Mechanisms on the inhibition of alkali-silica reaction in supersulfated cement

The supersulfated cementitious system gains increasing popularity for lowering carbon emissions of the construction industry. However, the alkali-silica reaction (ASR) behavior of this sulfate-rich cement is still unclear. This study first reports the characteristics and suppressing mechanisms of ASR in supersulfated cement (SSC). The results show that nearly no ASR-induced expansion is found in the SSC even if 100% glass aggregates are used, while the expansion ratio of the traditional OPC is twenty times higher than the SSC. In the SSC, the further hydration of unreacted slag during the ASR test refines the pore size and enhances the compressive strength of the matrix. Meanwhile, the consumption of the alkali ions in the pore solution during the formation of N-A-S-H gel reduces the concentration of the alkali ions and the contact possibility with the aggregates. The high bulk electrical resistance of the SSC can mitigate the diffusion of alkali ions from the external solution to the mortar. Moreover, the higher Al/Si ratio of C-A-S-H in the SSC than C–S–H in the OPC system results in a higher adsorption capacity of Na⁺ due to the more negatively charged surface, reducing the concentration of alkali ions in the pore solution. Furthermore, the high concentration of SO₄²⁻ in the pore solution of SSC can inhibit the diffusion of OH⁻. As a result, the low-carbon SSC system would be a promising cementitious material to mitigate the ASR risk.