From Waste to Resource: Valorization of Dimensional Stone Waste in Geopolymer Mortars for the Circular Economy in Construction

Abstract

The cement industry is a major source of global CO₂​ emissions, highlighting the need for sustainable alternatives that balance performance with reduced environmental impact. Geopolymers offer a promising low-carbon substitute to OPC, with reported emission reductions of up to 80%. Simultaneously, dimensional stone processing in India generates over 30 million tons of waste annually, causing serious air, water, and land pollution. Valorizing this waste in geopolymer binders provides dual benefits of waste mitigation and sustainable material development. The present study explores the use of dimensional stone waste with GGBS for geopolymer mortar production, focusing on optimizing strength and physical properties through mix design variables such as activator molarity and NaOH:Na₂​SiO₃​ ratios. Characterization of materials was conducted using XRF, XRD, and SEM. Results showed maximum compressive strength at 8 M NaOH with a 1:2.5 NaOH:Na_2​SiO₃​ ratio, along with higher density, and lower porosity and water absorption. The novelty lies in systematic optimization of activator parameters for stone waste-based geopolymers, which have not been studied in detail previously. Findings confirm the feasibility of converting challenging waste into high-performance binders, supporting circular economy goals. Beyond structural performance, the natural colour of stone waste enhances the aesthetic appeal of geopolymer products without synthetic pigments.