Properties, mineralogy and microstructure evolution of 4-year calcium silicate slag-based alkali-activated materials

Alkali-activated materials (AAMs) are considered promising alternatives to ordinary Portland cement (OPC). The long-term stability and safety of AAMs are not fully acknowledged due to the lack of sufficient studies. The AAMs were prepared with calcium silicate slag (CSS), ground granulated blast furnace slag, fly ash and liquid sodium silicate in this study. Then, the evolution of mineralogy, microstructure and mechanical properties of CSS-based AAMs cured in ambient air were investigated on a time scale of 4 years. The results showed that the continuous alkali-activation and gradual carbonation both occurred during the 4-year curing in ambient air. Despite this, the main products of 4-year CSS-based AAMs were still C(N)-(A)-S-H gels. The gel products derived from the continuous alkali-activation filled the pores and resulted in decreasing porosity. Consequently, the compressive strength of CSS-based AAMs progressively increased from 55.0 MPa at 28 days to 100.0 MPa at 4 years due to the increasing compactness of the matrix.