Physico-chemical study of cementitious materials based on binary and ternary binders

This research aims to study the physico-chemical phenomena occurring during hydration process of binary and ternary cementitious matrices, combining Portland cement (PC), blast furnace slag(BFS) and limestone filler (LF). For this purpose, measurements of the reaction rate and mechanical performances were performed on 12 mineral binders prepared with the same water-to-cementitious materials ratio (w/cm = 0.32) and various dosages of PC, BFS and LF. Three parameters are quantified using thermo-gravimetric analysis: the advancement of hydration characterized by the degree of hydration, the evolution of the chemically bound water as well as the quantity of Portlandite produced. Results show clearly that the knowledge of these parameters allows predicting correctly the evolution of compressive strength and young modulus at early age. The synergistic effects of ternary binders, formulated with moderate additions of BFS and LF, manifested in the form of an increased amount of hydration products compared to predictions based on the individual effects of BFS and the LF in the binary systems

Analyse multi-échelles du retrait endogène des matrices cimentaires

L'objectif de ce papier est de modéliser le retrait endogène d'une pâte de ciment dès le premier contact eau-ciment jusqu'à 2 jours d'hydratation en se basant sur un modèle d'homogénéisation multi-échelle. Le retrait endogène est composé de deux déformations issues de deux mécanismes différents. Une première déformation d'origine chimique issue d'un bilan volumique global négatif des réactions chimiques d'hydratation, qui apparaît dès le premier contact eau-ciment. A partir de la prise, le matériau se rigidifie progressivement et la déformation d'origine chimique est freinée par le squelette solide du matériau pour donner naissance à un phénomène de dépression capillaire à l'origine de la deuxième phase de déformation (retrait d'autodessiccation). Les entrées du modèle mis au point sont essentiellement la composition chimique du ciment ainsi que sa finesse, le rapport eau-ciment (E/C), la température et les propriétés mécaniques des principales phases. Les sorties sont l'évolution des phases dans le temps, la réaction chimique d'hydratation, le module d'Young, la dépression capillaire, le retrait chimique et endogène

Extrudable Reactive Powder Concretes Hydration, shrinkage and transfer properties

International audienceThe behavior of five reactive powder concretes (RPC), with four of them being extrudable, has been studied since the first minutes up to more than 90 days. The extrusion force, hydration rate, free autogenous shrinkage at early age, mechanical properties and durability parameters were measured. The performance analysis showed the benefits of a partial substitution of silica fume with crushed quartz on the RPC properties. The cost/performances analysis highlighted that the main advantage of using RPC lies in their potential of durability, which is 10 to 100 times higher than that of ordinary or high-performance concretes, according to the property considered

LUCENA GÓMEZ, ANTONIO Y FAMILIA [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

Propriétés physiques de bétons de chanvre

International audienceLe béton de chanvre est un biomatériau composite léger obtenu en mélangeant un liant à base de chaux hydraulique et aérienne, des particules végétales et de l'eau. Ce matériau n'est pas porteur ce qui conduit à l'utiliser principalement en matériau de remplissage associé à une ossature bois, trois procédés de mise en œuvre étant possible. Dans cette étude, différentes formulations utilisées pour le montage de paroi sont étudiées. La mise en œuvre est faite par trois procédés. Une relation de type loi-puissance est mise en évidence entre la résistance à la compression et la densité apparente. Des mesures de la conductivité thermique en fonction de la masse volumique et de la teneur en eau permettent de définir la capacité d'isolation des matériaux. La caractérisation hydrique qui repose sur les capacités de stockage et de transfert d'humidité des matériaux est réalisée par la détermination des isothermes de sorption-désorption et de la perméabilité à la vapeur

Étude expérimentale du retrait endogène, du fluage propre et de la fissuration des matrices cimentaires aux jeune et très jeune ages

NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocSudocFranceF

Influence of superplasticizer on activation energy and autogenous shrinkage of a cement paste

