Assessing the durability of biochar concrete: Performance under freeze-thaw cycles

This work investigates the effect of replacing cement with biochar on the mechanical properties and freeze-thaw resistance of concrete. Biochar, produced from wood pellets through thermal carbonization, was used as a partial substitute for cement at replacement ratios of 5%, 10%, and 15%. The fresh concrete properties, including slump and air content, were evaluated, followed by water curing for 14 and 28 days. The mechanical properties, including compressive strength, splitting tensile strength, and flexural strength, were measured under both standard curing and freeze-thaw conditions. Freeze-thaw durability was assessed based on the relative dynamic modulus of elasticity and mass-loss rates after 150 and 300 cycles. Scanning electron microscopy (SEM) was employed to analyze the bonding of biochar within the cement matrix and its interaction with hydration products. The results revealed that biochar replacement ratios within 10% improved both compressive and flexural strength while maintaining satisfactory freeze-thaw resistance. However, at 15% replacement, significant reductions in mechanical performance and durability were observed, with severe deterioration under freeze-thaw cycles.