Environmental safety and professional acceptance of wood biomass ash and sewage sludge ash in construction products

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Abstract

When developing innovative construction products, technical and durability aspects are often prioritised while environmental performance and user acceptance remain insufficiently addressed. Consequently, products incorporating secondary raw materials frequently face limited market recognition despite demonstrated performance, particularly for new waste sources where concerns about heavy metals and environmental risks remain alongside low professional awareness. This study addresses these challenges by integrating leaching-based environmental assessment with professional perception analysis to examine link between measured environmental performance and its acceptance in practice. Research focuses on wood biomass ash (WBA) and sewage sludge ash (SSA) investigated as secondary raw materials in ordinary Portland cement (OPC) systems and alkali-activated materials (AAM). Leaching tests showed that neither SSA nor WBA meets Croatian End-of-Waste criteria in raw form. In OPC systems, all monolithic samples were below regulatory limits for the measured parameters, although poor compaction of samples increased Cu (+43%), Cr (+27%), chlorides (+36%), and Cd/Ni (+13%). In AAM, Cd exceeded limits by 0.2 mg/m² in reference mix M4, while WBA based mix complied. After End-of-life of product, concentrations of the measured parameters remained below regulatory thresholds. Survey results (n=135) indicate that less familiar materials are associated with higher levels of uncertainty which is reflected in risk perception (51.1% and 45.9% of respondents perceive sewage sludge and slag as hazardous if improperly disposed). Only 7.4% have experience with leaching assessment, whereas 92.6% lack practical knowledge. Results indicate that environmental risk perception is driven more by familiarity and public discourse than by actual performance, highlighting limited awareness as a key barrier to the acceptance of less familiar materials such as SSA and WBA.

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