Discussion of the paper titled "Evaluation of the predictive ability of the in situ concrete strength through core drilling and its effects on the capacity of the RC columns by M. Vona and D. Nigro"

WOS:000373963700037International audienc

Contribution of metallic fibers on the performance of reinforced concrete structures for the seismic application

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Optimisation de la composition et caractérisation d'un béton incorporant des granulats issus du broyage de pneus usagés. (application aux éléments de grande surface.)

Les matériaux de construction par excellence que sont les matériaux à base cimentaire offrent une faible résistance à la traction ainsi qu une faible capacité de déformation. Ils sont fragiles et particulièrement sensible à la fissuration, notamment la fissuration due au retrait dans le cas d éléments à grande surface. Des joints de retrait judicieusement espacés permettent de localiser la fissuration et d éviter le désordre apparent. Malheureusement, ils constituent aussi le point de départ de futurs désordres (pénétration d agents agressifs, tuilage, etc.). Cette thèse est une contribution au développement d un nouveau composite cimentaire présentant une capacité de déformation améliorée. Dans cet objectif, des granulats en caoutchouc (G.C.) issus du broyage de pneus usagés ont été utilisés en remplacement partiel du sable. Les résultats obtenus montrent que la présence de ces granulats est préjudiciable vis-à-vis de la rhéologie du matériau à l état frais mais que l utilisation d un superplastifiant et d un agent de viscosité permet de réaliser les corrections nécessaires. A l état durci, une chute de la résistance mécanique et du module d élasticité est observée, en contrepartie la capacité de déformation au stade de la localisation de la macrofissuration est significativement augmentée. Des essais dédiés permettent de démontrer que cette incorporation de G.C. permet de réduire la sensibilité à la fissuration de retrait avec un intérêt évident pour les applications à grande surface comme les chaussées et dallages sur terre-plein. L influence de la présence de ces G.C. sur la cinétique de la fissuration a été analysée et confirmée par le biais d une variable d endommagement et par l activité (émission) acoustique accompagnant le processus de fissuration.Le potentiel du composite dans les applications à grande surface comme les chaussées en béton a aussi été abordé par le biais de l indice de qualité élastique qui a confirmé les promesses attendues. Compte tenu du rôle joué par le module d élasticité du composite sur ces nouvelles propriétés et les applications potentielles, les outils prédictifs de ce module en fonction du dosage en G.C. présentent un intérêt pratique évident. Dans ce sens, cette thèse a permis de tester la pertinence de quelques modèles analytiques. Dans ce cadre, la borne inférieure de Hashin-Shtrikman qui reste perfectible s est avérée la mieux indiquée.A côté de l intérêt en termes d application matériau Génie Civil, l incorporation de G.C. constitue une voie de valorisation de pneus usagés non réutilisables et une contribution à la protection de l environnementCement-based materials exhibit low tensile strength and poor strain capacity. They are brittle and are very sensitive to cracking particularly to shrinkage cracking in large area applications. Sawn joints allow shrinkage cracking to be localised a way to avoid unsightly cracking. Unfortunately they are also the starting point of future distress (ingress of aggressive agent, curling, etc.).This work is a contribution to the design of a cement-based material exhibiting an enhanced strain capacity. For a such objective rubber aggregates (RAs) obtained from grinding end of life tyres partly replacing natural sand have been used.Results showed that RAs are detrimental to the properties of the fresh materials (workability and segregation). However the use of optimized content of a superplasticiser and of a viscosity agent allows the required behaviour to be achieved.With regard to harden state, RAs reduce the strength and the modulus of elasticity of the composite but the strain capacity corresponding to the macrocracking formation is significantly improved. Specific tests showed that RAs reduced the propensity of the material for shrinkage cracking, offering an interest for large surface area such as pavements.Analysis by a scalar damage variable and by acoustic emission is in a good agreement with expected effect of RAs on the cracking kinetics and on the mechanical behaviour of the composite.The interest of the rubberized concrete in large area application such as concrete pavements has been studied and confirmed through the Elastic Quality Index. Given the major role of the modulus of elasticity of the composite on the new properties and expected applications, tools aimed to predict this modulus of elasticity as a function of RAs content are of practical benefit. With this purpose, the work allowed the relevance of some analytical models to be tested. In this context, the lower Hashin-Shtrikman bound which remains perfectible proved to be the most appropriate.Finally, apart from application of civil engineering material, the use of RAs from grinding end of life tyres is a solution of recovery of an industrial by-product and a contribution to a clean environmentTOULOUSE-INSA-Bib. electronique (315559905) / SudocSudocFranceF

Tensile, compressive and flexural basic creep of concrete at different stress levels

