microwave nondestructive evaluation of mortars with and without sodium hydroxide inclusion ashkan...
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Microwave Nondestructive Evaluation of Mortars with and without Sodium
Hydroxide Inclusion
Ashkan Hashemi, Kristen M. Donnell, and Reza ZoughiApplied Microwave Nondestructive Testing Laboratory (amntl)
Electrical and Computer Engineering DepartmentMissouri University of Science and Technology (S&T)
Rolla, MO 65409, USA
Kimberly E. KurtisSchool of Civil and Environmental Engineering
Georgia Institute of TechnologyAtlanta, GA 30332-0355, USA
Iman Mehdipour, Kamal H. KhayatCenter for Infrastructure Engineering Studies
Department of Civil, Architectural and Environmental EngineeringMissouri University of Science and Technology (S&T)
Rolla, MO 65409, USA
Outline
• Introduction • Microwave Approach• Sample Preparation• Measurement Results• Summary• Future Work
Introduction
• The concrete prism test, ASTM C1293, is considered among the more reliable laboratory test methods for assessment of potential for ASR
• But this test requires the addition of sodium hydroxide (NaOH) to the mix water in order to accelerate the ASR gel formation
• In this investigation, the influence of the NaOH addition is examined through microwave nondestructive dielectric constant measurements
What is ASR? • The chemical reaction between alkalis present in
portland cement and certain siliceous minerals/rocks present in some aggregates is known as ASR
Si-OH + OH- + Na+, K+ Si-O-Na, K + H2O
Si-O-Si + 2OH- + 2Na+, K+ 2(Si-O-Na, K) + H2O
• Portland cement• Other cementing
materials• Chemical admixtures• Wash water (if used)• Aggregates• External sources
(deicing chemicals)
SufficientAlkali
Concentration
Sources
Sufficient Reactive Silica
Sources
• Opal• Tridymite• Cristobalite• Chert• etc.
• Sustain chemical reaction• Provide water for gel
expansion
Sufficient Moisture
Role
Introduction
Introduction
ASR formation:
Sio2
Alkali elements in cement paste react
with reactive aggregates
Na+K+
Na+
K+OH-
OH-
alkali-silica gel forms around and within
the aggregate
ASR Gel
ASR gel imbibes water from its surroundings which leads to expansion and
cracking
H2O
H2O
H2O
Microwave Approach
• Interactions of materials with microwave signals is macroscopically described by the complex dielectric constant:
• It is an intrinsic property of material, independent of measurement technique
• Reflection and transmission coefficient as well as scattered signal properties are directly influenced by this parameter
• Temporal dielectric property characterization of such mixtures can provide invaluable information about the materials properties and any changes within them
Permittivity Loss Factor
Microwave Approach
• Pure water Vs. ionic water
• NaOH is an ionic solution which has higher ionic conductivity compared to pure water
• Since ionic conductivity affects loss factor of the material, microwave dielectric constant measurements should distinguish between samples with and without NaOH
02
02
'1 (2 )
2 ( )"
1 (2 )
w ww w
w
w w ww
w
f
f
f
02
02
0
'1 (2 )
2 ( )"
1 (2 ) 2
iw iwiw iw
iw
iw iw iw iwiw
iw
f
f
f f
Ionic conductivity [S/m]
Previous Work:
• For cement-based materials, microwave nondestructive characterization techniques have been utilized for evaluating: • Cure state,• w/c, s/c and ca/c,• coarse aggregate content distribution, aggregate
segregation, etc.,• cyclical chloride permeation in mortar along with
extensive EM modeling for the same,• Carbonation [1], and• formation of alkali-silica reaction (ASR) gel in
mortar with reactive and non-reactive aggregates [2]-[4]
Microwave Approach
Sample Preparation
• Two different sets of mortar samples, one with and the other without NaOH but both containing an alkali-reactive aggregate, were cast and cured at hot and humid conditions
• Dielectric constants of the samples were measured temporally at S-band (i.e., 2.6 – 3.95 GHz)
• Completely-filled waveguide techniques was used for dielectric constant measurements
R S X
109.2×54.6 mm
72.1×34 mm 22.8×10.1 mm
Measurement Setup
Vector Network Analyzer
SUT
Coaxial-to-Waveguide Adapters
Precision Cables
Sample Preparation
• Samples were put in hot and humid conditions for 28 days. Every 2-3 days, the dielectric constant of the samples were measured during curing period
• Curing conditions: 38° C ± 2° C @ 85%<RH<95%• The measurements were conducted for two different
alkaline-reactive aggregates• NaOH was added to the mixing water of both mixtures
(with NaOH) for a total equivalent alkali content of 0.9% by mass of cement
Mix ProportionsSample Type
Reactive I Reactive II
Cement Portland Type
I/IIPortland Type
I/II
Aggregate Las Placitas Grand Island
water-to-cement ratio (w/c)
0.47 0.47
aggregate-to-cement ratio (a/c)
2.25 2.25
Mix Design
Measurements - I
• Reactive aggregate type I – Permittivity
0 5 10 15 20 25 306
6.5
7
7.5
8
8.5
9
9.5
10
10.5
11
Day
Pe
rmitt
ivity
High AlkaliLow Alkali
• Since same material was used in both set of samples, the only difference between them is due to NaOH
• Samples with NaOH show higher permittivity compared to low alkali samples
Measurements - I
• Reactive aggregate type I – Loss Factor
• As it was expected, for samples with NaOH higher values of loss factor was measured
• This increase in loss factor in high alkali samples is attributed to higher ionic conductivity of the samples
0 5 10 15 20 25 30-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
Day
Lo
ss F
act
or
High AlkaliLow Alkali
Measurements - I
• Reactive aggregate type I – Mass Change
0 5 10 15 20 25 300.985
0.99
0.995
1
1.005
1.01
1.015
1.02
1.025
Day
No
rma
lize
d M
ass
Ch
an
ge
High AlkaliLow Alkali
• NaOH accelerates ASR formation, ASR creates microcracks and tends to imbibe water from it surrounding; hence, more water is absorbed from environment to high alkali samples compared to low alkali
Measurements - I
• Also, more cracks were created in samples with NaOH indication of ASR
Visible cracks on surface
Petrography
Without NaOH
With NaOH
Measurements - II
• The reason for repeating the measurements was to measure some mechanical properties of the two samples and see if they can be correlated to microwave measurements
• It is reported that the higher alkali content in the cement, the lower the ultimate strength of the corresponding sample*
• To evaluate this, the compressive strength of the new set was measured as well as dielectric constant measurements
*Reference: Smaoui, N., et al. "Effects of alkali addition on the mechanical properties and durability of concrete." Cement and concrete research 35.2 (2005): 203-212.
