Comprehensive evaluation of the environmental performance and durability of biochar-incorporated concrete

To achieve global carbon neutrality, the construction industry is increasingly focused on reducing the carbon footprint of cement-based materials. However, comprehensive evaluations of biochar-incorporated concrete integrating long-term mechanical performance, freeze–thaw durability, and environmental impact remain limited. To address these issues, this study presents a comprehensive experimental evaluation of wood-based biochar as an alternative supplementary cementitious material (ASCM) in concrete. The physical characteristics of the biochar were analyzed using scanning electron microscopy (SEM), SEM–EDX, and Brunauer–Emmett–Teller (BET) analyses, and the chemical characteristics were evaluated using XPS. Concrete performance was evaluated in terms of mechanical properties (compressive strength, flexural strength, and static modulus), freeze–thaw durability with quantitative image-based surface analysis, and a life cycle assessment (LCA) was performed to quantify global warming potential (GWP). The results indicate that concrete containing 5% biochar achieved the target design strength of 24 MPa, whereas 7% replacement resulted in a compressive strength reduction of up to 35.5% compared to the plain mix. After 300 freeze–thaw cycles, the 5% biochar mixture maintained a durability factor of 96.8% and reduced the increase in surface scaling and increase in void count by approximately 74 and 72%, respectively, compared with the plain specimen. LCA results revealed that increasing the biochar replacement ratio reduced GWP, with up to a 27.7% reduction at 7% replacement. Considering both mechanical performance and environmental impact, a biochar replacement range of 3–5% was identified as optimal. These findings demonstrate that wood-based biochar is a viable ASCM for sustainable and low-carbon concrete construction.