Greener cementitious composites incorporating sewage sludge ash as cement replacement: A review of progress, potentials, and future prospects

Abstract

Sewage sludge ash (SSA) is an unavoidable waste during the treatment of wastewater, and because it contains a significant amount of heavy metals, it constitutes a major pollution risk. Therefore, different approaches are proposed worldwide for the safe and sustainable disposal of SSA. One such approach is the incorporation of SSA in the preparation of cementitious composites as cement replacement like other industrial waste materials (e.g., fly ash, silica fume, and slag). This article comparatively analyses the characteristics (chemical composition, pozzolanic activity, and particle morphology) of SSA and properties of SSA modified cementitious composites, including hydration kinetics, mechanical properties, drying shrinkage, porosity, and microstructural properties. The study concludes that SSA can replace cement in the production of greener cementitious composites by 5–10%, which can be further increased to 20% by using pre-treated SSA. However, a detailed experimental investigation is required to assess the full potential of SSA as a cement replacement material and to address some contradictory observations reported by different researchers related to the properties of cementitious composites incorporating SSA.