Magnesium silicate hydrate (M-S-H) gel is the main product of MgO-based alkali-activated system (MAAS). The molecular structure and phase changes of M-S-H gel at different temperatures were characterised. The results showed that the initial MgO:SiO2 affected the Mg:Si ratio and the binding water content of M-S-H gel. With the decrease of Mg:Si ratio, the proportion of structural water in the gel decreases. Compared with structured water, the change of free water can more accurately characterise the content of M-S-H gel in the system. Below 600°C, the molecular structure and phase composition are relatively stable. When the temperature reached 1000°C, M-S-H gel transfers from amorphous phase to crystallized phase. The study characterised the evolution of MASS under different heat treatment conditions.
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