Influence of Type and Compositions of SCMs on Expansion of Mortar Bars from Alkali Silica Reaction

Abstract

The effect of different local pozzolans, as a supplementary cementitious material (SCM), on the expansion of mortar bar due to Alkali Silica Reaction (ASR) were reported in this paper. Accelerated test on specimens using local volcanic aggregates, rhyolite, was used to investigate and to compare the effects of fly ash (FA) and metakaolin (MK) on the suppression of the length change. In this study, three different percentages of FA, namely, 20, 35 and 50 and three of MK, namely, 10, 15 and 20 were used in cement replacement. The results showed the lowest expansions at 14 days were -0.036% and -0.001%, respectively for 35% FA and 10% MK, compared to 0.176 % of the control mix. Results from 28 days acceleration registered a slight increase in expansion for both FA and MK mixes.  Increase the SCMs to 50% FA and 15-20% MK yielded reduction of expansion to the innocuous level for both short and long term expansion. Chemical composition analysis revealed decrease in CaO/SiO₂ and CaO/Al₂O₃ of the cementitious systems. This could affect the expansion reduction.  But alumina in Al₂O₃/SiO₂ show the dominant effect on ASR suppression. Microstructures of all materials and casted specimens were also studied in detail. Considering all aspects, these SCMs were considered good candidates for ASR prevention in new concrete structures.