Progress and prospects of biochar as concrete filler: A review

This review examines the current progress and emerging trends in utilizing biochar as a concrete filler, highlighting its multifaceted benefits and challenges in sustainable construction. Recent research demonstrates that biochar incorporation significantly influences both fresh and hardened concrete properties through complex physical and chemical mechanisms. In fresh concrete, biochar affects workability, setting time, and rheological behavior through its high surface area and unique pore structure. The material's water retention capabilities contribute to enhanced hydration processes, while its presence modifies air void distribution and fresh density characteristics. In hardened concrete, optimal biochar dosages (2–5 % by mass of cement) demonstrate improved mechanical performance, with studies reporting up to 76 % increase in compressive strength. The modified pore structure and enhanced hydration products contribute to improved durability against chemical attack and freeze-thaw cycles. Microstructural analysis reveals distinctive interfacial transition zones and refined pore networks, directly influencing engineering properties. Environmental benefits include significant carbon sequestration potential, with studies showing up to 9.40 kg CO₂ sequestration per cubic meter of concrete. Life cycle assessments indicate substantial reductions in environmental impacts across multiple categories. However, challenges remain in standardization, quality control, and production scalability. Future research directions should focus on optimizing biochar properties, understanding long-term performance, and developing predictive models for broader commercial implementation.