In a comprehensive review published in the Alexandria Engineering Journal, researchers Yuan Zhou, Sheliang Wang, and Ling Chen delve into the transformative potential of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More as a concrete filler. Their work highlights how this carbon-rich material can revolutionize sustainable construction by significantly enhancing concrete’s mechanical properties and environmental footprint. This review synthesizes recent research, demonstrating that biochar’s incorporation profoundly influences both fresh and hardened concrete through intricate physical and chemical mechanisms, offering a pathway to greener, stronger building materials.

Biochar’s impact begins with fresh concrete, where its high surface area and unique pore structure influence workability, setting time, and rheological behavior. Critically, the material’s excellent water retention capabilities contribute to enhanced hydration processes, acting as an internal curing agent. Studies reveal that incorporating 2% biochar, particularly finer particles (less than 45 µm), can reduce initial setting times by approximately 15-20%. For ultra-high-performance concrete, this acceleration can be even more pronounced, with initial setting times decreasing by up to 25%. This effect is largely due to biochar particles providing numerous nucleation sites for the formation of calcium silicate hydrate (C-S-H) gel and other vital hydration products. Research further indicates that bamboo biochar can increase the heat release rate during the acceleration period of hydration by up to 18%, shifting the main hydration peak earlier by about 2-3 hours with a 5% addition. Overall, biochar-modified cement pastes have shown a 25% increase in cumulative heat release within the first 24 hours of hydration, underscoring more extensive early-age reactions.

Beyond fresh properties, biochar significantly improves hardened concrete performance. Optimal dosages, typically between 2% and 5% by mass of cement, have been shown to boost mechanical performance, with studies reporting an impressive increase of up to 76% in compressive strength. The material’s modified pore structure and enhanced hydration products also contribute to improved durability against aggressive environmental factors like chemical attack and freeze-thaw cycles. For instance, pre-soaked biochar samples demonstrated a 41% reduction in water absorption compared to control samples, indicating enhanced durability. Concrete containing 1-2 weight percent wood waste biochar exhibited 8-11% higher strength after 120 days of chloride exposure, while mortar composites with wood waste and rice husk biochar showed a 14-17% increase in compressive strength after 120 days of sulfate exposure. Additionally, 5% biochar content can increase electrical resistivity by 13% (9.10 KΩ·cm), suggesting improved resistance to chloride penetration. Microstructural analysis reveals that biochar refines the pore network, with a 5% replacement leading to a notable 55.6% reduction in large pore volume within the concrete. The biochar particles themselves contribute significantly to the composite’s overall porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More, exhibiting approximately 45.7% internal porosity.

Biochar also plays a crucial role in enhancing the thermal properties of concrete, leading to better insulation. Its inherent porous structure and lower thermal conductivity, compared to conventional concrete constituents, can reduce the thermal conductivity of composites by up to 50%. Specifically, incorporating just 1-10 weight percent of wood-derived biochar can reduce thermal conductivity by 16-39% in mortar samples. This creates discontinuities that impede heat transfer, contributing to improved thermal stability and energy efficiency in structures.

One of the most compelling aspects of biochar in concrete is its substantial environmental benefit, particularly its carbon sequestration potential. Biochar acts as a stable carbon storage medium, effectively locking away atmospheric carbon within the concrete matrix for its entire service life. Incorporating just 3% peanut shell biochar into concrete can increase carbon dioxide uptake by 2.5-3%, translating to approximately 7.20-9.40 kg of carbon dioxide sequestration per cubic meter of concrete. Wood fiber-based biochars are particularly effective, showing CO2 adsorption capacities up to 3.3 mmol/g. Furthermore, using biochar promotes circular economy principles by transforming agricultural and forestry residues into valuable construction materials.

While the prospects are exciting, challenges remain in standardization, quality control, and production scalability. Future research will focus on optimizing biochar properties, understanding long-term performance, and developing predictive models to facilitate broader commercial implementation. Despite these hurdles, the integration of biochar into concrete represents a significant leap forward in creating construction materials that are not only stronger but also more sustainable.

Source: Zhou, Y., Wang, S., & Chen, L. (2025). Progress and prospects of biochar as concrete filler: A review. Alexandria Engineering Journal, 128, 306-323.