezing and Thawing and the International Cooperative Tests on the Critical Degree of Saturation Method”, Materials and Structures, Vol. 10, No. 58, pp. 217-230, 1977. Fagerlund, G., “Service Life with Regard to Frost Attack. A Probabilistic Approach”, 8th International Conference on Durability of Building Materials and Components, May 30 – June 3, 1999, Vancouver, BC, Canada. Hance, R.M., Studies of the Frost Resistance of Segmental Retaining Wall Units, Master’s Thesis, Department of Civil and Environmental Engineering, Cornell University, May 2005. Janssen, D.J. and Snyder, M.B., Resistance of Concrete to Freezing and Thawing, SHRP-C-391 Report, Strategic Highway Research program, National Research Council, Washington, DC, 1994.
January 31, 2009
FINAL REPORT 219
Janssen, D.J., Setzer, M.J. and Snyder, M.B. (eds.), Frost Damage in Concrete, Proceedings of the International RILEM Workshop, RILEM Publication PRO 25, Minneapolis, MN, 28-30 June 1999. Kasparek, S. and Setzer, M.J., “Analysis of Heat Flux and Moisture Transport in Concrete During Freezing and Thawing”, Frost Resistance of Concrete, Proceedings of the International RILEM Workshop (eds. M.J. Setzer, R. Auberg and H.-J. Heck), RILEM Publication PRO 24, Essen, Germany, 18-19 April 2002, pp. 187-194. Littell, R.C., Milliken, G.A., Stroup, W.W. and Wolfinger, R.D., SAS System for Mixed Models, SAS Institute Inc., Cary, NC 1996. MnDOT, Minnesota Department of Transportation Program Support Group, Technical Memorandum No. 01-05-MRR-01, February 8, 2001. Naik, T.R., Malhotra, V.M. and Popovics, J.S., “The Ultrasonic Pulse Velocity Method”, Chapter 8 in Handbook of Non-Destructive Testing of Concrete (eds. V.M. Malhotra and N.J. Carino), 2nd edition, CRC Press, West Conshohocken, PA, 2004. Pigeon, M. and Pleau, R., Durability of Concrete in Cold Climates, E&FN SPON (an imprint of Chapman & Hall), London, UK, first edition, 1995. Sansalone, M.J. and Streett, W.B., Impact-Echo, Nondestructive Evaluation of Concrete and Masonry, Bullbrier Press, Ithaca, NY, 1997. Setzer, M.J., Auberg, R. and Heck, H.-J. (eds.), Frost Resistance of Concrete, Proceedings of the International RILEM Workshop, RILEM Publication PRO 24, Essen, Germany, 18-19 April 2002. Setzer, M.J., Auberg, R. and Palecki, S., “Non-Destructive Testing of Internal Damage of Concrete Caused by Frost Attack”, Frost Damage in Concrete, Proceedings of the International RILEM Workshop (eds. D.J. Janssen, M.J. Setzer and M.B. Snyder), RILEM Publication PRO 25, Minneapolis, MN, 28-30 June 1999, pp. 173-187. Siebel, E., “Standard Methods for Testing the Resistance of Concrete to Freezing and Thawing”, European Research Project No. 3085, Reference MAT1-CT9-0055, (Project leader: Eberhard Siebel), Commission of the European Communities Directorate General XII, Science, Research and Development Directorate C: Industrial and Materials Technologies, Synthesis Report (Be-TB-1489-5/1998), 1995..
FINAL REPORT A1
APPENDIX A RECOMMENDED PROCEDURE FOR SURVEY OF INTERNAL
TEMPERATURE DISTRIBUTION OF FREEZE-THAW CHAMBER This section covers procedures for conducting a thermal survey of the freezer. The purpose is to characterize the internal temperature distribution of the freezing environment (consisting of the freezer and the specimens inside it) in terms of Temperature vs Time (T-t) and Standard Deviation vs Time (σ-t) functions. Information drawn from this pre-testing survey (such as Reliability curves or R-curves) assist the planning and execution of subsequent tests. As such, this survey must be conducted in an environment that reproduces the environment that will exist in actual testing. Definitions In reference to the freezer air cooling curve shown in Figure A.1, the following terms are defined: - Cold soak is the time period during which the air temperature is –18 ± 5°C (0 ± 10°F). This means that during the cold soak the air temperature in the freezer cannot be warmer than -13C (10F), nor can the air temperature be colder than -23C (-10F). ASTM C 1262 Clause 8.2.1 requires that cold soak be maintained for at least 4 but no more than 5 hours. - Cooling ramp is the portion of the curve between the point at which the temperature starts falling until it reaches –13°C (10°F). (This is the air temperature at which the cold soak period begins.) Together, the cooling ramp and cold soak comprise what is shown as the Cooling branch of the curve. - Warm soak is the time period during which the air temperature is between 24 ± 5°C (75 ± 10°F); and ASTM C 1262 Clause 8.2.2 requires that warm soak be maintained for 2.5 to 96 hours. - Warming ramp is the portion of the curve between the end of cold soak and 19°C (65°F). Together, the warming ramp and warm soak comprise what is shown as the Warming Branch of the curve. With a sufficiently powerful freezer/heater, air temperature exceeds the upper limit for the cold soak almost immediately after warming begins.
