Biochar bricks and plasters: Early experiments with replacement viability in building materials

Even though buildings contribute 37% of global greenhouse gas emissions, the majority of efforts to reduce their GHG impacts have focused on reducing operational carbon emissions, while solutions for reducing embodied carbon of building materials lag behind. Bricks are a ubiquitous construction material utilized across the globe for their durability and excellent physical and mechanical properties. However, processes of manufacturing and curing most cementitious and clay bricks and plasters have a negative environmental impact, including damage to soil and workers’ health, high consumption of energy, and emission of GHGs.
Biochar is a charcoal-like material made from the thermal decomposition of biomass in the absence of oxygen at up to 800°C. Biochar can also sequester carbon and improve properties and net CO2 reductions in plasters and Portland cement-based concrete, respectively.
After extensive review of existing biochar studies, we conducted experiments in replacing cement, sand and lime with biochar in cementitious and clay mix designs for bricks and plasters. The biochar replacement mix recipes showed promising results and were focused on mix designs which include cement, lime, or clay. The mix designs were fabricated in two batches for testing. The first batch of samples (36) was fabricated with typical brick dimensions (3-ǫ” x 2-ó” x 7-ǫ”) utilizing a custom-designed reusable and adjustable mold for this project. The concrete bricks were tested for maximum compressive strength and three-point bending load capacities on both their horizontal and vertical axes. The second batch of samples (12) were fabricated as 1” thick plaster applications on two 6”x12” substrates (metal and wood furring strip lath), for testing. Six plaster mix designs applied to two different lath types. Common industry standard mix designs for lime, cement and clay bricks and plasters, without any biochar substitutions, served as a control for the qualitative and quantitative data collection process.