Numerical Modeling of Corrosion of Steel Reinforcement in Concrete

• Applicant: Professor Dr.-Ing. Josko Ozbolt
• Subject Area: Construction Material Sciences, Chemistry, Building Physics ; Applied Mechanics, Statics and Dynamics
• Term: from 2010 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 186716848

In the framework of the proposed research project the existing 3D chemo-hygro-thermo-mechanical model (CHTM) will be further improved. The proposal represents continuation of the preceding DFG project in which the CHTM Model was developed, implemented into the FE code and verified. The current model is able to calculate the transport processes in concrete before and after depassivation of reinforcement as well as the rate of corrosion. Moreover, the model can also simulate the non-mechanical and mechanical processes that occur as a result of chloride induced corrosion phase, i.e., after depassivation of reinforcement. These processes are the formation of corrosion products (rust) and their transport (distribution) through the pore system of concrete and cracks. The corrosion of reinforcement leads to decrease of its cross-section area and also to decrease of ductility. Furthermore, the increase in volume of corrosion products on the surface of reinforcement causes mechanical damage of concrete cover and thus leads to decrease of caring capacity of concrete structures. In the case of chloride-induced corrosion the transport of corrosion products through cracks, which is in the model treated as diffuse-convective process, is shown to be very important. These processes are in the present model formulated only in a qualitative sense. In the literature there are almost no experimental results related to the transport of corrosion products through the cracks. Therefore, the experiments will be carried out for different geometries and environmental conditions. The results of the experiments will be used for the calibration and verification of the improved model. The distribution of water has significant influence on the corrosion rate. In the current model the fact that the sorption isotherms for wetting and draying are not the same is not accounted for. Therefore, the hysteresis of sorption isotherm will be implemented into the model and the model prediction will be compared with the experimental results. It is well known that for the corrosion-induced damage the position and size of the anode and cathode are relevant. In the existing model these parameters of the model must be pre-defined. In the new research project a numerical algorithm for the determination of the most critical position of anode and cathode will be formulated, i.e., the position for which the corrosion rate is maximal (maximal entropy). To demonstrate the performance of the model, the prediction of the model will be compared with the available experimental evidence from the literature and also with own experimental results. The improved model is intended to serve as the theoretical basis for the formulation of engineering-based models that can be applied in practice to determine durability of reinforced concrete structures.

• DFG Programme: Research Grants