Effects of nano-SiO₂ and glass powder on mitigating alkali-silica reaction of cement glass mortars

Swelling caused by alkali-silica reaction (ASR) in concrete is a deleterious behavior due to reactions between alkaline pore solution and amorphous or metastable forms of silica in aggregates. Generally, mitigation by using pozzolanic materials is commonly adopted. This study compared the effectiveness of a highly-reactive nano-SiO₂ (NS) and a slowly-reactive waste glass powder (WGP) on mitigating ASR of cement mortars prepared with crushed glass cullet as aggregates. The experimental results showed that incorporating 2% NS or 10% WGP or a hybrid of the two in the mortar can decrease the ASR expansion. Using WGP resulted in larger reduction in the ASR expansion than using NS. Meanwhile, there was an improvement of strength from 7 d to 28 d for the mortar prepared with WGP. The composition of reaction products containing the ASR gel formed in a simulated ASR condition and the macro-/micro-structure of the tested mortars were further analyzed. It was found that the reaction products formed with high ratios of Na/Si and Ca/Si were favorable in mitigating the ASR expansion. For the specimen prepared with WGP, the increase in the ratio of Ca/Si would increase the stiffness of the ASR gel, and a higher Na/Si ratio would help reduce the osmotic pressure. The findings from this study would be useful for the selection of pozzolans to mitigate the ASR effect when using crushed glass cullet as aggregates in cement mortars.