Etude du retrait et des propriétés de transport d'Eco-BAPs à base d'additions minérales.

International audience Un des freins de l'utilisation plus massive des BAP est leur coût plus élevé, leur retrait souvent plus grand et le manque de recul concernant leur durabilité. Cette étude contribue à la formulation et la caractérisation de BAP plus écologiques basés sur l'utilisation d'additions minérales en substitution du ciment portland. 3 types d'additions sont traités :du métakaolin (MK),du laitier de haut fourneau et des cendres volantes. 4 BAP ont été formulés à partir d'une même composition où seule la nature du liant change : CEM I, CEM I+15% MK, CEM III et CEM V. L'effet de la nature du liant sur : l'évolution de la résistance à la compression, le retrait plastique, le retrait empêché, le retrait libre est quantifié. Deux indicateurs de durabilité ;le coefficient de migration des ions chlorures et la perméabilité au gaz sont évalués. Les résultats montrent l'effet indéniable des différentes additions étudiées sur l'amélioration de ces derniers. La substitution partielle du CEM I par 15% de MK permet le développement de très bonnes performances globales alors que celle du CEM III présente à la fois des effets positifs et des effets négatifs. Des premières analyses de la microstructure permettent d'apporter des explications. </div

Nano-scale modeling and elastic properties of a typical CSH (I) structure based on DFT and Molecular Dynamics Methods

International audience Les silicates de calcium hydratés (C-S-H) sont les constituants principaux de la pâte de ciment et ont donc une grande influence sur les propriétés mécaniques des matériaux cimentaires. Le modèle de tobermorite-11Å (formule chimique: Ca4Si6O14(OH)4•2H2O) est d'abord considéré comme configuration initiale pour décrire ces hydrates. Ce modèle est alors étudié par DFT (Density Functional Theory) et Dynamique Moléculaire. Les constantes élastiques sont calculées et comparées à des valeurs expérimentales. Un Silicate de Calcium Hydraté amorphe est obtenu par le biais d'une modélisation par Dynamique Moléculaire d'un processus de recuit de la tobermorite-11Å avec utilisation d'un potentiel de Born-Huggins-Meyer (BMH). Des tests uniaxiaux de traction et de compression d'un silicate de calcium hydraté amorphe (avec un rapport Ca/Si de 0,67), à une certaine vitesse de déformation, sont modélisés. Les courbes contrainte-déformation sont analysées. Les résultats montrent que: (1) les coefficients élastiques Cij sont obtenus dans la plage de pression de confinement 0-1GPa pour vérifier la fiabilité du modèle par comparaison avec des résultats de la littérature. (2) Un modèle de super-cellule à l'échelle nano montre des propriétés mécaniques isotropes (3) Après recuit pour obtenir un C-S-H (I) amorphe, le module de Young est en moyenne d'environ 21,4 GPa. </div

The influence of aggregate shape, volume fraction and segregationon the performance of Self-Compacting Concrete :3D modeling and simulation

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The Effect of Thermal Contact Conductance (TCC) Between Aggregate Inclusion and Matrix on Thermal Conductivity of Cement-Based Material

The effect of Thermal Contact Conductance (TCC) on thermal conductivity of mortar has been studied at the interface between the limestone and cement paste. A novel methodology, which involves the use of Scanning Electron Microscope (SEM) to scan the image of the interface in mortar, the software PlotDigitizer to create a set of points of the interface, and the FE software Abaqus/CAE to perform heat transfer simulation, is proposed in this study. Moreover, several hypotheses at the interface such as the gaps, flaws, and Interfacial Transition Zone (ITZ) are also highlighted. Temperature drop, thermal conductivity, and the TCC coefficient has been calculated for each model in order to understand the effect of TCC on cement-based materials thermal properties. The results show that the temperature drops at the interface are very low and the TCC coefficients are very high so that it can be ignored in heat transfer simulation except for a large air gap at the interface. Thus, it can be concluded that the TCC has no influence on the thermal conductivity of mortar

The Effect of Thermal Contact Conductance (TCC) Between Aggregate Inclusion and Matrix on Thermal Conductivity of Cement-Based Material