International audienceConcrete is brittle and highly sensitive to cracking, which is detrimental to the sustainability of its applications. Although it is well known that cracks occur mainly in tension, research on the mechanical behavior of concrete is usually limited to compression and investigations of creep behavior, a major concern for concrete structures, are no exception in this respect. This paper is intended to help remedy the situation. First, the new experimental set-ups developed to achieve tensile and bending creep are presented. The precautions taken to obtain relevant experimentation are also described. Results for specimens subjected to sustained stresses of 30, 40 and 50% of the tensile or compressive strength are then presented. The final discussion compares basic creep under the different types of loading for the three stress levels

Basic creep of concrete under compression, tension and bending

International audienceInvestigations on concrete creep are often limited to the compression behavior due to the difficulty of performing tensile tests on cement-based materials. This paper describes the experimental setup developed to achieve direct tensile and bending concrete creep. The precautions taken to obtain relevant data are described. For comparison, tensile, flexural and compressive basic creep test were conducted in parallel. Although the approach is still controversial, the basic creep strain was determined by subtracting the shrinkage strain and instantaneous strain from the total strain. Results available for specimens subjected to 50% of the strength in tension or in compression are presented. The final discussion compares the basic creep under the different types of loading

Étude expérimentale et numérique des interactions entre le fluage en traction et l'endommagement du béton

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Durabilité des réparations à base cimentaire (analyse comparée de l'influence des propriétés mécaniques du matériau de réparation)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

COMPARATIVE STUDY OF COMPRESSIVE AND TENSILE BASIC CREEP BEHAVIOR OF CONCRETE

International audienceDue to its poor strain capacity and a low tensile strength, concrete is brittle and highly sensitive to cracking detrimental to application sustainability. Despite this well-established knowledge, the irony today is that investigations on concrete are usually limited to the compression behavior. The creep behavior that is a major concern for concrete structures is no exception to this observation. Only one reason can explain this aberration: the difficulty to perform a tensile test on cement-based materials, particularly their fixture to the loading device. This paper describes the experimental setup developed to achieve direct tensile and bending creeps. The precautions taken to obtain relevant data are described. For comparison, tensile, flexural and compressive basic creep test were conducted in parallel. Although the approach is still controversial, the basic creep strain was determined by subtracting the shrinkage strain and instantaneous strain from the total strain. Results available for specimens subjected to 50% of the strength in tension or in compression are presented. The final discussion compares the basic creep under the different types of loading

Design and characterization of self-sensing steel fiber reinforced concrete

The purpose of this communication is to develop a self-sensing cement composite capable of detecting stress variation in concrete by monitoring its electrical property. The relationship between the electrical properties, i.e. electrical resistance of steel fiber reinforced concrete, and stress under loading as part of self-sensing study is presented in here. Amorphous metallic fibers (AMF) with two different lengths i.e. 10 mm and 30 mm are used as concrete reinforcement at a content of 40 kg/m3. A water to cement ratio of 0.39 was adopted for the mix proportions. Natural fine and coarse siliceous aggregates were used for this research. Superplasticizer was used to achieve the target of workability. The two-probe method is used for measuring electrical properties on cylinder specimens with diameter 100 mm and height 200 mm. The influence of different parameters such as fiber length, frequency of power input, maximum stress and variation of potential input on the sensitivity of the sensing are investigated. The results indicate that the electrical resistance of the concrete decreases reversibly during loading and increases reversibly during unloading. Good sensitivity obtained for the mix using 30 mm AMF length indicates that the addition of this type of fiber into concrete can be suitable to produce a self-sensing cement composite

Benefits of Low Modulus of Elasticity and of Fibre Reinforcement of Cement Based Mortars as Thin Bonded Overlay Materials

WOS:000326045800024International audienceThe paper, associating experiment and simulation approaches, deals with the debonding propagation between a thin bonded cement-based overlay and a substrate simulating a repair of old concrete structure. The material used for the overlay is a fibre reinforced and rubberised mortar. In the experimental investigations, three point static bending tests were carried out on composite specimens. The effects of shrinkage of the overlay, restrained by the substrate, and the role of fibre reinforcement are thus involved. Direct tensile tests on notched specimens were firstly conducted to obtain the tensile strength and the residual normal stress-crack opening relationship. The debonding opening-residual normal tensile stress relationship was investigated by static tensile tests. The propagation of the debonding interface was monitored using a video-microscope with an enlargement of 175x. On the basis of the parameters identified and quantified, the above mentioned static tests were modelled by the finite element method using CAST3M code developed in France by CEA (Commission for Atomic Energy). The model predictions showed good agreement with the experimental results. The shrinkage effect on the durability of the composite specimens was clarified. The results also proved the important role of fibre-reinforcement in restraining the crack opening by transferring stresses through the crack