Experimental Investigation to Elucidate the Combined Deterioration Mechanism of Alkali-Silica Reaction and Delayed Ettringite Formation

In addition to the alkali-silica reaction (ASR), delayed ettringite formation (DEF) has recently received more attention among deterioration due to the internal swelling reaction of concrete. In this study, concrete specimens in which both ASR and DEF occur simultaneously were prepared using ASR-reactive aggregates, covering specimens with nonwoven cloths containing an alkaline solution to promote ASR, and giving a high-temperature history at an early age to promote DEF to investigate the mechanism of combined ASR and DEF deterioration. At any given age, we measured the expansion, performed tissue observations, and analyzed the elements using an electron probe micro analyzer. When concrete was prepared with NaOH added primarily to promote ASR and with K2SO4 added primarily to promote DEF, ASR occurred in both cases, but DEF occurred only with K2SO4 addition. When both ASR and DEF occurred, the expansion was relatively large, and the estimated pH values calculated from the alkali concentration gradually decreased with age.