Page 443 - Handbook of Thermal Analysis of Construction Materials

418 Chapter 10 - Non-Portland Rapid Setting Cements

developed at 25°C (paste, w/c = 0.50) is also more than that registered for
the compact at 72°C. The total amounts of heat evolved for compacts
hydrated at 72°C (first 30 min), 25°C (2 days), and 25°C (w/s = 0.50, 1 day)
are, respectively, 56.0, 39.0, and 72.6 cal/g. It is apparent that at 80°C a
direct bond formation of C AH may occur on the surface of CA even within
3
6
30 minutes due to rapid conversion of the hexagonal phase. Strength
development occurring at 80°C in the first few days does not change during
further hydration over several months. This is contrary to general opinion
and is contingent upon a low initial water/solids ratio.

Figure 14. Conduction calorimetric curves of CA hydrated at 25°C or 72°C.

Strength of high alumina cement concrete has been estimated from
exponential expressions relating strength and porosity, e.g., S = S e -bp
o
where S is the strength, p is the porosity and S and b are constants. Talaber,
o
et al., have shown that thermal analysis (DTG, TG, and DTA) can be used
as input for calculation of a porosity change due to both transformation
[9]
(conversion to C AH ) and carbonation. The thermal method involves
3 6
analysis of both the original HAC concrete and the same concrete that has
been autoclaved. Hydrothermal treatment completes the reactions of the