Bond behavior between CFRP bars and coral seawater concrete

In order to study the bonding properties between coral sand seawater concrete (CSSC) and carbon fiber reinforced composite (CFRP) bars, 21 groups of 63 center-drawn specimens were pulled out with bonding length, protective layer thickness, concrete strength, concrete type and stir-bar constraint as test parameters. The results showed that the failure modes of the specimens could be categorized into two types, primarily depending on whether cracking occurred and where the damage was localized. Bond strength was observed to decrease progressively with increasing bond length. When the concrete cover thickness was relatively small (less than 5d_c), increasing the cover significantly enhanced bond strength; however, this enhancement diminished substantially when the cover exceeded 5d_c. Within a certain range, increasing concrete strength improved the bond performance between CFRP bars and CSSC. Compared to unconfined specimens, stirrup confinement increased the bond strength of CSSC specimens by an average of 7.7%. In addition, replacing CSSC with seawater sea-sand crushed stone concrete (SWSCC) led to an average increase of 8.2% in bond strength. Based on the experimental findings and supplemented by data from related studies, a bond strength prediction model for CFRP bars embedded in CSSC was developed. A bond coefficient K was introduced to characterize the bond interface, and a formula for the basic anchorage length was established. The proposed equations demonstrated good agreement with the test results and proved effective in predicting the bond performance between CFRP bars and CSSC.