In-situ alkali–silica reaction evolution of lightweight aggregate concretes prepared with alkali-activated cement and ordinary portland cement assessed by X-ray micro computed-tomography

Rather than evaluating the alkali–silica reaction (ASR) expansion using the conventional length comparator, in this study, the evolution of ASR-induced cracks and pore structure development in lightweight aggregate concrete was first quantified using X-ray micro-computed tomography (X-ray μCT). The reliability of the correlation between ASR expansion, ASR-induced cracks, and pore evolution revealed by X-ray μ-CT was verified for accurately evaluating ASR behavior. With the use of in-situ observation, the initially formed cracks and the ASR-induced cracks were successfully distinguished in the expanded perlite mortars. The in-situ evolution of the ASR test illustrated that the reaction products were produced in the rim within the pores in the expanded shale, but they filled the whole pores in the expanded perlite, which explained the larger expansion and the more severe ASR-induced cracks in the latter. The development of the expansive ASR reaction products in the lightweight aggregate was quantified by the rate of how the porosity decreased during the ASR test. The decrease in porosity reached a steady level in the ordinary Portland cement (OPC) mortars after 14 days of the ASR test but still continuously decreased in the alkali-activated mortars, which correlated well with the larger expansion and ASR-induced cracking in the alkali-activated mortars but no expansion in the OPC mortars.