Mechanical, durability, and microstructural performance of biochar-modified concrete using faecal sludge–derived biochar

Abstract This research explores the potentiality of biochar derived from faecal sludge collected at faecal sludge treatment plants (FSTP) by partially replacing cements used in concrete applications. These plants collect, treat, and manage human waste from septic tanks and sanitation systems. This study focuses on determining the optimal dose of biochar as application for concrete’s mechanical, durability properties, and microstructural changes. The biochar's pozzolanic activity was evaluated through the strength activity index, while parameters such as shrinkage, compressive strength, flexural strength, water absorption, and porosity were also measured to gauge its impact on concrete performance. Results indicate that incorporating biochar at specific dosages at 5% and 10% replacement yields significant improvements in concrete properties. After a 91-day curing period, concrete with a 10% biochar substitution demonstrated a 21% increase in compressive strength and a 42% increase in flexural strength, highlighting biochar’s contribution to mechanical performance. Water absorption and porosity values for concrete with a 15% biochar content were found to be comparable to those of conventional control mixes after 28 days of curing. After 120 days, the drying shrinkage observed in a 10% biochar mortar mix was like that in ordinary Portland cement (OPC) mortar, indicating the potential of biochar to maintain dimensional stability over extended periods. The reduction in heavy metal concentration in the concrete specimens due to the increased biochar content was also reported. This result successfully demonstrates, it is helpful to sustain environment by potentially lowering the leaching of harmful substances.