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Performance Screening of Concrete Materials and Proportions Using Thermal Testing
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Performance Screening of Concrete Materials and Proportions Using Thermal Testing
Session F113Friday, March 7, 2014
CONEXPO-CON/AGGLas Vegas
Tim Cost, P.E., F.ACISr. Technical Service EngineerHolcim (US) Inc.
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Overview & agenda
Thermal testing background and definitions
Managing, processing, and interpreting thermal profile data for common applications
Applications and examples of thermal and strength testing of paste in the lab
Managing, processing, and interpreting thermal profile data for common applications
Incompatibility of materials – evaluation with thermal testing, influences, remedies
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Thermal testing?
Background and definitions
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Some terms defined, conventions noted
calorimetry cal·o·rim·e·try (kal'-ə-rĭm'-ĭ-trē) n. –
Measurement of the amount of heat evolved or absorbed in a chemical reaction, change of state, or formation of a solution.
adiabatic adi·a·bat·ic (ā'-dē-ə-ba'-tik), adj. –
Occurring without loss or gain of heat.
isothermal i·so·therm·al (ī'-sō-thŭrm'-əl), adj. –
Occurring with no change in temperature.
“aluminates” – convention for tricalcium aluminate (C3A)
“silicates” – convention for tricalcium silicate (C3S)
(Dicalcium silicate or C2S has little influence within the timeframe of the thermal data to be studied.)
“sulfates” – convention for calcium sulfate (CaSO4) and/or cement SO3 level, as an indication of calcium sulfate content.
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Thermal testing vs. “calorimetry”
Thermal testing or thermal profile testing may sometimes be referred to as “calorimetry” or “semi-adiabatic calorimetry” but neither is a technically correct description.
Heat given off in hydration is not actually being quantified. Conditions are not usually very close to adiabatic and are not
precisely controlled.
Thermal testing is simply measuring mixture temperature changes over time and plotting them as an indication of evolved heat.
The value and use of the data is in comparison of trends for similar mixtures tested under the same conditions.
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True calorimetry methods quantify heat
Isothermal or near-adiabatic calorimetry can be used to evaluate mix performance and can accurately measure the heat evolved.
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Thermal testing vs. isothermal calorimetry
IsoCal results at 73 F Concrete Isothermal
Thermal profiles
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Heat released in the first few hours as indicated in a typical thermal profile documents C3A and C3S hydration rates and CaSO4 (gypsum) interaction.
Cement hydration and heat evolution
Useful performance indications include timing and magnitude of peaks and the profile shapes, which are influenced by any abnormal hydration trends.
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There are ASTM and European standards for certain calorimetry applications for concrete and cement
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A thermal testing Standard Practice document is currently under development in ASTM
DRAFT
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Thermal profile testing variations and options
Testing options:
Concrete, mortar, or paste In the lab or at the plant or job site Using project concrete or simulated
mixtures of similar proportions Manufactured or adapted equipment Lab ambient temps or simulated
project field temps Data processing / evaluation with
either special software or common spreadsheets
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Inexpensive temperature sensors and loggers
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Manufactured and adapted equipment
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Laboratory paste mixtures (modeling concrete paste fractions) – an especially efficient evaluation tool
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Data collection setups used for presented data
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Performance evaluation, troubleshooting, & QC tool for concrete & other cementitious mixtures:
Setting time trends due to changes of cement source, SCM’s, admixtures, dosages, project field temps
Evaluation / selection of cements, SCM’s, admixtures Checking for incompatibility potential of combinations Qualifying a new mix design under field extremes Evaluating material source variability or new sources Substitute (w/ care…) for C 403 set time test, field or lab Troubleshooting field or product problems
Cement production QC uses:
Sulfates optimization, sulfate balance checks – effects of new fuels or raw materials, gyp sources, mill temps, etc.