Figure A.1 Freezer air cooling curve definitions
-30
-20
-10
0
10
20
30
0 1 2 3 4 5 6 7 8 9 10
Time (hours)
Tem
p. (º
C)
-22
-13
-4
5
14
23
32
41
50
59
68
77
86
Tem
p. (°
F)
cold soak
cooling branch
warm soak
warming branch
warming ramp
-13°C (10°F)
cooling ramp
-23°C (-10°F)
29°C (85°F)
19°C (65°F)
FINAL REPORT A2
Initial planning The overall goal of this initial planning is to identify as many variables as possible that will affect test conditions in actual tests and ensure that these conditions are reproduced during survey of the freezer. Variables that must be first identified include:
♦ Freezer to be used ♦ Size and shape of test containers. These may in turn depend on geometry of specimens to be
tested. ♦ Number of specimens to be tested. ♦ Proposed arrangement of specimens in the freezer, which depends on various factors such as
total number of specimens, shape of containers and available space or shelving units in the freezer. Also, the arrangement of specimens must also consider the ASTM C 1262 requirements that a minimum 13 mm (½ in) space separate specimens in the freezers.
Dummy specimens Dummy specimens to be used for the freezer survey shall be of the same shape and mass as the actual test specimens that will be tested. Although specimens of the same SRW mix may not be necessary for the survey, it is important however that similar geometries be used. These specimens are to be placed in the same containers that will be used in the actual tests. Following this, the dummy specimens shall be placed in the freezer in precisely the same arrangement as will be used in actual tests (specimen arrangement as determined from initial planning) and filled with the same volume of test solution (water or saline) as will be used in actual tests. Temperature sensors The temperature sensors to be used such as thermometers or thermocouples must be calibrated to improve the precision as well as accuracy of temperature measurements. Hance (2005) investigated thermocouple calibration in detail and determined that when uncalibrated type T thermocouples were used, any given measurement could be within ±1.3°C (2.3°F) of a reference thermometer at the 95% confidence level and within ±2.0°C (3.6°F) at the 99% confidence level. Calibration allows for more precise measurements of variations of temperatures within a freezer. On a separate issue, since the T-t and σ-t characteristics are of interest, these temperature sensors must be connected to a data acquisition system capable of recording and storing multiple measurements over a specified time period (at 5-minute intervals or less). For this purpose, thermocouples connected to data acquisition computer are preferred, although other data logging alternatives may be used.
Placement of temperature sensors As a general guide, temperature sensors shall be strategically placed in such manner that the recorded temperatures are representative of the conditions surrounding the specimens (note that it is this surrounding condition that needs to be as uniform as possible to reduce variability arising from freezer internal variation). Sensors shall therefore be placed on each shelf where specimens are located to capture variations at each of the different levels. Within each shelf, sensors shall also be placed around the perimeter of the specimen group, say at the corners of the shelf. In this manner, the sensors placed at each shelf level capture overall temperature variations in the vertical direction, while sensors placed within each shelf capture front-back and left-right variations. In addition, sensors shall also be placed in between specimens on each shelf to capture the conditions in this region. Examples of container and external temperature sensor placement on a given shelf of a freezer are shown in Figure A.2. Other considerations for external temperature sensor placement include:
FINAL REPORT A3
a.) Ensuring that the sensors are not in contact with any other part of the freezer (e.g. wall or shelf) as it is the freezer air temperature that is sought. Thus, sensors shall be placed about 25 mm (1 in) off the shelf level. b.) Ensuring that the sensors are not in contact with the specimens, especially the bottom part of the container where the solution is, since the latent heat liberated by the solution during freezing can lead to misleading sensor measurements. Again, sensors shall be kept at least 25 mm (1 in) away from container surfaces. c.) In addition to these sensors, it is recommended that temperature sensors be placed in the vicinity of the freezer internal (built-in) temperature sensors (specifically, the freezer sensor that controls operation of the unit). This enables verification of the freezer’s own sensors.
Figure A.2 Examples of container and sensor placement on various freezer shelves.
Cycles It is recommended that at least 3 full freeze-thaw cycles be run to ensure consistency between cycles. For the survey, the duration of cooling ramp may be kept the same as that used in actual tests. However, the total length of the cooling branch in each cycle shall be at least equal to (length of cooling ramp + 5 hours), to ensure that data is collected for the entire cold soak period. From studies at Cornell University, the length of cooling ramp was about 1 hour for a chest freezer, < 2 hours for a Tenney freezer and up to 2.5 hours for a walk-in chamber loaded with 40 specimens. As such, the cooling branch for these freezers under the conditions tested would then need to be at least 6, 7 and 7.5 hours respectively. A trial run shall be carried out to determine this cooling ramp length. Temperature data shall be continuously collected either using a dedicated computer with data acquisition system or through other data loggers. Data shall be collected at intervals of not more than 5 minutes. The graphs shown throughout this annex were based on data collected at 1 minute intervals. Data processing The results for the various cycles collected shall be treated separately and independently. The cycles shall not be averaged together (i.e. Tlocation X = average (Tlocation X, cycle 1 + …+ Tlocation X, cycle n), as this may mask any cycle-to-cycle variations. The various cycles shall be examined for cycle-to-cycle consistency, which is a requirement in ASTM C 1262 (Clause 5.1.1). For each cycle, the following steps shall then be performed:
(i) (ii) (iii) (iv) = temperature sensor
1.0 m (39 in)
0.75 m (30 in)
containers with coupons
FINAL REPORT A4
a.) Plot graphs of the T-t, Tavg-t and σ-t. The T-t graph is simply the collection of Temperature vs Time data for all available sensors. The Tavg-t graph is a plot of Average Temperature vs Time where Tavg is the average temperature of all sensors at any given time. The σ-t graph is a plot of Standard Deviation vs Time where σ is the temperature standard deviation of all sensors at any given time. Examples of these plots for measurements in a Tenney freezer are shown in Figure A.3. b.) The T-t plots for all locations shall be inspected for patterns in spatial variation of temperature (i.e. Are locations near the fan colder? Are there any locations which did not get cold enough (i.e. stagnant locations)? By how much does temperature vary from front-to-back, left-to-right or top-to-bottom? Familiarity with these variations will inform decisions about the frequency and pattern of specimen rotation. For example, if front-back variations are observed to be more pronounced than left-right variations, it will then be necessary to rotate specimens more frequently in which front and back specimens are switched around every 10 cycles.
