Mitigation effect of lithium nitrate on the alkali-silica reaction in alkali-activated slag mortars

Although lithium nitrate is a commonly used method to mitigate the alkali-silica reaction (ASR) in conventional Portland cement systems, such kind of research has not been conducted on alkali-activated material (AAM) systems. In this study, the mitigation effect of lithium nitrate on the ASR in an AAM system was investigated for the first time. The results indicate that lithium nitrate is not effective in mitigating the ASR in alkali-activated slag (AAS) mortars because of its inherently high alkalinity and dense microstructure. Although the lithium nitrate reduced the expansion of AAS mortars, the reduction was limited, and when the concentration of lithium nitrate further increased from 1.11 mol/L to 1.48 mol/L, the expansion did not reduce any more. No Li-Si crystals were found in the AAS pastes/mortars exposed to lithium nitrate-containing solutions. The SEM/EDS analysis revealed that there were still many ASR products that could be observed in AAS mortars exposed to the solution containing 1.48 mol/L lithium nitrate for 56 days, and the Na/Si ratio of the ASR products remained almost unchanged, while the Ca/Si ratio decreased.