Analysis of the Sewage Sludge Ash from a WWTP as a Partial Substitute for Structural Concrete

Abstract

The construction industry is one of the world’s leading polluters, producing high levels of greenhouse gases; furthermore, within this sector, the inadequate use of wastewater treatment plants (WWTPs) has led to significant environmental problems. For this reason, the Sustainable Development Goals (SDGs) seek alternatives to combat these problems. Peru is part of this initiative by promoting sustainable implementation projects. To address these challenges, this study evaluated the feasibility of using sewage sludge ash from a WWTP as a partial cement substitute for structural concrete (210 kg/cm2). The sewage sludge underwent a process of incineration, artisanal crushing, and screening to obtain the substitute sample. The particle size analysis of the ash revealed the material’s high fineness; furthermore, the conventional chemical characterization of the sewage sludge ash was found to be compatible with Class N pozzolan, as required by ASTM C618, with the total content of reactive oxides (SiO2 + Al2O3 + Fe2O3) exceeding the required minimum of 70%. Compressive strength tests were also performed using replacement levels of 5%, 10%, and 15% during days 1, 3, 7, 14, and 28 of curing. The results showed that the replacement levels of 5% and 10% have optimal mechanical performance with a resistance of 296 kg/cm2 and 271 kg/cm2 at 28 days. A one-way ANOVA supported the findings obtained in the research. This research concludes that sewage sludge ash is a sustainable and technically viable alternative as a partial replacement for cement when used in concentrations of a maximum of 10%.