Waste Quartz Sand as a Sustainable Modifier for Bituminous Binders: An Experimental Performance Assessment

Waste quartz sand (WQS), a silica-rich by-product of the glass manufacturing industry, is commonly disposed of, creating environmental and resource-management concerns. This study addresses the limited knowledge regarding the use of WQS as a mineral-based modifier for bituminous binders. Fine WQS (<0.075 mm) was incorporated into B50/70 penetration-grade bitumen at 0%, 1%, 2%, 3%, and 4% by weight. The morphology and chemical composition of WQS were characterized, and the modified binders were evaluated for conventional physical properties, storage stability, temperature-dependent rheological response, short- and long-term aging behavior, low-temperature performance, and aggregate–binder adhesion. WQS incorporation decreased penetration and increased the softening point while maintaining satisfactory storage stability. A 2% WQS content provided the most favorable high-temperature rheological performance and rutting-related response. Low-temperature performance was largely maintained, while adhesion performance remained satisfactory at 1–3% WQS but decreased at 4% WQS. Overall, 2% WQS exhibited the most favorable balance among the evaluated binder properties. The screening-level environmental and economic assessment indicated potential reductions in virgin bitumen consumption, greenhouse gas emissions, and binder cost. These findings demonstrate the potential of finely processed WQS as a waste-derived mineral modifier for bituminous binders and provide an alternative pathway for the valorization of glass-industry waste in pavement materials.