Thermally Stabilized Agricultural Biochar Composites for High Strength Low Emission Concrete Systems (Published)
Concrete production contributes approximately 8% of global CO₂ emissions, while agricultural waste remains widely underutilized, often disposed of through open burning. Although raw biochar has been explored as a lightweight additive in concrete, its high porosity, water absorption, and weak interfacial bonding typically reduce mechanical strength, limiting its adoption in structural applications. This study addresses these challenges by engineering agricultural biochar through thermal stabilization to create high-strength, low-emission concrete composites.The objective was to transform agricultural waste-derived biochar into an active reinforcement phase for high-performance concrete. Rice husk biochar, initially pyrolyzed at 500°C, underwent secondary thermal stabilization at 600–900°C. The treated biochar replaced fine aggregate at 1–5% in a high-strength concrete mix targeting 60 MPa. Mechanical performance was evaluated via compressive strength testing, while microstructure, water absorption, and carbon balance were analyzed using SEM, mercury intrusion porosimetry (MIP), and thermogravimetric analysis (TGA), respectively.Thermal stabilization at 750°C reduced biochar water absorption from 300% to 85%, enhancing compatibility with the cement matrix. Concrete incorporating 3% stabilized biochar achieved a 28-day compressive strength of 58.2 MPa, retaining 95% of the control mix strength (61.5 MPa). Porosity decreased from 14.2% to 11.8%, and CO₂ emissions were reduced by 35% (from 480 to 310 kg CO₂-eq/m³). SEM imaging revealed a dense interfacial transition zone with C–S–H precipitation inside biochar pores, confirming its role as an active reinforcement rather than a passive filler.Thermally stabilized biochar enables carbon-negative, high-strength concrete, with 750°C treatment offering an optimal balance between mechanical performance and environmental benefit.
Keywords: Carbon Sequestration, Thermally stabilized biochar, agricultural waste valorization, high-strength concrete, interfacial transition zone