Impact of pond ash as fine aggregate on mechanical and microstructural properties of geopolymer concrete

In this research, geopolymer concrete (GPC) was produced using pond ash (PA) as a fine aggregate replacement to river sand (RS). The focus of the study is to investigate the effect of PA as fine aggregate on the mechanical and microstructural properties of GPC. The present study detailed characterization of PA which includes particle size distribution, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) analysis, energy dispersive X-ray (EDAX) studies, and chemical analysis including reactive silica (R-SiO2). PA replaced RS at percentages of 0, 20, 40, 60, 80 and 100% in GPC. Properties like compressive strength, flexural strength, split tensile strength and water permeability of GPC were studied. It was found that compressive strength, flexural strength and split tensile strength of GPC with 80% PA as fine aggregate are, respectively, 26%, 29% and 31% greater compared to concrete with RS as aggregate. The inclusion of reactive sand-like PA increased the R-SiO₂/Na₂O ratio from 3.2 to 5.4 in GPC mixes with up to 80% replacement and contributed to higher compressive strength. SEM studies, R-SiO₂, EDAX and Fourier-transform infrared spectroscopy (FTIR) analysis of GPC confirmed the participation of PA particles in polymerization thereby contributing to higher strength. Utilization of pond ash as fine aggregate provides a valuable addition to GPC in aspects of strength and economics as well as alleviates the environmental problems caused by coal ash ponding.