Bond stress-slip properties and analytical models between high-strength lightweight aggregate concrete and high-strength steel bars

Twenty-eight pull-out specimens in thirteen groups were tested to investigate the bond properties between high-strength lightweight aggregate concrete (HSLC) and HRB600 bars with different bond lengths, steel fiber contents, concrete strength, and cover thickness. The analytical expressions for radial deformation, radial stress, and bond strength based on four deformation assumptions were derived and compared by incorporating the thick-walled cylinder model, bilinear softening constitutive curve, and fracture energy model of HSLC. Eventually, a three-segment bond stress-slip model was proposed. The test results showed that the increase in research parameters apart from bond length could improve the failure mode, bond strength, descending slope of curves, and bond toughness. The bond strength was in the range of 24.99 ∼ 39.79 MPa except for LC70–0S-L80 with splitting failure. The optimal match of mixture LC70–0.6S and HRB600 bars could fully utilize the mechanical properties of both materials, for which the allowable minimum ratio of cover thickness-to-rebar diameter was recommended to be 3.75. The bond toughness of specimens cast with LC70–0S, LC70–0.3S, LC50–0.6S, and LC70–0.6S increased sequentially at the same bond length. The calculation results indicated that the assumptions of constant and elastic deformation provided upper and lower predictions of bond strength, respectively, and the assumption of equivalent elastic deformation slightly overestimated the bond strength due to the nonlinear deformation of cracked concrete. The assumption of equivalent elastic deformation at cohesive stress equaling half of the tensile strength of concrete obtained satisfactory calculated bond strengths, and the predicted bond stress-slip curves agreed well with the experimental curves, describing accurately the cracking characteristics and bond behavior between HSLC and HRB600 bars.