Utilisation of biomass and waste-derived ashes in the extrusion of fired clay bricksŽibret, Lea (Avtor) Pavlin, Majda (Avtor) Ducman, Vilma (Korespondenčni avtor) biomass and waste derived ashesclayextruded fired bricksceramic-technological testsmicrostructureleachingWith the trend towards renewable alternatives to fossil fuel sources, further uses of biomass and waste ash instead of landfilling are being explored. This study investigates the potential of fly and bottom ashes from burning wood (alone or with coal), as well as coal-co-combustion of municipal solid waste, sewage sludge, and paper sludge, for use in extruded fired bricks fired at 950 °C. The influence of ash content (0 to 15 wt% ash) and ash type (10 wt% ash) on the physical, mechanical, and microstructural properties of the fired bricks was studied. The compressive strength of the reference sample without ash was 72.6 MPa and decreased gradually with an increasing ash content. Open porosity ranged from 28% (reference, no ash) to 43% (15 wt% ash), and water absorption from 12% to 28%, reflecting the pore-forming role of the added ashes. All samples had a compressive strength above the 10 MPa limit specified in EN 772-1, except for bricks with 5 wt% paper sludge bottom ash (B4, W-PS BA). The leaching concentrations indicate that heavy metals were effectively immobilised within the ceramic structure of the fired bricks, relative to inert and non-hazardous waste limit values under EN 12457-2 test conditions. These results suggest that 5% substitution of primary raw materials with ashes may contribute to the production of bricks with reduced environmental impact and improved resource efficiency. The study provides a basis for further formulation of extruded bricks with biomass and waste-derived ashes.Elsevier20262026-06-15 13:28:35Neznano30098sl© 2026 The Authors