Evaluation of setting time trends with SCMs & admixtures
Applications of thermal profile testing
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Test method variables & considerations
Concrete, mortar or paste? Mixing method / equipment Sample volume / mass? How much insulation? Initial mixture temperature Environment temperature Control of environment Sensor contact w/ sample
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General guidance:
Concrete or mortar vs. paste: Concrete or mortar: more convenient on
the job site, representative set times Paste: better for multi-variable lab studies
Sample size (mass): Larger samples for mortar & concrete:
- 3” x 6” cylinders work well for mortar- 4” x 8” or larger for concrete
Smaller samples (2” x 4”) for paste
Insulation of container: Accentuates peaks, amplifies hydration Little to none for paste samples More for mortar, most for concrete Choice depends somewhat on objectives
but mostly to produce reasonable curves
Test method variables & considerations
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Sample mass and insulation:
Should be balanced for the application Consider sample type and ambient temps Objectives:
Drive sufficient hydration peaks for clean data signal and adequate signal-to-noise
Peak temps should be representative of in-place application but no higher
Test method variables & considerations
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Mortar Wet-sieved concrete C 305 (4 min.) Others
Paste C 305 (2¼ min.) Hand-held kitchen mixer 1 minute or less may be
adequate mixing time Blender mixing
Mixing shear differences may influence results
Test method variables & considerations
Mixing equipment and procedures:
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Strength data is also recommended
Hardened specimens strength tested after thermal testing Extra samples can be used for
strengths at different ages
Parallel mortar cubes –another option
Strength bars presented with thermal profiles may be helpful with data interpretation
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90° F mixtures with 25% Class F ash and water reducer
Paste @ 0.52 w/cm, 500g powder content
Mortar @ 0.52 w/cm, 500g powder content, 1425g SSD concrete sand, mixed via C305
Effects of test method variablesMortar vs. paste, equal volume specimens, no insulation
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Mortar vs. paste, all specimens in 3” x 6” cylinder molds, no insulation
73° F mixtures:
A) no ash or admix, w/c = 0.54
B) 25% C ash + 3 oz/cwttype A WR, w/cm = 0.51
C) 25% F ash + 4 oz/cwtMR WR, w/cm = 0.51
A
A
B
B
C
C
paste
mortar(expanded temp scale)
Effects of test method variables
11° C peak
4° C peak
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Hydration time, hours Hydration time, hours
Sample mass effects (minimal insulation)
Paste samples of increasing mass, with 25% Class C ash and water reducer at 73° F – cylindrical samples of similar h/d
Mortar samples of different mass at 73° F, same proportions as paste mixtures + sand @ 2.75 x cementitious mass
Effects of test method variables
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Insulation effects
Mortar mixture with 25% Class C ash and water reducer at 73° F in 3”x6” cylinders with varying levels of insulation
Effects of test method variables
3”x6” cylinder wrapped with ½” foam insulation
3”x6” cylinder wrapped with 2” foam insulation
3”x6” cylinder, no insulation
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Managing, processing, and interpreting thermal profile data for common applications
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General guidelines
Data should include an accurate mix time for each channel
Plotting can be done with special software or a spreadsheet
Plot several (3 to 8, typically) profiles on a single graph for comparison, synchronized to a common time scale
Zero time = first wetting of cement at mixing
Consider effects of ambient temp changes during test period
Review reference temp (inert specimen) & evaluate the effects of ambient changes on data
Plotting the data with reference temperatures subtracted for each point (Tsample – Treference) usually improves comparisons
Plotting profiles from different days or testing events on the same graph is not generally recommended
Unless ambient controls were especially good Repeat controls and referenced mixtures with each new series
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The “reference” channel is a synched temp record of an inert specimen of similar mass (sand and water, etc.)
These graphs show the same data plotted without (at left) and with (below) subtraction of the reference channel, to essentially remove influences of the changing ambient temps.
