Influence of Alkali on Early Age Hydration Process and Microstructure of Low Heat Cement

Abstract:

The alkali content(by mass, the same below) of low heat cement was adjusted to 080%, 120% and 160% by adding Na2SO4. Isothermal calorimetry test was used to investigate the influence of alkali on early age hydration process of low heat cement. The influence of alkali on the hydration stage of low heat cement was analyzed by the hydration kinetic model. The structure of silicon phase and migration form of the aluminum phase in low heat cement hydration products were observed by 29Si and 27Al magic angle spinning nuclear magnetic resonance. The results show that alkali can promote hydration process of low heat cement, but the hydration process does not increase with the increment of alkali content in certain content. The promotion effect of alkali on low heat cement is mainly due to increase of nucleation and crystal growth rate of low heat cement and the stage of interaction at phase boundaries is prolonged. Besides, alkali is more likely to increase aluminum substitution ratio in calcium silicate hydrate(C S H) chain and the degree of polymerization of C S H. However, with the increment of alkali content, aluminum tends to shift to ettringite(AFt) rather than to C S H chain.