A wet carbonation enhancement approach to synergistic preparation of alkali-activated artificial aggregates from waste concrete powder and ground granulated blastfurnace slag

Abstract

To address the dual challenges of environmental pollution caused by recycled concrete powder (RCP) and the scarcity of natural aggregates (NA), this study developed an eco-friendly artificial aggregates (AA) composed of 50 % (RCP) and 50 % ground granulated blast furnace slag (GGBS). The synergistic effects of Ca(OH)₂ alkali activation, GGBS dosage, and curing conditions on the properties of AA were systematically evaluated through compressive strength, water absorption and bulk density, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and carbonation depth analysis. The results indicate that the AA prepared through the synergistic effect of Ca(OH)₂ alkali activation and wet carbonation in concrete wastewater exhibit superior performance, meeting the ASTM C330 standard. The compressive strength reaches 9.87 MPa, while water absorption decreases to 11.61 %. The addition of the alkali activator promotes the formation of C-(A)-S-H gels, which enhances apparent density and strength while reducing water absorption. Compared to dry carbonation, wet carbonation effectively accelerates both hydration and carbonation reactions, resulting in increased carbonation depth. Furthermore, microstructural analysis reveals that the deposition of calcite further fills pores, leading to improved aggregate density and durability. A life cycle assessment (LCA) confirms the environmental benefits of the AA. Compared to natural aggregates, the AA demonstrate a significant reduction in global warming potential (GWP), primarily attributed to the avoidance of RCP/GGBS landfilling and a tenfold reduction in transportation distance. Overall, the AA promote the resource utilization of solid waste, and exhibit strong potential for engineering applications.