AbstractThe application of fiber-reinforced polymer (FRP) reinforcement in coral aggregate concrete (CAC) structures is a new solution to the shortage of construction materials on islands and reefs far from the mainland and to the insufficient durability of steel-reinforced concrete members. However, the understanding of the durability of FRP bar-reinforced CAC members is not yet clear, which greatly limits the evaluation and design of their long-term performance. In this paper, accelerated degradation tests were carried out in a high-temperature and high-humidity marine environment to study the durability of CAC beams reinforced with basalt FRP (BFRP) bars and stirrups. Four-point flexural tests were performed on beams that have been subjected to environmental conditions to study the effects of environmental time, temperature, and concrete type on the failure mode, cracking and ultimate moment, midspan deflection, crack width and pattern, and ductility. In addition, an engineered cementitious composite (ECC)–CAC composite beam reinforced with BFRP bars was proposed to improve the mechanical properties and durability of the CAC beam reinforced with BFRP bars. The results showed that, in the early stage of environmental conditions (1–2 months), the effect of the environment on the mechanical properties of the CAC beam reinforced with BFRP bars was beneficial. With increasing environmental condition time, the effect of environmental conditions on the mechanical properties of the CAC beam reinforced with BFRP bars gradually weakened. The failure mode, deflection, crack width, and crack pattern of the ECC–CAC composite beam reinforced with BFRP bars were greatly improved compared with those of the CAC beam reinforced with BFRP bars.