BIOCHAR-BASED CONCRETE BLOCKS FROM RICE HUSK: A SUSTAINABLE SOLUTION FOR LOW-CARBON CONSTRUCTION

Abstract

This study investigates rice husk biochar (RHB) as a partial cement replacement in concrete blocks to enhance sustainability and reduce the environmental footprint of construction materials. RHB, produced via pyrolysis of agricultural residues, offers high porosity, silica content, and carbon sequestration potential, making it a promising additive. Experimental mixes were prepared with 5–30 wt. % RHB, using Ordinary Portland Cement, natural siliceous sand, and tap water. Tests included compressive and flexural strength, ultrasonic pulse velocity (UPV), water absorption, permeability, and thermal conductivity. Results showed that replacing 20–30 wt. % cement with RHB increased compressive strength by up to 15% when pre-mixed in a water-super plasticizer solution, while 20% replacement improved flexural strength by ~30%. UPV readings (~3 km/s) indicated no significant compromise in material integrity. Pre-soaked biochar reduced water absorption by up to 41% at 30% replacement, due to reduced porosity. Thermal conductivity decreased steadily with higher biochar content, confirming its insulation benefits. However, replacement levels above 15% in load-bearing applications led to strength reductions, indicating the need for optimal proportioning. Environmental assessment confirmed substantial carbon sequestration potential, with literature reporting up to 870 kg CO₂-eq mitigation per ton of dry feedstock. Additionally, using RHB supports waste valorization, reduces landfill pressure, and lowers embodied carbon. The mix designs required no specialized production methods, enabling immediate adoption in industry. These findings demonstrate that RHB-based concrete blocks offer mechanical adequacy, improved thermal performance, and significant environmental benefits, making them suitable for non-load-bearing and energy-efficient applications. Future work should optimize mixes for structural uses and assess long-term performance under real-world conditions.

Keywords Rice Husk Biochar, Sustainable Concrete, Carbon Sequestration, Thermal Insulation, Eco-Friendly Construction, Green Building Materials