Valorization of Industrial Wastewater Treatment Sludge in Eco-Friendly Mortars: Enhancing Thermal Insulation and Sustainability

The construction industry increasingly seeks sustainable solutions to reduce environmental impact and energy consumption. This study explores the innovative use of industrial sludge generated from the wastewater treatment of detergent manufacturing as a partial substitute for Portland cement in mortar production. The sludge, characterized by high SiO₂ (46.58%) and CaO (28.66%) content, was incorporated at substitution rates of 0% to 30%. Mortars were prepared and tested according to NF EN 196-1 standards for mechanical strength, and thermophysical properties were assessed using the Hot Disk TPS 1500 system. Results demonstrate that up to 20% sludge replacement maintains acceptable mechanical performance (compressive strength: 12.63 MPa at 28 days vs. 13.91 MPa for control; flexural strength: 3.93 MPa vs. 4.65 MPa) while significantly enhancing thermal insulation. Thermal conductivity decreased from 1.054 W/m·K (0% sludge) to 0.797 W/m·K (20% sludge), and thermal diffusivity dropped from 0.6096 mm²/s to 0.504 mm²/s. XRD analysis revealed the formation of new phases, such as gismondine, indicating beneficial pozzolanic activity. These findings highlight the dual benefit of valorizing detergent sludge and improving building energy efficiency, offering an eco-efficient alternative to traditional mortars aligned with circular economy and low-carbon construction goals.