Corrosion development in cracked concrete and the mechanical performance of corroded reinforced concrete beams

Abstract : One of the aims of the thesis is to study corrosion development in cracked concrete, in relation to the effect of concrete cover depth, exposure direction, load-induced transverse cracks, defects in the steel-concrete interface under horizontal bars caused by top-casting and self-healing of the transverse cracks. The other aim is to study the mechanical performance of reinforced concrete beams damaged by corrosion accelerated by a climate accelerated method (wetting/drying cycles in salt fog). Two main parts are included in this thesis. The first part discusses corrosion development, including corrosion initiation and propagation, in cracked concrete. The second part discusses the mechanical performance of slender and deep beams damaged by climate accelerated corrosion, in terms of failure mode, yield capacity, ultimate capacity and ultimate deflection. According to the experimental study, it was found that, corrosion always initiated under the load-induced cracks. It should be noted that corrosion initiation is related to appearance of cracks but not crack width. The surface exposure condition is also an important parameter influencing corrosion development. Top-tensioned surface is the worst exposure condition, because corrosion development was accelerated by both ponding and gravity effect of chloride solution. Furthermore, top-casting-induced defects formed in steel-concrete interface under horizontal top-cast bars due to bleeding, segregation and settlement of fresh concrete, and they were favorable for both corrosion initiation and propagation. Self-healing occurred when the cracked samples were cured in a humidity room with 100% R.H due to the formation of ettringite in the inner zone and calcite in the outer zone of crack planes. Self-healing reduced air flow through the cracks and reduced the risk of corrosion considerably. The flexural performances of slender beams were tested. Corrosion of the reinforcements modified the failure mode of reinforced concrete beams. Both yield and ultimate capacity were correlated to the maximum cross-sectional loss of tensile bars. The experimental results indicated that 1% reduction in cross-section corresponds to 1% reduction in yielding capacity and ultimate capacity. For mechanical performance of deep beams, the results show that, serious pitting corrosion on the tensile bars changed the failure mode from shear to flexure. The failure mode of corroded deep beams depends not only on span to effective depth ratio and corrosion degree of tensile bars, but also on the corrosion degree of stirrups.Résumé : Un des objectifs de la thèse est d'étudier le développement de la corrosion dans le béton armé fissuré, en fonction de l’enrobage des armatures, des conditions d’exposition, de l’endommagement de l’interface acier-béton induit par le chargement et des défauts de l'interface acier-béton sous les barres horizontales liés à la mise en œuvre du béton frais en prenant en compte l'auto-cicatrisation des fissures transversales. L'autre objectif est d'étudier la performance mécanique des poutres en béton armé endommagées par la corrosion naturelle en ambiance agressive (des cycles humifification/séchage en brouillard salin). Deux parties principales constituent cette thèse. La première partie traite du développement de la corrosion, à la fois initiation et propagation, dans le béton armé en présence de fissures. La deuxième partie traite de la performance mécanique des poutres longues et courtes endommagés par la corrosion des armatures, en termes de mode de défaillance, seuil de plastification, capacité ultime résiduelle et flèche ultime à rupture. Les résultats de l'étude expérimentale confirment que la corrosion est toujours initiée dans les fissures induites par le chargement. Il convient de noter que la corrosion est liée à la présence des fissures mais pas à leur largeur. Les conditions d'exposition sont également un paramètre important influençant le développement de la corrosion. Ainsi, une surface tendue correspondant à la surface supérieure est la pire condition d'exposition, parce que le développement de la corrosion est accéléré par les effets de l’accumulation des chlorures ainsi que l’effet gravitaire favorisant leur pénétration. En outre, les dommages induits par le “top-cast effect” qui sont formés à l'interface acier-béton sous les barres horizontales par le ressuage et le tassement du béton frais, sont favorables à la fois à la l’initiation et à la propagation de la corrosion. Le phénomène d’auto-cicatrisation des fissures survient lorsque les échantillons fissurés sont conservés à 100% d'humidité relative en raison de la formation d'ettringite dans la zone intérieure et de la calcite dans la zone extérieure du plan de fissuration. L’auto-cicatrisation réduit le débit d'air à travers les fissures et réduit considérablement le risque de corrosion. Les performances en flexion de poutres longues ont été testées. La corrosion des armatures modifie le mode de défaillance des poutres en béton armé. La diminution de la charge de plastification et de la capacité ultime a été corrélée à la perte de section transversale des barres tendues. Les résultats expérimentaux indiquent qu’une réduction de 1% de la section transversale correspond à une réduction de 1% de la charge de plastification et de la capacité ultime. En ce qui concerne les performances mécaniques des poutres courtes, les résultats montrent qu’une corrosion sévère par piqûres sur les armatures tendues change le mode de défaillance par cisaillement à celui en flexion. Le mode de rupture des poutres courtes corrodées dépend non seulement du ratio entre la portée et la hauteur utile, mais également du degré de corrosion des cadres d’effort tranchant

