Geopolymer from sand washing waste: Mechanical, rheological, and sustainability perspectives

SWW fully used as sole precursor for sustainable geopolymer mortar Optimized 12 M NaOH mix achieved 27.3 MPa compressive strength Dense N-A-S-H gels improved strength, durability, and stability SWW geopolymers cut CO₂ by 50% and eco-costs by 53.5% vs OPC This study presents a sustainable approach to producing geopolymer mortar by fully utilizing sand washing waste (SWW) as the sole aluminosilicate precursor, offering an eco-efficient alternative to conventional cement-based materials. Despite growing research on industrial waste valorization, the direct application of SWW in geopolymer systems remains limited. In this work, sodium hydroxide (NaOH) activators with concentrations of 4, 8, and 12 M were combined with varying water glass (WG) ratios to assess their effects on strength development and microstructural evolution. The optimized formulation with 12 M NaOH achieved a compressive strength of 27.3 MPa, confirming effective gel formation and structural densification. Microstructural analyses (SEM, EDS, XRD, XPS, and NMR) verified the formation of a dense sodium aluminosilicate hydrate (NASH) gel network, contributing to enhanced durability and reduced porosity. A life cycle sustainability assessment revealed over 50% reduction in CO₂ emissions and a 53% decrease in eco-costs compared with ordinary Portland cement. These findings highlight the novelty and feasibility of employing SWW as a single precursor for high-performance, low-carbon binders, supporting circular economy principles and sustainable construction applications.