Effects and mechanisms of lithium nitrate on controlling alkali-silica reaction

This thesis presents the results of a study on the effects of LiNO3 on alkali-silica reaction (ASR) in concrete and the underlying mechanisms. Five alkali-silica reactive aggregates and glass were selected as the materials of interest. The effects of LiNO3 on ASR expansion, on silica dissolution, and on concrete pore solution were investigated with different lithium dosages at 38°C and 80°C. Results showed that LiNO 3 could effectively suppress the deleterious expansion for all five reactive aggregates when they were crushed to sand size, while in concrete-prism and concrete microbar tests where larger size aggregate was used, the response of the aggregates to lithium varied. LiNO3 could significantly reduce the total amounts of silica dissolved, but it could not discriminate the difference between aggregates.;Based on the above findings, a new mechanism for the suppressive effects of LiNO3 on controlling ASR-induced expansion is proposed. The suppressive effects of LiNO3 on ASR expansion are attributed to the formation of a layer of Li-Si crystals intimately at the reactive SiO 2 particle surface which serves as a diffusion barrier and protective layer to keep the reactive aggregate particles from further attack by alkalis; and the formation of Li-bearing, low-Ca ASR gel products with a CIS ratio below 0.2, which have denser gel structure, stronger bond with the aggregate particles, and lower mobility than conventional ASR gel. With sufficient thickness of the reaction products, less and less OH- ions can pass through the diffusion barriers. As a result, the alkali silica reaction and resulting expansion will be completely suppressed.;For the mechanistic work, the ASR reaction products were investigated through the application of several advanced analytical techniques such as SEM, XRD, and LA-ICP-MS. The observations elucidated that Ca ions played an important role in the formation of ASR gel products. The Na and Li diffusion studied by MRI revealed that Na had a greater effective diffusion coefficient than that of Li ions, thus Na ions could reach the reactive aggregate particle surface before Li ions.