Figure A.3 Sample T-t, Tavg-t and σ-t graphs for Tenney freezer.
-25
-20
-15
-10
-5
0
5
10
15
20
25
0 1 2 3 4 5 6 7
Time (hr)
Tem
pera
ture
(ºC
)
0.0
1.0
2.0
3.0
4.0
0 1 2 3 4 5 6 7Time (hr)
Stan
dard
dev
iatio
n (ºC
)
Tavg
cooling branchalso the range of interest
for Tavg-t model
range of interest for σ-t model
FINAL REPORT A5
c.) Subsequent reliability analysis will require values for Tavg and σ at a number of specific times over the duration of the cooling branch, and the database from which graphs such as in Figure A.3 were generated is likely to be sufficient for the purpose. Temperature data collected in the survey can be used to construct a table of time, Tavg and σ.
If one desired to automate the subsequent reliability analysis it can be helpful (but not required) to generate regression equations that will return approximate values for Tavg and σ for any given time. For this latter approach, regression routines such as those available in Microsoft Excel, or other statistical analysis packages can be used. For the work conducted here, the software package “TableCurve 2D,” version 4, from AISN Software Inc., copyright 1989-1996 was employed, and it was thus determined that the values of Tavg could be approximated with the greatest precision via an exponential function, while a simple linear function was adequate for σ. These relationships were of the form:
Tavg = a1 + b1 exp (–t / c1) (A.1) and
σ = a2 + b2t (A.2) Examples of curve fits for the measured data displayed in Figure A.3 are shown in Figure A.4. For the Tavg-t graph, two separate fits were required for the data before 2.9 hrs and for the data after 2.9 hrs. This is because the Tavg-t measurements performed in the Tenney freezer typically displayed a “kink” (in this particular case at 2.9 hrs) which prompted the use of two curves for the model. While it is clear that a simple linear equation would be a suitable model for Tavg after 2.9 hr, it is convenient to maintain the same form of function for both temperature curves. The standard error of the estimate of Tavg was 0.1oC (0.18oF) prior to 2.9 hr, and 0.06oC (0.11oF) for the nearly linear branch after 2.9 hr. This bilinear response may not occur in other freezers as shown by the Tavg-t response for the walk-in freezer in Figure A.5, where a single curve fit was sufficient to model the entire cooling branch. In the σ-t response of the Tenney freezer (Figure A.4), data before about 0.3 hrs was truncated for the simple linear curve fit. R2 for the estimate of σ was 0.96.
d.) Using these data and/or regression equations, R-curves can then be constructed as follows1.
1. Select a trial length for the cooling branch, ttrial. This is equivalent to selecting a trial value for the elapsed time from the start of cooling to the start of warming.
2. Compute t4 hr = (ttrial – 4) = time by which air temperature must reach C 1262 limit to
complete a 4 hr cold soak prior to warming. Since the cold soak period cannot be shorter than four hours, any specimen that is not surrounded with freezer air that has not been chilled to 13C (10F) as of t4 hr will not have a long enough cold soak. Such a specimen will be undercooled as of the proposed time to start warming.
3. Compute t5 hr = (ttrial – 5) = time before which air temperature must not reach C 1262 limit or
a 5 hr cold soak will be exceeded prior to warming. Since the cold soak period cannot be longer than five hours, any specimen that has already been surrounded with freezer air chilled to 13C (10F) as of t5 hr will have an excessively long cold soak. Such a specimen will be overcooled as of the proposed time to start warming.
1 The concepts of reliability and methods of analysis were developed with the assistance of Prof. Mark Turnquist, School of Civil and Environmental Engineering, Cornell University to whom the authors are grateful.
FINAL REPORT A6
4. Find values for Tavg(t4 hr) and σ(t4 hr)
This is done by either looking-up values of Tavg(t4 hr) and σ(t4 hr) from the freezer-temperature survey data, or by inserting the value of t4 hr into previously developed regression equations (such as Equations A.1 and A.2, for example). Reasonable values can also be retrieved from sufficiently clear graphs of Tavg and σ.
5. Find values for Tavg(t5 hr) and σ(t5 hr)
This is done by either looking-up values of Tavg(t5 hr) and σ(t5 hr) from the freezer-temperature survey data, or by inserting the value of t5 hr into previously developed regression equations (such as Equations A.1 and A.2, for example). Reasonable values can also be retrieved from sufficiently clear graphs of Tavg and σ.
