Study on the behaviour of class F and C fly ash blended geopolymer concrete

Abstract

With the increasing pollution levels and the extensive carbon footprint by the construction industry, there is a need for the development of sustainable construction materials possessing excellent binding property. At present, many industrial by-products such as fly ash, ground Granulated Blast Furnace Slag (GGBS), etc. are used as a supplementary cementitious material in concrete for replacing cement either partially or completely. Geopolymer Concrete (GPC) is a potential replacement for conventional cement concrete characterised by the formation of two/three-dimensional alumino-silicate (Si-O-Al-O) gel structure. It has numerous advantages such as high strength and enhanced durability along with environmental benefits. newlineSeveral researchers have worked on GPC to explore and utilize its unique properties using low calcium content Class F Fly Ash (FFA). But, the drawback of GPC which hinders the widespread practical application is the requirement of elevated temperature for curing. This elevated temperature is essential for the effective polymerization and strength attainment as the major binding material Class F fly ash contains less than 10% of Calcium Oxide (CaO), which is insufficient to generate heat through hydration. The prime objective of this research work is to explore the possibility of using blended high calcium content Class C fly ash and low calcium content Class F fly ash for the development of cast-in-situ GPC members. Class C fly ash was incorporated for inducing polymerization at ambient sunlight conditions and eliminating the requirement of elevated temperature either by steam or heat. The mix design for the GPC was prepared based on the trial and error procedure. The mixture of Sodium Hydroxide (NaOH) and Sodium Silicate (Na2SiO3) solutions was used as alkaline activators. To determine the appropriate mix design for in-situ applications, different proportions of Class F and Class C fly ash were employed along with different molarities of NaOH solutions. newline newline