ASR expansion of alkali-activated cement glass aggregate mortars

Abstract

Previous studies showed using calcium aluminate cement (CAC) can effectively mitigate the alkali-silica reaction (ASR) expansion of alkali-activated cement (AAC) mortars incorporating glass cullet (GC) as fine aggregates but the mechanism was not clear. This study presents a systematic study on exploring the underlying mechanism to fill in the knowledge gap and to ascertain the safe use of GC in AAC to maximize the possibility of recycling of waste glass in construction materials. The results showed that the ASR expansion of alkali-activated glass mortars was more than 1000 με after 1 day of alkaline immersion when using glass cullet as fine aggregates. The incorporation of CAC could decrease the expansion to less than 1000 με even after 14 days of alkaline immersion. The ASR expansion decreased with the increase of CAC content up to 20%. That was due to several reasons. Firstly, aluminum (Al) in CAC was incorporated in the AAC matrix with tetrahedral and octahedral units. The tetrahedral unit increased with the increase of CAC content, which required more Na ions to balance the excessive charge. Therefore, the alkalinity of the pore solution decreased and the ASR expansion decreased consequently. Besides, more AAC gel was formed due to the CAC incorporation, which decreased the alkalinity of the pore solution as well. But further increase the CAC content (25%) increased the ASR expansion, which might be due to the formation of zeolite that decreased the strength of AAC mortars.