Characterizing Sewage Sludge Ashes in Dry and Wet States for Use as SCM

International audienceThe increasing production of sewage sludge, a residue from wastewater treatment, has led to the need for disposal methods that reduce environmental impact. The calcination of this mud residue produces the sewage sludge ashes (SSA), a powdery by-product with valuable characteristics that can serve as a secondary material source. This study explores the feasibility of incorporating SSA, as a partial substitution for Ordinary Portland Clinker, in cement-based materials. The chemical, mineralogical and physical properties of SSA were characterized to understand its impact on the cement matrix. Following that, cement paste samples and mortars were prepared with substitution rates of 0, 10, 20, 30%, and 25% respectively. The results of the work show that SSA has a possible porosity, resulted in an increase in the water demand after SSA incorporation. In addition, SSA was found to contain heavy metals, phosphorus, sulfate and lime which affects the cement hydration reaction. The modified SSA-cement pastes showed a delay in the early hydration period. A long-term positive effect on mechanical properties of mortars was noticed, with a Strength Index Activity of 86% at 28 days. The results obtained in this study encourages the use of SSA in cement-based materials in cement-composites