Structural performance of nano-silica modified fly-ash based geopolymer concrete

Abstract The fly ash based geopolymer concrete generally requires heat activation of different temperatures, which has been considered as an important limitation for its practical application. Such limitation can be overcome by the addition of appropriate amount of nano-silica in the mixture. Therefore, a fly ash based geopolymer concrete can be developed using 6% nano silica replacing fly ash. The structural performance of such geopolymer concrete in terms of bond strength, flexural strength and micro structural behaviour has been explored. Such nano silica modified fly ash based geopolymer concrete shows appreciable improvement in structural behaviour at different ages without any heat activation. The bond strength between reinforcement bars (deformed or mild steel) and surrounding geopolymer concrete materials (with/without nano silica) has been also compared to the conventional cement concrete. The nano silica modified geopolymer concrete exhibits better structural performance than heat cured geopolymer concrete (without nano silica) and conventional cement concrete samples. The microstructural properties of such geopolymer concrete (with/without nano silica) and cement concrete have been analyzed through Field Emission Scanning Electron Microscope (FESEM) with Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) analysis and X-ray Diffraction (XRD) techniques. The enhancement of structural performance is mainly due to the transformation of amorphous phase to crystalline phase in the geopolymer concrete matrices in the presence of nano-silica.