Effect of fiber reinforcement on bond behavior between coral aggregate concrete and GFRP bar

The increasing construction activities on islands make FRP reinforced coral aggregate concrete (CAC) more and more promising. However, the poor mechanical performance of CAC reduces the bond properties between CAC and GFRP bars, which poses a threat to engineering safety and long-term service. Therefore, fibers were added as reinforcement in CAC to improve the bond properties. In the present study, the effect of fiber reinforcement on the bond behavior between CAC and GFRP bars was studied by pull-out tests. The mechanical properties of fiber reinforced coral aggregate concrete (FRCAC) were also investigated as a comparison to the bond properties. The microstructure and failure characteristics of the interface between FRCAC and GFRP bars were observed through scanning electron microscopy. The results showed that adding fibers as reinforcement can inhibit the development of cracks in FRCAC and even change the failure mode of bonding specimens from concrete splitting to bar pull-out. The mechanical and bond properties of CAC reinforced by fibers were all improved, although the improvement was not as significant as that observed in traditional normal aggregate concrete. The reinforcing effect was more significant on mechanical properties than on bond properties as the fiber content increased. Among polypropylene fiber, basalt fiber, and copper-surfaced steel fiber, basalt fiber and copper-surfaced steel fiber demonstrated a more significant reinforcing effect on the bond properties between FRCAC and GFRP bar than polypropylene fiber. A calculation method for determining the bond strength between FRCAC and GFRP bar was proposed.