Use of an inert specimen “reference”
Unadjusted temps
Reference channel temps subtracted (∆T)
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For any thermal profile of a normally hydrating mixture, the time at which setting begins is simply indicated by the onset of the main peak (C at left)
“Thermal” set times of concrete or mortar may be used to approximate C 403 set times
Setting comparisons of different mixtures can be visually made or spreadsheet quantified as long as the records use a common time scale relative to mixing
Studying setting time w/ thermal profiles
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ASTM Subcommittee C09.23 “round robin” testing event –Atlanta, November 2008
12 teams from suppliers, testing labs, universities
3 different concrete mixtures
C403 in triplicate, each mixture, each team
Thermal set determinations –devices provided by each team as per a draft Standard
ASTM work toward a “thermal” alternative to C403
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Thermal setting terms and use of data
Common thermal setting time convention – the hydration time at which a given “fraction” of the main hydration peak temperature rise occurs
Shown below are 20% and 50% fraction times (about 4.9 and 6.4 hours)
Using fractions, thermal setting times can be visually estimated, scaled from graphs, or calculated in data spreadsheets
50% is a convenient fraction for visual estimates
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Comparisons for concrete – time of set by thermal methods vs. C403
Fractions of 21% and 42% have found to be good default values for using thermal testing to estimate C403 times (initial and final set)
42% fraction vs. C403 final set
21% fraction vs. C403 initial set
From: Sandberg and Liberman, “Monitoring and Evaluation of Cement Hydration by Semi-Adiabatic Field Calorimetry,” ACI SP-241-2, American Concrete Institute, 2007.
95% confidence interval limits
95% confidence interval limits
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Six concrete mixtures used for set time comparisons
Using lab paste mixtures to study concrete setting
Paste proportions identical to concrete mix designs, without aggregates
Example to follow uses 50% fraction thermal set indications of paste for simplicity, but lower fractions could be used to better estimate C403
50% fraction values can be spreadsheet-calculated or estimated (visually) Useful approach for quick evaluation of multiple variables
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Thermal profiles with indicated 50% fractions, lab paste mixtures
Set time comparisons: C403 concrete initial set times vs. paste 50% fraction times
Hydration time, minutes
Paste 50% fractions compared with concrete C403 initial set times
50% paste fraction times are 141% to 151% of concrete C403 initial set
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Paste “thermal set” responses to key influences are similar to those in concrete
Mix temperature Admixtures and dosages SCM’s and replacement rates Comparing different cements
Exceptions:
Water-cementitious ratio effects on concrete set times are not reflected in paste mixtures
Retardation effects of certain admixtures may be slightly exaggerated in paste
Lab set time studies using paste mixtures
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Applications and examples of thermal and strength testing of paste in the lab
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Approximate 1-day compressive strengths, psi
Similar neat paste mixtures ranging in w/c from 0.38 to 0.54
Set time effects of ∆w/c are not reproduced
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Thermal profiles with 50% fraction markers, all mixtures @ 90°F with 25% F ash and indicated doses of type A/D water reducer & retarder
Influence of admix dose & retarder
Relative set time example with lab paste
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Thermal profiles of paste mixtures @ 90°F with and without 25% ash and 3.75 oz/cwt of type A/B/D WR
Influence of Class C and Class F fly ash
Relative set time example with lab paste
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Two admixtures compared for temperature & dosage effects
Thermal profiles of lab paste @ 0.40 w/c
cement-only mixtures @ 73 or 50°F, with 3 or 6 oz/cwt of two different mid-range admixtures
Relative set time example with lab paste
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Selection of a water reducer for minimal set time impact in a 30% Class C ash mix
5 different WR admixtures (2 Type A/D, 2 Type A/F, 1 MR) Dosages selected for approx. 6% water reduction A single Type II cement sample, w/cm = 0.40 Paste mixtures @ 70°F mix and cure temps
“A/F 1” is clearly has the least retardation influence.
