Alkali-silica reactivity of lightweight aggregates in alkali-activated slag cement and ordinary Portland cement systems

For alkali-activated slag cement (AAC), an environmentally-friendly material, high-alkalinity activators are normally utilized for activation, which can lead to possible concrete degradation owing to alkali-silica reaction (ASR) when alkali-active aggregates were used. This study explored the effectiveness of lightweight aggregates in mitigating ASR behaviors of the AAC system. Alkali-reactive expanded perlite and non-alkali-reactive expanded shale were used as lightweight aggregates to compare ASR behaviors in ordinary Portland cement (OPC) and AAC systems. The formation of ASR gel in the expanded perlite was expansive, whereas the higher Ca/Si ratio calcium-aluminate-silicate-hydrate (C-A-S-H) in the non-alkali-reactive expanded shale did not cause expansion. In contrast with the OPC system, the larger amount of lower Ca/Si ratio ASR gel caused more deleterious ASR expansion and cracks in the AAC system. Furthermore, replacing expanded perlite with expanded shale effectively mitigated the ASR expansion. Discussion on the ASR mitigation mechanism of lightweight aggregates was provided for predicting the influence on the concrete.