Effects of pre-cracks on both initiation and propagation of re-bar corrosion in pure carbon dioxide

WOS:000342340900033International audienceThis paper deals with effects of pre-cracks on both initiation and propagation of reinforcement steel corrosion due to carbonation. The ring shaped mortar samples with 8 mm steel bar inside were cracked with different crack widths ranging from 12 micrometers to 600 micrometers and then subjected to carbon dioxide environment for different terms to assess the carbonation profile in cracks and along the interface between steel and concrete, damaged by the internal pressure applied to the ring samples. After carbonation of interface, ring samples were submitted to wetting-drying cycles to study the propagation of corrosion and the effect of corrosion products on healing and then repassivation of steel bar or corrosion cracks development. Results show that irrespective of width of cracks, the carbon dioxide reaches the interface between steel and mortar and propagates along this interface. The samples then subjected to wetting-drying cycles exhibit corrosion development all along the interface, the appearance of oxides does not lead to create corrosion cracks for the duration of the experiments

Propagation of corrosion in pre-cracked carbonated reinforced mortar

WOS:000358336500016International audienceThis paper deals with the initiation and propagation of corrosion in mortar specimens pre-cracked under mechanical loading and carbonated in climate accelerated conditions (50 % CO2-65 % RH) for 15-23 weeks. Mechanical loading led to transverse macro-cracks and damage at the steel-mortar interface characterized by micro-cracks (cover controlled cracking) which favour the carbonation of crack walls and the interface with the steel bar. Wetting-drying cycles performed after carbonation favoured corrosion initiation all along the steel bar because of the carbonated interface and corrosion propagation because of the creation of corrosion cracks which appear to develop from the micro-cracks induced by the mechanical load. Results also show that rust develops all around the perimeter of the carbonated steel bar but that the corrosion layer is thicker in the lower half surface of the reinforcement than that observed in the upper half. Results indicate that the distribution and composition of corrosion products depend on the thickness of the rust layer and that the multilayered structure of rust depends mainly on its thickness

Carbonation of low-alkalinity mortars: Influence on corrosion of steel and on mortar microstructure

International audienceThe ability of carbonated mortar to provide corrosion protection of embedded steel was studied on mortars prepared with low-alkalinity binders. Three mortars were investigated, mortar based on ordinary Portland cement, mortar based on high volume of fly ash and silica fume and mortar based on slag and nano-silica. Analysis of impedance spectra after carbonation revealed an increase in electrical resistivity of mortar based on OPC and significant decrease in electrical resistivity of low-alkalinity mortar. After exposure to cycles of wetting and drying steel embedded in carbonated low-alkalinity mortars has lower open circuit potential, lower charge transfer resistance and significantly higher corrosion current density compared to steel embedded in OPC mortar. To explain differences in corrosion protection properties, an extensive microstructural testing of carbonated mortar was performed. Difference in corrosion properties were explained by the changes in mortar microstructure, mainly changes in pore size distribution

Development of chloride-induced corrosion in pre-cracked RC beams under sustained loading: Effect of load-induced cracks, concrete cover, and exposure conditions

WOS:000347502100024International audienceThis paper deals with corrosion initiation and propagation in pre-cracked reinforced concrete beams under sustained loading during exposure to a chloride environment. Specimen beams that were cast in 2010 were compared to specimens cast in 1984. The only differences between the two sets of beams were the casting direction in relation to tensile reinforcement and the exposure conditions in the salt-fog chamber. The cracking maps, corrosion maps, chloride profiles, and cross-sectional loss of one group of two beams cast in 2010 were studied and their calculated corrosion rates were compared to that of beams cast in 1984 in order to investigate the factors influencing the natural corrosion process. Experimental results show that, after rapid initiation of corrosion at the crack tip, the corrosion process practically halted and the time elapsing before corrosion resumed depended on the exposure conditions and cover depth. (C) 2014 Elsevier Ltd. All rights reserved

Structural performance of RC beams damaged by natural corrosion under sustained loading in a chloride environment

WOS:000356119300004International audienceThis paper discusses the effect of corrosion on the load-bearing capacity and ultimate deflection of corroded beams exposed to wetting-drying cycles in a chloride environment under sustained loading without impressed current. The mechanical performance of one control beam and two corroded beams was tested. Corroded bars in the beams were extracted for tensile tests and the cross-sectional losses were measured. The experimental results were compared with those obtained in a previous long-term aging program in a chloride environment. The experimental results confirmed that corrosion of the reinforcements modified the failure mode of reinforced concrete beams. The control beam failed due to crushing of the concrete in the compressive zone, while deteriorated beams failed due to the rupture of one tensile bar. As a result, the maximum cross-sectional loss on tension bars allows the residual yielding and ultimate capacity to be predicted since 1% reduction in cross-section corresponds to 1% reduction in yielding capacity and ultimate capacity. The results also show the importance of the initial ductility of the steel bars. Corrosion leads to more brittle behavior of steel bars in tension but the influence of corrosion on the ductility of RC beams depends on the initial ductility of the steel bar. In consequence, highly ductile steel bars belonging to Class C according to Eurocode 2 could prevent brittle collapse of corroded RC beams because of sufficient residual ductility of the corroded steel bars. (C) 2015 Elsevier Ltd. All rights reserved