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Thermal profile testing used in the concrete mix design development process
Materials selection – avoiding incompatibility influences, maximizing synergies, minimizing retardation contributions
Screening tests with lab paste, thermal profiles & strengths:
Establishment of performance targets via reference mixes Effects of increasing SCMs to proposed levels W/cm adjustments with admixtures to restore early strengths Compensating for retardation effects with admixtures Sulfate balance checks at field temps
Concrete trials & final mix refinement
Additional adjustments, if needed, for changing temps
Example: development of a sustainable, high SCM mix with acceptable performance for flatwork applications
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Performance of traditional low-SCM mixtures
“Reference” mixtures to establish performance targets for mix development 15% C ash, 15% F ash, 30% slag cement with mild WR dosages For these examples, criteria to be based on these mixtures (green bands),
50% fraction thermal set indications and 1-day strengths in bar charts
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Effects of SCM replacement rate increased to 50%
Same temps & admix dosages, with the addition of an F ash mix w/ A/F WR Set time with F ash and A/D WR driven by admix Good set performance with slag and F ash + A/F C ash set time goes quite long (indication of potential issues) 1-day strengths all now unacceptable
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Effects of lower w/cm using HRWR dosages
Lower w/cm needed to restore early strengths, A/F WR dose increased All 1-day strengths now marginally acceptable, slag mix healthiest 60% replacement mix with slag added, still acceptable strength All set times now unacceptable, need help from accelerators (esp. C ash)
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Compensating for delayed set with accelerators
All mixtures repeated with varying & incremental dosages of non-chloride accelerator (NCA)
Moderate dosages restore acceptable set for F ash and slag
NCA less effective with C ash and seems to create sulfate balance issues (incompatibility) at higher dosages (in pursuit of restored set)
1-day strengths benefit from NCA
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Verification of proportions at extreme field temps
F ash and slag mixtures with same A/F dose & max NCA dose repeated at highest envisioned concrete field temps: 36ºC (96ºF) mix and cure temps
No sulfate balance issues indicated; NCA dosages could be reduced OK to proceed to trial concrete mixtures
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Incompatibility of materials – evaluation with thermal testing, influences, remedies
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What is incompatibility of materials?
What we’re talking about:
Mild to extreme deviations from normal set time, rheology, and/or early strength development that result from abnormal early cement hydration due to inadequate available calcium sulfate.
“Incompatibility” has sometimes been used in reference to some other issues (not discussed): Air void system issues Early-age cracking Other durability issues (ASR, ACR, DEF, etc.)
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Incompatibility examples from the field:
1. Severely delayed set :No problems were experienced all week with several pours on a big project. On Friday, with good weather, a morning pour of the same mix design used all week had not set up by 7 pm (finishing had been completed by lunch time every other day). Related issues included plastic shrinkage cracking and poor surface durability and appearance.
2. Flash set with delayed strength gain:A new project required a high-strength mix which had not been used since cement sources were changed. The project began on a hot day and the first loads poured began to set up right out of the chute. The pour was stopped, as finishing was severely impacted, but the next day the concrete was still so green that a screwdriver could easily be tapped into the concrete several inches deep.
What is incompatibility of materials?
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3. Slump loss:In the middle of a large project with no other issues, excessive slump loss began to occur in transit, along with a noticeable trend toward lower early strengths. Higher dosage of the mid-range water reducing admixture raised initial slump but did not change the slump loss or early strength trends. The problem went away after a few days. 28-day strengths were unaffected.
What is incompatibility of materials?
In each case, as part of routine troubleshooting, all materials were sampled and tested; plant records and delivery tickets were reviewed.
There were no out of spec materials, deviations from normal procedures, or batching errors!
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C3S = 3CaO SiO2
(Tricalcium silicate)
C2S = 2CaO SiO2
(Dicalcium silicate)
C3A = 3CaO Al2O3
(Tricalcium aluminate)
C4AF = 4CaO Al2O3 Fe2O3
(Tetracalcium aluminoferrite)
Technical background - cement chemistry
Compounds in portland cement clinker:
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C3S = 3CaO SiO2
(Tricalcium silicate)
C2S = 2CaO SiO2
(Dicalcium silicate)
C3A = 3CaO Al2O3
(Tricalcium aluminate)
C4AF = 4CaO Al2O3 Fe2O3
(Tetracalcium aluminoferrite)
Hydration of these compounds produces significant, measurable heat during the first 24 hours of hydration
Compounds in portland cement clinker:
Technical background - cement chemistry
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Ample CaSO4 (gypsum) interaction for several hours is necessary for normal set and strength!
The interaction of CaSO4 with C3A not only delays and controls set but is necessary for normal C3S hydration. Less CaSO4 availability = less C3A control = interrupted or abnormal C3S hydration.
