Mechanisms underlying the mitigation of alkali-silica reaction by surface passivation in lightweight foam glass concrete

Alkali-silica reaction (ASR), a major durability concern of lightweight foam glass concrete, can be properly mitigated by the surface passivation on the aggregate, but the underlying mechanism remains unclear. In this work, surface passivation was applied to the foam glass aggregate using lithium hydroxide, and a systematic investigation was performed to reveal the mitigation mechanism of surface passivation. The results showed that a passivation layer mainly composed of lithium silicate formed on the aggregate surface, with a thickness of several tens of micrometers. When exposed to an alkaline environment, using aggregates with surface passivation effectively slowed down the rate of the ASR-induced length expansion by nearly 2.6 times. Elemental analysis indicated that because of the chemical bonding of lithium in the passivation layer, no significant change in the chemical composition of ASR products was induced. The key mechanism of restriction on the ASR process was due to the passivation layer acting as a buffer zone, which impeded the ion ingress. As a result, the limited availability of calcium and alkali delayed the progression of ASR. Finally, from the performance comparison of the lightweight foam glass concrete, passivated foam glass aggregates improved resistance to ASR while having little effect on thermal and mechanical properties. • Surface passivation with LiOH solution was applied to foam glass aggregates by forming a lithium silicate layer. • ASR expansion was effectively mitigated owing to the buffer zone effect of the passivation layer. • The influence of surface passivation on the thermal and mechanical performance of the concrete was limited.