Production of environmentally friendly sand-like products from granitoid waste sludge and coal fly ash for civil engineering

Processing granitoid rock for civil engineering, countertops, and paving generates sub-economical (transportation costs exceed their retail value) granite powder sludge. This paper evaluates the possibility of mixing granite waste (GW) produced at the Spanish quarries of Galicia with a second sub-economical substance, Class F coal fly ash (FA <20 wt% CaO). The GW would reduce the leachability of toxic trace elements enriched in Colombian fly ashes and form a sand-like product that could serve as a substitute product and would reduce the costs in industrial concrete and civil engineering projects. To investigate both the capability of the GW to reduce FA leaching (by physical adsorption) and the potential use of the aggregate product as a partial substitute in industrial concrete, the physical (e.g. morphology, crystallographic patterns, and surface area), mineralogical, and chemical (including leachability and chemical composition) properties of the aggregate product were tested. Moreover, properties of the concrete (compressive strength, ion penetration, workability, and electron microscope scanning results (SEM)) were also analyzed. The use of the end scrubbed product in the concrete mixture was found to enhance the performance of the concrete mixture, reducing the leaching of the hazardous elements, and improving the concrete produced.