A coupled chemical-electro-mechanical model for multi-ion corrosion-induced degradation in offshore reinforced concrete: Development and potential for residual life assessment

Reinforced concrete (RC) structures degrade over time throughout their service life. Particularly, offshore RC structures are vulnerable to premature deterioration due to rebar corrosion and cracking of the concrete cover, caused by exposure to multiple aggressive ions such as sulphate, chloride, and carbon dioxide. Although much effort has been spent to understand the fundamental corrosion mechanism of RC structures, the synergistic effects of the multiple aggressive ions attack under marine environment have not been fully understood. In the present study, a coupled chemical-electro-mechanical model was developed to predict the residual life of offshore RC structures by assessing the corrosion rate of reinforcement embedded inside the structures. The model integrates the synergistic effects of chloride, sulphate, and carbonation on both the concrete cover and embedded reinforcement based on the critical failure indicators defined in the code of practice, such as the remaining bond area and the residual rebar diameter. The model predictions agree with experimental observations reasonably well. It demonstrates that multi-ion corrosion caused in marine environments could significantly reduce the residual life of the RC structures by around 70 % compared to that in inland environments through accelerating internal stress development and depassivation of the protective layer around the reinforcement. Furthermore, the model is applied to quantify the impact of different protective strategies on corrosion behaviour. In terms of cover depth, a 10 % increase extends the service life of the RC panel by 18 %, primarily by delaying the initiation of rebar corrosion. In contrast, aggregate surface treatment—particularly with silica fume—not only achieves a remarkable delay in corrosion initiation but also significantly reduces the subsequent rebar corrosion rate, resulting in up to a 62 % increase in service life and a 45 % reduction in the average rebar corrosion rate. These findings highlight the superior effectiveness of aggregate surface treatment in enhancing long-term durability of the RC panel. • A coupled chemo-electro-mechanical model is developed for RC structures lifespan. • The model accounts for chloride, sulphate and carbonation effects on corrosion. • Expansive stresses generated by ettringite and rust are both considered. • Multi-ion effects are assessed using code-based and engineering-practice indicators. • Strategies to extend the lifespan of RC panels in marine environments are compared.