Experimental and numerical studies on bond between seawater volcanic scoria aggregate concrete and GFRP rebars

The bond between glass fibre-reinforced plastic (GFRP) rebars and seawater volcanic scoria aggregate concrete (SVSAC) were systematically studied through a series of pull-out tests combined with numerical analyses. Fourteen groups and 42 specimens were fabricated, including five parameters: concrete type (SVSAC and ordinary concrete (OC)), concrete strength (C30 and C40), bond length (three, five, and eight times the rebar diameter), concrete cover thickness (67 and 42 mm), and rebar parameters (rib spacings of 8, 12.7, and 18 mm). An MTS-SANS universal loading system was adopted in this study, and a displacement-loading mode with a 0.2 mm/min loading rate was used during the pull-out test. The failure modes, strengths, bond-slip curves and bond mechanism (i.e., wedge action and mechanical interlocking) of the specimens were systematically investigated. Generally, the failure pattern of the SVSAC specimen with the GFRP rebar (SVSAC-GFRP) was a splitting failure, and its bond strength increased by 6.42 % on average compared with that of the OC specimen with the GFRP rebar (OC-GFRP). The bond strength of SVSAC-GFRP increased with increasing concrete strength and cover thickness and decreasing bond length. The bond-slip curve of SVSAC-GFRP changed with variations in the critical parameters. The curvature of the curve decreased after the adoption of the SVSAC and GFRP rebars. However, the decline in the curve tended to be smooth with increasing cover thickness and decreasing bond length. The peak slip of the SVSAC-GFRP specimen was 18.92 % smaller than that of the OC-GFRP specimen, and the difference was made negligible by improving the concrete strength. Furthermore, the effects of critical variables on the bond mechanism were also investigated through numerical simulations, indicating the characteristics of GFRP rebars greatly changed the wedge action and mechanical interlocking of specimen, causing a variation in macroscopic bond performance. In general, the bond strength of the SVSAC-GFRP specimens first increased and then decreased with increasing the rib height, obtaining its maximum value when the rib height was 6 % of the diameter. Finally, analytical model describing the bond properties of SVSAC-GFRP were established, which provide a basis for the practical application of marine composite structures.