This study evaluated the viability of biomass bottom ash (BBA) as a supplementary cementitious material (SCM) and sand substitute in cement-based materials. Physical and chemical characterization of BBA from eucalyptus forestry biomass and BBA from olive industry residues was performed. BBA underwent processing through grinding for SCM application and carbonation for sand substitution. Mortar mixtures were prepared with 25% ground BBA replacement for cement and 25% and 50% BBA replacement for sand, both carbonated and non-carbonated. Mechanical behaviour tested through flexure and compressive strength and water absorption at 28 days were assessed. Pulverised BBA enhance compressive strength of mortar compared to a conventional CEM II type cement and Carbonated BBA mortar mixtures improved 28-day compressive strength by 35-55% compared to non-carbonated BBA. BBA from eucalyptus forestry biomass, with pozzolanic activity, exhibited superior strength. The findings support the technical feasibility of BBA in cementitious materials, contingent on adequate processing.

This study evaluates mortars that incorporate mixed recycled aggregates, biomass bottom ash, chamotte, wood waste, and expanded clay as partial substitutes for cement and natural aggregates. Three series of mortars were investigated: with 25% cement replacement, partial sand replacement, and simultaneous replacement of cement and sand. Mechanical, physical, durability, and thermal properties were evaluated, along with their relationships through a correlation analysis. Cement substitution did not result in a drastic reduction in compressive strength and produced limited thermal improvements, whereas sand substitution led to substantially greater reductions in thermal conductivity, ranging from approximately 10.3% for MRA to 59.1% for wood waste compared to the control. Expanded clay reduced thermal conductivity by 24.7%, while BBA-L showed greater insulating potential than BBA-PG but resulted in a reduction in compressive strength. The combination of chamotte, limestone filler as a cement substitute, MRA, and expanded clay as an aggregate substitute provided the best balance between thermal and mechanical performance, achieving a compressive strength of approximately 39 MPa at 90 days and reducing thermal conductivity by nearly 22% compared to the reference mortar. The results demonstrate that thermal performance depends largely on density and porosity, although the optimal selection of materials requires simultaneously considering both mechanical and physical properties.