Effect of biochar on compressive strength and fracture performance of concrete

The production of cement aggravated the release of CO2 into the atmosphere. The replacement of cement by carbon neutral biochar will reduce CO2 emissions. In this study, therefore, the effects of biochar addition and age on compressive strength and fracture performance of concrete were investigated. The results revealed that the compressive strength, load bearing capacity, and initial fracture toughness of biochar-modified concrete increased firstly and then decreased with the increase of biochar addition. 1 wt% replacement of cement with biochar was identified as the optimal content in terms of compressive strength. For three-point bending beams, the biochar-modified concrete with 3 wt% replacement of cement with biochar showed better load bearing capacity and crack resistance, and the damage scale was lower at the same loading stage. The biochar addition reduced the ductility of concrete and fracture energy. When the biochar addition was 3 wt%, the fracture energy of biochar-modified concrete at different ages (7d, 14d and 28d) reduced by 3.6%, 33.3% and 33.2%, respectively, compared with that of plain concrete. The compressive strength, load bearing capacity and initial fracture toughness gradually increased with the increase of curing time. The replacement of cement by biochar promoted the compressive strength and fracture performance of concrete, which provided a CO2-reducing way for the production of concrete.