Fresh, Hardened and Microstructural Behaviour of Fly Ash based Geopolymer Mortar Modified with Ground Granulated Blast Furnace Slag

Abstract

Geopolymer (GP) technology is an emerging, environmentally benign approach to concrete production utilizing waste materials and could provide a real alternative to Portland cement concrete. Conventional fly ash - based GPs generally require oven or steam curing to develop sufficient strength properties, and this curing requirement develops some limitations for cast-in-situ concrete applications. This present study focuses on developing GP mortar to achieve sufficient workability and strength properties in ambient temperature itself by replacing Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBS) for every 10% with low molar (3.5M and 5M) NaOH solutions. From the results, it was identified that in both 3.5M and 5M NaOH mixes, the GP mortar workability is inversely proportional to GGBS content. While studying the Compressive Strength (CS) for 90 days, the strength increases gradually up to a certain percentage of GGBS replacement (60% fly ash + 40% GGBS for 3.5M NaOH and 70% fly ash + 30% GGBS for 5M NaOH), and strength began to decrease after 28 days for further GGBS replacement. This decrease in strength after 28 days was validated by using Ultrasonic Pulse Velocity (UPV), Water Absorption (WA), porosity and microstructural parameters.