engleski

Technical and Environmental Study of Sewage Sludge Ash Utilization in Concrete Industry

This research is part of a wider feasibility study on the possible recycling and use of Croatian sewage sludge ash (SSA). Sewage sludge was sourced from Zagreb WWTP and SSA was produced by laboratory incineration. Physical and chemical characteristics of SSA were investigated, since the possibility of its recycling depends a great deal on its composition. SSA was also tested for soluble heavy metals according to EN 12457 and results considered in the context of EU landfill Waste Acceptance Criteria. With SSA alone, the main soluble elements/ions of concern were Mo, Se and Cl-. On the other side, when obtained ash was incorporated into cement mortars at cement replacement rates of up to 20%, leaching of the crushed mortars demonstrated compliance with the strictest limits for inert landfill. Also, leaching of the mortar monoliths with incorporated SSA was the same order of magnitude as leaching of the reference mortar. The overall results reveal that leaching of heavy metals and other ions is not a significant concern that would prevent the potential use of SSA in cement mortars or concretes. Technical requirements for mortars are not compromised by the addition of up to 20% of SSA which was confirmed by series of tests in fresh and hardened state. The main negative effect was reduced workability of experimental mortars, but this problem has been successfully overcome by the addition of superplasticizer. Strengths of experimental mortars with incorporated SSA were at par the strength of reference mortar. Results of the research carried out on cement mortars point to the great possibilities of SSA incorporation in the concrete industry, from both, technical and environmental point of view, should Zagreb wastewater treatment plant opt for sewage sludge incineration as an alternative sludge disposal and management option.

Sewage sludge ash ; cement mortar ; strength ; leaching

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