Cette ´etude a mis au point une m´ethodologie pour la gestion durable des structures en b´eton arm´e soumises `a la p´en´etration des chlorures. `A cette fin, l’approche propos´ee int`egre des mod`eles pro- babilistes de d´egradation, d’inspection et de r´eparation au sein d’une m´ethodologie pour l’analyse de l’impact environnemental. Cette approche a ´et´e formul´ee et mise au point en tenant compte des recommandations des principaux acteurs qui sont li´es `a ce type d’ouvrages pendant sa dur´ee de vie. Cette collaboration a jou´e un rˆole crucial pour proposer des solutions techniquement et ´economiquement r´ealisables.
Afin d’am´eliorer les mod`eles de d´egradation et d’inspection/r´eparation d´evelopp´es dans cette th`ese, les recherches futures dans ce domaine doivent ˆetre dirig´ees vers plusieurs domaines. Par exemple, l’addition d’autres ph´enom`enes physiques, l’am´elioration de la mod´elisation probabiliste, la mise en œuvre d’autres techniques d’inspection ou crit`eres de r´eparation, ... Les perspectives en recherche sont donc class´ees par rapport au type de mod`ele `a explorer.
Mod`ele de p´en´etration des chlorures
• d´etermination des param`etres du mod`ele pour un large ´eventail de types de b´eton et mat´eriaux de r´eparation `a base de ciment ;
• formulation et mise en œuvre d’un mod`ele qui tient compte de la cin´etique entre la fissuration du b´eton et la p´en´etration des chlorures ;
• ´etude de l’influence des variations horaires, journali`eres et hebdomadaires de la temp´erature et l’humidit´e sur la p´en´etration des chlorures ;
• ´evaluation et prise en compte de la corr´elation des propri´et´es du mat´eriau et des conditions climatiques `a partir des donn´ees exp´erimentales ;
• prise en compte de la variabilit´e spatiale du ph´enom`ene ; et
• caract´erisation et mod´elisation de la propagation de l’erreur dans le processus de d´egradation. Mod`ele d’inspection/r´eparation
• mise `a jour des probabilit´es de transition `a partir des donn´ees d’inspection par une approche bay´esienne (i.e., Corotis et al. (2005)) et mod´elisation de l’inspection bas´ee sur des techniques de contrˆole non-destructifs ;
• combinaison des strat´egies de r´eparation pr´eventives et correctives pendant une dur´ee de vie structurale plus importante ;
• formulation et ´etude de l’efficacit´e d’une strat´egie de management qui consid`ere les intervalles d’inspection d´ependants du temps ;
• int´egration des coˆuts d’utilisation `a l’analyse et calcul de l’intervalle d’inspection optimal sur la base des grandeurs diff´erentes de l’esp´erance des coˆuts (i.e., Schoefs et al. (2009a)) ; • optimisation de l’efficacit´e des techniques et des mat´eriaux de r´eparation ; et
• consid´eration des incertitudes inh´erentes `a la production de d´echets et aux ´emissions de CO2
Core of the thesis
Requirements for management of corroding
RC structures
2.1
Introduction
Reinforced concrete (RC) structures are subjected to actions that affect performance, serviceability and safety during their operational lives (Husni et al., 2003). Depending on their origin, these actions can be external or internal and produce physical, chemical, biological and mechanical damage (Table 2.1). External actions are divided into operational and environmental actions. While operational actions result from the existence and the use of the structure (e.g., service loading, storage of chemical or biological products, etc.), environmental actions are produced by exposure to the surrounding environment (e.g., temperature, humidity, carbonation, chloride ingress, biodeterioration, etc.). On the other hand, internal actions are divided into intrinsical and induced. Intrinsical actions are related to volumetric changes that depend on material properties, construction procedures and other factors such as drying or thermal shrinkages. Induced actions are produced by changes made to improve the strength of RC or are the result of RC behavior under constant loading (i.e. prestressed or post-tensioned concrete and creep).
Under optimal conditions, the durability of RC structures is high and the variation of the structural reliability over time is not significant. However, for structures located in aggressive environments this might not be the case. Some examples of aggressive environments are those characterized by:
• high relative humidity (i.e., between 60% and 98%);
• cycles of humidification and drying, of freezing and defrosting;
• high carbon dioxide concentrations (e.g., carbonation in urban atmospheres); • high concentration of chlorides or other salts (e.g., marine environments); or
• high concentration of sulfates and small amounts of acids (e.g., sewer pipes or residual water treatment plants).
There is a larger number of RC structures subjected to the action of chloride-induced corrosion. According to Bhide (1999), about 173,000 bridges of the interstate highway system in the United States are structurally deficient or functionally obsolete, due in part to corrosion. Other examples of structures exposed to this type of damage are ports, quays, offshore platforms, chimneys and towers situated close to the sea or exposed to the application of de-icing salts. Yunovivh et al. (2001)
Table 2.1 —Actions affecting the performance of RC structures
Origin Actions Related damage
External Operational Physical, chemical and biological
Environmental Physical, chemical and biological
Internal Intrinsical Physical and mechanical
Induced Mechanical
reported that up to $2.93 billion is spent annually on the repair of RC bridge decks and estimated that improved maintenance strategies can reduce this amount by up to 46%. This means that better practices of management of deteriorating RC structures will produce appreciable economic benefit.
The main objectives of this chapter are:
1. to describe the life-cycle of RC structures subjected to corrosion;
2. to present and to study the approaches for modeling deterioration and maintenance of de- teriorating RC structures available in the literature and, based on this review, to select an appropriate method; and
3. to establish the research targets for modeling the deterioration process.
Section 2.2 covers the stages of the life-cycle of RC structures subjected to corrosion. Section 2.3 describes the requirements of a maintenance management system as well as the different approaches for its modeling. The conceptual framework for the proposed methodology is discussed in section 2.4. Finally, section 2.5 focuses on the needs for a comprehensive deterioration model.