The effect of trass and fly ash in minimizing alkali-carbonate reaction in concrete

•Trass as cement replacement can reduce carbonate alkali reactivity.•The compressive strength increased with using trass and fly ash up to 20%.•Based on petrography, trass cannot control the reactivity in the long-term.•The optimum percentage of fly ash to reduce ACR expansion was 20%.•The size and the shape of aggregates can affect their reactivity effectually. The influence of natural pozzolans on the controlling of the alkali-carbonate reaction (ACR) and the alkali-silica reaction (ASR) has not been studied comprehensively, regardless of the research studies conducted on utilizing natural pozzolans as supplementary cementitious materials. Nevertheless, the performance of natural pozzolans toward the ACR and ASR was investigated in recent studies. The primary purpose of this research is to evaluate the alkali-carbonate expansion of mortar specimens, which contain trass and fly ash in the short-term. For the short-term, the extent of expansion due to ACR was monitored for fourteen 7-day intervals. Based on the test result, fly ash and trass meaningfully reduced the expansion due to ACR in the short-term. Moreover, long-term test results for trass were presented as well. For the long-term, samples were kept at 80°C in NaOH solution for curing in 56days according to ASTM C1260 and 390days according to ASTM C1293. The observations by optical microscopy have been conducted on thin sections.