Caractérisation de l'épaisseur et du module d'élasticite du béton des dalles par des techniques acoustiques

La connaissance des caractéristiques géométriques et mécaniques des ouvrages en béton armé est indispensable pour toute évaluation préalable à une opération de maintenance ou de réhabilitation. Or, souvent, les maîtres d’ouvrage ne disposent pas les informations nécessaires, surtout lorsque les ouvrages sont relativement anciens. Disposer des outils de caractérisation fiables, faciles à mettre en œuvre et, dans la mesure du possible, non destructifs répond donc à un vrai besoin compte tenu du nombre d’infrastructures en béton armé vieillissantes. Pour répondre à ce besoin nous avons développé au Laboratoire de Mécanique et Matériaux du Génie Civil de l’Université de Cergy-Pontoise une méthodologie originale qui combine deux techniques acoustiques complémentaires, la technique d’Impact-écho et la technique micro-sismique, permettant d’évaluer, d’une part, l’épaisseur de l’élément en béton ausculté et, d’autre part, la qualité du béton sur la base de son module d’élasticité dynamique et de l’identification d’éventuelles fissures ou d’autres défauts compromettant l’intégrité mécanique de l’élément ausculté. La technique d’impact écho exploite la propagation des ondes de compression à travers le béton suite à un impact mécanique en surface alors que la technique micro-sismique exploite la propagation des ondes de Lamb en surface de l’élément ausculté. L’application in situ de cette méthodologie fut effectuée lors de deux études en collaboration libre avec les Aéroports de Paris, à l’aéroport du Bourget sur des dalles de l’aire de stationnement d’avions dont les conditions de fabrication étaient inconnues. Ces travaux ont donné des résultats probants et convaincants et ont permis de répondre pleinement aux besoins de connaitre les caractéristiques de ces structures

Optimization of the Performance of Earth Mortars at Elevated Temperatures

Publisher Copyright: © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.This study investigates the behavior of three earth mortars exposed to elevated temperatures, considering the nature of the aggregates used. Earth mortars made from a combination of a silty-clay earth, silica-calcareous sand (S) and fired bricks waste (W) were investigated. One volumetric fractions of sand/earth and two percentages of sand/fire bricks waste substitution were considered and test specimens were prepared for each mortar. After drying to have constant mass, tests were carried out to determine physical and mechanical properties at room temperature and after being subjected to heating-cooling cycles at temperatures of 200 ℃, 400 ℃, 600 ℃ and 800 ℃. Notable observations were made, in particular the negative effect of the silico-calcareous sand fraction after 400 ℃. At the highest temperature of 800 ℃, mortar containing sand showed significant degradation due to decarbonation of the calcareous aggregate. The effect of using fire bricks waste as additional aggregate was very positive. The results obtained can be used to optimize the performance of earth mortars at elevated temperatures.authorsversionpublishe

Contribution of polypropylene and steel fibres in improving the behaviour of concrete subjected to high temperature

Le but de ce travail de recherche est d'étudier l'effet de fibres de polypropylène et de fibres métalliques sur le comportement du béton soumis à une température élevée. D'une part, les fibres de polypropylène ont été ajoutées au béton pour améliorer sa stabilité thermique, et d'autre part les fibres métalliques ont été ajoutées au béton pour améliorer ses propriétés mécaniques résiduelles. De nouvelles formulations de béton ont ensuite été définies, en utilisant un cocktail de fibres de polypropylène et métalliques, afin d'améliorer à la fois la stabilité thermique et les propriétés mécaniques résiduelles du béton. Quatre familles de bétons ont été étudiées : - bétons témoins sans fibres, - bétons contenant des fibres de polypropylène, - bétons contenant des fibres métalliques, et – bétons contenant un cocktail de fibres de polypropylène et métalliques. Trois rapports eau/ciment sont utilisés : 0.30, 0.45 et 0.61. Les éprouvettes de béton, issues de ces compositions, ont été soumises à des cycles de chauffage – refroidissement de la température ambiante à une température de consigne de 150°C, 300°C, 450°C et 600 °C. La vitesse de chauffage a été fixée à 1 °C.min-1. Les teneurs en fibres étaient de 0.11, 0.17 ou 0.22 % en proportion volumique pour les fibres de polypropylène et de 0.25, 0.38 ou 0.51 % pour les fibres métalliques. Les proportions volumiques de cocktail de fibres étaient de 0.49, 0.60, 0.62 et 0.73%. La stabilité thermique, les propriétés mécaniques (résistance en compression, résistance en traction, module d'élasticité), la porosité initiale et résiduelle des bétons formulés ont été analysées. La perte de masse des éprouvettes lors des différents chauffages a été aussi mesurée.Cette étude expérimentale aboutit à la formulation de bétons dont à la fois la stabilité à haute température et le comportement mécanique après refroidissement sont améliorés.The aim of this study was to investigate the effect of polypropylene and steel fibres on the behaviour of concrete subjected to high temperature. Polypropylene fibres were added to the studied concrete mixes in order to improve the concrete thermal stability. Steel fibres were added to the studied concrete mixes in order to improve the concrete residual mechanical properties. News concretes mixes were then designed by adding a cocktail of polypropylene fibres and steel fibres in order to improve both the thermal stability and the residual mechanical properties of the studied concrete. Four groups of concrete mixes were studied: - concretes without fibres, - concretes with polypropylene fibres, - concretes with steel fibres, and - concretes with a cocktail of polypropylene and steel fibres. Three water/cement ratios were used: 0.30, 0.45 and 0.61. The concrete specimens were subjected to various heating – cooling cycles from the room temperature to 150°C, 300°C, 450°C and 600 °C. The heating rate was fixed at 1 °C.min-1. The amounts of fibres in the concrete were 0.11%, 0.17% or 0.22% in volume for polypropylene fibres and 0.25%, 0.38% or 0.51% in volume for steel fibres. The amounts of fibres in concrete with a cocktail of polypropylene and steel fibres were 0.49, 0.60, 0.62 and 0.73%, in volume. The thermal stability, the initial and residual mechanical properties (compressive strength, tensile strength, modulus of elasticity), the porosity and the mass loss of the studied concrete mixes were investigated.This experimental study shows a way to design a concrete mix in order to improve both the thermal stability and the residual mechanical properties

