Caractérisation du comportement mécanique des bétons de sol

International audience RÉSUMÉ. Les travaux de recherche présentés concernent plusieurs formulations constituées de sable, d'argile, de ciment et d'eau. Différents taux de substitution de sable par l'argile et deux dosages en ciment sont testés. L'objectif est d'améliorer la connaissance des mécanismes de déformation et de rupture des bétons de sol et d'analyser l'influence des paramètres de formulation sur leurs propriétés mécaniques. Des essais de compression simple sont menés afin de déterminer le module d'Young (Estat), le coefficient de poisson (ν) et la résistance à la rupture (fc) de ces matériaux. La dégradation des propriétés élastiques en fonction de la contrainte axiale est également évaluée, en réalisant des essais de compression cycliques. Par ailleurs des mesures par ultra-son du module d'Young dynamique (Edyn) ont été réalisées. Les résultats montrent un plus fort impact de la teneur en argile du sol sur les propriétés élastiques que sur les résistances à la rupture. La prédiction du module par les méthodes non destructives est fortement liée à la valeur de ν, qui varie selon la teneur en argile du sol. Enfin, les valeurs expérimentales sont comparées aux valeurs calculées à partir des formules de l'EC2 et de l'ACI. </p

State-of-the-art of construction stones for masonry exposed to high temperatures

The consequences of fires on cultural heritage building and monuments can be deleterious, as historic and recent cases demonstrate. In particular, devastating fires have ravaged stone masonry monuments, which must be properly repaired and retrofitted with rational, performance-based design. Updated quantitative knowledge and design tools – especially about materials’ properties – is necessary to implement such performance-based stra-tegies. Under this perspective, the paper takes into account a number of references to present a state-of-the-art about the current knowledge of high-temperature behaviour of different families of construction stones – namely granites, marbles, sandstones and limestones. The stones’ strain behaviour, thermal properties (conductivity and specific heat) and mechanical properties (compressive strength, elastic modulus, peak compressive strain, Poisson’s ratio and tensile strength) are accounted for. The residual mechanical properties, i. e. after high temperature exposure, are under particular consideration in view of evaluating the residual structural reliability of stone masonry structures after a fire with numerical methods. The micro- and macroscopic level are put into relationship, linking the information about the chemical and physical transformation of component minerals under high temperatures to the changes in the stones’ properties and thermal strain. The aim is to provide quantitative information, namely mean values and intervals of confidence, for the considered properties to be appliable in the performance-based fire design and evaluation of stone masonry structure

A new Compton scattered tomography modality and its application to material non-destructive evaluation

International audienceImaging modalities exploiting the use of Compton scattering are currently under active investigation. However, despite many innovative contributions, this topic still poses a formidable mathematical and technical challenge. Due to the very particular nature of the Compton effect, the main problem consists of obtaining the reconstruction of the object electron density. Investigations on Compton scatter imaging for biological tissues, organs and the like have been performed and studied widely over the years. However in material sciences, in particular in non-destructive evaluation and control, this type of imaging procedure is just at its beginning. In this paper, we present a new scanning process which collects scattered radiation to reconstruct the internal electronic distribution of industrial materials. As an illustration, we shall look at one of the most widely used construction material: concrete and its variants in civil engineering. The Compton scattered radiation approach is particularly efficient in imaging steel frame and voids imbedded in bulk concrete objects.We present numerical simulation results to demonstrate the viability and performances of this imaging modality

Influence of lightweight aggregates on the physical and mechanical residual properties of concrete subjected to high temperatures

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Influence of chemical and mineralogical composition of concrete aggregates on their behaviour at elevated temperature

International audienc

High temperature effects on the properties of limestones: post-fire diagnostics and material's durability

