Examination of the effects of LiOH, LiCl, and LiNO3 on alkali-silica reaction

Lithium additives have been shown to reduce expansion associated with alkali-silica reaction (ASR), but the mechanism(s) by which they act have not been understood. The aim of this research is to assess the effectiveness of three lithium additives—LiOH, LiCl, and LiNO₃—at various dosages, with a broader goal of improving the understanding of the means by which lithium acts. The effect of lithium additives on ASR was assessed using mortar bar expansion testing and quantitative elemental analysis to measure changes in concentrations of solution phase species (Si, Na, Ca, and Li) in filtrates obtained at different times from slurries of silica gel and alkali solution. Results from mortar bar tests indicate that each of the lithium additives tested was effective in reducing expansion below an acceptable limit of 0.05% at 56 days. However, different lithium additive threshold dosages (Li₂O]/Na₂O_e]) were required to accomplish this reduction in expansion; these were found to be approximately 0.6 for LiOH, 0.8 for LiNO₃, and 0.9 for LiCl. Quantitative elemental analysis indicated that sodium and lithium were both bound in reaction products formed within the silica gel slurry. It is also believed that lithium may have been preferentially bound over sodium in at least one of the reaction products because a greater percent decrease in dissolved lithium than dissolved sodium was observed within the first 24 h. It appears that lithium additives either decreased silica dissolution, or promoted precipitation of silica-rich products (some of which may be nonexpansive), because the dissolved silica concentration decreased with increasing dosage of lithium nitrate or lithium chloride additive.