Study on the mechanical properties of NPR steel bars and the bonding properties with marine concrete

Negative Poisson's Ratio (NPR) steel bar is a new type of high-strength, high-ductility and corrosion-resistant steel. In this paper, the chemical composition, metallographic structure, mechanical properties of NPR bar and its bond properties with marine concrete are studied and analyzed, and compared with ordinary (HRB400) steel bar. The metallographic structure of the NPR bar shows that it is the fully austenitic material. Furthermore, the mechanical properties such as yield strength, tensile strength, elongation after fracture, and total elongation at maximum force of NPR bar are significantly higher than ordinary steel bars. The results of central pull-out test show that the shape of ribs on the surface of the bar influences directly on the bond strength, and the bond strength of NPR reinforcement is lower than ordinary reinforcement. Moreover, the bond strength of NPR reinforcement increases with the decrease of bond length and the increase of strength grade of marine concrete. Finally, based on bond stress-slip curve obtained from the test, the bond stress-slip constitutive model between NPR reinforcement and marine concrete are proposed, and the calculated values are compared with the measured values. This results of study can provide a theoretical basis for the promotion and application of NPR new type reinforcement.