Civil Engineering Reference
In-Depth Information
polymer formation which is responsible for strength development. A
shoulder also appears corresponding to a zeolite crystallization process.
[67]
In DTA, an endothermal peak appearing at 165-175°C is attributed to the
process of dehydroxylation of the amorphous and crystalline zeolite.
[68]
At ambient temperatures, MK is known to react with Ca, Na and K
hydroxides, and hydrated cement. Attempts have been made to increase the
rate of strength development by autoclaving mixtures of cement-quartz or
lime-quartz.
[69][70]
DTA of the system cement-quartz treated with MK are
shown in Fig. 27.
[71]
Aluminum substituted C-S-H is identified by a peak at
865-880°C. The presence of hydrogarnet is indicated by a small exotherm
at 940°C. Unreacted quartz can be recognized by the endotherm at 573°C.
The gradual decrease of the endothermal effect of C-S-H at 170°C and also
that at 865-880°C indicates formation of decreased amounts of C-S-H and
that more aluminum is substituted in the C-S-H phase. According to the
work of Klimesch and Ray,
[70]
a better delineation of the thermal peaks is
possible in the autoclaved systems using the second derivatives of thermal
curves.
Figure 27.
Thermograms of cement-quartz (50:50) mixture autoclaved with different
amounts of MK.
