Effects of external confinement on steel reinforcement corrosion products monitored by X-ray microcomputer tomography

Abstract

Rebar corrosion destroys the bond interface between concrete and the original rebar and, thus, affects their collaborative performance. External confinement, such as a concrete cover or fiber reinforced polymer (FRP) jackets, is a promising method to solve this problem since both can improve the bond properties between corroded rebars and concrete. However, existing tests results have shown the expected bond performance between rebars and its external concrete surroundings to be unstable for corrosion condition, and much of the bond strength data of corroded specimens is highly discrete. Traditional test methods such as cutting specimen are difficult to explain the instability of bonding phenomenon since it likely to destroy the rebar’s bonding interface during processing the specimen. In this study, X-ray microcomputed tomography (X-ray μCT), a new type of non-destructive testing method, was adopted to scan the inside of the corroded specimens and perform a three-dimensional reconstruction enabling a complete understanding of corrosion development. This paper also presents a thorough research analysis that focuses on the effects of variation in corrosion rates as well as the thickness of the concrete cover and FRP layers on the distribution of rust products and the volume change of rust products on the bond interface. Test results indicate that the distribution of corrosion products in 2D/3D is directly related to the location of cracks in the concrete cover, and increasing confinement (concrete cover thickness, FRP layer number) leads to a more uniform distribution of corrosion products. In addition, by using X-ray μCT, the “hollow volume,” defined as the volume between the surface of the uncorroded steel bar and the inside of the concrete cover, could be accurately obtained. Most importantly, this hollow volume was found to be the main factor affecting the bond performance of corroded reinforced concrete.