Page 432 - Handbook of Thermal Analysis of Construction Materials

408 Chapter 10 - Non-Portland Rapid Setting Cements

Addition of metakaolinite or zeolites to CAC systems can favor the
[2]
formation of strätlingite (C ASH ). This phase has a DTA peak in the
2
8
temperature range 201–203°C. Metakaolinite-calcium hydroxide
mixtures (1:1) prepared at a water:solid = 0.75 and hydrated at 40°C
produce a significant amount of C ASH and C AH , and large quantities
– 2 8 4 13
of C ACH and C AH (detected by XRD).
4 11 3 6
Figure 4 is a DTA thermogram of the hydrated mixture indicating
a large peak at 120°C and a sharp peak at 192°C. The low temperature peak
is attributed to alumina gel and C-S-H. The higher temperature peak
represents all four aluminate phases referred to previously. This under-
scores the necessity (in this case) for a complementary technique such as
XRD to separate out and identify the individual aluminate phases.

Figure 4. DTA and XRD data obtained from the metakaolin-calcium hydroxide mixture
hydrated at 40°C. [1]

The presence of AH can be detected by DTA showing a strong
3
endothermic peak at about 270 to 300°C and (when large amounts form) an
additional endothermal peak at temperatures up to 240°C.