Distribution of corrosion and pitting factor of steel in corroded RC beams

WOS:000360417000038International audienceThe purpose of this work was to study the corrosion distribution along a steel bar in beams of sizes typically used in the construction industry and the ratio between maximum cross-sectional loss and average cross-sectional loss of the steel bar. This work was based on three beams exposed to accelerated natural corrosion for 19-36 months. The cracking maps and crack widths were recorded. After the steel bars had been extracted from the beams and cleaned with Clarke's solution, cross-sectional losses were measured. The experimental results show that average cross-sectional loss of the steel bar correlated well with maximum corrosion crack width. The pitting factors of steel bars were mainly between 2.5 and 5.0, and decreased with the increase of average cross-sectional loss. More measurements would be desirable in further research on the pitting factor before this factor is used for predicting the residual mechanical performance of corroded structures. (C) 2015 Elsevier Ltd. All rights reserved

Effect of crack openings on carbonation-induced corrosion

WOS:000400880100027International audienceReinforced concrete is widely used in the construction of buildings, historical monuments, infrastructures and nuclear power plants. For a variety of reasons, many concrete structures are subject to unavoidable cracks that accelerate the diffusion of atmospheric carbon dioxide to the steel/concrete interface. Carbonation at the interface induces steel corrosion that could cause the development of new cracks in the structure, a determining factor for its durability. The aim of this article is to study the effect of existing cracks on the development of carbonation induced corrosion. The results indicate that, after the initiation phase, the corrosion kinetics decreases with time and the free corrosion potential increases independently of the crack opening. In addition, the corroded zone matches the carbonated one. The interpretation of these results allows the authors to conclude that, during the corrosion process, corrosion products seal the crack and act as a barrier to oxygen and water diffusion. Consequently, the influence of crack opening on corrosion development is masked and the corrosion development is limited. (C) 2017 Elsevier Ltd. All rights reserved

Effect of accelerated carbonation conditions on the characterization of load-induced damage in reinforced concrete members

WOS:000404147000016International audienceReinforced concrete is widely used in the construction of buildings, historical monuments and also nuclear power plants. For various reasons, many concrete structures are subject to unavoidable cracks that accelerate the diffusion of atmospheric carbon dioxide to the steel/concrete interface. Carbonation at the interface induces steel corrosion that may cause the development of new cracks in the structure, and this is a determining factor for its durability. It is therefore important to accurately characterize the length of the load-induced damage along the steel/concrete interface in order to understand the effect of cracking on corrosion initiation and propagation. The aim of this paper is to present an experimental procedure that allows the load-induced damage length to be assessed. The procedure consists in subjecting specimens to accelerated carbonation and determining the length of the carbonated steel/mortar interface, which is assumed to be equal to the length of the damaged steel/mortar interface. Suitable conditions should therefore be found for the accelerated carbonation in order to obtain an accurate characterization of the damaged steel/mortar interface length. To this end, two carbonation concentrations (3, 50%) and several carbonation durations were tested. The results indicate that a strong carbonation shrinkage phenomenon develops at high carbon dioxide concentration and leads to new cracking along the steel/mortar interface. These cracks allow the carbon dioxide to spread along the interface over a length greater than the damaged length. This is not the case when the accelerated carbonation test is performed at lower carbon dioxide concentration. Consequently, accelerated carbonation at high carbon dioxide concentration (50%) cannot be used neither for the estimation of the length of the mechanically damaged steel/mortar interface nor for the carbonation-induced corrosion studies because it will lead to an overestimation of the size of the corroded area

Preservation of historical buildings: understanding of corrosion mechanisms of metallic rebars in concrete

International audienceNumerous monuments of the 20th century made of reinforced concrete are decaying due to the corrosion of their metallic reinforcements, the growth of the corrosion products generally inducing spalling. In order to prevent these degradations before the concrete cracks, it would be interesting to determine by non destructive methods the state of corrosion of the embedded rebars. Three types of corrosion forms have been evidenced on samples collected on three monuments: first is original and contains wüstite, the second is a mixture of the first and thicker layers containing oxy-hydroxides, characteristic of the third typ

Corrosion diagnosis of reinforced concrete beams after 40 years exposure in marine environment by non destructive tools

International audienceThis paper describes the detailed experimental program of the French national project “benchmark des poutres de la Rance”. It presents a corrosion diagnosis of prestressed beams after 40 years exposure in natural marine environment. It includes results from non destructive testing tools, complementary laboratory tests and destructive analyses. This project will provide a large database on the corrosion state of reinforced concrete beams after 40 years exposure in a marine environment (mechanical, electrochemical and physico-chemical properties) and will allow studying the sensitivity of NDT tools to evaluate corrosion risk within reinforced concrete structures. These results will be given to the modellers in order to complete their test conditions in the framework of the validation of mechanical models.Cet article decrit le programme experimental mis en place dans le cadre du Benchmark des poutres de la Rance. Il presente le diagnostic vis-a-vis de la corrosion de poutres en beton precontraint ayant sejourne 40 ans en environnement marin. Ce papier inclut les resultats issus des techniques d-auscultation non destructive, les tests complementaires en laboratoire et les analyses destructives. Ce projet permet de beneficier d-une large banque de donnees sur l-etat de corrosion des poutres apres 40 annees (mecanique, electrochimiques et proprietes physico-chimiques) et d-apprecier la sensibilite des techniques non destructives pour evaluer des risques de corrosion au sein de structures en beton precontraint. Ces resultats sont fournis aux equipes de modelisation afin de completer leurs conditions de tests en vue de la validation des modeles de comportement mecanique