Formation and evolution of the hydrotalcite-like phase during ageing of dolomite-cement mortars under various conditions

Abstract

In this work, the reactions of dolomite powder in the mixture with Portland cement during ageing under accelerating conditions (60°C, water or alkaline medium) are considered. The phase composition and microstructure of cement-dolomite mortars were studied by X-ray diffraction, thermal analysis, and scanning electron microscopy with X-ray microanalysis. The results showed that the alkalinity of the medium increased the dolomite reaction rate but did not effect on the composition of the reaction products. The formation of the hydrotalcite-like phase with the general formula Mg₄Al₂(CO₃)_1-x(OH)_12+2x·nH₂O proved to be the predominant route of dolomite consumption in the presence of available aluminium in the hardened cement paste. Then, after three months of ageing, an interlayer anions replacement became noticeable: carbonate anions in the structure of hydrotalcite are gradually replaced by hydroxide ones.