Exploring the Use of Sewage Sludge Ash in Concrete: Assessing Mechanical Properties and Environmental Impacts

Concrete is a widely used structural material, but its production, especially the manufacture of clinker, is energy-intensive and emits significant pollutants. While alternative materials have emerged, concrete remains essential in many applications. To reduce its environmental impact, partial substitution of clinker with materials like natural pozzolans or industrial by-products has gained attention. Sewage sludge is the residue from the wastewater treatment process, which needs further treatment. One of the potential disposals is mono-incineration. We can have a dual benefit through this treatment: energy production and a circular waste management strategy, by valorising the obtained ashes. This study analyses the mechanical and environmental performance of mortars made with cement in which clinker is partially replaced with sewage sludge ash (SSA). The main objective of this research is to conduct a Life Cycle Assessment (LCA) following a consequential approach to evaluate the environmental performance of concrete incorporating varying percentages of sewage sludge ash. At the same time, the study aims to assess the mechanical properties of concrete mixtures to determine their suitability for structural applications. Preliminary results demonstrate that mortar with SSA has similar mechanical performance to the reference mortar. LCA results show that the treatment of sewage sludge through mono-incineration could lead to a significant reduction of the environmental impact. These results show that this type of treatment is very promising, however, a more extensive assessment of the mechanical properties is needed. Moreover, a deeper uncertainty assessment of the inventory data, including parameter variability, is required to draw more robust conclusions.