Corrosion development in cracked concrete and the mechanical performance of corroded reinforced concrete beams

Abstract : One of the aims of the thesis is to study corrosion development in cracked concrete, in relation to the effect of concrete cover depth, exposure direction, load-induced transverse cracks, defects in the steel-concrete interface under horizontal bars caused by top-casting and self-healing of the transverse cracks. The other aim is to study the mechanical performance of reinforced concrete beams damaged by corrosion accelerated by a climate accelerated method (wetting/drying cycles in salt fog). Two main parts are included in this thesis. The first part discusses corrosion development, including corrosion initiation and propagation, in cracked concrete. The second part discusses the mechanical performance of slender and deep beams damaged by climate accelerated corrosion, in terms of failure mode, yield capacity, ultimate capacity and ultimate deflection. According to the experimental study, it was found that, corrosion always initiated under the load-induced cracks. It should be noted that corrosion initiation is related to appearance of cracks but not crack width. The surface exposure condition is also an important parameter influencing corrosion development. Top-tensioned surface is the worst exposure condition, because corrosion development was accelerated by both ponding and gravity effect of chloride solution. Furthermore, top-casting-induced defects formed in steel-concrete interface under horizontal top-cast bars due to bleeding, segregation and settlement of fresh concrete, and they were favorable for both corrosion initiation and propagation. Self-healing occurred when the cracked samples were cured in a humidity room with 100% R.H due to the formation of ettringite in the inner zone and calcite in the outer zone of crack planes. Self-healing reduced air flow through the cracks and reduced the risk of corrosion considerably. The flexural performances of slender beams were tested. Corrosion of the reinforcements modified the failure mode of reinforced concrete beams. Both yield and ultimate capacity were correlated to the maximum cross-sectional loss of tensile bars. The experimental results indicated that 1% reduction in cross-section corresponds to 1% reduction in yielding capacity and ultimate capacity. For mechanical performance of deep beams, the results show that, serious pitting corrosion on the tensile bars changed the failure mode from shear to flexure. The failure mode of corroded deep beams depends not only on span to effective depth ratio and corrosion degree of tensile bars, but also on the corrosion degree of stirrups.Résumé : Un des objectifs de la thèse est d'étudier le développement de la corrosion dans le béton armé fissuré, en fonction de l’enrobage des armatures, des conditions d’exposition, de l’endommagement de l’interface acier-béton induit par le chargement et des défauts de l'interface acier-béton sous les barres horizontales liés à la mise en œuvre du béton frais en prenant en compte l'auto-cicatrisation des fissures transversales. L'autre objectif est d'étudier la performance mécanique des poutres en béton armé endommagées par la corrosion naturelle en ambiance agressive (des cycles humifification/séchage en brouillard salin). Deux parties principales constituent cette thèse. La première partie traite du développement de la corrosion, à la fois initiation et propagation, dans le béton armé en présence de fissures. La deuxième partie traite de la performance mécanique des poutres longues et courtes endommagés par la corrosion des armatures, en termes de mode de défaillance, seuil de plastification, capacité ultime résiduelle et flèche ultime à rupture. Les résultats de l'étude expérimentale confirment que la corrosion est toujours initiée dans les fissures induites par le chargement. Il convient de noter que la corrosion est liée à la présence des fissures mais pas à leur largeur. Les conditions d'exposition sont également un paramètre important influençant le développement de la corrosion. Ainsi, une surface tendue correspondant à la surface supérieure est la pire condition d'exposition, parce que le développement de la corrosion est accéléré par les effets de l’accumulation des chlorures ainsi que l’effet gravitaire favorisant leur pénétration. En outre, les dommages induits par le “top-cast effect” qui sont formés à l'interface acier-béton sous les barres horizontales par le ressuage et le tassement du béton frais, sont favorables à la fois à la l’initiation et à la propagation de la corrosion. Le phénomène d’auto-cicatrisation des fissures survient lorsque les échantillons fissurés sont conservés à 100% d'humidité relative en raison de la formation d'ettringite dans la zone intérieure et de la calcite dans la zone extérieure du plan de fissuration. L’auto-cicatrisation réduit le débit d'air à travers les fissures et réduit considérablement le risque de corrosion. Les performances en flexion de poutres longues ont été testées. La corrosion des armatures modifie le mode de défaillance des poutres en béton armé. La diminution de la charge de plastification et de la capacité ultime a été corrélée à la perte de section transversale des barres tendues. Les résultats expérimentaux indiquent qu’une réduction de 1% de la section transversale correspond à une réduction de 1% de la charge de plastification et de la capacité ultime. En ce qui concerne les performances mécaniques des poutres courtes, les résultats montrent qu’une corrosion sévère par piqûres sur les armatures tendues change le mode de défaillance par cisaillement à celui en flexion. Le mode de rupture des poutres courtes corrodées dépend non seulement du ratio entre la portée et la hauteur utile, mais également du degré de corrosion des cadres d’effort tranchant

