Evaluating the mechanical properties and durability of portland cement mortars with sewage sludge ash as a partial replacement

This study explores the valorization of sewage sludge ash (SSA) as a sustainable partial cement replacement in Portland cement mortars, aligning with environmental and performance-driven objectives. SSA was subjected to a two-step thermal treatment: dried at 105°C, then calcined at either 550°C (BC550) or 700°C (BC700). Comprehensive physicochemical and mineralogical characterizations were performed, followed by the preparation of mortar samples with 0%, 5%, 10%, 15%, and 20% SSA substitution by mass. The mechanical properties, apparent porosity, resistance to sulfate attack, and chloride ion penetration were rigorously assessed.The results demonstrated that BC550 and BC700 significantly influenced mortar performance. Mortars with 5% BC550 and 10% BC700 exhibited optimal mechanical strength, with 5% BC550 achieving the best balance between strength and durability. The 5BC550 samples maintained comparable chloride ion resistance to the control, indicating minimal impact on permeability, while showing enhanced resistance to sulfate attack. In contrast, 10% BC700 substitution, despite initial strength gains, led to increased porosity and reduced resistance to chemical degradation. The study reveals that calcining SSA at 550°C is sufficient to enhance mortar performance without compromising environmental sustainability, positioning 5% BC550 as an eco-friendly alternative for partial cement substitution. These findings underscore the dual benefit of mitigating waste and reducing cement consumption in construction materials.