Mechanical and microstructural properties of fly ash-based engineered geopolymer mortar incorporating waste marble powder

Abstract

The marble processing industry produces a large volume of unmanaged waste in the form of microfine marble particles, usually referred as waste marble powder (WMP). Unregulated and open disposal of WMP has adverse effects on the environment. Marble is usually rich in calcium content, which can be used in geopolymer technology, thereby enhancing its recycling value. This research sought to determine the viability of WMP as a supplementary binder and polymerisation potential of its high calcium content (55.96%). For this purpose, WMP was used as fly ash replacement by weight (0, 5, 10, 15 and 20%) in geopolymer mortar (GPM) while other mix proportions are kept the same. The results indicated that WMP substitution adversely affected the water absorption (WA), ultrasonic pulse velocity (UPV), compressive and flexural strengths of engineered GPM. The mechanical strength trends were supported by, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy tests, which revealed that the calcium content of WMP showed poor alkali activation. Marble particles remained unreacted in the GPM matrix and failed to form additional geopolymeric compounds as Ca/Si ratio was found to consistently decrease with higher WMP substitution. Accordingly, WMP can be used in geopolymers in combination with siliceous binder (fly ash) without significantly reducing the mortar mechanical properties and thus the resulting GPM can find broad applications in practice.