6. From the values at t4 hr, compute Probability of undercooled locations (PU). This is based on the assumption that the temperatures at various locations within the freezer are normally distributed with a mean of Tavg(t4 hr) and a standard deviation of σ(t4 hr). The probability of having undercooled specimens is taken as the probability of finding a freezer location that is still warmer than the required -13C (10F) when t = t4 hr. Probabilities are computed (or tabulated) for the Normal Distribution on the basis of the so-called “Z-statistic,” which in this case is the [difference between -13C (10F) and the average freezer temperature Tavg(t4 hr)], divided by the Standard Deviation of temperature, σ(t4 hr). This is shown as Equation A.3. The order of the terms in the numerator is critical as it determines the sign of z.
Z = )σ(t
)(tT )(T
hr 4
hr 4avgstartsoak cold − (A.3)
where Tcold soak start is –13°C (10°F)
Having determined Z, the probability of finding a freezer location warmer than -13C (10F) as of t = t4 hr can be found by consulting standard statistical tables, but it is found most conveniently, perhaps, by means of the Microsoft Excel function “NORMDIST” as follows:
Using the NORMDIST function built into Microsoft Excel: PU = 1 – NORMDIST(Tcold soak, Tavg, σ, TRUE)
where Tcold soak start is –13°C (10°F) Tavg is Tavg(t4 hr) σ is σ(t4 hr)
TRUE is a command to indicate cumulative distribution function
Alternatively, the calculation performed by Excel can be computed by hand using the long-form equation (A.4) shown below.
PU =
22 3
1 0.436 0.120 0.937exp( Z /2)(1 0.333z) (1 0.333z) (1 0.333z)2π
⎧ ⎫− − +⎨ ⎬+ + +⎩ ⎭
(A.4)
FINAL REPORT A7
Figure A.4 Curve fits to Tavg-t and σ-t graphs of Figure A.3 for Tenney freezer.
7. From the values at t5 hr, compute Proportion of overcooled locations (PO). Like PU, this calculation can also be done in one of two ways:
This is likewise based on the assumption that the temperatures at various locations within the freezer are normally distributed with a mean of Tavg(t5 hr) and a standard deviation of σ(t5 hr). The probability of having overcooled specimens is taken as the probability of finding a freezer location that is already colder than the required -13C (10F) when t = t5 hr. Probabilities are computed (or tabulated) for the Normal Distribution on the basis of the so-called “Z-statistic,” which in this case is the [difference between the average freezer temperature Tavg(t5 hr) and -13C (10F)], divided by the Standard Deviation of temperature, σ(t5 hr). This is shown as Equation A.5. The order of the terms in the numerator is critical as it determines the sign of z.
z = )σ(t
)(T )(tT
hr 5
startsoak coldhr 5avg − (A.5)
-25-20-15-10
-505
10152025
0 1 2 3 4 5 6 7
Time (hr)
Tem
pera
ture
(°C
)
Tavg = –20.8 + 41.4 exp (– t / 1.16)
T = –19.3 + 5.56 exp (– t / 3.34)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3 4 5 6 7
Time (hr)
Std.
Dev
. (°C
)
σ = 1.00-0.11t
FINAL REPORT A8
where Tcold soak start is –13°C (10°F)
Having determined Z, the probability of finding a freezer location cooler than -13C (10F) as of t = t5 hr can be found by consulting standard statistical tables, but it is found most conveniently, perhaps, by means of the Microsoft Excel function “NORMDIST” as follows:
Using the NORMDIST function built into Microsoft Excel:
PO = NORMDIST(Tcold soak, Tavg, σ, TRUE)
where Tcold soak start is –13°C (10°F) Tavg is Tavg(t5 hr) σ is σ(t5 hr)
TRUE is a command to indicate cumulative distribution function
Alternatively, the calculation performed by Excel can be computed by hand using the long-form equation (A.6) shown below.
PO =
22 3
1 0.436 0.120 0.937exp ( /2)(1 0.333z) (1 0.333z) (1 0.333z)2π
z ⎧ ⎫− − +⎨ ⎬+ + +⎩ ⎭
(A.6)
Figure A.5 Curve fit to Tavg-t response of walk-in freezer (single curve).
8. The total probability of having specimens which are not in compliance with the cold soak requirements of ASTM C 1262 (PNC) is thus:
PNC = PU + PO (A.7)
9. The Reliability (R) is then given by: R = (1 – PNC) × 100% (A.8)
-25-20-15-10
-505
10152025
0 1 2 3 4 5 6 7
Time (hr)
Tem
pera
ture
(ºC
)
Tavg = –16.2 + 35.5 exp (– t / 0.67)
FINAL REPORT A9
10. Repeat steps i to ix for various values of ttrial, and plot R versus ttrial. This curve is the R-curve which for the Tavg-t and σ-t graphs in Figures A.3 and A.4 is shown in Figure A.5.
