Interlocking concrete pavers with wood biochar as partial cement replacement: engineering performance, embodied carbon, cost, and supply-demand analysis

Interlocking concrete pavers (ICPs) require substantial cement consumption, resulting in considerable embodied carbon emissions, while the regional availability of conventional supplementary cementitious materials is becoming increasingly constrained. Wood-biomass-derived biochar (WD-BC) valorizes forest residues while potentially lowering concrete’s embodied carbon. However, its feasibility in factory-produced ICPs, particularly at relatively high cement replacement levels, remains insufficiently understood. This study, therefore, evaluated WD-BC as a partial cement replacement through laboratory screening followed by plant-scale paver manufacturing, with emphasis on production feasibility, engineering performance, embodied carbon, and cost.Ball-milled WD-BC (median particle size = 15 μm) was screened, in the laboratory, in Portland limestone cement (PLC-IL) mortar at 2%, 5%, and 10% cement mass replacement, based on compressive strength performance. It was found that 10% WD-BC mortar can deliver statistically comparable 28-day strength compared to control (100% PLC-IL); therefore, it was selected for durability characterization and factory production. At 28 days, 10% WD-BC mortar exhibited 20% higher permeable voids, 76% higher initial water absorption, and 20% lower calcium-silicate-hydrate, indicating higher capillary porosity to control.In the factory trial, 10% WD-BC pavers achieved comparable early strength but 17.7% lower 28-day strength. The cradle-to-gate assessment indicated 4%-19% lower embodied CO2-equivalent per paver, depending on biochar’s carbon-credit, and 7%-10% cost savings. Overall, WD-BC pavers delivered carbon and cost benefits, but compliance-grade performance was not achieved under the production conditions evaluated. This study serves as an initial assessment of the industrial production feasibility of WD-BC in ICPs and identifies the improvements needed to enhance mixture uniformity and performance.