Page 136 - Handbook of Thermal Analysis of Construction Materials

Section 8.0 - CaO-SiO -Al O -H O and Related Systems 119
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Figure 34. DTA curves of 1.0 and 1.33 C/S solids before and after extraction of free lime
with acetoacetic ester.

Autoclaving is employed to produce articles of high early strength
and reduced shrinkage. The strength attained in 24 hrs may be equivalent
to that obtained at 28 days of normal curing. Many types of materials can
be mixed with lime or cement and processed in high-pressure steam to
produce concrete products of good strength. The materials that have been
used are silica flour, pumice, scoria, tuff, cinder, calcined clay, fly ash, and
blast furnace slag.
Several investigators have investigated the effect of autoclave
curing on the products formed with mixtures of cement/lime , silica, and
water. In an investigation, the effect of quartz (of different surface areas)
added in different amounts to cements was investigated by DTA/TG
techniques. [65] The main phases identified included CH (endothermal peak
at 453°C), α-C SH (endothermal peak at 523°C), and C-S-H (a broad
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endothermal effect in the range of 100–700°C). An exothermal effect at
843–846°C indicated the crystallization of β-wollastonite, β-CS due to
aluminous tobermorite or C-S-H of C/S ratio 0.8 to 1.0. The intensity of