Towards Carbon-Neutrality in Concrete: The Role of Biochar in Air-Entrained and Non-Air-Entrained Systems as Sand Replacement

Biochar is a carbon-rich solid residue resulting from the pyrolysis or devolatilization of waste biomass (e.g., wood chips, sawdust, grass) at elevated temperatures in an oxygen-limited furnace. Biochar provides an effective pathway for atmospheric CO2 removal via photosynthesis in biomass, which is subsequently converted to biochar while also producing energy. Due to its carbon-negative footprint (-2.4 to -2.9 kg CO2eq/ kg biochar), biochar could be used to reduce or eliminate the net CO2 emission of concrete. This study aims to produce low-carbon to carbon-negative concrete mixtures by utilizing biochar as a partial to total replacement of natural sand while leveraging its internal curing capacity to meet the performance requirements of workability, air content, and compressive strength of concrete. Specifically, concrete mixtures for two applications are produced: A non-air-entrained (NAE) concrete with 2500 psi minimum 28-day strength for basements, foundations, and walls not exposed to weather and an air-entrained (AE) concrete with 4000 psi minimum 28-day strength and 7% air content for pavements. Proper practices for the pre-treatment of biochar and mixture proportioning of biochar-augmented concrete will be shared.