Modelling the service life of concrete until cover cracking due to reinforcement corrosion

The service life design of reinforced concrete structures requires material models capable of reliably describing both mechanisms of damage and the general progression of damage over time. However, most models that are currently being used only capture the process of carbonation and chloride penetration into the uncracked concrete that is at the initial phase of degradation. Typically, these models disregard the actual damage, i.e. the corrosion of the reinforcing steel. As a result, the service life design established to date only considers the end of the initiation phase of the degradation process, or, in other words, the onset of damage (time of depassivation or onset of corrosion) as a critical limit state. The corrosion of the reinforcement and its consequences, i.e. the crack formation and spalling of concrete, are not considered, which may lead to a substantially shorter estimated service life of the structures. Comprehensive investigations were recently undertaken on the depassivation of steel reinforcement and on crack formation in concrete which have resulted in an analytical prediction model for corrosion-induced cracking occurring in the surface zones of structural components. This paper presents a holistic approach which combines two models used for determining the time to depassivation (initiation phase) and the time to cover cracking as a result of reinforcement corrosion (propagation phase). An example is provided of a structural element which has been designed for the serviceability limit state of concrete cover cracking