The effect of Thermal Contact Conductance (TCC) on thermal conductivity of mortar has been studied at the interface between the limestone and cement paste. A novel methodology, which involves the use of Scanning Electron Microscope (SEM) to scan the image of the interface in mortar, the software PlotDigitizer to create a set of points of the interface, and the FE software Abaqus/CAE to perform heat transfer simulation, is proposed in this study. Moreover, several hypotheses at the interface such as the gaps, flaws, and Interfacial Transition Zone (ITZ) are also highlighted. Temperature drop, thermal conductivity, and the TCC coefficient has been calculated for each model in order to understand the effect of TCC on cement-based materials thermal properties. The results show that the temperature drops at the interface are very low and the TCC coefficients are very high so that it can be ignored in heat transfer simulation except for a large air gap at the interface. Thus, it can be concluded that the TCC has no influence on the thermal conductivity of mortar

Tests d’indentation instrumentée sur granulats de Mâchefers d’Incinération de Déchets Non Dangereux. Influence de la taille de l’indenteur sur le module élastique

Des tests d’indentation instrumentée ont été effectués sur des particules isolées de Mâchefers d’Incinération de Déchets Non Dangereux (MIDND) provenant des carrières de la Garenne à Vignoc (Bretagne, France). Deux indenteurs sphériques en carbure de tungstène de rayon respectifs 0,5 et 140 mm ont été utilisés pour les séries de tests «A» et «B». Les particules étudiées ont des diamètres variant entre 20 et 25 mm. Avec un indenteur de rayon 0,5 mm, des modules élastiques réduits moyens variant de 15 à 68 GPa ont été trouvés. Un module élastique réduit moyen de 15 GPa a été trouvé avec l’indenteur de rayon 140 mm

Reactivity tests for supplementary cementitious materials: RILEM TC 267-TRM phase 1

A primary aim of RILEM TC 267-TRM: “Tests for Reactivity of Supplementary Cementitious Materials (SCMs)” is to compare and evaluate the performance of conventional and novel SCM reactivity test methods across a wide range of SCMs. To this purpose, a round robin campaign was organized to investigate 10 different tests for reactivity and 11 SCMs covering the main classes of materials in use, such as granulated blast furnace slag, fly ash, natural pozzolan and calcined clays. The methods were evaluated based on the correlation to the 28 days relative compressive strength of standard mortar bars containing 30% of SCM as cement replacement and the interlaboratory reproducibility of the test results. It was found that only a few test methods showed acceptable correlation to the 28 days relative strength over the whole range of SCMs. The methods that showed the best reproducibility and gave good correlations used the R3 model system of the SCM and Ca(OH)2, supplemented with alkali sulfate/carbonate. The use of this simplified model system isolates the reaction of the SCM and the reactivity can be easily quantified from the heat release or bound water content. Later age (90 days) strength results also correlated well with the results of the IS 1727 (Indian standard) reactivity test, an accelerated strength test using an SCM/Ca(OH)2-based model system. The current standardized tests did not show acceptable correlations across all SCMs, although they performed better when latently hydraulic materials (blast furnace slag) were excluded. However, the Frattini test, Chapelle and modified Chapelle test showed poor interlaboratory reproducibility, demonstrating experimental difficulties. The TC 267-TRM will pursue the development of test protocols based on the R3 model systems. Acceleration and improvement of the reproducibility of the IS 1727 test will be attempted as well

Numerical study of ITZ contribution on mechanical behavior and diffusivity of mortars

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Predicting the evolution of mechanical and diffusivity properties of cement pastes and mortars for various hydration degrees - A numerical simulation investigation

International audiencePredicting the time-dependent performance of cement-based materials during hydration has been a challenge to many researchers from all over the world. In this context, numerical approaches present many advantages and can be considered as the only real alternative to obtain the properties starting from the microstructure. This paper presents a multi-scale strategy based on the development of the MuMoCC platform (Multi-scale Modelling of Computational Concrete). A combination of the NIST cement hydration model (CEMHYD3D) and the FE software Abaqus is proposed and applied to study the diffusion and mechanical behaviours of cement-based materials during hydration. The evolution of the effective diffusion coefficient, the elastic modulus and the compressive strength of mortar according to the capillary porosity and the degree of hydration is put into evidence. For mechanical computations, both elastic and inelastic behaviours are considered. Firstly, the methodology was applied to a water-to-cement ratio (w/c) 0.4 cement paste and mortar. Then and based on numerical simulations, a set of simplified formula relating the main engineering parameters of transport and mechanical behaviour to capillary porosity is proposed and addressed to researchers involved in modelling at meso-scale and who need input data coming from the cement paste scale. (C) 2012 Elsevier B.V. All rights reserved