Combination of Biochar and Silica Fume as Partial Cement Replacement in Mortar: Performance Evaluation Under Normal and Elevated Temperature

Utilization of waste derived materials to replace part of cement is an effective strategy for cost effective and sustainable concrete constructions. This study investigates a blend comprising of different proportions of silica fume (SF) and biochar, prepared from wood (MWBC) and food waste (FWBC) respectively, to replace 10 wt.% of cement in mortar mixes. Mechanical and permeability properties of the developed cement-biochar composites were tested under normal and elevated temperature (500 degrees C). Experimental results show that combination of biochar and silica fume enhance compressive strength (by up to 18-20%) and structural efficiency (strength to density ratio) compared to control mixtures. Water permeability results confirmed that blend of biochar and silica fume play a significant role in reducing capillary water absorption by 50-60% compared to control mortar, which is attributed to filler effect and water retention by fine biochar particles. Mortar with combined admixtures (biochar and SF) had higher resistance to damage at elevated temperature, which was evident from 22% higher strength and lower permeability (22-24%) compared to control mix after thermal damage. Finally, economic analysis highlights that using blend of biochar and silica fume to replace cement is more economic than using only silica fume, due to relatively lower cost and waste recycling associated with biochar production. In summary, this study suggests that biochar may be a sustainable and economic alternative to reduce usage of cement and more expensive pozzolanic fillers in cementitious composites.