Dubrovnik, Croatia, September 15-18, 2019

Modelling Corrosion of Steel in Concrete: Past, Present and Future

Joško Ožbolt, University of Stuttgart, Institute of Construction Materials, Stuttgart, Germany

Chloride-induced corrosion of steel reinforcement in concrete is one of the major causes for deterioration of reinforced concrete (RC) structures. RC structures exposed to aggressive environmental conditions, such as structures close to the sea or highway bridges and garages exposed to de-icing salts, very often exhibit damage due to corrosion. This damage is usually manifested in the form of cracking and spalling of concrete cover, caused by the expansion of corrosion products around the steel reinforcement bar. Repair of corroded concrete structures results in relatively high direct and indirect costs. Therefore, to predict durability of RC structure it is important to have a numerical tool, which is able to predict corrosion processes and their consequences for the structural safety.

Principally, to predict the rate of rust production and related effects, it is necessary to simulate the following physical, electrochemical and mechanical processes: (1) Transport of capillary water, oxygen and chloride through the concrete cover; (2) Immobilization of chloride in the concrete; (3) Crystallization and dissolution of free chloride as a consequence of drying and wetting of concrete as well as hysteretic property of concrete; (4) Transport of OH- ions through electrolyte in concrete pores; (5) Cathodic and anodic polarization; (6) Transport of corrosion products in concrete and cracks; (7) Creep and shrinkage of concrete and (8) Damage of concrete due to mechanical and non-mechanical actions.

In the first part of the presentation an overview of different models developed in the past will be shortly presented and discussed. Subsequently, the recently developed coupled 3D chemo-hygro-thermo-mechanical model for concrete will be presented. The model is aimed to simulate the above mentioned complex non-mechanical and mechanical processes before and after depassivation of steel reinforcement. It was implemented into a 3D FE code and its application and performance will be illustrated through several numerical examples. Furthermore, the differences between accelerated corrosion, usually used in the experimental tests, and natural corrosion will be discussed through several numerical examples. It will be demonstrated that the maximum entropy production related to the corrosion of steel reinforcement leads to maximum corrosion induced damage of concrete. Finally, current and future work related to objective modelling corrosion of steel reinforcement in concrete will be discussed.