Experimental Study on Compressive Strength and Chloride Permeability Improvement of Recycled Aggregate Concrete Modified by Glazed Hollow Beads, Fly Ash, and Fiber Composites

Recycled concrete aggregates (RCAs) typically exhibit higher chloride permeability and lower strength compared to natural aggregates, potentially accelerating steel corrosion and compromising the durability of reinforced concrete structures. While functional additives like fibers, fly ash (FA), and glazed hollow beads (GHBs) are known to improve concrete properties, the quantification of the synergistic effects of their hybridization in RAC and a systematic multicriteria-based performance assessment are still lacking. This study experimentally investigates the individual and combined effects of GHB, FA, BF, and PPF on the compressive strength and electric flux of RAC. Fourteen mixtures were designed with different RCA replacements (0, 30, 50, and 100%), FA contents (0, 10, 20, and 30%), GHB dosages (0, 15, and 30%), and PPF and BF hybridization (0, 0.1 and 0.2%). Compared to unmodified RAC with 50% RCA replacement, the addition of 30% GHB significantly decreased the electric flux by 34.1% but comprised the compressive strength by 9.4%, whereas FA provided a weaker electric flux reduction of 16.3% alongside a lower strength decrease of 6.0%. A multicriteria analysis revealed that the synergistic GHB-FA-BF-PPF hybridization achieved the best performance of all formulations, exhibiting a remarkable 40.7% reduction in electric flux and a slight 1.3% increase in compressive strength compared to the unmodified RAC specimen. These findings demonstrate that the practical use of RAC modified by GHB-FA-BF-PPF hybridization would be highly beneficial in terms of mechanical performance as well as chloride permeability.