Corrosion Profile Characteristics Of Corroded Steel Bar And Its Bonding Performance Between Concrete Under Different Current Density

Steel corrosion is one of the most important factors affecting the durability of reinforced concrete structures.Corrosion of steel bar will generate rust between steel bar and cause the transverse rib rust wear or concrete cover cracking.All will affect the bond performance between steel bar and concrete,so it is particularly important to study the bond performance between corroded steel bar and concrete.At present,in order to shorten the test time,most of scholars use constant current to accelerate corrosion instead of natural corrosion to achieve the target corrosion rate of steel bars in concrete,but selected current density several to thousands times that of natural conditions.The large difference in current density makes the difference between the bonding performance of corroded steel bar and concrete,including the profile of steel bar and the natural corroded steel bar.This thesis studies the bonding performance between corroded steel bar and concrete under the factors of current density and corrosion rate,and use fractal theory and statistics to characterize the roughness of surface profile of corroded steel bar.At the same time,XCT technology and image processing technology are used to track the corrosion profile of the same steel bar,and the relationship between the roughness,current density and corrosion rate is obtained and verified.Finally,the relationship between the bonding performance of corroded reinforced concrete and the surface roughness of corroded reinforced concrete is discussed.In this paper,researcher hope to find out both the bonding performance between corroded steel bar and concrete,and the corrosion profile characteristics of corroded steel bar,under different current density and different corrosion rate.The following conclusions can be drawn.1)With the increase of corrosion rate,the ultimate bond strength between corroded steel bar and concrete shows a trend of increasing first and then decreasing.Under the same corrosion rate,the bond strength at low current density is higher than at high current density.In addition,the sample with high current density is more prone to internal crack.With the increasing of current density,the highest ultimate bond strength showed a trend of decreasing which were 28.98,28.16,27.3 and 25.24 MPa,respectively.At high corrosion rate,the ultimate bond strength at 300、150、75μA/cm~2current density decreased steadily and the trend was consistent,while the ultimate bond strength at 600μA/cm~2 current density decreased rapidly.2))Low current density are both conducive to improving the level of energy consumption and bonding rigidity of components.3)According to the fractal geometry,the fractal dimension D and the characteristic profile parameter r~*were obtained.Under the same corrosion rate,the roughness of low current density(20,75μA/cm~2)is larger than that of high current density(150,300,600μA/cm~2).4)The arithmetic mean deviation of corroded steel bar profile shows that:under the same corrosion rate,the arithmetic mean deviation of low current density(75μA/cm~2)is larger than that of high current density,which proves that the corrosion steel bar profile is rougher under the influence of low current density.The result also verifies the feasibility of using fractal geometry method to characterize the roughness of corrosion steel bar.5)The minimum cross section diameter of corroded steel bar decreases with the increase of corrosion rate.Under the same corrosion rate,the minimum cross section diameter under the influence of low current density is smaller.6)under the same corrosion rate,the ultimate bonding performance between corroded steel bar and concrete and the roughness of corroded steel bar profile increase with the decrease of current density.The lower current strength affects the roughness of steel bar surface,and then affects the ultimate bonding strength between corroded steel bar and concrete.