Flexural behavior of FRP bars reinforced seawater coral aggregate concrete beams incorporating alkali-activated materials

Cement-based coral aggregate concrete (CAC) and its structures reinforced with fiber-reinforced polymer (FRP) bars suffer from low strength, poor anti-permeability resistance, and insufficient durability. To overcome these drawbacks, this study employs well-durable slag-based alkali-activated materials as alternatives to ordinary Portland cement to develop FRP bars reinforced alkali-activated coral aggregate concrete (AACAC) beams. The effects of the type of FRP bars (GFRP, BFRP, and CFRP bars), the longitudinal reinforcement ratio (0.48–1.12%), and the diameter of FRP bars (8 and 10 mm) on the flexural behavior of CAC and AACAC beams were evaluated. The results revealed that with the increased reinforcement ratio, the number of cracks in AACAC beams increased, and their crack height and crack spacing gradually lowered. Furthermore, the cracking load, ultimate load, and slope of load–deflection curves at the ascending stage (i.e., flexural stiffness) exerted a significant improvement with increasing reinforcement ratio, but the mid-span deflection and the strength utilization of internal FRP bars decreased. When the reinforcement ratio increased from 0.48 to 1.12%, the ultimate load capacity for BFRP bars reinforced AACAC beam was enhanced by about 47.8%, but the strength utilization of internal FRP bars reduced from 66.8 to 55.1%. Compared with cement-based CAC beams, AACAC beams exhibited a smaller crack width under the same concrete strength and load value, but contained a lower ultimate loading capacity and mid-span deflection, demonstrating that AACAC beams had a bigger brittleness than CAC beams.