Mechanism understanding of alkali-silica reaction in alkali-activated materials system

To provide a better understanding of the mechanism of alkali-silica reaction (ASR) in alkali-activated materials (AAMs) system, in this work, the ASR behavior of alkali-activated slag (AAS)/fly ash (AAFA) mortars were investigated, and compared with ordinary Portland cement (OPC) mortars. It is found that although the AAS mortar bars experience the shrinkage first, the onset of ASR-induced expansion of AAS mortar bars is earlier than OPC mortar bars. In AAMs system, the reactive silica from aggregates is evidently dissolved and participated in the early-age alkali-activation, and thereby leads to the reduction of reactive silica for ASR. The Ca/Si ratio of amorphous ASR products in AAS mortars was lower, while Al/Si and Na/K ratios were higher than that of OPC mortars. Based on the obtained experimental evidences, a conceptual model was proposed to interpret and compare the ASR behavior in OPC, AAS and AAFA systems.