Strength of alkali activated slag and fly ash-based geopolymer mortar

Abstract

This paper presents a summary of experimental work that has been conducted to compare the strength of two types of alkali activated cementitious materials, i.e. an alkali activated slag (AAS) and a fly ash based geopolymer, using two alkaline activators. One type of mortar was prepared with fly ash and another with slag, both activated by high concentration alkali solution over a range of activator modulus. The use of two different types of fly ash was also employed to determine the influence of chemical composition on compressive strength. Microstructure studies were conducted using Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) to determine the microstructure characteristics for both materials. Both the AAS and the fly ash based geopolymer mortar had greater early strength than the OPC mortar and comparable ultimate strength. The reduction in the compressive strength at the higher activator modulus between the two fly ash mortars is attributed to the higher concentration of Silicate (Si) in the fly ash which resulted in unreacted Si remaining following the reaction phase