Biochar-concrete composite: manufacturing, characterization and performance evaluation at elevated temperature

Abstract

Filler additives in concrete influence its mechanical and permeability properties under normal and elevated temperature during serviceability stage of structure. However, there is limited investigation about influence of bio-based fillers material on strength and durability of structural concrete at elevated temperature. This study explores the mechanical and permeability performance of biochar-concrete composites under normal condition and after thermal damage at elevated temperature (300 ˚C and 550˚C). Biochar is prepared by pyrolysis of locally collected wood waste at 500˚C (BC500). The strength and permeability performance of BC 500 concrete are compared with plain concrete and concrete with silica fume (added at 10% replacement of cement) exposed to similar conditions. The findings show that addition of 0.50 %-1 % BC500 increase compressive strength at 7-day and 28-day age compared to control mix by 15-20% under normal condition. This is linked to densification effect of biochar through filler effect and reduction of effective water-cement ratio. Concrete with silica fume and 1-2 wt.% of BC 500 show similar improvement in water tightness (35-45%) compared to control concrete. At elevated temperature, addition of 1-2 wt.% BC 500 is found to minimize loss in weight and strength compared to control and concrete with silica fume. Investigations show that biochar addition leads to lower damage to microstructure of concrete during thermal treatment, leading to 22-25% higher residual strength and water tightness compared to control mix. The findings suggest that addition of biochar has the potential to improve serviceability performance of concrete structures, which is also an effective way to promote recycling of wood waste.