Good aluminate control, normal C3S hydration
Poor aluminate control, abnormal C3S hydration
CaSO4 starvation, little aluminate control, interrupted C3S hydration
Three mixtures with incrementally higher admixture dosages
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So why wouldn’t there be enough gypsum in cement?
It’s not just about the amount – there are different specific forms of CaSO4 and they vary in solubility.
The test for cement CaSO4 “optimization” is usually done using cement-only mortars, and other materials in concrete (SCM’s and admixtures) may increase “demand” for sulfate.
CaSO4 forms and purity vary among gypsum sources, which may change from time to time at any given plant.
CaSO4 level is not a sensitive parameter to performance for most typical cement applications.
Optimum sulfate determination practices vary widely.
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Sulfate demand factors in cementitious mixtures
Sulfate demand is low in neat paste / mortar mixtures at standard lab ambient temperatures
Under-sulfated cements work fine and appear normal Thus C563 may be an unrealistic procedure
Most chemical admixtures raise sulfate demand
By accelerating aluminate hydration and other mechanisms Some more than others, dosage effects also critical No useful sulfates contributed by admixtures
Class C fly ash, other aluminate-rich additives raise sulfate demand
Contain C3A (some C ash sources as much as 20 to 30%) No useful sulfates are generally contributed by SCM’s & additives
High temperatures raise sulfate demand Sulfate solubility decreases as temperature increases
Cement is usually the only source of soluble sulfate in the mix
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Sulfate demand and hot weather
A counter-intuitive trend:
Higher temperatures increase the solubility of most materials i.e. sugar in hot coffee
But gypsum solubility decreases with higher temperature Especially the most soluble
form (hemihydrate, or plaster)
Higher temps also increase aluminate hydration rates
from - Gypsum and Anhydrite in Portland Cement, 3rd edition, US Gypsum Company, 1988, p 37.
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Sustainability implications
Sustainability-related trends in concrete projects:
Blended cements and/or - Multiple SCM’s with higher
replacement rates More aggressive admixture
use may be needed
These influences contribute to greater variability of setting and early strength and potential for incompatibility.
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What happens when sulfates are inadequate?
Baseline mix - 20% ash, 5oz/cwt WR, 90°F Mild cases:
Increased slump loss and water demand
Admixtures are less effective
Set time delays Poor early
strengths
Severe cases:
No set for days or… flash set (!) No measurable
strength gain for several days
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What happens when sulfates are inadequate?
Baseline mix - 20% ash, 5oz/cwt WR, 90°F
“Threshold” zone is quite narrow!
For an “on the edge” mixture, even a slight change in mix temperature or in the properties of any one material can quickly cause extreme performance issues…
Thus, compatibility issues can come and go mid-project
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A simulated “on the edge” mix in mortar cubes
Testing performed to investigate cement role in a field issue Cements from 11 sources 25% Class C fly ash from project Type A/D water reducer from project @ 6 oz/cwt Mix and cure temps 90° F to approximate field temps
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Testing for incompatibility & its potential
Useful test methods:
Modified C109 mortar cubes & C191 Vicat set times Mini-slump paste mixtures Isothermal calorimetry Thermal profile testing
Testing plan should include:
Baseline cases with normal performance Increments of SCM’s & admixtures bracketing
envisioned project levels, significantly higher & lower Field temps & 1 or 2 levels higher Alternative SCM’s or admixtures Multiple samples of cement chosen so as to include
extremes of normal SO3 variability
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Normal vs. abnormal hydration behaviorSulfates-related abnormalities are clearly evident in thermal profiles: Normal behavior = traditional thermal profiles with normally timed peaks Abnormal behavior = misshapen profiles or non-traditional behavior,
indicating a mixture sulfate imbalance (incompatibility)
A: Normal hydration – robust silicate peak and smooth, rapid attenuationB: Essentially normal behavior but diminished peak, slower attenuation, significant retardation C: Marginal silicate hydration is interrupted by recurring aluminate activityD: Uncontrolled aluminate exotherm @ 7 hours, no silicate hydration until 20+ hoursE: Flash set from immediate, uncontrolled aluminate activity, no silicate hydration thru test period
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Flash set from uncontrolled aluminates
Flash set can occur when sulfates in solution are immediately depleted and aluminates hydrate uncontrolled (rare but occasionally reported).