EXAMPLE R-CURVE CALCULATIONS The Tavg-t and σ-t response from the Tenney freezer shown in Figure A.3 will be used to illustrate the calculations of Reliability following the steps outlined above. The curves in Figure A.3 are modeled by exponential equations shown in Figure A.4. This iteration begins with assuming a total duration of the cooling branch of 6.0 hr, meaning that warming will begin 6.0 hours after the start of cooling. 1. Select ttrial = 6.0 hrs (total duration from start of cooling to start of warming) 2. t4 hr = 6 – 4 = 2 (latest time that air can reach -13C(10F) for valid 4-hour cold soak) 3. t5 hr = 6 – 5 = 1(earliest time air can reach -13C(10F) to avoid longer than 5-hour cold soak) 4. Find Tavg(t4 hr) and σ (t4 hr) From the data collected in the initial freezer survey, 2 hours after the start of cooling:
Tavg(t4 hr) = Tavg(2) = -13.8C σ (t4 hr) = σ (2) = 0.76 (as retrieved directly from freezer survey data)
Using the curve-fit equations: Tavg(t4 hr) = Tavg(2) = –20.8 + 41.4 exp (– 2 / 1.16) = –13.4C
(Note that the curve fit to the region before 2.9 hrs was used in this case) σ (t4 hr) = σ (2) = 1-0.11t = 0.78
5. Find Tavg(t5 hr) and σ (t5 hr) From the data collected in the initial freezer survey, 1 hour after the start of cooling:
Tavg(t5 hr) = Tavg(1) = -2.9C σ (t5 hr) = σ (1) = 0.87 (as retrieved directly from freezer survey data)
Using the curve-fit equations: Tavg(t5 hr) = Tavg(1) = –20.8 + 41.4 exp (– 1 / 1.16) = –3.3C
(Note that the curve fit to the region before 2.9 hrs was used in this case) σ (t5 hr) = σ (1) = 1-0.11t = 0.89
6. From the values at t4 hr, PU is calculated as follows: Elect to use values directly obtained from freezer survey
Tavg(t4 hr) = Tavg(2) = -13.8C σ (t4 hr) = σ (2) = 0.76
Using the NORMDIST function built into Microsoft Excel: PU = 1 – NORMDIST(–13, –13.8, 0.76, TRUE) = 0.15 Alternatively:
z = (-13) (-13.8)
(0.76)−
= 1.05
This means that the required cold-soak temperature of -13C is 1.05 standard deviations warmer than the average freezer temperature at 2 hours after the start of cooling. Consulting standard statistics tables will show that only 15% of the specimen locations are likely to be warmer than -13C (confirming the result from Excel’s NORMDIST).
FINAL REPORT A10
Alternatively: PU =
22 3
1 0.436 0.120 0.937exp (1.05 /2)(1 0.333 1.05) (1 0.333 1.05) (1 0.333 1.05)2π
⎧ ⎫− − +⎨ ⎬+ × + × + ×⎩ ⎭
= 0.15
The long-form equation likewise confirms the result from Excel’s NORMDIST, thus demonstrating that a tool such as Excel may be convenient but is not required for these calcultions. Regardless of method, it is concluded that since the average temperature at 2 hours is only 0.8oC cooler than the cold soak temperature at 2 hours after the start of cooling, it is likely that about 15% of the specimens will not have experienced at least a 4-hour cold soak for a 6 hour total cooling branch.
7. From the values at t5 hr, PO is calculated as follows:
Elect to use values directly obtained from freezer survey Tavg(t5 hr) = Tavg(1) = -2.9C σ (t5 hr) = σ (1) = 0.87
Using the NORMDIST function built into Microsoft Excel: PO = NORMDIST(–13, –2.9, 0.87, TRUE) ≈ 0 Alternatively:
z = (-2.9) (-13)
(0.87)−
= 10.9
This means that the required cold-soak temperature of -13C is 10.9 standard deviations colder than the average freezer temperature at 1 hour after the start of cooling. Consulting standard statistics tables will show that essentially 0% of the specimen locations are likely to be colder than -13C (confirming the result from Excel’s NORMDIST). Alternatively: PO =
22 3
1 0.436 0.120 0.937exp (10.9 /2)(1 0.333 10.9) (1 0.333 10.9) (1 0.333 10.9)2π
⎧ ⎫− − +⎨ ⎬+ × + × + ×⎩ ⎭
≈ 0
The long-form equation again confirms the result from Excel’s NORMDIST. It is concluded that since the average temperature at 1 hour is so much warmer than the cold soak temperature, there is virtually no chance of a specimen being within cold-soak temperatures for more than 5 hours for a 6 hour total cooling branch.
FINAL REPORT A11
8. PNC = 0.15 + 0 = 0.15
The probability of specimens being tested in a freezing environment that does not comply with the requirements of ASTM C 1262 is 15% (undercooled) plus 0% overcooled = 15%.
9. R = (1 – 0.15) × 100% = 85%
The reliability with which the freezer unit complies with ASTM C1262 requirements when operating under the conditions monitored in the survey is 85%, for a total length of the cooling period of 6 hours.
10. Repeating steps 1 to 9 for various values of ttrial, the values in Table A.1 are obtained which are then used to plot the R curve shown in Figure A.6.
Table A.1 R values for ttrial ttrial (hr) R (%)
5.7 3 5.8 21 5.9 57 6.0 84 6.1 96 6.2 99 6.3 100 6.4 100 6.5 100 6.6 100 6.7 97 6.8 79 6.9 43 7.0 16 7.1 4
Figure A.6 Reliability (R) curve for the Tavg-t and σ-t graphs shown in Figure A.3.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
5 5.5 6 6.5 7 7.5 8
Length of Cooling Branch (hr)
Rel
iabi
lity
(%)
For this particular freezer and number of specimens, the freezer should be programmed such that the length of Cooling Branch is between 6.1 and 6.7 hrs.