Contribution des fibres de polypropylène et métalliques à l'amélioration du comportement du béton soumis à une température élevée

Le but de ce travail de recherche est d'étudier l'effet de fibres de polypropylène et de fibres métalliques sur le comportement du béton soumis à une température élevée. D'une part, les fibres de polypropylène ont été ajoutées au béton pour améliorer sa stabilité thermique, et d'autre part les fibres métalliques ont été ajoutées au béton pour améliorer ses propriétés mécaniques résiduelles. De nouvelles formulations de béton ont ensuite été définies, en utilisant un cocktail de fibres de polypropylène et métalliques, afin d'améliorer à la fois la stabilité thermique et les propriétés mécaniques résiduelles du béton. Quatre familles de bétons ont été étudiées : - bétons témoins sans fibres, - bétons contenant des fibres de polypropylène, - bétons contenant des fibres métalliques, et bétons contenant un cocktail de fibres de polypropylène et métalliques. Trois rapports eau/ciment sont utilisés : 0.30, 0.45 et 0.61. Les éprouvettes de béton, issues de ces compositions, ont été soumises à des cycles de chauffage refroidissement de la température ambiante à une température de consigne de 150C, 300C, 450C et 600 C. La vitesse de chauffage a été fixée à 1 C.min-1. Les teneurs en fibres étaient de 0.11, 0.17 ou 0.22 % en proportion volumique pour les fibres de polypropylène et de 0.25, 0.38 ou 0.51 % pour les fibres métalliques. Les proportions volumiques de cocktail de fibres étaient de 0.49, 0.60, 0.62 et 0.73%. La stabilité thermique, les propriétés mécaniques (résistance en compression, résistance en traction, module d'élasticité), la porosité initiale et résiduelle des bétons formulés ont été analysées. La perte de masse des éprouvettes lors des différents chauffages a été aussi mesurée.Cette étude expérimentale aboutit à la formulation de bétons dont à la fois la stabilité à haute température et le comportement mécanique après refroidissement sont améliorés.The aim of this study was to investigate the effect of polypropylene and steel fibres on the behaviour of concrete subjected to high temperature. Polypropylene fibres were added to the studied concrete mixes in order to improve the concrete thermal stability. Steel fibres were added to the studied concrete mixes in order to improve the concrete residual mechanical properties. News concretes mixes were then designed by adding a cocktail of polypropylene fibres and steel fibres in order to improve both the thermal stability and the residual mechanical properties of the studied concrete. Four groups of concrete mixes were studied: - concretes without fibres, - concretes with polypropylene fibres, - concretes with steel fibres, and - concretes with a cocktail of polypropylene and steel fibres. Three water/cement ratios were used: 0.30, 0.45 and 0.61. The concrete specimens were subjected to various heating cooling cycles from the room temperature to 150C, 300C, 450C and 600 C. The heating rate was fixed at 1 C.min-1. The amounts of fibres in the concrete were 0.11%, 0.17% or 0.22% in volume for polypropylene fibres and 0.25%, 0.38% or 0.51% in volume for steel fibres. The amounts of fibres in concrete with a cocktail of polypropylene and steel fibres were 0.49, 0.60, 0.62 and 0.73%, in volume. The thermal stability, the initial and residual mechanical properties (compressive strength, tensile strength, modulus of elasticity), the porosity and the mass loss of the studied concrete mixes were investigated.This experimental study shows a way to design a concrete mix in order to improve both the thermal stability and the residual mechanical properties.CERGY PONTOISE-Bib. electronique (951279901) / SudocSudocFranceF

