Chemo-hygro-thermo-mechanical model for simulation of corrosion induced damage in reinforced concrete

by Filip Orsanic

Institution: University of Stuttgart
Department: Fakultät Bau- und Umweltingenieurwissenschaften
Degree: PhD
Year: 2015
Record ID: 1109843
Full text PDF: http://elib.uni-stuttgart.de/opus/volltexte/2015/9882/


Reinforced concrete (RC) elements exposed to chloride induced corrosion have a shortened service life which presents a major challenge for durability of structures. The extensive costs of repair heighten the importance of developing a model as a numerical assessment tool of corrosion induced damage effects. A three dimensional (3D) chemo-hygro-thermo-mechanical (CHTM) model has been recently developed (Ožbolt et al. 2010, 2011). The model is implemented into a finite element code and is capable of predicting the non-mechanical processes before and after depassivation of steel, for both un-cracked and cracked concrete elements. Here presented work is a further development of the model, focused on predicting the rate of rust production and the corresponding damage (cracking and spalling) of the concrete cover surrounding the embedded steel bars. The extent of the damage and its progress in time are highly dependent on the ingress of corrosion products into pores and cracks. Therefore, the transport of corrosion products is incorporated into the model as a convective diffusion problem. The expansion of rust and the subsequent compressive pressure on the cover is taken into account by developing one-dimensional corrosion contact elements. To ensure a realistic simulation of the corrosion induced damage, the model couples the mechanical with the non-mechanical processes, and vice versa. Validation of the CHTM model's ability for simulating corrosion induced damage is performed on concrete specimens with a single embedded reinforcement bar and for multi-rebar cases, without and with stirrups. Comparison of the numerical results with the existing experimental data shows that the model is capable of realistically capturing the damage of the concrete cover and its effects on the mechanical properties of the investigated RC elements. Hysteretic moisture model for concrete is a further addition to the CHTM model. It accounts for the hysteretic behaviour of concrete which is characterized by the ability to contain different degrees of water saturation for the same value of relative humidity, at a constant temperature. Hence, the water content values are highly dependent on the exposure to cyclic wetting and drying conditions. The hysteretic moisture model is validated directly through existing experimental studies by verifying the calculated scanning curves and the distribution of relative humidity, i.e. the water content in concrete, respectively. The importance of incorporating the moisture hysteresis in the CHTM model is demonstrated by comparing the experimentally and numerically obtained distribution of chloride ions in concrete specimens exposed to cyclic wetting and drying conditions. Eine der wesentlichen Aspekte der Dauerhaftigkeit von Bauwerken stellt die chloridinduzierte Korrosion dar, die die Lebensdauer von Stahlbetonelementen beeinträchtigt. Relativ hohe Instandsetzungskosten zeigen den Nutzen, den ein numerisches Modell zur Bewertung der korrosionsinduzierten Schäden darstellt. Ein dreidimensionales…