Modèle d'évolution de l'état des ponts-routes en béton

The management of existing road infrastructures is a multidisciplinary activity that involves structural engineering, material science, management, economics and ecology. The objective is to achieve maximum availability of road links at minimum societal costs. Recently, tools (Bridge Management Systems, BMSs) have been developed to help decision makers to determine the optimal management strategies within available resources. The condition development model is a key element of the BMSs. Currently this model is using empirical approach making use of data collected during inspections and is formulated with Markov chains. The assessment units are structural elements and these are classified into condition classes according to their visual appearance. The condition assessment is therefore rather subjective since no measurements are involved in it. Consequently, the condition development based on visual inspections will reflect this subjectivity. In order to improve the objectivity of condition forecasts physical and chemical phenomena governing deterioration has to be incorporated in the condition development model. Observations made on a bridge sample representative of the Swiss highway bridges showed that chloride-induced corrosion is the main deterioration mechanism. For this reason this research was focused upon modeling the chloride-induced corrosion. In this research, the condition development model is established, based physical and chemical phenomena involved in chloride induced corrosion. This analytical model is able to yield quantitative results on condition development. Accuracy and availability of input data govern the level of accuracy of such an analytical model. The existing knowledge on chloride induced corrosion and inspection techniques available on site are examined in order to develop a simple and reliable condition development model. Firstly, non-destructive testing methods are used in addition to visual observations, to determine quantitative values (permeability and thickness of the concrete cover) of parameters governing the segment deterioration. The structural elements are divided into areas i.e. segments where the parameters governing chloride-induced corrosion are assumed to be constant. It is proposed to divide structural elements into segments based on three concrete cover permeability classes, concrete cover thickness and three types of surface exposures to chloride contaminated water. Secondly, a chloride transport model is developed to simulate the real exposure of reinforcement to chloride contaminated water, taking into consideration the transport mechanisms of water and chloride ions. Simulations are performed for the various segment parameters that have been identified in the segmental approach. Thirdly, a relation is established between the free chloride ion content and the corrosion initiation probability. Using the results of the chloride transport model, the development of the corrosion initiation is determin