Effects of Partial Replacement of Cement with Biochar in Concrete for Carbon Sequestration

The cement industry accounts for approximately 8% of globally anthropogenic CO₂ emissions and requires sustainable solutions. The use of the commercially available BBQ coal biochar for partial cement replacement for carbon sequestration in concrete was studied. Five different concrete mix proportions were designed using a constant water-cement ratio of 0.7 and a concrete mix ratio of 1:2:4 with biochar at 0%, 5%, 10%, 15%, and 20% by the weight of Ordinary Portland Cement (OPC). The biochar had a carbon content of 32.20% and alkaline pH of 9.1. Physical, mechanical and thermal properties were determined at 7 and 28 days along with a theoretical carbon sequestration calculation. Results showed the bulk density and the compressive strength decreasing gradually with the increasing amount of biochar. But the 5% replacement mix (BCC-5) produced 28-day compressive strength of 21.03 N/mm², which is just 4.45% less than the control and above the minimum requirement for M20 grade. BCC-5 also exhibited good flexural strength and thermal resilience at 500C, and sequestered 17.73 g CO₂-equivalent/block. Hence, the dosage of 5% BBQ biochar is found to be the optimum, providing a compromise between structural strength and eco-friendly properties for sustainable building.