Page 348 - Handbook of Thermal Analysis of Construction Materials
P. 348
Section 6.0 - Metakaolinite 325
The addition of MK influences the hydration of cement signifi-
cantly. The DTA curves of cement pastes treated with various amounts of
MK are presented in Fig. 26. [63] The first peak at 135°C is due mainly to the
dehydration of C-S-H (I). The endothermal effect at about 175°C is caused
by the decomposition of C AH and that at 480°C is due to the decompo-
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sition of CH. Two other endotherms at 740° and 765°C are ascribed to the
decomposition of the amorphous and crystalline forms of calcium carbon-
ate respectively. The peak effects of C-S-H (I) and C AH increase as the
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amount of MK increases up to a 30% addition signifying an acceleration
effect. The decrease in the peak area of CH is attributed to the reaction
between MK and CH liberated by the hydration of the cement.
Figure 26. Differential thermal curves of cement pastes containing different amounts of
MK.
