Prognosis and safety evaluation of fatigue and corrosion-induced damages in reinforced concrete beams

The prognosis of a structural member's remaining life is subject to the durability of its materials. Chloride corrosion compromises concrete designed life, especially in the presence of cracks, which accelerate the initiation and propagation of corrosion. This thesis highlights the importance of considering load-induced cracks in the assessment and prediction of the service life. Different levels of damage were produced on four beams (2200x150x200 mm3) by static and fatigue loading, then, they were assessed using non-destructive electrochemical techniques in terms of reinforcement electrical potential and concrete electrical resistivity. The latter was simulated in a finite element model to compare the measured data with the numerical evaluations. Results revealed that the level of fatigue damage in concrete was directly related to the increase in corrosion risk assessed by resistivity and potential measurements. However, few studies discussed the change in resistivity with the mechanical response under compression. So, in order to study the relationship between mechanical load damage and concrete resistivity, an experiment was conducted on four concrete cylinders (150 x 75 mm2). Results showed a multi-phase behaviour with exponential correlation as follows: decreasing during elastic stage, quasi-constant in plastic, and increasing in post-failure stage. Additionally, the current codes limit the crack width to 0.2-0.4 mm depending on the exposure classes, these ranges do not satisfy the durability requirements as a narrower crack reduces the service life significantly. Therefore, a case study chosen from the literature was used to incorporate Torres’s chloride diffusion crack model as an alternative to Kwon’s model in the analytical solution for service life prediction of corroding structural element (i.e. the current model adopted by the fib MC). The suggested modification resulted in similar values yet with a higher accuracy in some cases.