Can happen with under-sulfated cements and high sulfate-demand mixtures.
Expanded scale, 1st hour
Indication of flash set from rapid aluminate hydration due to very early sulfate depletion
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Sulfate demand & SCM’s
At left, thermal profiles and 1-day strengths comparing 3 SCM’s (C ash, F ash, and slag cement) in otherwise identical mixtures, with incremental cement replacement rates. The Type A/D WR admix was selected because of its known high sulfate-demand tendencies.
A single sample of Type I/II cement was used, w/cm = 0.40, upper-limit dosage of admixture, 32ºC (90ºF) mix and cure temps.
C ash mixtures – incompatibility detected at higher replacement rates – symptoms at 20%-25%, true incompatibility beyond 25%.
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Thermal profiles of paste with parallel mortar cubes, high-sulfate demand mix with 10% to 35% C ash
10% ash
25% ash
35% ash
6 oz/cwt type A/D water reducer dose, 90°F mix and cure temps, a single Type I/II cement sample, Class C ash at 10%, 25%, and 35%
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A
B
C
D
Thermal profiles of paste with parallel mortar cubes, high-sulfate demand mix with different A/D WR’s
25% C ash, 90°F mix and cure temps, a single Type I/II cement sample, admix dosages at upper end of Type A recommended range
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9 oz/cwt
6 oz/cwt
Thermal profiles of paste with parallel mortar cubes, high-sulfate demand – admix dosage comparison
25% Class C fly ash replacement, 90°F mix and cure temps, a single Type I/II cement sample, Type A/D admixture used at 6 or 9 oz/cwt
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9 oz/cwt
6 oz/cwt
Flash set occurs at around 25 minutes –sudden aluminate excursion indicates sulfate depletion
Expanded scale, 1st hour
Thermal profiles of paste with parallel mortar cubes, high-sulfate demand – admix dosage comparison
25% Class C fly ash replacement, 90°F mix and cure temps, a single Type I/II cement sample, Type A/D admixture used at 6 or 9 oz/cwt
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Paste mixture with 50% Class C fly ash replacement, 74°F mix and cure temps, a single Type I/II cement sample, w/cm = 0.32, sulfate balance-friendly Type A/F (polycarboxylate) admixture used at 14 oz/cwt, non-chloride accelerator dosages 0-40 oz/cwt.
Incompatibility influences of a NCA: high-volume Class C fly ash mixture with HRWR
∆Te
mp
(Ts
am
p–
Tre
f), °
C
Hydration time, hours
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If the profile shape changes and lack of strength improvement are truly related to sulfate depletion, this could be confirmed with CaSO4 additions.
∆Te
mp
(Ts
am
p–
Tre
f), °
C
Hydration time, hours
Sulfate balance of this mix to be explored using CaSO4
additions (next slide).
Incompatibility influences of a NCA: high-volume Class C fly ash mixture with HRWR
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Incompatibility influences of NCA explored using incremental CaSO4 mixture additions
∆Te
mp
(Ts
am
p–
Tre
f), °
C
Hydration time, hours
30 oz/cwt NCA mixture (previous slides) repeated with incremental additions of Terra Alba gypsum (+0.33%, +0.67%, and +1.0% SO3).
Note that the additions restore normal profile shapes and improve 1-day strengths.
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∆Te
mp
(Ts
am
p–
Tre
f), °
C
Hydration time, hours
Investigated mix –no added sulfate
+ 0.38% SO3
+ 0.75% SO3
Evaluation of performance questions using repeated mixtures with incremental sulfate additions
A 90°F paste mixture with 25% Class C ash and upper-limit dosage of Type A/D admixture is repeated with sulfate additions to evaluate possible sulfate balance issues.
