Micro-Mechanical Analysis of Corrosion Products Formed During Long-Term Carbonation Induced Corrosion of Steel

During corrosion distinct types of corrosion products form, composed of different ratios of ferrous ions and oxide, hydroxides. Corrosion products have different physical and mechanical properties, mainly density, resistivity, volume and modulus of elasticity compared to iron. Knowing properties of corrosion products is indispensable for service life modelling of structures and can give valuable insight into the long-term corrosion propagation process. In this study micro-indentation method was used to evaluate mechanical properties of different layers formed during long-term carbonation induced corrosion of steel in concrete. Investigation was performed on three sets of reinforced concrete samples, that underwent corrosion during 50, 60 and 70 years. Raman microspectroscopy was performed locally to determine and locate the constitutive phases of the corrosion system and to correlate them to the results of micro-indentation. Using grid technique, spatial distribution of phases with different mechanical properties was obtained for samples of different age. Comparison of values of mechanical properties for the same phases obtained on different samples, allowed hypothesis on their long-term behaviour

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

This 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

Microstructure and diffusion coefficient of an old corrosion product layer and impact on steel rebar corrosion in carbonated concrete

International audienceCorrosion is the major degradation pathway affecting reinforced concrete structures. In the long-term, the rust layer might become thick and slow down the diffusion of oxygen from the atmosphere to the steel. With this in mind, the mineralogy, microstructure and diffusion properties of an old and thick corrosion product layer were investigated. Despite the presence of macropores, the gas diffusion coefficient was found to be low. The impact of the layer on the oxygen diffusion was evaluated using Fick’s law. The results showed that the layer could reduce the flux of oxygen only in a specific configuration

Contribution to a better understanding of long-term hydration, structuration and mechanical properties of slag based cementitious materials: Experimental and modeling approaches

International audienceHighlight Proposing a new hydration model for slag-blended cement Avrami's exponential model is used to describe the hydration kinetics Modified version of Kolani's stoichiometric laws describes the chemical reactions Cement porosity is influenced by clinker substitution with slag rate Analytical links between hydration and mechanical properties can be establishe

Characterization of Steel/Concrete Interface for a Long-Term Corroded Beam Stored in Chloride Environment

International audienceThis paper deals with the steel/concrete interface of a corroded beam B2CL1 after a 23 years exposure in chloride environment. XRD, SEM and Raman techniques were performed to investigate the chemical compositions and the spatial distribution of corrosion products. The experimental results illustrate that the corrosion product layer is a multi-layer constituted as marbling structure. It is composed of a mix of iron oxides and iron oxi-hydroxides. Iron species were found in the vicinity of concrete mainly in cracks, as it was already observed in the literature

Mismatch negativity as EEG biomarker supporting CNS drug development: A transnosographic and translational study

The lack of translation from basic research into new medicines is a major challenge in CNS drug development. The need to use novel approaches relying on (i) patient clustering based on neurobiology irrespective to symptomatology and (ii) quantitative biomarkers focusing on evolutionarily preserved neurobiological systems allowing back-translation from clinical to nonclinical research has been highlighted. Here we sought to evaluate the mismatch negativity (MMN) response in schizophrenic (SZ) patients, Alzheimer’s disease (AD) patients, and age-matched healthy controls. To evaluate back-translation of the MMN response, we developed EEG-based procedures allowing the measurement of MMN-like responses in a rat model of schizophrenia and a mouse model of AD. Our results indicate a significant MMN attenuation in SZ but not in AD patients. Consistently with the clinical findings, we observed a significant attenuation of deviance detection (~104.7%) in rats subchronically exposed to phencyclidine, while no change was observed in APP/PS1 transgenic mice when compared to wild type. This study provides new insight into the cross-disease evaluation of the MMN response. Our findings suggest further investigations to support the identification of neurobehavioral subtypes that may help patients clustering for precision medicine intervention. Furthermore, we provide evidence that MMN could be used as a quantitative/objective efficacy biomarker during both preclinical and clinical stages of SZ drug development