Carbon capture potential and environmental impact of concrete weathering in soil

The enhanced weathering of concrete in soil has potential to capture atmospheric CO₂. The objective of this research was to conduct a laboratory experiment and evaluate the environmental impacts and carbon capture potential of concrete as an enhanced weathering material in soil. A column study was conducted with four treatments comprised of: 1) 100 % soil (S treatment), 2) 90 % soil and 10 % concrete by weight of 0.25-0.71 mm diameter fragments (S + C_fine treatment), 3) 90 % soil and 10 % concrete by weight of 8-25 mm diameter fragments (S + C_coarse treatment), and 4) 100 % concrete composed of 8-25 mm diameter fragments (C treatment). Deionized water was added to the columns for 16 weeks. The S + C_fine treatment experienced a significant increase in soil pH (8.0 ± 0.07) compared to the S (6.9 ± 0.22) and S + C_coarse (7.1 ± 0.08) treatments. The C treatment experienced a significant increase in leachate pH. Leachate NO₃^- concentrations in the S + C_fine (33 ± 18 mg L^-1) samples were significantly greater than those in other treatments. Soil microbial community concentrations were significantly less in the S + C_fine treatment. The S + C_fine treatment had a calculated average HCO₃^- concentration of 350 ± 120 mg L^-1 which was significantly greater than the S (230 ± 100 mg L^-1), C (270 ± 170 mg L^-1), and S + C_coarse (260 ± 50 mg L^-1) treatments. Increased concentrations of Ca²⁺, SO₄^2-, H₄SiO_4, and HCO₃^- in the mixed concrete and soil samples are evidence that chemical reactions occurred due to the soil-concrete interaction and are likely capturing atmospheric CO₂.