FINAL REPORT A12
Interpretation of R-curve R-curves are guides to understand freezer behavior and to help plan cycle times. Figure A.6 shows an R-curve that is “flat topped”. Actual freeze-thaw tests should be run in the region where R is maximum, which for the curve in Figure A.6 would be in the “flat topped” region between 6.1 and 6.7 hours. It is generally advisable to operate the freezer in the middle of this “flat topped” region, i.e. about 6.4 hrs. Operating near the end of this “flat topped” zone, i.e. either at 6.1 or 6.7 hrs, can lead to fluctuations in freezer performance, causing R to suddenly drop. For example, if the freezer were set for 6.1 hr cooling branch and a fluctuation in freezer performance resulted in the cooling branch ending prematurely by 10-minutes (0.2 hrs), R would drop from 96 to 57%. When the results of a freezer survey indicate that certain variables need to be changed (e.g., reduce number of specimens or change freezer control program) to obtain higher R values, these changes should be made and be followed by another survey with the new set of conditions. The data acquired with the new set of conditions should be analyzed in the manner described above, and R-curves be produced to determine optimum cycle lengths. The R-curve can also be used to determine the proportion of compliant locations had the cycle been operated using a different “control temperature”. In the Tenney freezer used for the NCMA studies, the freezer internal sensor used to control the cycle length was located at the coldest measured location in the freezer. From the T-t graphs in Figure A.3, it is seen that the coldest location reached –13ºC at 1.7 hrs. If cold soak were set for 4.0 hrs starting from this point, the cooling branch would only be 5.7 hrs long. In reference to Figure A.6, the corresponding R is about 3%. This means that almost all specimen locations in the freezer would be undercooled (i.e. receive less than the minimum 4-hr cold soak required by ASTM C 1262).
Freezer surveys should precede actual freeze-thaw testing to assist planning the test program, and should also be conducted when:
• Changing specimen conditions including: a) changes in total specimen quantity (either by removing “failed” specimens or adding new test specimens), b) change of containers used or c) changes in the spatial arrangement of the specimens in the freezer.
• Changing freezer conditions such as for maintenance or if the freezer is moved to a different environment (e.g. temperature controlled room or room with variable temperature conditions)
Even for constant conditions there is no guarantee that cycles will be identical over say, 100 cycles, and thus surveys should be conducted periodically to check uniformity of operation. Preferably 5 cycles of every 25 cycles should be surveyed. Dedicated temperature logging equipment is particularly useful for monitoring overall freezer performance. Actual cycles can be compared to the R-curves and appropriate adjustments made. References Hance, R.M., Studies of the Frost Resistance of Segmental Retaining Wall Units, Master’s Thesis, School of Civil and Environmental Engineering, Cornell University, May 2005. Fagerlund, G., “The Significance of Critical Degrees of Saturation at Freezing of Porous and Brittle Materials”, ACI Special Publication, SP-47, American Concrete Institute, Detroit, MI, pp. 13-65, 1975. Fagerlund, G., “An Introduction to RILEM Methods of Testing Resistance of Concrete to Freezing and Thawing and the International Cooperative Tests on the Critical Degree of Saturation Method”, Materials and Structures, Vol. 10, No. 58, pp. 217-230, 1977. Scherer, G.W. and Valenza II, J.J., “Mechanisms of Frost Damage”, Materials Science of Concrete VII (eds. J. Skalny), The American Ceramic Society, 2005.
FINAL REPORT B1
APPENDIX B STATISTICAL ANALYSIS OF FACTORS AFFECTING MASS LOSS
IN THE VARIABILITY TEST SERIES
Given the repetitive nature in which ASTM C 1262 mass loss measurements were
made (i.e., mass loss being determined at every 10th cycles), one form of statistical
analysis applicable to these situations is what is known as Repeated Measures
Analysis1. As with any Analysis of Variance method, Repeated Measures Analysis
tests the equality of means between data sets. However, Repeated Measures Analysis
is used when all data points in a sample are measured under a number of repeated
trials, and the its primary advantage rests in its capability of modeling the correlation
between repeated measures2. Figure B.1 shows an example of this type of analysis to
help establish terminology. Here, subjects in two separate groups are repeatedly tested
over time. For this example, analysis results reveal that: a) the between-subjects
effects are significant, i.e., group 1 not equal to group 2 as the lines are quite distinct,
b) the within-subjects effects are significant, i.e., the means vary with time, and c) the
group-time interaction effects are significant, i.e., the means change over time but at
different rates (lines are not parallel). In our case, the various Test Sets in the
Variability Series comprise the groups and the number of freeze-thaw cycles
comprises the time effect. Further information on this method of analysis can be
found in the reference for footnote 2, and in Littell et al. (1996).
Analysis of the mass loss data using Repeated Measures Analysis was carried out
using the software SAS 9.1 TS Level 1M3 (SAS Institute Inc, Cary, NC, 2003).
