Service-Life Estimation of a Reinforced Concrete Bridge Structure Exposed to Chloride-Contaminated Environments and Variable Traffic Loads

The long-term performance of reinforced concrete (RC) structures is influenced by several environmental factors along with various loading conditions. Structures such as RC bridges exposed to the marine environment, essentially in chloride-contaminated environments, are highly susceptible to chloride-induced corrosion. In recent years, with the exponential increase of traffic intensity on highways, RC bridges have essentially experienced fatigue damages. High frequencies of cyclic loading due to traffic in combination with corrosion may expedite the deterioration mechanism and reduce the structure's service life significantly. This paper presents a novel framework to calculate the service life of a structure subjected to chloride-induced corrosion and fatigue due to traffic loads. The presented model takes care of the following phenomena: corrosion initiation due to chloride ingress, reduction of steel reinforcement area due to corrosion of reinforcement, concrete cracking due to the accumulation of corrosion products and nucleation and the propagation of cracks in reinforcing bars due to fatigue loads. The framework comprises the calculation of three significant deterioration stages: corrosion initiation time, pit-to-crack transition time, and time until structural failure. The novelty of the proposed approach resides in its ability to model pitting corrosion as a realistic corrosion deterioration mechanism rather than the traditional uniform corrosion process. This model takes into account the nonlinearity of the corrosion rate after the initial cracking of concrete to calculate the corrosion-fatigue lifetime. Comparisons are drawn for general and pitting corrosion. The application of the model is done to evaluate the service life of an RC bridge girder subjected to cyclic loading of varying frequencies subjected to three different chloride-contaminated environments. The results indicate that the total lifetime of a structure is strongly affected by environmental aggressiveness. Under lower frequencies of traffic loading, an increase in environmental aggressiveness can result in reductions of lifetime ranging between 30% and 35%, but under the higher frequency of cyclic loading, the total reduction in a lifetime could go up to 70%. Parametric investigations of the structural parameters revealed an increase in the lifetime performance of the structure under a lesser water binder ratio and higher cover thickness.