Biochar-amended high-strength engineered cementitious composites

Abstract

This study evaluates biochar as a sustainable cement replacement in high-strength engineered cementitious composites (ECC), focusing on mechanical performance, durability, microstructural characteristics, and environmental impacts. A biochar product was incorporated at 5 %, 10 %, 20 %, and 30 % replacement levels by weight of cement, and its effects were assessed through compressive strength test, tensile performance analysis, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and life cycle assessment (LCA). The biochar enhanced internal curing of the ECC, which led to 28-day compressive strengths ranging from 95.4 MPa to 99.6 MPa. The tensile strength of ECC was improved by the biochar addition, reaching 8.58 MPa at 20 wt% biochar content, though the strain capacity decreased at higher biochar levels. TGA revealed a reduction in the portlandite amount, suggesting enhanced pozzolanic activity of the binder, and SEM images confirmed a denser interfacial transition zone (ITZ) at 5–10 % biochar, improving the fiber-matrix bonding. Although higher biochar dosages increased the water sorptivity and gas permeability of ECC, they reduced the total shrinkage by up to 24%. The LCA indicated a carbon emission reduction of up to 80 %, sequestering 2.0 kg of CO₂-eq per kg of biochar. However, the source of biochar can influence the amount of emissions. These findings underscore the potential of biochar-ECC as a viable solution for sustainable construction, combining high mechanical performance with reduced environmental impacts.