Utilization of ceramic polishing sludge in masonry cement mortar: Mechanical strength and thermal behavior

Ceramic polishing sludge (CPS), a byproduct of ceramic tile manufacturing, presents challenges in terms of disposal. Meanwhile, masonry mortar production relies on ordinary Portland cement (OPC), which has significant environmental impacts. This study addressed the dual problem of waste management and environmental burden of cement production by integrating environmental assessment, comprehensive multi-property evaluation, and validation of high CPS replacement levels. We explored the use of CPS as a sustainable partial replacement for OPC in masonry cement mortar at 0%–50% replacement levels. A comprehensive analysis was conducted to determine the mechanical properties, hydration behavior, thermal conductivity, and microstructure. CPS demonstrated strong pozzolanic reactivity owing to its high silica and alumina contents, which enhanced the hydration and microstructural refinement. Mortars containing 10%–20% CPS demonstrated optimal performance, achieving a compressive strength in the range 37.9–39.0 MPa at 28 days, a reduction in thermal conductivity of up to 21.5% at 40% CPS, and a densified microstructure as confirmed via scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction. SEM analyses revealed reduced porosity and a favorable Ca/Si molar ratio of 2.47–2.86 at 10%–20% CPS, indicating improved compactness. Additionally, an energy and CO₂ emission assessment based on the thermal resistance of CPS-incorporated wall mortars revealed that the annual heating fuel consumption and CO₂ emissions could be reduced by up to 26 kg/m² and 82 kg/m², respectively, at 30%–40% replacement levels. The findings confirm that CPS is a promising eco-friendly cement substitute, especially at 10%–20% replacement.