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 + Cfine treatment), 3) 90 % soil
and 10 % concrete by weight of 8–25 mm diameter
fragments (S + Ccoarse 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 + Cfine treatment
experienced a significant increase in soil pH
(8.0 ± 0.07) compared to the S
(6.9 ± 0.22) and
S + Ccoarse (7.1 ± 0.08)
treatments. The C treatment experienced a significant increase in leachate
pH. Leachate NO3− concentrations in the
S + Cfine (33 ± 18 mg L−1) samples were significantly greater than those in other treatments. Soil microbial community concentrations were significantly less in the S + Cfine treatment. The S + Cfine 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 + Ccoarse (260 ± 50 mg L−1) treatments. Increased concentrations of Ca2+, SO42−, H4SiO4, 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.