Comparison of alkali-silica reactions in alkali-activated slag and Portland cement mortars

Alkali-silica reactions (ASR) in alkali-activated slag (AAS) and Portland cement (PC) mortars were studied to compare their expansions and products. ASR expansions were measured following ASTM C1260 with modified curing and exposure conditions. Scanning electron microscope equipped with an energy-dispersive X-ray analyzer (SEM/EDX) was used to characterize the ASR products in both types of mortar after 28 days of testing. The concentration of OH- in the extraction solution of all the mortars at different ages was determined by ex situ extraction method. The results showed that AAS mortars exhibited lower ASR expansion than the PC mortars when they were exposed to 1 N NaOH solution. The observation of ASR products in the AAS mortars under water and steam exposure conditions supported the presence of their minor ASR expansions, which were not observed in the corresponding PC mortars. SEM/EDX observation and analyses demonstrated obviously different morphologies of AAS mortars under different exposure conditions. The lower ASR expansion of mortars can be explained by their lower concentration of OH- in the extraction solution, which might reflect the relative alkalinity in their pore solution.