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Influence of initial mixture and cure temps on behavior of similar mixtures with wide range of sulfate demand
Two different mix / cure temp ranges: 70°F and 93°F
4 paste mixtures, same materials and proportions for each temp range series:
100% OPC, no WR, w’c = 0.45 25% C ash, no WR w/cm = 0.45 25% C ash, 4 oz/cwt WR, w/cm = 0.40 25% C ash, 6 oz/cwt WR, w/cm = 0.40
WR admix is a high sulfate-demand Type A/D with a recommended dosage range of 3-6 oz/cwt on total cementitious content.
Note that higher temps alone drive incompatible behavior in the mixtures with WR!
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Field Issue – 15% C ash, multiple admixtures, low 1-day strengths, summer temps – sulfate balance issue?90° F paste mixes, 4 oz/cwt admix dose, varying SO3 cement samples:
Cement source “A” is the project source to be evaluated – 5 samples obtained at different times vary slightly in SO3,within normal variability.
A sample of cement source “B”, which is known to be well balanced, is included for comparison.
Performance Screening of Concrete Materials and Proportions Using Thermal Testing
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Field Issue – in otherwise identical mixes, to check mix sensitivity to sulfate demand, WR dose was doubled.90° F paste mixes, 8 oz/cwt admix dose, varying SO3 cement samples:
In the higher sulfate-demand mix, incompatibility is evident for essentially all but the highest SO3level sample of “B”; control cement “A” still appears normal.
Conclusion: At lower SO3 levels, cement source “A” may be under-sulfated for use in aggressive mixes at higher temperatures.
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Evaluation of different cements for sulfate adequacy
7 different cement sources compared in neat paste mixtures
Paste with no SCM’s, no admixture, w/cm = 0.40, 90°F mix & cure temps
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Same cements in high sulfate-demand paste mixtures
Paste with 25% C ash, 6 oz/cwt Type A/D WR, w/cm = 0.40, 90°F mix & cure temps
Evaluation of different cements for sulfate adequacy
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Cement production – gypsum source evaluation: grinds at the same SO3 levels with different gyps, high sulfate-demand mixes
paste specimen compressive breaks @ 24 hrs, psi
Gyp “A”, 9 oz/cwt
Gyp “A”, 6 oz/cwt
Gyp “B”, 9 oz/cwt
Gyp “B”, 6 oz/cwt
90°F paste with 25% C ash + Type A/D WR(6 or 9 oz/cwt)
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Confirm sulfates influences with thermal profiles and/or strength testing (paste or mortar cubes) Incremental sulfate demand approach (overdose
admixtures, increase SAC %, higher mix temps) Incremental sulfate supply approach (different cement
samples at varied SO3, sulfate additions to mixtures)
Change one or more of the key influences: Replacement rate of Class C fly ash Admixture dosage or type Review / evaluate retardation strategy Cement SO3 level Mix temperatures
Re-evaluate in the lab under the most extreme field conditions envisioned
Conclusions and recommendations:Resolution process - compatibility issues in concrete
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Evaluate unfamiliar materials and the proposed mix(es) under all extremes of possible project temperatures
Compare against controls (materials from other projects) Check set time and main peak variability with temperature
Check sensitivities of proposed materials to incompatibility
Test at highest expected mix temp Include overdoses of admixtures and SCM’s Compare against known mixtures with familiar materials
Test regularly to gage materials variability
Test when materials sources are changed or a new mix design is first used
Troubleshoot unexplained trends in set time, slump loss, early strengths
Conclusions and recommendations:Thermal testing for concrete QC – when to test?
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References, suggested reading
Bauset, R., “Abnormally Delayed Setting of a Low-Heat Portland Cement with Calcium LignosulfonateAdmixtures,” 5th International Symposium on Cement Chemistry, Vol. IV, 1968, p 53-57.
Cost, V. T., “Incompatibility of Common Concrete Materials – Influential Factors, Effects, and Prevention,” National Concrete Bridge Conference 2006, National Concrete Bridge Council, Skokie, IL, 2006.
