The effect of chemical- versus microbial-induced calcium carbonate mineralization on the enhancement of fine recycled concrete aggregate: A comparative study

This paper studies the effects of chemical- and microbial-based calcium carbonate mineralization on the enhancement of CDW-derived fine recycled concrete aggregate (RCA) in terms of microstructural, physical, and mechanical properties. The chemical mineralization process was conducted via carbonation cabinet with adjusted CO2 gas concentration, temperature, and relative humidity through 7 days of curing. The microbial-induced carbonation method was implemented by submerging RCA into the solution of nutrients and nonaxenic nitrate reducing biogranules under ambient conditions. After that, scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric (TG/DTG) analysis were applied to evaluate the crystallographic structure of carbonation products. Mortar specimens were prepared using untreated RCA (U-RCA), chemically-treated RCA (C-RCA) and microbially-treated RCA (M-RCA) to reveal the effects on the workability and, mechanical properties of the cementitious system. The results indicated that chemical carbonation significantly affected the water absorption of RCA, the volume of the permeable void, workability and, the compressive strength of the cementitious system. On the other hand, microbial-induced carbonation slightly influenced the compressive strength of mortar specimens and adversely affected the physical properties of MRCA. Despite the greater calcium carbonate precipitation on M-RCA observed via TG/DTG and XRD analysis, heterogeneous precipitation of carbonation products and the presence of bacterial remains on M-RCA indicated that chemical-derived carbonation could have more pronounced effects on RCA improvement. Additionally, comparative cost analysis revealed that chemical carbonation is economically more feasible.