Influence of load-induced cracks coupled or not with top-casting-induced defects on the corrosion of the longitudinal tensile reinforcement of naturally corroded beams exposed to chloride environment under sustained loading

International audienc

Corrigendum to “Study on the Mitigative Effect of Controlled Permeable Formwork (CPF) Liner on Early-Age Shrinkage of Box-Girder Concrete”

Because of its high binder content and severe construction environment, early-age cracking is one of the most important threats to concrete used in continuous box-girder bridge structures. In this study, controlled permeable formwork (CPF) liner was used to mitigate the early-age shrinkage and reduce the early-age cracking risk of box-girder concrete. Early-age shrinkage was measured by a noncontact method and started at 30 min after adding mix water until 7 d. Internal relative moisture content and pore distribution tests were also carried out to reveal the working mechanism of CPF liner. The results show that covering the concrete surface with CPF liner decreased early-age shrinkage significantly. Under the temperature of 20°C and the relative humidity of 60%, two-surface-covering and three-surface-covering CPF liner on concrete decreased the shrinkage by 44% and 48%, respectively, at 7 d compared with concrete without CPF liner covered on it. The main reason is that CPF liner enhanced the internal relative moisture content and resulted in better performance of the surface concrete

Influence of steel-concrete interface defects induced by top-casting on development of chloride-induced corrosion in RC beams under sustained loading

WOS:000380236800018International audienceThis paper discusses the effect of defects in a steel-concrete interface under horizontal top-cast steel bars on the development of corrosion in reinforced concrete beams under sustained loading exposed to a chloride environment. The work was based on four beams exposed to climate accelerated natural corrosion for 29 months. The corrosion-induced cracking patterns were drawn after 8 and 24 months of exposure to the chloride environment, and cracking maps with crack widths were recorded at 29 months. The experimental results show that corrosion-induced cracks always developed much more quickly along the top-cast steel bars due to the existence of top-casting-induced defects. Such defects formed at the steel-concrete interface under horizontal top-cast bars due to bleeding, segregation and settlement of fresh concrete, and they were favorable to both initiation and propagation of corrosion

Mechanical performance of deep beams damaged by corrosion in a chloride environment

International audienc

Influence of top-casting-induced defects on the corrosion of the compressive reinforcement of naturally corroded beams under sustained loading

International audienceThis paper discusses the effect of top-casting-induced defects on the corrosion development of compressive bars in reinforced concrete beams exposed to a chloride environment, under sustained loading. Four reinforced concrete beams, exposed to artificial climate of accelerated natural corrosion for 38 months and 48 months, respectively, were tested. The cracking maps, chloride profiles, cross-sectional loss, and corrosion distribution around the perimeter and along the re-bars of four beams were studied and compared with each other. Experimental results show that top-casting-induced defects encouraged corrosion to develop first at the bottom surface of compressive bars and their presence strongly accelerated the corrosion process. Without top-casting-induced defects, the corrosion was more prominent on the outside part of re-bars facing the concrete surface exposed to chloride ingress. After the appearance of corrosion-induced cracks, corrosion gradually developed all around the perimeter of re-bars, with the result that top-casting-induced defects no longer affected the corrosion process

An energy-efficient VM placement in cloud datacenter

IEEE Computer SocietyInternational audienc

Advanced Modeling and Simulation of Electromechanical Actuator for Flight Control System Based on Two Degrees of Freedom (2-DoF) Bond-Graph Method

International audienceElectromechanical actuator (EMA) is a key element that is being developed for safe critical embedded application in next-generation electrical aircraft. Designers and manufacturers must carefully consider the parasitic effects in the frame of the model-based design and development of EMA. Thus, conducting accurate simulation analysis of natural dynamics, power losses, thermal behavior, reaction forces, and faults to failure performance is crucial and necessary before EMA operates in service. This communication proposes a two degree-of-freedom (2-DoF) modeling approach considering EMA translational and rotational motion. The key principle includes decomposing the EMA into to several generic subcomponents with mechanical “quadriport” model that can easily combine the 2-DoF motion. The proposed approach is developed by the intensive use of bond graph modeling. This approach enables the bearings, joints, and end-stops to be added for component-level performance analysis. This 2-DoF modeling approach is a useful support for EMA architecture selection, sizing, assessment of response to failure, health monitoring, and control design. The proposed 2-DoF lumped parameters models are helpful to evaluate EMA’s thermal balance and analyze energy losses through system-level thermal behavior modeling and simulation