The effect of temperature on the formation of the hydrated calcium aluminate cement structure

Abstract

The effect of temperature on the formation of the structure and phase composition of the Gorkal 70 grade calcium aluminate cement (CAC) during its hydration (W/C=1) at the temperature of +5 ºC, +20 ºC and +40 ºC is investigated. The scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray microanalysis were used in investigations. It has been found that after 3 days of hydration were formed such crystalline hydration products: at 5 ºC only CAH10 is formed in the CAC stone, at the temperature of 20 ºC - CAH10 and C2AH8, at the temperature of 40 ºC - the hydrates C3AH6 and AH3. In the cement stone heated at 800 ºC, the hydrates are decomposing, and the minerals CA, CA2 and C12A7 are being formed, though the contours of the hydrate crystals’ forms (prisms, plates, irregular cubes) actually remain unchanged, when the process of heating is over. Considerable changes in cement stone microstructure observed, after a heating at a temperature of 100 ºC - there had been significant increase in the quantity of fine particles and pores. The results of XRD analysis showed that, at this temperature the reactions in solid state materials proceed and as a result the amounts of mineral C12A7 are decreasing, while those of minerals CA and CA2 are increasing.