Co-valorization of rice husk biochar and recycled concrete fine aggregate under NaHCO₃-solution immersion:...

To improve the synergistic valorization of construction and demolition waste and agricultural solid waste, this study used recycled concrete fine aggregate (RFA) and rice husk biochar (RHB) as the primary waste-derived materials to produce low-carbon recycled concrete cured in a NaHCO₃ solution. The RFA replacement ratio was fixed at 50%, while RHB was used to replace cement at levels ranging from 0% to 8%. Compressive strength, pore structure, phase composition, and microstructure were characterized. Life-cycle assessment and cost analysis were also conducted to evaluate the effects of the RHB replacement level on material performance and environmental and economic indicators.The mixture containing 3% RHB achieved a 28-day compressive strength of 40.5 MPa, which was 17.12% higher than that of the control mixture without RHB. This improvement was associated with reduced pore connectivity and an enhanced interfacial structure. The net global warming potential of this mixture was 346.78 kg CO₂-eq/m³. Its performance-normalized global warming potential and cost were approximately 17.4% and 10.1% lower than those of the control mixture, respectively. The carbon-reduction benefits were mainly attributed to cement substitution and stable carbon storage in the biochar.Although higher RHB replacement levels further reduced carbon emissions per unit volume, the resulting cement-dilution effect adversely affected mechanical performance. Considering waste utilization, structural performance, environmental impacts, and economic efficiency, the 3% RHB replacement level achieved the most favorable overall balance within the investigated range. These findings provide an experimental basis for the synergistic and high-value utilization of recycled concrete fine aggregate and rice husk waste.