Flexural Behaviour of Rice Husk Biochar and Metakaolin Modified Concrete Beam

Abstract Although concrete is commonly utilized, it results in high CO 2 emissions from the production of cement and has limited durability in specific applications. In this context, this research examines the impact of partially replacing cement with rice husk biochar (RHB) and metakaolin (MK) both combined and individually on the mechanical properties and flexural behavior of reinforced concrete (RC) beams. The cement is replaced with 1% to 5% for RHB and MK and their mechanical properties and flexural behaviours were examined. The findings indicate that incorporating RHB beyond 1% resulted in decreased mechanical strength, while the combined replacement of 5% RHB and 5% MK (RBMC5) significantly improved concrete performance. The concrete mix containing 5% RHB and 5% MK exhibited a 15.5%, 15.4%, and 15.46% increase in compressive strength, split tensile strength and flexural strength as relative to Conventional concrete (CC), attributed to enhanced pozzolanic reactivity, pore refinement and interfacial bonding. Flexural tests on RC beams demonstrated that RBMC5 attained first crack, yield and ultimate loads that were 27.78%, 26.32% and 25.93% higher than the CC beam, along with enhanced ductility marked by increases in ultimate deflection and strain of 21.71% and 28.57%. The crack control was also enhanced, with a 13.10% reduction in maximum crack width, a 17.86% reduction in crack spacing, and a 50% increase in crack distribution. It was concluded that although RHB and MK showed specific advantages, their combined use as a replacement to cement resulted in the most significant enhancement in strength, deflection and cracking behavior.