Bond behavior and anchorage length of deformed bars in steel-polyethylene hybrid fiber engineered cementitious composites

Steel-polyethylene hybrid fiber engineered cementitious composites (HECC) featuring relatively high tensile strength and ductility, high elastic modulus, and high temperature resistance, making it an ideal alternative material under severe loading conditions. To understand the bond behavior between the HECC and rebar, direct pullout tests were conducted to systematically investigate the effects of rebar diameter d, anchorage length la, and cover thickness c on the bond performance. The experimental results indicate that the variation of bond strength with d is not apparent; la affects negatively while c influences positively on the average bond strength; and the critical c for HECC is about 4d. Additionally, the bond strength of HECC specimen is obviously higher than that of ECC and stirrups-confined concrete due to the crack-bridging effect of hybrid fibers at different scales. As noted, the ductility of HECC specimens is comparable with that of stirrups-confined concrete specimens, indicating that stirrup can be partially replaced when HECC is used which can simplify construction. Then, a calculation equation for the average bond strength of HECC is proposed, and the critical anchorage length of the rebar embedded in HECC is about 40% less than that embedded in ECC. Lastly, the design anchorage length of the rebar embedded in HECC is suggested based on a reliability analysis which is much smaller compared with the minimum embedment length of rebar in concrete predicted by the existing standards, providing a useful reference for reinforced HECC structural design.