Influence of polypropylene and steel fibres on thermal spalling and physical-mechanical properties of concrete under different heating rates

International audienceAbstractThis study investigates three concrete compositions: a control concrete, a reinforced concrete containing 60 kg/m3 of steel fibres, and a hybrid concrete containing 60 kg/m3 of steel fibres and 0.75 kg/m3 of polypropylene fibres. Cylindrical specimens were manufactured and subjected to two heating rates (10 °C/min and the ISO 834 fire standard) to study their spalling sensitivity. Moreover, unidirectional heat transfer and pressure measurements were performed on slabs heated at 10 °C/min to 600 °C. To understand the influence of fibres on spalling processes more clearly, the thermal properties were studied during heating and cooling: the gas permeability, compressive strength, and Young’s modulus of specimens were measured after a heating and cooling cycle at 0.5 °C/min. The results show that the spalling phenomenon was more severe for cylindrical specimens than for slabs. The addition of 60 kg/m3 of steel fibres had an unfavourable influence on spalling, especially during the ISO 834 fire test. The addition of 0.75 kg/m3 of polypropylene fibres allowed the concretes containing steel fibres to avoid spalling, regardless of the thermal loading conditions

Influence of steel and/or polypropylene fibres on the behaviour of concrete at high temperature: Spalling, transfer and mechanical properties

In this study different mixtures of high strength concretes (70 MPa) were prepared with different naturesof aggregates, moisture content, length and dosage of polypropylene fibres (PPF) and steel fibres (SF) andsubjected to the standard ISO 834 fire. Concretes with 60 kg/m3 of SF show spalling while plain concrete(without fibres) and concrete with 0.75 kg/m3 of PPF and 60 kg/m3 of SF did not spall. Microstructure,thermal, hydric and mechanical properties of concretes were investigated. PPF increase the porosityand permeability of concretes. Steel fibres control crack development which reduce the stress relaxationphenomenon and the size of new pores

Influence de fibres flexibles sur la rhéologie de bétons auto-plaçants

National audienc

Influence of elevated temperature on properties of radiation shielding concrete with electric arc furnace slag as coarse aggregate

The development of value-added materials from by-product of the steel-making process can promotesustainability in construction to move towards a circular economy. The use of Electric Arc Furnace(EAF) steel slag as heavyweight coarse aggregate to develop sustainable radiation shielding concretecould provide both technical and economic benefits with less environmental impact. This contributioninvestigates the behaviour at high temperature of a sustainable radiation shielding concrete. Thermalbehaviour of EAF slag concrete was compared to another heavyweight concrete made of barite aggregatesand to a normal-weight concrete. On one hand, the thermal stability of the three different aggregates wasdetermined via simultaneous Thermogravimetry and Differential Scanning Calorimetry analyses andvisual observations after 10 C/min heating. On the other hand, the evolution of thermal conductivityof concretes during heating, the residual mechanical properties and the assessment of potential spallingoccurrence were investigated. Stereo-microscope and Scanning Electron Microscope pictures provideadditional explanations by showing the paste-aggregate interface after heating at 450 C. The results indicatedthat EAF concrete displayed less strength reduction at increasing temperature. This improved behaviouris attributed to both the strong bond between the paste and the aggregates, and the better thermalbehaviour of the EAF slag aggregates compared to barite aggregates

High-temperature behavior of heavy-weight concretes

Heavy-weight concretes may be efficiently used to design shields for radioprotection in strategic structures, such as reactor vessels, nuclear research facilities, hospitals, etc. However, for many applications, they can undergo high-temperature exposition, or even accidental fire. In this work, the behavior of three types of concrete are analyzed, when exposed to increasing temperatures at two heating rates. The heavy-weight mixes are realized with barite (BAR) and Electric Arc Furnace (EAF) slag; additionally, a normal-weight concrete is tested too, made with natural aggregates (REF). Concretes were exposed at 150 \u2013 300 \u2013 450\ub0C at low rate of heating (1\ub0C/minute), to study their behavior under high temperature; then, they were subject to 600\ub0C with high rate of heating (10\ub0C/minute), to assess potential spalling occurrence. After such exposition, specimens were analyzed in terms of mass loss, density, residual compressive strength and dynamic modulus of elasticity. Results demonstrate that it is possible to design heavy-weight concrete shields with similar (or even better) performances at high temperature than normal concrete. Particularly, EAF concrete displayed less strength reduction at increasing temperatures, and at the same time, it is characterized by high gamma-ray attenuation coefficient

Experimental and numerical investigation of energy performance of building using biobased materials for sustainable construction

International audienc