An Appropriate Indicator for Bond Strength Degradation due to Reinforcement Corrosion

In the paper an appropriate indicator for degradation of bond strength due to corrosion of reinforcement is investigated. Common indicators, which are currently in use, are the mass loss and the average corrosion penetration of steel. The crack width in concrete cover is not frequently used as an indicator of corrosion induced damage in bond. A comparison between the average cor- rosion penetration and the crack width in concrete cover with respect to bond strength is discussed. For this reason, experimental and numerical investigations on beam-end specimens were carried out. Within the experimental investigations the specimens were corroded to different states before bars were pulled-out. A modest corrosion rate close to the maximum natural corrosion rate under splash conditions was chosen. Maximum values of current density were between 15 and 25 µA/cm². In addition investigations on morphology and distribution of corrosion products in the vicinity of the reinforcement surface were performed. In numerical investigations a detailed 3D-FE model was employed. The reinforcement is discretized by 3D finite elements. In order to model expansion, due to different levels of corrosion, 1D radial contact elements on the reinforcement-concrete contact surface were used. The contact elements can take up axial compressive forces and shear forces due to friction between reinforcement and concrete. In the numerical analyses the damage due to the radial expansion of corrosion products is simulated first. This is modeled by radial expansion of the contact elements. Subsequently, the reinforcement bar is pulled-out from the concrete beam-end specimen. The study confirms that the crack width is a good indicator for the degradation of bond resistance due to corrosion of reinforcement. The bond strength is dependent on the concrete con- finement and thus on the crack state of the surrounding concrete. In fact from the mechanical point of view crack width should be a better indicator for degradation of bond strength, however, the dif- ficulty is the fact that crack width depends on bar diameter and concrete cover.