Sorptivity and acid resistance of ambient-cured geopolymer mortars containing nano-silica

This study investigated the effects of nano-silica on flowability, strength development, sorptivity and acid resistance properties of fly ash geopolymer mortars cured at 20 °C. The changes in mass, compressive strength and microstructure of the specimens after immersion in acid solutions for different durations were determined. The microstructures were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis. It was found that addition of nano-silica in geopolymer mortars based on fly ash alone or fly ash blended with 15% GGBFS or 10% OPC improved the compactness of microstructure by reducing porosity. Thus, the nano-silica reduced sorptivity and increased compressive strength of the mixes. The average mass loss after 90 days of immersion in acid solutions reduced from 6.0% to 1.9% by addition of 2% nano-silica. Similarly, significant reduction in strength loss after immersion in acid solution was observed in the specimens by using nano-silica.