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Practical Semi-Adiabatic Calorimetry

for Concrete Mixture Evaluation

Tim Cost, PESenior Technical Service Engineer

TTCC/NCC Conference

September 23, 2008


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2CostHolcim (US) Inc.

Definitions

calorimetry calorimetry (kl'-rm'-tr) n.

Measurement of the amount of heat evolved orabsorbed in a chemical reaction, change of state,or formation of a solution.

adiabatic adiabatic (-d--ba-tik), adj.

Occurring without loss or gain of heat.

For our purposes:

semi-adiabatic calorimetry, n.

Indication of the heat evolved from a cementitiousmixture hydrating in an environment or container

having some thermal insulation properties,according to a record of the mixtures changingtemperatures over time.


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Isothermal versus semi-adiabatic calorimetry

IsoCal results at 73 F

ConcreteIsothermal

Semi-adiabatic

Source: W. R. Grace


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Applications of semi-adiabatic calorimetry

Comparing set time effects & hydration efficiency

Different admixtures, SCMs or cements

Sensitivity of admix dose, SCM replacement rate

Effects of mix temperature

Troubleshooting concrete field problems

Incompatibility (sulfate balance) influences

Set time & other early hydration issues

Cement production QC optimizing sulfates content Coming soon alternative time of set (C 403) method


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CostHolcim (US) Inc.

Measuring & recording temperature changes


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Test method variables and considerations

Mortar or concrete versus paste

Lab vs. field

Concrete & mortar better represent

field set times

Paste is preferred for comparingsome hydration effects

Paste mixing is faster

Choice should also consider samplemass effects


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90 degrees 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

Mortar vs. paste



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Mortar vs. paste

73 deg F mixtures:

A) no ash or admix,w/c = 0.54

B) 25% C ash + 3

oz/cwt type A WR,w/cm = 0.51

C) 25% F ash + 4oz/cwt MR WR,

w/cm = 0.51

A

A

B

B

C

C

paste3x6 cyl

mortar3x6 cyl


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Sample mass & insulation

Affect magnitude of peaks and possibly timing Affect rate of heat decay after exotherm peaks

Insulation choices should depend on

Importance of ambient temp effects Magnitude of peaks expected

Test objectives

Main peak shapes can be influenced by sample

mass and/or insulation value of container


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Sample mass comparison, paste (minimal insulation)Mixtures with 25% Class C ash and water reducer at 73 degrees F

Cylindrical samples ranging from 135cc (2 x 2.6) to 1070cc (4 x 5.2)



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Insulation effects, paste

Paste mixtures with 25% Class C ash and water reducer at

73 degrees F in 3x6 cylinders with varying levels of insulation


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Set time evaluation with SAC

Methods under development for a C 403 alternative:

Highly insulated samples of concrete or mortar Mathematical procedures for determining set time from data

- Derivatives- Fractions- 4th order fit

Relative time-of-set comparisons can be made using a

simple visual indication of the point half-way up the

C3S heat rise (50% of peak).


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Comparison of C 403 concrete initial set (lab mixes) andpaste thermal set (50% of peak) indications, SAC

100-0-0 75-0-25C 75-0-25F 75-0-25C 75-0-25F 50-35-15CNo admix WR A WR A WR B WR B WR B

Lab concrete vs. semi-adiabatic paste calorimetry: all mixtures @ 73 degrees F, with and withoutnormal doses of water reducing admix and indicated cementitious blends of cement-slag-ash(C/F)


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Relative set times

Two admixtures

compared fortemperature &dosage effects

Semi-adiabatic pastecalorimetry: 0.40 w/c

cement-only mixtures@ 73 or 50 deg F,with 3 or 6 oz/cwt of2 different candidatemid-range admixtures

73 F

50 F


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4x8 concrete cylinders - Adiacal

517 pcy concrete mixtures at constant slump, with or without 25% C ash,3 oz/cwt type A/B/D WR, 2 different type I cement samples (same source)

A no admix or ashA ash + WR

B ash + WR


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4x8 concrete cylinders - Adiacal

With air- mortar

No air mortar

With air concrete

No air - concrete

Mortar vs. concrete 470 pcy concrete at constant slump, with10% C ash and 3.2 oz/cwt type A/B/D WR, with or without AE.


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Developing ASTM set time method

Current draft of

C09.23 thermal

set time documentspecifies highly

insulated 6 to 7-

diameter samples

of concrete

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25

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0 200 400 600 800 1000 1200 1400 1600

Time from contact of cement and water (minutes)

Temperature(C)


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Responsible for certain concrete performance issues

Cement SO3 content is spec limited and typically optimizedusing procedures that do not account for other influences.

