Tensile Behavior of Corroded Steel Bars at Elevated Temperatures

Abstract

Corroded steel bars frequently exist in concrete structures under chloride exposure conditions. Tensile behaviors of corroded steel bars at high temperatures are important in the fire-resistance evaluation of corroded reinforced concrete structures. This paper presents an experimental investigation on the tensile behavior of corroded steel bars at elevated temperatures. Corroded steel bars with different corrosion degrees are obtained by using the impressed current method. Then, a three-dimensional (3D) laser-scanning technique is applied to geometrically modeled corroded steel bars to quantify the corrosion degree. To investigate the influence of corrosion degree and temperature on the mechanical properties of steel bars, steady-state tensile tests were conducted at elevated temperatures. According to test results, the fracture initiation of an uncorroded steel bar occurs at the center of the fracture surface, whereas for a corroded steel bar, it moves to a corrosion pit on the surface. The effective elastic stiffness decreases significantly with the increase of temperature, whereas the influence of corrosion on the elastic stiffness could be ignored. The yield and ultimate strength in terms of the average cross-sectional area decrease with the increase of both the temperature and corrosion degree, and corrosion shows a decreased impact at a higher temperature. For a steel bar with a corrosion degree of 0.15, the yield and ultimate strength reduce by 11% and 17% at room temperature and by 9% and 10% at 500°C, respectively. However, the influence of corrosion on the yield and ultimate strength in terms of minimum cross-sectional area can be neglected. The yield plateau shortens with the increasing temperature and disappears at the critical temperature, which is around 300°C for uncorroded steel bars, and decreases linearly with the increase of corrosion degree. As temperature increases, the ultimate strain firstly decreases to the lowest value at about 400°C, and then increases, and it further decreases with the development of corrosion at a certain temperature.