Formation and Evolution of the Hydrotalcite-Like Phase During Ageing of Dolomite-Cement Mortars under Various Conditions

This work considers the reactions of dolomite powder mixed with Portland cement during ageing under accelerating conditions (60 degrees C, water or alkaline medium). The phase composition and microstructure of cement-dolomite mortars were studied using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy with X-ray microanalysis (SEM-EDS). The results showed that the alkalinity of the medium increased the dolomite reaction degree but did not affect the reaction products' composition. The formation of the hydrotalcite-like phase with the general formula Mg4Al2(CO3)(1-x)(OH)(12+2x)center dot nH(2)O 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.