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

Properties and hydration behavior of blended clinker and portland-sediment cement pastes

In recent years, an increase of the interest in the use of secondary raw materials (sediment, sludge…) in construction has been observed.  This paper aims to contribute to the use of dredging sediments in the cement industry. Despite the literature on this subject, the available data on the aspects and phenomena related to the hydration process of such mixtures are incomplete. This paper aims to specify the calorimetric curves of hydration of mixtures made, from the sediment trapped at the site of Lyvet in the Brittany region of France. The mixtures are made ??using in one hand clinker and in the other hand Portland cement. Pastes with 8%, 16% and 33% of clinker or Portland cement substituted by sediment are used to determine the hydraulic properties of mixtures. The physico-chemical characterization of materials is made by different techniques to determine the chemical composition and physical properties. X-ray diffraction is used to determine the mineralogical compositions of samples before and after treatment. A  Tian-Calvet microcalorimeter is used to explore hydration behavior of the blended Sediment-Portland cement pastes. The addition of untreated sediment to both clinker or Portland cement increase the dormant period duration. On the contrary, this period becomes shorter when the sediment is thermally treated. The results show that 8% of treated sediment improve hydration of blended Sediment-Portland cement pastes. Mechanical properties of blended sediment-cements are also investigated. After 28 days of curing in water, the mortar containing 8% of treated sediment exhibits a compressive strength equal to 93.7% of the one of the reference mortar, maintaining it in the same cement class (52.5)

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

National perioperative outcomes of flap coverage for pressure ulcers from 2005 to 2015 using American College of Surgeons National Surgical Quality Improvement Program

Background Complication rates after flap coverage for pressure ulcers have been high historically. These patients have multiple risk factors associated with poor wound healing and complications including marginal nutritional status, prolonged immobilization, and a high comorbidities index. This study utilizes the National Surgical Quality Improvement Program (NSQIP) to examine perioperative outcomes of flap coverage for pressure ulcers. Methods Data from the NSQIP database (2005–2015) for patient undergoing flap coverage for pressure ulcers was identified. Demographic, perioperative information, and complications were reviewed. One-way analysis of variance and Pearson chi-square were used to assess differences for continuous variables and nominal variables, respectively. Multivariate logistic regression was performed to identify independent risk factors for complications. Results There were 755 cases identified: 365 (48.3%) sacral ulcers, 321 (42.5%) ischial ulcers, and 69 (9.1%) trochanteric ulcers. Most patients were older male, with some degree of dependency, neurosensory impairment, high functional comorbidities score, and American Society of Anesthesiologists class 3 or above. The sacral ulcer group had the highest incidence of septic shock and bleeding, while the trochanteric ulcer group had the highest incidence of superficial surgical site infection. There was an overall complication rate of 25% at 30-day follow-up. There was no statistical difference in overall complication among groups. Total operating time, diabetes, and non-elective case were independent risk factors for overall complications. Conclusions Despite patients with poor baseline functional status, flap coverage for pressure ulcer patients is safe with acceptable postoperative complications. This type of treatment should be considered for properly selected patients