Physical properties and material characterisation of fly ash-based geopolymer composites having nano silica and micro glass
Khaled Mohamed Elhadi, Ali Raza, Nejib Ghazouani, Dawood Khan
Abstract
This study aims to explore the mechanical and microstructural characterisation of fly ash-based geopolymer composites (GC) having varying amounts of nano silica (NS). Four different concentrations of NS − 0%, 1%, 2% and 3% by weight – with a constant 1% micro-glass fibres (MGF) by weight of the mix were produced. The compressive stress-strain curves, bending stress-strain curves, impact strength, hardness, fracture toughness, toughness indices, compressive strength (CS), flexural strength and bending load-deflection behaviour were determined. To determine the samples’ chemical composition, scanning electron microscopy, X-ray diffraction (XRD), thermogravimetric analysis and Fourier transform infrared spectroscopy were used. One-way analysis of variance statistical analysis was also performed to check the significance of variation in the results due to the addition of NS in GC mixes. The findings showed that by strengthening interfacial transition zones and forming a denser matrix, the inclusion of NS considerably improved the mechanical and microstructural properties of MGF-reinforced GC. The incorporation of 2% NS significantly enhanced the CS of GC, achieving up to 171.32% of the CS exhibited by the control paste. Among the tested values, the optimal concentration of NS for GC is 2% for the highest mechanical and microstructural properties. Furthermore, XRD analysis revealed the formation of calcium silicate hydrate (C−S−H) after the presence of the primary binder, that is, sodium aluminosilicate (N−A−S−H). Asymmetric stretches in Si−O−Al bonding were observed to be responsible for positioning the absorption bands from 1006 cm−1 to 975 cm−1 in GC binders showing the development of C−S−H gels.