Controlled rate thermal treatment of reactive powder concretes

Controlled rate thermal analysis (CRTA) was applied to the thermal curing of a reactive powder concrete. Heating was adjusted to keep the rate of gas evolution constant and in dynamic equilibrium at a pressure of 3 Pa. In this way, all internal gradients were kept constant and homogeneous samples were produced. Six different solid-state transformations were detected below 900 degrees C, four of them occurring below 250 degrees C. Under these conditions, no xonotlite or other crystalline silicate hydrates were detected even up to temperatures of 250 degrees C, contrary to what is observed when heating is carried out in regular, nonkinetically controlled conditions, which generate local hydrothermal water vapor pressures inside of the samples. Our results show that controlled rate thermal treatment in dynamic equilibrium with fixed water vapor pressures is a promising method for the accurate control of hydrate crystallization. (C) 1997 Elsevier Science Ltd.