Since, as mentioned in the preceding section, mass loss appeared to follow a 2nd order
1 Consultation with Dr. Freedom King, Department of Biological Statistics and Computational Biology, Cornell University, January 2006. 2 UCLA SAS library website: www.ats.ucla.edu/stat/sas/library/repeated_ut.htm
FINAL REPORT B2
relationship with respect to cycles, a generalized model was thus constructed with the
following form:
Figure B.1 Simple example of Repeated Measures Analysis (from http://www.ats.ucla.edu/stat/sas/seminars/sas_repeatedmeasures/default.htm)
y = α + β x + γ x2 + e (B1)
where y = mass loss
x = cycles
α, β, γ = coefficients to be determined
e = random variation
The software accepts data in the form of mass loss vs. cycles for various groups and
yields output consisting of the parameters that best fit the coefficients α, β and γ
above, as well as the statistical significance of the various effects (sets, cycles and
(cycles)2). As far as correlation between measurements in a single specimen is
FINAL REPORT B3
concerned, the Autoregressive (1) form was utilized in which the covariance structure
is of the form:
1 ρ ρ2 . . ρk-1
ρ . ρ ρ2 . ρk-2
. . . . . .
ρk-1 . . . ρ 1
This covariance structure was preferred as it assigned stronger correlation among
successive measurements (e.g., between cycles 90 and 100) and less correlation
between measurements that are spaced farther apart (e.g., between cycles 10 and 150).
Trials were also carried out in which a constant correlation matrix was used
(Compound Symmetry covariance structure) with results that were similar to those
using the Autoregressive (1) form.
Analyses were carried out for all mass loss data up to 50, 100, 150 and 200 cycles.
Results of these analyses are summarized in Table B1 which shows the value of the F
ratio as well as the probability of exceeding this F value for each of the effects
evaluated. Typically, an effect is considered “significant” if its Pr value is less than
0.05. In general, it is seen that:
a) after 50 cycles: Sets, Cycle and (Cycle)2 were all significant
b) after 100 cycles: Sets, Cycle and (Cycle)2 were all significant
c) after 150 cycles: Sets, Cycle and (Cycle)2 were all significant; although for
the effect of “Sets”, the Pr value approached 0.05
σ2
FINAL REPORT B4
d) after 200 cycles: Sets was insignificant, while Cycle and (Cycle)2 were
significant
These results suggested that up to 150 cycles, the observed differences among the
various Test Sets in the Variability Series were statistically significant. However,
from approximately 150 to 200 cycles, these differences were not statistically
significant. It is interesting to relate these observations to those in Table 16 (Section
5) showing the number of cycles to 1% mass loss, which in most cases was less than
150 cycles. Tying these two observations together (Tables 16 and B.1) implies that
systematic variations in testing (such as container sizes relative to specimen sizes as
done in this study) can cause statistically different results which affect how fast a mass
loss of 1% is reached. Moreover, it is seen from Table B.1 that the effect of
“Cycle*Cycle*Sets” (i.e., the 2nd order effect of cycle) was significant in all cases,
which indicated that the observation of a 2nd order mass loss vs. cycles relationship
was statistically significant, in addition to the fact that different Sets responded
differently to the effect of (Cycle)2.
FINAL REPORT B5
Table B.1 Repeated Measures Analysis of various effects
in mass loss vs. cycles relationship. Effect
Sets Cycle*Sets Cycle*Cycle*Sets
50 cycles F value 41.1 43.8 3.9 Pr > F <0.0001 <0.0001 0.0007 100 cycles F value 7.9 43.8 12.8 Pr > F 0.0001 <0.0001 <0.0001 150 cycles F value 2.6 45.9 24.6 Pr > F 0.0431 <0.0001 <0.0001 200 cycles F value 0.2 10.5 15.1 Pr > F 0.9763 <0.0001 <0.0001
The analysis also provided the values of the coefficients α, β, and γ that best fit
Equation B1 above. Using these coefficients, it was thus possible to model the mass
loss vs. cycles relationship using for the various Test Sets using data from start of test
up to 50, 100, 150 and 200 cycles. These equations follow (mass loss abbreviated
ML):
• Using data up to 50 cycles: (B2) Set A ML = – 0.0036 – 0.00009 x + 0.000047 x2 Set B ML = – 0.0059 + 0.00074 x + 0.000031 x2 Set C ML = – 0.0054 + 0.0029 x + 0.0000079 x2 Set D ML = – 0.0012 + 0.00078 x + 0.000062 x2 Set E ML = – 0.0016 – 0.00081 x + 0.000078 x2 Set F ML = – 0.0020 – 0.0010 x + 0.000094 x2 Set G ML = – 0.0081 + 0.0016 x + 0.000016 x2
FINAL REPORT B6
• Using data up to 100 cycles: (B3) Set A ML = – 0.00006 – 0.00035 x + 0.000048 x2 Set B ML = 0.0035 – 0.0047 x + 0.00011 x2 Set C ML = – 0.00043 + 0.0015 x + 0.00005 x2 Set D ML = 0.000011 + 0.0015 x + 0.000037 x2 Set E ML = – 0.00013 – 0.00085 x + 0.000081 x2 Set F ML = – 0.00051 + 0.00041 x + 0.000056 x2 Set G ML = – 0.00036 + 0.00057 x + 0.000039 x2
• Using data up to 150 cycles: (B4) Set A ML = 0.000018 – 0.00033 x + 0.000048 x2 Set B ML = 0.0024 – 0.013 x + 0.00021 x2 Set C ML = 0.00042 – 0.00089 x + 0.000078 x2 Set D ML = 0.00054 – 0.00085 x + 0.000063 x2 Set E ML = – 0.00015 – 0.00086 x + 0.000086 x2 Set F ML = 0.00050 – 0.0031 x + 0.0001 x2 Set G ML = – 0.00008 + 0.00088 x + 0.000035 x2
• Using data up to 200 cycles: (B5) Set A ML = 0.028 – 0.024 x + 0.00023 x2 Set B ML = 0.24 – 0.28 x + 0.0021 x2 Set C ML = 0.19 – 0.18 x + 0.0015 x2 Set D ML = 0.44 – 0.39 x + 0.0032 x2 Set E ML = 0.036 – 0.032 x + 0.00033 x2 Set F ML = 0.16 – 0.17 x + 0.0015 x2 Set G ML = 0.0082 – 0.0063 x + 0.000093 x2
The objective in developing these expressions using data up to 50, 100, 150 and 200
cycles was to observe how well the models constructed based on the data at each of
these stages predicted subsequent mass loss. The question to be answered is: “Are
FINAL REPORT B7
data up to 50 cycles capable of predicting mass loss after say, 150 cycles?” Or, “Does
one need to use data up to 100 cycles to predict 150 cycle mass loss?” Hence, the
predicted mass loss based on Equations B2 to B5 were plotted together with actual
mass-loss data to observe this behavior. These plots are shown in Figures B.2, B.3,
and B.4 for predictions obtained using data up to 50, 100, 150 and 200 cycles,
respectively.
