Study on the Performance Enhancement of Recycled Fine Aggregate Through Carbonation with Calcium Source Supplied by Industrial Waste Residue

With the rapid advancement of urbanization, the reuse of waste concrete has become more and more important. Recycled aggregate inevitably develops microcracks during the crushing process of waste concrete, resulting in undesirable characteristics such as low density and strong water absorption. This study employed an external calcium source combined with wet carbonation to optimize the performance of recycled fine aggregate (RFA). A series of microscopic analytical techniques, including scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and the Brunauer-Emmett-Teller (BET) method, were used to elucidate the underlying mechanisms. The results indicate that calcium-rich leachate can be obtained by soaking alkali residue in 0.3 mol/L acetic acid at a solid-to-liquid ratio of 1:6. When this leachate was further used to soak the aggregate at a solid-to-liquid ratio of 1:2, followed by carbonation in a carbonation chamber, the carbonation effect reached its optimum. Under these conditions, the saturated water absorption of the recycled fine aggregate decreased to 16%, the carbon sequestration efficiency increased by 66.8%, and pores smaller than 50 nm accounted for 62.9% of the total pore volume. Furthermore, a Bacillus strain capable of producing carbonic anhydrase was introduced to enhance the carbonation reaction. The results demonstrated that when Bacillus was added to acetic acid-modified recycled fine aggregate, the saturated water absorption further decreased to 14.6%, while the carbon sequestration efficiency significantly increased to 109.04%. Additionally, pores smaller than 50 nm constitute 79.2% of the total pore volume. These findings suggest that utilizing calcium-containing industrial waste as a calcium source for recycled fine aggregate, followed by carbonation modification, is highly effective. This approach not only improves the performance of recycled aggregates but also promotes the reutilization of industrial waste, contributing to sustainable construction practices.