Other materials and conditions affect demand for sulfates:

Admixtures Some SCMs, especially Class C fly ash

Hot weather

If early C3A hydration becomes uncontrolled due to the

depletion of soluble sulfates, erratic behavior results: Unpredictable (sometimes extreme) set effects and / or slump loss

Interrupted silicate hydration & strength gain

Sulfate balance influences and issues

Incompatibility of concrete materials


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Mild influences - typically with higher temps:

Some increase in slump loss Slight extending of set time

Unexpected responses to admixtures

Nearer the incompatibility threshold:

Sluggish strength gain

More severe slump loss, extended set

True incompatibility behavior:

No normal set, 24 to 48 hours or longer, or Flash set (extreme cases)

Interrupted strength gain for several days

Sulfate balance influences and issues

Related concrete behavior


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Example: sulfate balance effects of changes intemperature, fly ash %, or water reducer dosage

baseline mix has 20% ash with 5 oz/cwt water reducer at 90F

normalset

marginal slumploss, longer set

thresholdzone

extremelydelayed set flash set

increasingly delayed strength gain

normal strength

gain

MIX TEMP, F

FLY ASH, %

WR DOSE, oz/cwt

baseline mix properties

85 90 95 100 105

15 20 25 30 35

4 5 6 7 8


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compressivestrength,psi


T(Tsample

Tambient),

F

4.1-35%

3.3-10%

3.7-25%

3.7-35%

3.3-25%

3.3-35%

Hydration time, hours

T(Tsample

Tambient),

F

4.1-35%

3.3-10%

3.7-25%

3.7-35%

3.3-25%

3.3-35%

Hydration time, hours

Semi-adiabatic paste calorimetry & mortar cubes: effects of fly ash content, mixtures

with 6 oz/cwt type A/B/D water reducer, 90 F initial temp, cement SO3 = 3.3 or 3.7%


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T(Tsample

Tambient),

F

hydration time, hours

LwrA, 6oz

CSwr, 6oz

LwrB, 6oz

LwrC, 8oz

Semi-adiabatic paste calorimetry & mortar cubes: effects of dif ferent admixtures

compared in mixtures with 25% fly ash, 90 F initial temp, cement SO3 = 3.3%


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Comparison of effectsof different gypsum

sources on cementsmade from twodifferent clinkers

Clinker A + Gyp A + 9 oz

Clinker A + Gyp B + 9 oz

Clinker B + Gyp A + 9 oz

Clinker B + Gyp B + 9 oz

Clinker A + Gyp A

Clinker A + Gyp B

Clinker B + Gyp B

Clinker B + Gyp A

Clinker C + blend

Cement plant QC

testing effects ofdifferent gypsum

sources, 90 degree

F mixtures with 25%

Class C ash + 6

oz/cwt admix (upper)or 9 oz/cwt (lower)

Clinker A + Gyp A + 6 oz

Clinker A + Gyp B + 6 oz

Clinker C + blend + 6 oz

Clinker B + Gyp A + 6 oz

Clinker B + Gyp B + 6 oz


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Cement sulfates evaluation: semi-adiabatic paste calorimetry, 0.40 w/cm mixtures

@ 95 deg F, 25% Class C ash, 4 oz/cwt WR, cement samples @ various SO3 %

paste specimen compressive breaks @ 18 hrs, psi

A1, SO3= 3.08

A5, SO3= 3.06

B, (control)

optimized SO3

A3, SO3= 3.21

A4, SO3= 3.28

A2, SO3= 3.16

A1, SO3 = 3.08

A2, SO3 = 3.16

A3, SO3 = 3.21

A4, SO3 = 3.28

A5, SO3 = 3.06

B, SO3 = 3.5 (opt.)

Cement source Ais being evaluated.


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Cement sulfates evaluation: admixture sensitivity comparison, same mixtures

with admix dosage doubled, to 8 oz/cwt WR

paste specimen compressive breaks @ 18 hrs, psi

A1, SO3= 3.08

A5, SO3= 3.06

A3, SO3= 3.21

A4, SO3= 3.28

A2, SO3= 3.16

A1, SO3 = 3.08

A2, SO3 = 3.16

A3, SO3 = 3.21A4, SO3 = 3.28

A5, SO3 = 3.06

B, SO3 = 3.5 (opt.)

B, (control)

optimized SO3

Conclusion: At thelower SO3 levels,cement source A

may be under-sulfated for use inaggressive mixes athigher temperatures.


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ASTM methods - hydration kinetics using calorimetry

Standard practice for

Measuring hydration kinetics of hydraulic cementitious mixtures using

isothermal calorimetry

1.Scope1.1This practice describes the apparatus and procedure for measuring relative differences in

hydration kinetics of hydraulic cementitious mixtures, either in paste or mortar (Note 1),including those containing admixtures, various supplementary cementitious materials (SCM),

and other fine materials, by measuring the thermal power using an isothermal calorimeter.

NOTE 1- Paste specimens are often preferred for mechanistic research when details ofindividual reaction peaks are important or for particular calorimetry configurations. Mortarspecimens may give results that have better correlation with concrete setting and early strength

development and are often preferred to evaluate different mixture proportions for concrete. Bothpaste and mortar studies have been found to be effective in evaluating concrete field problems

due to incompatibility of materials used in concrete mixtures.


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Hotel room calorimetry


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Initial temp rise, all mixes (1:25 into testing)


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+/- 16 hours into testing


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+/- 16 hours into testing


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Graph of data using Report Generator


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Questions?

Tim Cost, PESenior Technical Service Engineer

[email protected]

Practical SAC for Concrete Mixture Evaluation

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