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

Abstract

In this work, the effect of curing temperature (+5ºC, +20ºC, +40ºC) and thermal treatment temperature (800ºC and 1000ºC) on the microstructure and phase composition of calcium aluminate cement (CAC, Al2O3>70%) binder with microsilica (MS) additive (5%), when W/(CAC+SiO2)=1 was investigated. The methods of thermal analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used. It has been found that after 3 days of hydration were formed such crystalline hydration products: at 5ºC only CAH10 hydrate is formed in the CAC binder, at the temperature of 20ºC – CAH10, C2AH8 and AH3 hydrates, at the temperature of 40ºC – C3AH6 and AH3 hydrates. In the cement binder heated at 800ºC, 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) changing slightly, when the process of heating is over. SEM tests revealed significant changes in CAC binder microstructure caused by the added 5% of the microsilica additive. Considerable changes in cement binder microstructure observed, after a heating at a temperature of 1000ºC 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 intensity of the diffraction maximum of mineral C12A7 are increasing, while those of minerals – CA and CA2 are decreasing.