Influence du séchage sur le développement des hétérogénéités dans les structures à base de matériaux cimentaires : Impact sur les propriétés mécaniques

Ce travail décrit l’ensemble des phénomènes qui gouvernent le développement des hétérogénéités dans les structures à base de matériaux cimentaires lorsqu’elles sont soumises au séchage ainsi que leur influence sur les propriétés mécaniques du matériau mis en oeuvre. Il s’agit notamment des facteurs influents tels que la porosité, la teneur en humidité, le degré d’hydratation. Tous ces facteurs contribuent à la tenue du matériau in situ ainsi que son comportement au regard de la  fissuration. Il a été démontré pour ces matériaux que, les fissures s’amorcent dans la partie du matériau qui présente les propriétés les plus médiocres et qu’elles se propagent par la suite dans le reste du volume. Dans cette étude, nous nous sommes intéressés à la caractérisation et la quantification des gradients de propriétés tels que les gradients hydriques, les gradients d’hydratation et les gradients de porosités. Pour finir nous avons étudié leur impact sur l’évolution des propriétés mécaniques des matériaux mis en oeuvre. L’étude a révélé une parfaite adéquation entre la progression du front de séchage et les différentes hétérogénéités observées en terme de caractéristiques mécaniques.Mots-clés : matériaux cimentaires, béton, mortier, séchage, hétérogénéités, propriétés mécaniques

Improving the reliability of on-site concrete strength estimation with non-destructive techniques

The non-destructive assessment of concrete strength in existing structures is a complex issue. While many standards exist addressing the way non-destructive measurements must be carried out, few exist for the strength assessment itself. Many questions remain unanswered, like for instance the reliability of the strength estimation, the possibility of estimating the concrete variability, or the advantages of combining several non-destructive techniques. These problems have been tackled by a recent RILEM committee (TC ISC 249) whose Guidelines and Recommendations are to be released soon. This paper details their main innovations and how they are expected to improve the engineering practice and the reliability of strength estimation in existing structures

Structural characterization of intrinsically disordered proteins by NMR spectroscopy.

Recent advances in NMR methodology and techniques allow the structural investigation of biomolecules of increasing size with atomic resolution. NMR spectroscopy is especially well-suited for the study of intrinsically disordered proteins (IDPs) and intrinsically disordered regions (IDRs) which are in general highly flexible and do not have a well-defined secondary or tertiary structure under functional conditions. In the last decade, the important role of IDPs in many essential cellular processes has become more evident as the lack of a stable tertiary structure of many protagonists in signal transduction, transcription regulation and cell-cycle regulation has been discovered. The growing demand for structural data of IDPs required the development and adaption of methods such as 13C-direct detected experiments, paramagnetic relaxation enhancements (PREs) or residual dipolar couplings (RDCs) for the study of 'unstructured' molecules in vitro and in-cell. The information obtained by NMR can be processed with novel computational tools to generate conformational ensembles that visualize the conformations IDPs sample under functional conditions. Here, we address NMR experiments and strategies that enable the generation of detailed structural models of IDPs

Identification of inhomogeneous concrete cover by non-contact ultrasonic method

International audienceConcrete cover degradation is induced by aggressive agents in ambiance, chemicals, moisture, or temperature variations. Due to this degradation concrete becomes inhomogeneous and usually a thin surface layer appears with porosity and elastic modulus different than the properties of deeper sound concrete. Therefore the on-site nondestructive evaluation of concrete cover is important to monitor the integrity of concrete structures and prevent their irreversible damage. In this paper the methodology applied by the classical technique used for ground structure recovery called Multichannel Analysis of Surface Waves (MASW) is used as the NDT tool to characterize the thickness and elastic modulus of concrete cover. The procedure consists in generation and reception of surface waves within the required frequency band, using the non-contact transducers which scan evaluated profiles. Then the phase velocity dispersion characteristic V(f) is extracted, and concrete cover is characterized using as the proposed velocity gradient. The dispersion characteristics are exploited by the inversion software in order to obtain the variation of shear wave velocity as a function of depth

Waterfront Depth Analysis in Hardened Concrete by Means of the Nondestructive Ground-Penetrating Radar Technique

© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Durability of concrete structures depends mainly on the ease whereby water and any aggressive chemical agents dissolved therein can penetrate. Therefore, measuring water penetrability in concrete structures is crucial mostly when structures are in service. In this context, nondestructive techniques play an important role. In particular, the electromagnetic waves emitted by ground-penetrating radar (GPR) are very sensitive to the water content of the medium through which they propagate. This fact provides an interesting opportunity to analyze if the GPR technique allows the assessment of water penetrability in concrete with enough accuracy. In line with this, this paper describes the laboratory experiments and relevant analysis carried out to study the capability of GPR to assess water penetrability in hardened concrete. For this purpose, concrete specimens were fabricated and dried in an oven after 90 days of curing. They were then dipped into water and GPR measurements were taken at different intervals, based on coupling a 2.0 GHz antenna. The results showed that the agreement between velocity increments and the waterfront advance was excellent. In addition, a specific processing of the data acquired was developed. This process included the isolation of the reflection due to the waterfront, produced just before the reflection of the bottom of the samples. As a result of this processing, the in-depth waterfront location at different times was determined with high reliability.This work was supported by the Universitat Politecnica de Valencia (Spain) under the PAID-06-12 research plan through a project entitled: "Analisis de la durabilidad del hormigon por medio de la tecnica no destructiva del georradar."Rodríguez-Abad, I.; Klysz, G.; Martínez-Sala, RM.; Balayssac, JP.; Mene-Aparicio, J. (2016). Waterfront Depth Analysis in Hardened Concrete by Means of the Nondestructive Ground-Penetrating Radar Technique. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 9(1):91-97. https://doi.org/10.1109/JSTARS.2015.2449737S91979

Evaluation of concrete structures by combining non-destructive testing methods (SENSO project)

The management and maintenance of the built heritage is one of the main interests of the owners of concrete structures. The engineers wish to obtain quantitative information about concrete properties and their variability. Non-destructive testing (NDT) is very popular in this context as it quickly provides relevant information on the integrity and evolution of the material, but several kinds of indicators representative of the concrete condition need to be evaluated. A French Project, named SENSO, aims to develop methods for the non-destructive evaluation of concrete based on a multi-techniques approach. Several families of techniques are concerned (ultrasonic, electromagnetic, electrical, etc.). The main objective is to define the sensitivity of the techniques and the variability of the evaluation for each indicator concerned. To achieve this, a large experimental programme, involving a representative range of concretes and several indicators, has been carried out. A large database, linking the NDT observables and the indicators, allows the different observables to be distinguished in terms of quality (linked to the variability) and in terms of relevance for the characterisation of each indicator. The improvement of the indicator evaluation by means of technique combinatio

Comparison of durability indicators obtained by Non Destructive Testing methods to monitor the durability of concrete structures

International audienceThis paper deals with the use of non destructive testing methods (NDT) to assess indicators of concrete durability and mechanical properties of reinforced concrete structures. On site, NDT methods based on electromagnetic or ultrasonic wave propagation (such as radar, impact echo, ultrasonic transmission deviceÉ) are used because they are more or less sensitive to water content and mechanical properties depending on the method. It has been shown, in a former project [1, 2], that the NDT results called Òobservablesî are linked to mechanical and durability indicators (YoungÕs modulus, compressive strength, porosity and saturation degree). Meanwhile, the relationship between observables and indicators depends on the concrete mix design. A calibration protocol is then proposed to get this relationship for the right mix of the reinforced structure studied by using a minimal number of cores. The cores are non-destructively characterised in laboratory or used to determined reference indicators by standardised destructive methods. The aims of this paper are first to present the ND calibration protocol on cores and then to validate this proposed calibration protocol. To achieve this goal, some NDT results obtained on site and on the corresponding core are compared and durability indicators deduced from NDT calibration are compared with reference durability indicators

Proposition d'une méthodologie de calibration de la vitesse de propagation des ondes radar pour la mesure de la teneur en eau du béton

Le radar de type GPR est très utilisé en Génie Civil pour le repérage des armatures de renforcement du béton. La technique s’est imposée face à des appareils d’un prix de revient plus faible grâce, d’une part à son rendement élevé et d’autre part à ses capacités d’investiguer des profondeurs importantes. Ce rendement élevé peut également être mis à profit pour la caractérisation physico-chimique du béton, en particulier pour la mesure de sa teneur en eau. Des travaux en laboratoire ont montré qu’un des observables les plus sensibles à la teneur en eau volumique, indépendamment de la salinité, est la vitesse de propagation du signal direct, qui se propage en surface. Une base de données conséquente entre cet observable et la teneur en eau a été constituée et elle devrait permettre de déterminer la teneur en eau à partir d’une mesure de vitesse. Sa mise en œuvre sur ouvrages réels a révélé les limites de cette approche. En effet, même si la teneur en eau est le paramètre le plus influent, la vitesse de propagation est sensible à d’autres facteurs, en particulier la nature des granulats. Il parait donc nécessaire de calibrer la mesure pour chaque ouvrage, de façon simple et rapide. Une méthodologie de calibration est proposée sur la base d’une mesure de la vitesse en transmission sur une carotte de béton prélevée dans l’ouvrage et conditionnée à différentes teneurs en eau. Un dispositif simple de mesure de la vitesse en transmission sur carottes est testé et son efficacité est démontrée. Les vitesses mesurées en transmission et en surface étant bien corrélées, il est possible d’établir le modèle de corrélation entre vitesse de l’onde transmise et teneur en eau volumique propre au matériau testé, qui pourra ensuite être utilisé pour la calibration des mesures réalisées en surface sur l’ouvrage réel