Alternative method of determination of heat of hydration by isothermal conduction calorimetry

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Alternative method of determination of heat of hydration by isothermal conduction calorimetry

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Alternative Method of Determination of

Heat of Hydration by Isothermal

Conduction Calorimetry (Final Version)

Round Robin Results and

Recommendations

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Background

 ASTM has introduced isothermal conduction

calorimetry (ICC) as standard C1702 to provide an alternative method of determining heat of hydration of cements.

 The method is simpler, safer and faster than A3004-B7 (ASTM C186).

 In principle, it is equally or more accurate.

 No round-robin testing of the method in the standard has been done.

 Work reported here was done to test the method and determine if it should be incorporated in CSA A3004.

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Isothermal Conduction Calorimetry

 Calorimeter holds samples at constant temperature and measures heat flow during the hydration reaction.

 Difference in heat flow between sample and inert control is reported by instrument.

 Inert control must have same heat capacity as sample

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Types of Sample Mixing and Their

Implications



ASTM allows external or internal mixing of the

samples to support legacy instruments.

• Modern instruments either allow both types of mixing or are internal mixing only.



External mixing can create transient signals

when the sample is placed in the instrument.



Temperature differences between the sample

and instrument can also create transients



ASTM uses secondary tests to measure the

heat of mixing and compensate for the effects

of external mixing

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Participants



11 Participants in total, including:

• Universities in Canada, U.S. and Germany

• Cement manufacturers

• Equipment suppliers



Additional participants lost due to economic

downturn



Three different instruments used, but almost

all results are from TA TamAir

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Round Robin Scope



Four ICC heat of hydration tests on each of

four cements (3 GU {similar to US Type I}, 1

ternary blend) at 0.5 w/cm ratio.



Heat of mixing measured 4 times using

calcium carbonate as the solid, rather than

cement.



Temperature rise as the cement was

Heat of Mixing was not included in the

external mixing calculation as it was already

removed by the use of the Temperature Rise

Heat

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Overview of Results



Some participants supplied data for both the

internal and external mixing methods and are

analyzed separately



IRC did a second set of isothermal

calorimetry runs 6 months after the original

ones, which were also analyzed separately



Not all requested data was returned:

• Best participation for calorimetry measurements, but not all participants did four measurements of each cement

environment, heat due to skin contact):

• 1o C ≈ 3 J/g heat difference

Cement D (Ternary Blend)

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Summary of Results

 Measuring heat of hydration by isothermal conduction calorimetry produces results that are similar to those produced by A3004-B7 (C186).

• It will take some time before a direct comparison is possible. CCRL is just beginning to ask participants to run isothermal conduction calorimetry.

 If either external or internal mixing is used, lab to lab variations are better than those from CCRL C186 round robin (similar standard deviations, but fewer outliers)

 If only internal mixing is used, lab to lab variations appear to be much better than those from C186

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Additional Comments



ASTM C802 for inter-laboratory test programs

suggests that external and internal mixing

results need to be considered separately

• Insufficient internal mixing data for full precision statement, but preliminary values promising

• Variation in external mixing results higher than desirable



External mixing by hand may produce strong

operator effects



All round robin ICC use either internal mixing

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Recommendations

1. Implement an alternative method of measuring heat of hydration based on isothermal conduction

calorimetry

• Results as good or better than A3004-B7

• Safer, simpler, easier test

• Compatibility with ASTM C1702 2. Allow only internal mixing

• Significantly better reproduceability, simpler protocol

• Minor investment in additional equipment required 3. A standard listing of material heat capacities is

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