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.

土壤中混凝土的强化风化（enhanced weathering）作用具备捕获大气二氧化碳（CO₂）的潜力。本研究旨在开展室内实验，评估作为土壤中强化风化材料的混凝土的环境影响与碳捕获（carbon capture）潜力。本研究设置了四组柱实验（column study）处理，具体如下：1）100%土壤（S组）；2）按重量计含90%土壤与10%粒径0.25–0.71 mm的混凝土碎屑（S + Cfine组）；3）按重量计含90%土壤与10%粒径8–25 mm的混凝土碎屑（S + Ccoarse组）；4）全部由粒径8–25 mm混凝土碎屑组成的混凝土（C组）。向各柱体中加入去离子水（deionized water），持续时长为16周。相较于S组（6.9 ± 0.22）与S + Ccoarse组（7.1 ± 0.08），S + Cfine组的土壤pH值显著提升至8.0 ± 0.07；C组的渗滤液（leachate）pH值则出现显著升高。S + Cfine组样品的渗滤液硝酸根（NO₃⁻）浓度为33 ± 18 mg·L⁻¹，显著高于其余各组。S + Cfine组的土壤微生物群落浓度显著降低。S + Cfine组测算得到的平均碳酸氢根（HCO₃⁻）浓度为350 ± 120 mg·L⁻¹，显著高于S组（230 ± 100 mg·L⁻¹）、C组（270 ± 170 mg·L⁻¹）与S + Ccoarse组（260 ± 50 mg·L⁻¹）。混凝土与土壤混合样品中钙离子（Ca²⁺）、硫酸根（SO₄²⁻）、原硅酸（H₄SiO₄）与碳酸氢根（HCO₃⁻）浓度升高，表明土壤与混凝土之间发生了化学反应，且该反应大概率可捕获大气二氧化碳。