Study on bond properties of corroded NPR (negative Poisson's ratio) steel bar embedded in marine concrete

In this work, 48 pull-out test specimens of 150 mm x 150 mm x 150 mm have been examined to assess the bond behavior between corroded NPR (negative Poisson' s ratio steel bar) and marine concrete with different anchorage bond length. Three variables are considered: two types of steel bar (NPR bar and HRB400 steel bar), theoretical corrosion ratio of steel bar (rho = 0, 1\% , 2\% , 3\% ), anchorage length (5 or 7 times of steel bar diameter). Experiment results showed that under the same extent of bars theoretical corrosion ratio and anchorage length, the bond between NPR and marine concrete exhibits lower value than that of HRB400. Moreover, as measured mass corrosion ratio increases, the bond strength of NPR and HRB400 embedded in marine concrete shows a trend of first rising and then falling. For NPR bas, the measured mass corrosion ratio corresponding to the peak value of bond strength is about 1.8 %. Furthermore, considering the condition of rho = 0, 1\% , 2\% , NPR bar specimens with anchorage length of 7d show slightly lower bond capacity than that of specimens with anchorage length of 5d due to the inhomogeneity of bond stress distribution of steel bar and surrounding concrete. Finally, the bond stress-slip constitutive model between two types of steel bars and marine concrete considering different working conditions has been proposed.