Environmental evaluation of concrete with sewage sludge ash based on LCA

Using sewage sludge ash (SSA) as a substitute for part of cement in concrete provides environmental, social and economic benefits with the aim of achieving basic sustainability principles. The potential environmental benefits from using SSA as a supplementary cementitious material have been investigated and quantified by life cycle assessment (LCA) model on a concrete example. Controlled combustion of sewage sludge collected in Croatia from wastewater treatment plant (WWTP) Zagreb produced SSA that was used to substitute for cement in concrete production. The paper compares environmental impacts of production of ordinary concrete and landfilling of SSA with the production of “green” SSA-concrete where the need for additional SSA disposal in non-hazardous landfills is eliminated. The results presented indicate that 10% replacement of cement by SSA produces concrete of the same technical and environmental characteristics as the reference (no any significant changes in compressive and flexural strengths, maximum water penetration depth, total shrinkage and total leaching concentrations of selected heavy metals, while increased water requirements and reduced workability was overcome by higher amount of used superplasticizer). At the same time this resulted in 9% lower environmental impacts expressed as global warming potential (GWP) in kg CO2 eq. In the case of redirecting the total amount of SSA, that would be generated on this WWTP, in the concrete industry, it is possible to expect annual reduction in the global warming potential of more than 10 million kg CO2 eq. Presented research has a potential for reducing greenhouse gas emissions and helping to conserve non-renewable natural resources, but also reducing the amount of waste that is landfilled, where there are benefits for both, cement and concrete industry, as well as for the industry of wastewater treatment.