The research aims at investigating the temperature dependency of important properties of construction limestones, in the temperature range that could be reached during fires (200-800 degrees C). Limestones, through their different species and geographical origins, show a great variability in basic properties. The presented data will be useful to the post-fire recovery design of stonework buildings, by supporting the judgement on the perspects of durability based on the post-fire state of stones. The research features six varieties of construction limestones from different zones of France. The tests-colorimetry, ultrasonic P-wave velocity, total porosity, mercury intrusion porosimetry (MIP), scanning electron microscope (SEM) observations, capillary water absorption-are performed after high temperature exposure in a controlled furnace oven. The samples and heating conditions are designed to attain a uniform maximum temperature inside the samples. Nondestructive investigation techniques have a great potential usefulness in the perspect of post-fire investigations; on the other hand, the changes in the porous network, porosity and capillarity-investigated in laboratory-are direct indicators of post-fire materials' decay. The individuated temperature-property relationships of the single stone species, as well as correlations between P-wave velocity to porosity and compressive strength, are generally reliable. Finally, the detrimental effect of post-cooling rehydration has been observed through the kinetics of deterioration for all the investigated varieties of limestone. The results demonstrate the need of integrating non-destructive techniques to laboratory tests for cost-effective diagnostics on fire-damaged stonework buildings

Efficiency and durability of protective treatments on cultural heritage copper corrosion layers

International audienceTo protect copper artefacts of the cultural heritage from atmospheric degradation protective treatment must be applied. Two types of protective treatments: microcrystalline wax (Cosmolloïd wax) and decanoate solution (HC10) were tested. Two aspects were considered: the penetration of the treatments in the corrosion layers, and its durability. Equivalent efficiencies for both treatments were demonstrated. The penetration of the treatments seems to depend essentially on its application mode. Re-corrosion experiments of treated samples under immersion in D2O demonstrate that the efficiency and the durability with time or after water leaching depend on the penetration of the treatments in the corrosion layers

Influence of the Nature of Cement on the Physical and Mechanical Properties of Soil Concretes from Sandy Clay and Laterite

Soil concrete is a material produced by mixing the soil at the site with a hydraulic binder. This paper aims to study the influence of the nature of binder on the physical and mechanical properties of soil concrete. For the mixtures, three types of soil were chosen and studied: sandy clay with a granular class of 0/5 (SA5), laterite with a granular class of 0/5 (LA5), and laterite with a granular class of 0/10 (LA10). Three different cements were used: CEM I 52.5, CEM II 42.5, and CEM III 32.5, with cement contents of 150 and 250 kg/m3. The soil concretes were designed for a constant spread of 32–33 cm measured on a mini-slump. The results showed that LA5-based soil concrete has a higher water content of about 8.8% more than SA5 and LA10-based soil concretes. For all the mixtures, the lowest porosity values were obtained with CEM III 32.5, followed by CEM I 52.5, and finally CEM II 42.5. For the three types of cement and the same soil granular size, the compressive strength, static, and dynamic modulus of SA5-based soil concretes are higher than LA5. It was noted that the mechanical properties of soil concretes made with CEM III 32.5 are higher than those made with CEM I 52.5 and CEM II 42.5. Regardless of the type of cement used, the mechanical properties obtained on LA10-based soil concrete are higher than those on LA5-based soil concrete

Protection of bronze statuary, comparison of classical treatments and approaches with carboxylates

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High temperature behavior of self-compacting concretes

In order to obtain the desired fluidity and stability characteristics in the fresh state, SCC composition is significantly different to that of conventional concretes (Chapter 1). This composition is characterized first of all by higher chemical admixture proportions (high range water reducing admixtures and viscosity enhancing admixtures). But SCCs also contain higher paste volumes than conventional concrete (CC). For economic reasons, the large paste volume is commonly achieved by adding supplementary cementitious materials (SCM) to the cement, particularly fillers. Furthermore, the granular skeleton in SCCs is markedly different to that of conventional concretes. The maximum grain diameter is often reduced relative to that of conventional concretes and the CA/S (coarse aggregate/sand) ratio is usually close to 1 while in conventional concretes it is generally greater than 1.5. These particular composition details are likely to significantly modify the mechanical behavior of SCCs, particularly their high temperature behavior. This chapter presents state of the art understanding of high temperature SCC behavior. First, the physico-chemical changes which occur inside SCCs when a high temperature exposure is examined, from the perspective of knowledge acquired on high temperature behavior of conventional vibrated concretes. Next, the evoluation of physical properties, such as porosity and permeability, and mechanical properties (compressive and tensile strength, and elastic modulus) when a rise in temperature is studied and compared with data on conventional concretes. Finally, the stability of SCCs at high temperatures and the effectiveness of polypropylene fibers with regard to explosive spalling are presented