Ceramics-Silikáty 37, (2) 76 - 78 (1993)

Hydration of the paste of powderec C₃A^*) in liquid water was studied by the method of differential hydrothermal analysis over the temperature range of 0-350 °C. The process takes place in two stages. During the first, at temperatures of up to 40 °C, a continuous layer of C₃AH₁₃⁻₁₉ is formed on the surface of C₃A grains, and a layer of the more stable C₃AH₆ at up to 80 °C. At 100 °C, the rate of the reactions falls virtually to zero as a result of slow water diffusion through the layer of the product The second stage starts at 180 °C, producing non-crystalline calcium hydroaluminate with the approximate composition C₁₂A₇H_x, and the process proceeds up to 300 °C until the C₃A has been spent. The share of hydroaluminates formed during the first stage increases with increasing specific surface area of the initial C₃A. The hexagonal aluminates are converted at 130 °C to cubic C₃AH₆ which is then decomposed to C₄A₃H₃ and CH on attaining the temperature of 250 °C.