Effect of slag composition on hydration characteristics of weak alkaline activator used for alkali-activated cement

Alkali-activated cement (AAC) systems prepared with weak alkaline activator (WAA) shows low shrinkage and good durability. In this study, AACs were prepared using three types of ground granulated blast-furnace slag (GGBFS) and WAA. The setting times, mechanical properties and hydration heat evolution of the three AAC systems were studied. The hydration products were analysed by X-ray diffraction, Fourier transform infrared spectroscopy and 27Al and 29Si magic-angle rotating solid-state nuclear magnetic resonance. The results showed that the fineness of the GGBFS mainly affected the early properties of the AAC systems. The chemical properties of the GGBFS affected the early and late compressive strengths, but the influence on the late strength was more obvious. The hydration heat evolution of the AAC systems activated with WAA belonged to type II, influenced by a combination of both physical and chemical properties. The cumulative hydration heat was mainly affected by the chemical properties of the GGBFS. There was no difference in the types of hydration products of in the three AAC systems activated with WAA, mainly C-(A)-S-H gel, calcite, hydrotalcite and more crystal phases. The higher the alkali reactivity index and the glass phase content, the higher the reaction degree, the higher polymerisation degree of reaction products and the smaller the mean aluminosilicate chain length.