Cost, V. T., and Knight, G., “Use of Thermal Measurements to Detect Potential Incompatibilities of Common Concrete Materials,” Concrete Heat Development: Monitoring, Prediction, and Management, ACI SP-241-4, Atlanta, GA, April 2007, 39-58.
Cost, V. T., and Gardiner, A., “Practical Concrete Mixture Evaluation via Semi-Adiabatic Calorimetry,” 2009 Concrete Technology Forum – Focus on Performance Prediction, Cincinnati, OH, May 2009.
Cost, Tim, “Thermal Measurements of Hydrating Concrete Mixtures – A Useful Quality Control Tool for Concrete Producers,” NRMCA Publication 2PE004, National Ready Mixed Concrete Association, 900 Spring Street, Silver Spring, MD, August 2009.
Cost, V. T., “Concrete Sustainability versus Constructability – Closing the Gap,” 2011 International Concrete Sustainability Conference, Boston, MA, August, 2011.
Cost, Tim, “Optimization of Concrete Paving Mixtures for Sustainability and Performance,” accepted for the 10th
International Conference on Concrete Pavements, Quebec City, Quebec, July 8-12, 2012
Helmuth, R., Hills, L. M., Whiting, D. A., and Bhattacharja, S., Abnormal Concrete Performance in the Presence of Admixtures, Portland Cement Association No. RP333, Skokie, IL, 1995, p 1, 3, 8-9, 11-12, 14, 17-18.
Hills, L., and Tang, F., “Manufacturing Solutions for Concrete Performance,” IEEE-IAS/PCA Cement Industry Technical Conference, Chattanooga, TN, 2004, p1-6.
Khalil, S. M., and Ward, M. A., “Influence of SO3 and C3A on the Early Reaction Rates of Portland Cement in the Presence of Calcium lignosulfonate,” CeramicBulletin, Vol. 57, No. 12, 1978, p 1116-1122.
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References, suggested reading (continued)
Roberts, L. R., and Taylor, P. C., “Understanding Cement-SCM-Admixture Interaction Issues,” Concrete International, V. 29, No. 1, January 2007, pp. 33-41.
Sandberg, P., and Liberman, S., “Monitoring and Evaluation of Cement Hydration by Semi-Adiabatic Field Calorimetry,” Concrete Heat Development: Monitoring, Prediction, and Management, ACI SP-241-2, Atlanta, GA, April 2007, pp. 13-24.
Sandberg, P., and Roberts, L. R., “Studies of Cement-Admixture Interactions Related to Aluminate Hydration Control by Isothermal Calorimetry, Seventh CANMET/ACI International Conference on Superplasticizers and Other Chemical Admixtures in Concrete, Berlin, 2003, 12 pp.
Sandberg, P. J., and Roberts, L. R., “Cement-Admixture Interactions Related to Aluminate Control,” Journal of ASTM International, V. 2, No. 6, June 2005, pp. 219-232.
Sullivan, G., Cost, T., and Howard, I., “Measurement of Cementitiously Stabilized Soil Slurry Thermal Profiles,” accepted for Geo Congress 2012 – State of the Art and Practice in Geotechnical Engineering, American Society of Civil Engineers, Oakland, CA, March 25-29, 2012.
Tuthill, L., Adams, R., Bailey, S., and Smith, R., “A Case of Abnormally Slow Hardening Concrete for Tunnel Lining,” Proceedings, American Concrete Institute,Vol. 57, March, 1961, p 1091-1109.
Wang, H., Qi, C., Farzam, H., and Turici, J., “Interaction of Materials Used in Concrete,” Concrete International, V. 28, No. 4, April 2006, pp.47-52.
Wang, K., Ge, Z., Grove, J., Ruiz, M., Rasmussen, R., and Ferragut, T., Developing a Simple and Rapid Test for Monitoring the Heat Evolution of Concrete Mixtures for Both Laboratory and Field Applications, National Concrete Pavement Technology Center, Ames, IA, January 2007, 58 pp.
Tim Cost, P.E., F.ACIHolcim (US) Inc.tim.cost@holcim.com
Performance Screening of Concrete Materials and Proportions Using Thermal Testing
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