Influence of Alkali–Silica Reaction on Geopolymer Concrete

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Geopolymer concrete (GPC) is an emerging environmental-friendly construction material. Extensive research related to strength and durability studies is being carried out on this material. However, it is essential to check the mechanism of potential reactive aggregates with geopolymer binder. Alkali–silica reaction (ASR) is one of the major problems faced by concrete structures. ASR is a chemical reaction that occurs between the hydroxyl ions present in pore water within the concrete matrix and certain forms of silica present in aggregate leading to the formation of silica gel. Volumetric expansion of silica gel produces internal stresses in the concrete and leads to strength loss, cracking and failure of the structure. In the present investigation, quartz is selected as a reactive aggregate in combination with geopolymer binder. Mortar bar test is conducted based on IS 2386-Part-7 (1963). Further fly ash and GGBS are selected as binding materials for five different proportions. Special fabricated container is used to store the specimen until the day of test. Length measurements are carried out on mortar bar specimen using length comparator after 1, 2, 3, 6, 9 and 12 months as specified by Indian standards. Elongations of all geopolymer mortar mixes at 180 days are within 0.06% as specified by IS 2386-Part 7, i.e. geopolymer binder is not deleterious with reactive aggregates and hence economical in the areas having inadequate availability of high-quality aggregates. Further, no clear trace of ASR gel is visualized through microstructure of geopolymer mortar specimen. However, bright ASR gel is identified on controlled mortar specimen prepared using Ordinary Portland Cement (OPC) as binder through scanned electron microscope (SEM).