Generally, it is seen that, except for the data up to 200 cycles, these equations were
capable of modeling the actual mass loss up to the number of cycles for which each
particular set of equations was developed (i.e., equations developed based on 50 cycle
data modeled well the actual up to 50 cycles). However the effectiveness by which
these equations predicted mass loss of future cycles depended on the particular Test
Set. For instance, using the 50-cycle data, mass loss in Test Set A was modeled
effectively up to about 160 cycles and Test Set E up to about 100 cycles. The model
under-predicted 100-cycle mass loss in Test Sets B, C and G (i.e., model was not
conservative) and over-predicted 100-cycle mass loss in Test Sets D and F (i.e., model
was conservative). The predicted number of cycles to 1% mass loss (based on the 50-
cycle data) is compared to the actual number of cycles to 1% mass loss in Table B.2,
where it is seen that data from 50 cycles may not be sufficient to model longer term
response (note large errors). These results also reinforce the point mentioned in
Section 5 that relative performance among the various Test Sets after 50 cycles are not
necessarily duplicated after 100 or 150 cycles.
FINAL REPORT B8
Test Set A
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)Test Set B
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set C
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set D
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set E
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set F
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set G
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Figure B.2 Actual vs. predicted mass loss based on data up to 50 cycles.
actual
predicted
FINAL REPORT B9
Test Set A
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)Test Set B
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set C
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set D
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set E
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set F
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set G
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Figure B.3 Actual vs. predicted mass loss based on data up to 100 cycles.
actual
predicted
FINAL REPORT B10
Test Set A
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)Test Set B
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set C
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set D
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set E
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set F
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set G
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Figure B.4 Actual vs. predicted mass loss based on data up to 150 cycles.
actual
predicted
FINAL REPORT B11
Test Set A
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)Test Set B
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set C
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set D
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set E
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set F
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Test Set G
0
1
2
3
4
5
0 50 100 150 200Cycle
Mas
s lo
ss (%
)
Figure B.5 Actual vs. predicted mass loss based on data up to 200 cycles.
predicted
actual
FINAL REPORT B12
Table B.2 Actual vs. predicted number of cycle to 1% mass loss (using 50-cycle data)
Test Set Predicted Actual Error, % A 147 148 -1 B 168 114 47 C 217 123 76 D 121 137 -12 E 118 109 8 F 109 123 -11 G 206 154 34
When using the 100-cycle data, the predicted and actual mass loss values were similar
up to 160 cycles for Test Sets A and G and up to about 130 cycles for the other Test
Sets. Using the 150-cycle data, the predicted and actual mass loss values were also
similar up to about 160 cycles. However, when using the 200-cycle data, the
effectiveness of this model broke down as shown by the lack of correspondence
between predicted and actual mass loss in Figure 53. From these results, it appears
that the 2nd order mass loss behavior ceased to be valid at around 150 cycles, which
reflects the results shown in Table 11.
In practical terms, the results of this statistical analysis can be summarized as follows:
• The observed differences in mass loss among the various Test Sets (at mass
loss below 1%) were significant at the 95% confidence level. This means that
variations in surrounding solution volume, specimen size and container size are
expected to yield differences in measured mass loss, which in turn affect how
fast a 1% mass loss is reached. In other words, it is expected that variation in
these test parameters will lead to variability of test results.
FINAL REPORT B13
• Statistical analyses also confirmed results in Section 5 in that mass loss
followed a 2nd order behavior, and this behavior appeared to be valid up to
about 150 cycles.
• The above analyses also confirmed results in Section 5 in that patterns
observed in the short term (up to 50 cycles) could not be used to effectively
predict longer term (after 100 and 150 cycles) mass loss. Using 50-cycle data
to predict 100-cycle values resulted in both over and under-predictions. This
must be considered in any variant of the test method that seeks to accelerate
the test and use fewer test cycles.