Measurements - II
• Reactive aggregate type II - Permittivity
0 5 10 15 20 25 307
8
9
10
11
12
13
Day
Pe
rmitt
ivity
Low AlkaliHigh Alkali
• The same behavior was observed for the other type of reactive aggregate
• Permittivity, loss factor, and mass change followed the same trend as the previous case
Measurements - II
• Reactive aggregate type II – Loss Factor
0 5 10 15 20 25 30-6
-5.5
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
Day
Lo
ss F
act
or
Low AlkaliHigh Alkali
• The same behavior was observed for the other type of reactive aggregate
• Permittivity, loss factor, and mass change followed the same trend as the previous case
Measurements - II
• Reactive aggregate type II – Mass Change
0 5 10 15 20 25 300.985
0.99
0.995
1
1.005
1.01
1.015
1.02
1.025
1.03
1.035
Day
No
rma
lize
d M
ass
Ch
an
ge
Low AlkaliHigh Alkali
• The same behavior was observed for the other type of reactive aggregate
• Permittivity, loss factor, and mass change followed the same trend as the previous case
Measurements - II
• Reactive aggregate type II – Compressive Strength
0 5 10 15 20 25 3035
40
45
50
55
60
Day
Co
mp
ress
ive
Str
en
gth
(M
Pa
)
Low AlkaliHigh Alkali
• As it was expected, high alkali samples showed less compressive strength compared to the low alkali samples
• This can be attributed to microcracks and possible ASR gel production in samples with NaOH
Measurements - II
• Cumulative heat evolution
High Alkali
Low Alkali
• Trend: The graph shows a faster reaction and a greater extent of reaction during the first 3 days of hydration for the high alkali samples
• Reason: NaOH accelerates the reaction of the cement, which creates more bound water - in the hydrated cement paste - during these early periods
Summary and Future Work
• For better correlation between lab test and field performance, it is critical to understand the effect of NaOH in concrete mix
• Due to sensitivity of microwave signals to ionic conductivity of materials, microwave dielectric constant measurements manifested the difference between the two types of samples
• Microwave dielectric measurements can also be correlated to mechanical properties of samples such as compressive strength
• Future studying of other chemical properties such as rate of reaction and microstructure of the two different sets of samples, can further expand applicability of microwave nondestructive techniques in material characterizations
Acknowledgements
• This work was supported by the National Science Foundation (NSF), as a Collaborative Grant between Missouri University of Science and Technology (S&T) and Georgia Institute of Technology, under Award No. 1234151. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF.
References
• [1] Hashemi, Ashkan, et al. "Microwave detection of carbonation in mortar using dielectric property characterization." Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, 2014 IEEE International. IEEE, 2014.
• [2] Hashemi, A., et al. "Microwave NDE method for health-monitoring of concrete structures containing alkali-silica reaction (ASR) gel." 40TH ANNUAL REVIEW OF PROGRESS IN QUANTITATIVE NONDESTRUCTIVE EVALUATION: Incorporating the 10th International Conference on Barkhausen Noise and Micromagnetic Testing. Vol. 1581. No. 1. AIP Publishing, 2014.
• [3] Hashemi, A., et al. "Effect of humidity on dielectric properties of mortars with alkali-silica reaction (ASR) gel." Instrumentation and Measurement Technology Conference (I2MTC), 2015 IEEE International. IEEE, 2015.
• [4] Hashemi, A.; Horst, M.; Kurtis, K.E.; Donnell, K.M.; Zoughi, R., "Comparison of Alkali–Silica Reaction Gel Behavior in Mortar at Microwave Frequencies," Instrumentation and Measurement, IEEE Transactions on , vol.64, no.7, pp.1907,1915, July 2015.
Thank You!