Special Publication of the American Concrete Institute, SP-217, Eds ACIThree superplasticizers (SP) have been studied in this research: the first is based on modified polycarboxylic ether and is used to improve the workability of concrete and to obtain high mechanical characteristics at early age; the second, which contains naphthalene sulphonate, is used to reduce drastically mixing water in concrete and improve mechanical strength at early age; the third SP investigated is melamine-based and is used to improve the workability of concrete creating electrostatic repulsion between cement grains. The intention of the present investigation was to provide more information about the role of these SP in concrete at early age. The apparent activation, initial and final set times by Vicat needle, chemical and autogenous shrinkage were measured for cement pastes having a water/cement ratio of 0.25. The apparent activation energy has been determined by the "setting times method" at different temperatures: 10, 20, 30 and 40 °C. The volumetric autogenous shrinkage was measured at the same temperatures immediately after setting. The experimental results show that the apparent energy activation is slightly modified by the presence of SP. Also, the evolution of chemical shrinkage shows clearly that the SP acts on the hydration kinetic of cement. The effect of a particular SP on autogenous shrinkage at different temperatures can be correctly predicted by means of the maturity concept

Application of the maturity concept for the prediction of restrained autogenous shrinkage of cement pastes

This research work concerns the study of the autogenous restrained deformations of cement pastes at an early stage in controlled-temperature conditions. Portland cement and slag cement pastes prepared with a water-to-cement ratio W/C equal to 0.3, are investigated at 15, 20, 30 and 40°C. The measurement method for restrained shrinkage is the ring test. The experimental device is equipped with a peripheral water circulation system to keep the specimen in quasi-isothermal conditions. The results show that the curing temperature significantly influences the age of the first through crack and the ring strain at cracking. The capacity of the traditional maturity concept to quantify the thermal effect on the age of cracking has then been assessed by calculating apparent activation energies from Vicat setting times and from cracking ages measured with the ring test

A study of the apparent thermal conductivity of cement paste at very early age of hydration: An attempt of modelisations

International audienceThe measurement results of the apparent thermal conductivity of cement paste at very early stages ofhydration are described and an attempt of modelisations of these results is presented.The experimental method is based on the “hot wire” method. The results show an evolution of the apparentthermal conductivity of the cement paste at very early age. Two types of modelling are proposed to explain thisevolution: First, the apparent thermal conductivity is calculated assuming the fresh cement paste as a multiphasematerial. This model enables to take account of the material chemical evolution. The second modelling approach is based on the theory of heat and mass transfer in non-saturated porousmedia. It enables to take account of two main phenomena observed during the hydration of cement-basedmaterials. The first one is the creation of an internal porosity, partially saturated; the second one is thetemperature elevation of the material, due to the exothermic character of hydration reactions.The results of this second modelling seem to fit better to our experimental results

Effets thermique et mécanique de l'incorporation de déchets de mousse de polyuréthane dans un mortier

International audienceThis article presents the results of an experimental study on the use of polyurethane foam waste for the manufacture of insulating mortars. Five mortars containing various foam proportions (0%, 51%, 54%, 61% and 69% of the mortar volume) were prepared and the determination of thermal and mechanical properties, shrinkage and mass loss per desiccation made it possible to measure the influence of the foam incorporation. The thermal conductivity of the mortars with polyurethane foam is a half to a third as high as that of the reference mortar (without foam) while compressive strength decreases in a ratio from 2 to 6 according to the foam proportion. In addition, the presence of polyurethane foam in the mortars results in an important increase in shrinkage and in mass loss per desiccation.Cet article présente les résultats d'une étude expérimentale sur l'utilisation de déchets de mousse de polyuréthanne pour la fabrication de mortiers isolants. Cinq mortiers contenant différents dosages de mousse (0%, 51%, 54%, 61% et 69% du volume de mortier) ont été préparés et la détermination de leurs propriétés thermiques et mécaniques, de leur retrait et de leur perte de masse par dessiccation a permis de mesurer l'influence de l'incorporation des déchets de mousse. La conductivité thermique des mortiers avec mousse de polyuréthanne est 2 à 3 fois inférieure à celle du mortier référence (sans mousse) tandis que la résistance en compression diminue dans un rapport de 2 à 6 selon le dosage en mousse utilisé. Par ailleurs, la présence de mousse de polyuréthanne dans les mortiers se traduit par une augmentation importante du retrait et de la perte de masse par dessiccation. Ces résultats s'expliquent par la forte porosité et la faible résistance mécanique du polyuréthanne alvéolaire