Time-dependent bending reliability of reinforced concrete sections under carbonation corrosion

Abstract

Greenhouse gases, especially CO2 emissions, drive the greenhouse effect, impacting the planet’s temperature and relative humidity. Changes in CO2 concentration, temperature, and relative humidity alter the internal moisture content, which significantly influences the progression of carbonation in existing concrete structures. Therefore, studying the safety of concrete structures in the context of their degradation over time is of great importance in structural engineering. This paper presents an approach for evaluating the time-dependent reliability index of reinforced concrete sections subjected to climatic conditions that promote carbonation-induced corrosion. The proposed method combines a mathematical model that predicts the advance of the carbonation front based on exposure time with a mechanical model that determines the resistant moment of corroded reinforced concrete cross-sections. Various loading conditions and longitudinal reinforcement ratios were simulated to investigate the impact of carbonation-induced corrosion. The reliability index was calculated using the Monte Carlo method, incorporating nine random variables. Additionally, the effects of longitudinal reinforcement ratio and concrete cover depth were analyzed. For concrete cover depths recommended by Model Code 2010, reinforcement depassivation due to carbonation was found to occur after 39 years on average, with a standard deviation of 18 years. The longitudinal reinforcement ratio influenced the time required to reach the target reliability index for the Ultimate Limit State, which ranged between 30 and 60 years. A 12% variation in the target reliability index after 50 years was observed when the concrete cover varied between 2 and 3 cm. The proposed approach proved effective in assessing the time-dependent reliability index at the Ultimate Limit State. It serves as a valuable tool for evaluating structural maintenance and supports decision-making regarding the timing and necessity of interventions to restore the reliability levels recommended by design guidelines.