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 CAH 10 is formed in the CAC stone, at the

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... emperature of 20 ºC -CAH 10 and C 2 AH 8 , at the temperature of 40 ºCthe hydrates C 3 AH 6 and AH 3 . In the cement stone heated at 800 ºC, the hydrates are decomposing, and the minerals CA, CA 2 and C 12 A 7 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 ºCthere 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 C 12 A 7 are decreasing, while those of minerals CA and CA 2 are increasing.