Characteristics of Waste Concrete Powder-Based Artificial Fine Aggregate and Its Application in Concrete

Waste concrete powder (WCP), characterized by low reactivity and limited utilization potential, is rapidly accumulating due to the increasing volume of demolition and recycling activities, creating significant environmental and resource challenges. Meanwhile, the shortage of natural fine aggregate (NFA) has become increasingly severe. To address these issues, this study develops a sustainable approach that utilizes WCP as the main raw material, together with fly ash (FA), ground granulated blast-furnace slag (GGBFS), ordinary Portland cement (OPC), and sulphoaluminate cement (SAC), to produce a WCP-based artificial fine aggregate (WAFA) through a cold-bonding process. The physical, mechanical, and microstructural properties of WAFA were systematically analyzed, and its concrete performance was evaluated by replacing NFA at 100% volume. The results show that WAFA exhibits a regular spherical morphology and, after grading adjustment, meets the Zone II sand requirements of GB/T 14684-2022. Increasing the cement content from 2% to 10% raises the 28-day single-particle compressive strength (SPCS) from 12.98 MPa to 23.08 MPa (a 77.8% increase), while enhancing WCP reactivity improves SPCS from 16.17 MPa to 22.80 MPa (a 29.1% increase). Higher cement content and WCP reactivity also promote the formation of C–S–H gel and ettringite (AFt), resulting in higher bulk density, reduced water absorption, and a denser microstructure. In concrete applications, WAFA substantially improves workability, with slump values exceeding those of NFA and recycled fine aggregate (RFA) concretes. Although WAFA concrete exhibits slightly lower compressive and splitting tensile strengths compared with NFA concrete, optimized mix design allows the achievement of target strength grades from C30 to C50, with the C50-W10-50 mixture showing the most favorable mechanical performance. In summary, WAFA shows potential for contributing to the high-value utilization of construction waste and the reduction in natural sand consumption.