Abstract
Arabian Peninsula possesses large deposits of scoria rocks (SR) of different grain sizes around pyroclastic volcanic cones along the Arabian shield. SR grains are commonly used as lightweight aggregates in the production of lightweight concrete. Mineral admixtures from local resources are unavailable in the Arabian Peninsula; therefore, searching for local alternatives becomes a necessity. In this study, SR is proposed for the use as natural pozzolan. Three SR samples procured from different sources, defined by GPS international coordinates, were characterized using stereomicroscope and FESEM techniques. SR samples were then ground for a definite time of 120 min. The SR powders obtained were investigated using laser particle size, X-ray diffraction analysis (XRD), X-ray fluorescence (XRF) and field emission scanning electron microscope -energy dispersive X-ray spectroscopy (FESEM-EDS) analyses. The strength activity indices of mortars with water-to-binder (W/B) ratio of 0.5 and a replacement level of 20% ground SR powders at curing ages of 28 and 180 days were determined. The strength activity index was found to depend on SR physicochemical properties. FESEM analysis has shown how SR particles react in the cementitious system. It is concluded that SR particles react according to the chemical and physical nature of their constituting phases (silicic, aluminic and ferric). The particle size is not the only parameter that controls the pozzolanic activity of SR powders. It is verified that SR grain surface contamination greatly affects the microstructure of the cementitious system. SR samples are found to provide different latent pozzolanic properties. SR3 powder has shown the best potential for use as an alternative supplementary cementitious material in the Arabian Peninsula.