At high replacement levels, recycled aggregate concrete (RAC) has durability consequences because of its porosity and weak interfacial transition zones (ITZs). This study examines how alkali-resistant glass fiber (ARGF) and calcined kaolin clay (CKC) work together to produce high-performance RAC (HP-RAC). Recycled coarse aggregate (RCA: 0–100%), CKC (0–15% by mass), and ARGF (0–1.5% by mass of concrete) were used in a full factorial design with a constant low water–binder ratio of 0.37. The freshness, mechanical qualities, and durability up to 91 days of 80 mixtures were assessed. According to the results, ARGF increased tensile and flexural performance through crack-bridging without compromising transport characteristics, whereas CKC reduced sorptivity, chloride ingress, and sulphate damage while also significantly improving matrix densification. Performance was negatively impacted by RCA replacement above 50%, although liabilities were lessened at about 25% replacement when 10–15% CKC and 0.5% ARGF were added, resulting in compressive strengths above 60 MPa and compliance with protective durability classes. With substantial RCA×CKC interactions, statistical analysis (ANOVA, R2 = 0.977, p < 0.0001) validated the importance of mix design parameters. The results show that ARGF is a serviceability modifier and CKC is the main durability lever in HP-RAC, providing a verified route for sustainable structural concrete made from demolition waste.
