Advances in the modelling of the corrosion onset and the corrosion propagation

Abstract

The time to initiation of reinforcement corrosion and the chloride threshold or corrosion onset, have being the subject of numerous studies. The chloride threshold has been found to be very variable in function of several technological and environmental characteristics. A dependence of the corrosion threshold was found with the steel electrical potential. Regarding the carbonation, the corrosion onset is associated to the arrival to the rebar of the carbonation front, although the time that this front needs to depassivate the whole perimeter, is usually neglected in the calculations. Regarding the corrosion propagation, the period has been modelled in function of the corrosion rate and of the concrete resistivity which give satisfactory results, although it is desirable to have the corrosion rate predicted from the concrete microstructure. In present paper advances are presented on the integration of the initiation to the propagation period by calculating the probability of failure due to the arrival of a certain chloride threshold or the carbonation front. Taking into account the depassivated reinforcements, the propagation period is coupled and it is calculated the corrosion depth until the 95% of the reinforcements have been depassivated. Then the progress of the corrosion is taken as the parameter to define the most technically suitable probability of depassivation. The corrosion rate developed is made a function of the diffusion coefficient and of the saturation degree through their relation to the concrete resistivity. Several examples are presented to illustrate the approach.