Activation of fly ashes by the high temperature and high alkalinity in ASR tests

High temperature and high alkalinity are typical testing conditions to accelerate the appraisal process of the suppressing effect of fly ashes on alkali silica reaction (ASR), but the reaction mechanism of fly ashes would be quite different under such conditions compared to the normal condition of temperature and alkalinity. To make a reasonable analysis of the suppressing effect of fly ashes, 13 types of fly ashes were tested in this paper by both the accelerated mortar bar test method and the 60A degrees C accelerated concrete prism test method. The results showed that the effect of fly ashes would be magnified under the condition of high temperature and high alkalinity. The XRD analysis showed that all the phases of fly ash could react with the hot alkaline solution except for mullite and a small amount of quartz. Fly ash could be significantly activated by the 80A degrees C 1 mol/L NaOH solution, and form mainly C-S-H phase and P type zeolite, but its effect on inhibiting ASR was exaggerated then. According to the mortar strength test and the ASR suppressing test results, C-S-H phase contributed to mortar strength, but its amount did not decide the ASR suppressing effect of fly ash.