Effect of silica fume and curing conditions on the strength and microstructure of fly ash based geopolymers

Abstract

Geopolymer concrete (GPC) is a sustainable alternative to ordinary Portland cement (OPC) newlineconcrete, offering significant reductions in COand#8322; emissions and promoting effective solid waste newlinemanagement. Despite its advantages, significant gaps remain in developing standard mix newlinedesigns and understanding the influence of critical factors such as alkaline blend concentration, newlinecuring conditions, and blending of SF on GPC performance. This study addresses these gaps newlineemploying a series of experimental investigations on the influence of NaOH concentration, newlinesilica fume (SF) particle size and dosage, alkaline liquid-to-binder ratio, Naand#8322;SiOand#8323;-to-NaOH newlineratio, sand-to-binder ratio, and curing conditions on the strength and microstructure of SF newlineblended fly ash (FA)-based geopolymer mortars (GPM). The findings aim to establish newlinecorrelations between these parameters and compressive strength, providing insights into newlineoptimizing mix design and curing conditions for enhanced compressive strength. Experimental newlinestudies investigated the compatibility of low-calcium FA, SF, and alkaline blends, focusing on newlinereaction products and corresponding compressive strength to understand the expansion newlinebehaviour of SF blended FA-based GPMs. FA-based GPMs were tested using two distinct SFs newlinewith varying particle sizes (SF1 = 9.5 µm and SF2 = 16.2 µm) and two varying dosages of SF newline(2.5% and 5%). A key finding revealed that the expansion of SF-blended FA-based GPM was newlineinfluenced by the specific combination of the type of SF and FA. Analytical techniques such as newlineX-ray diffraction (XRD), Rietveld analysis, Fourier transform infrared spectroscopy (FTIR), newlineand Thermo Gravimetric Analysis (TGA) were employed to comprehensively investigate newlinereaction product(s) that led to the expansion of such GPMs. The chemical analysis confirmed newlinethe presence of excess analcime in the mortars fabricated by blending SF1 and FA at 12M NaOH newlineconcentration. newline