Development and Performance Evaluation of Waste Concrete Powder-Based Geopolymer Recycled Concrete

To achieve a green recycled concrete with excellent mechanical properties and workability, this paper utilized recycled concrete powder, fly ash and granulated ground blast furnace slag as primary materials. Recycled concrete aggregates served as coarse aggregates in the formulation of a recycled concrete powder-based geopolymer recycled concrete (RCPGRC). The study investigated the impact of additional water consumption (AWC), recycled fine aggregate content (RFAC) and the mass ratio of solid powder to aggregate (P/A) on both the mechanical property and workability of RCPGRC. Employing variance and range analysis, the research comprehensively assessed the contributing factors to the concrete's performance and identified the optimum mixture ratio. Characterization of the phase composition and micromorphology were characterized through X-ray diffraction and scanning electron microscopy. The results show that: (1) The AWC had the greatest influence on the unconfined compressive strength (UCS), slump, and setting times, while RFAC and P/A were smaller. AWC of 3%, RFAC of 10%, and P/A of 26% were the inflection points of the UCS, slump, and setting times with AWC, RFAC, and P/A, respectively. (2) The production rate and quantity of geopolymer gels production, as well as the cracks and voids, were affected when the mixture ratios deviated from these optimal inflection points. (3) These inflection points can be utilized as the indexes for rapid judge the optimum mixture ratio of RCPGRC.