Structural Effects of Reinforcement Corrosion in Concrete Structures

Doktorsavhandling, 2016

Reinforcement corrosion is a common cause of deterioration in reinforced concrete. The corrosion mechanism involved and the consequent structural behaviour of deteriorated reinforced concrete members have been studied by several researchers. Nevertheless, the knowledge obtained is primarily based on experimental investigations of artificially corroded specimens whereas natural corrosion may affect structural behaviour differently. This thesis aims to deepen the understanding of the structural effects of natural corrosion deterioration with a focus on the remaining anchorage capacity between deformed bars and concrete, as well as the investigation of possible links between visual inspection data and structural damage. Tests on the anchorage capacity of naturally corroded reinforcement were carried out. The specimens were taken from the concrete edge beams of a 32-year old bridge that had been exposed to the outdoor environment. The tests were carried out using an indirectly supported four-point bending test. The overall structural behaviour of the specimens was examined through measurements of loads, vertical deflections and endslip of the tensile rebars. The failure mode consisted of a splitting-induced pull-out failure in all tests. It was observed that the specimens with cracking and cover spalling had an average of 6 and 9 %, respectively, lower load-carrying capacity compared with the un-cracked ones. Two methods were used to quantify the corrosion level: gravimetric measurements and advanced 3D optical scanning. The correlations between the measured corrosion levels, splitting crack widths and the anchorage capacity of the corroded specimens were investigated, and the results were compared with artificial corrosion tests from literature. For the same crack widths, the specimens in this study had much less corrosion level and slightly higher bond capacity compared to other studies found in literature with artificially induced corrosion. Furthermore, it was also investigated how well analyses on different levels can describe the structural behaviour - from advanced modelling to a simplified approach that can be used in practice. In the most advanced approach, three-dimensional non-linear finite element (3D NLFE) analyses employing previously developed bond and corrosion models were carried out. This approach yielded results that were most consistent with the experimental observations; however, the analyses were computationally expensive. In the most simplified approach, a constant bond stress was assumed together with the available anchorage length measured, which underestimated the capacities. Thus, the simplified method applied was the most efficient analysis with results on the safe side. Ultimately, this study contributes to the knowledge on how the structural effects of reinforcement corrosion in existing structures can be assessed. The results indicate that using the available knowledge of artificial corrosion to formulate a damage indicator in the form of crack widths would yield estimations of the structural capacity on the safe side. The present study was based on a limited amount of experiments. Thus, more experiments on real structures are needed.