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Le, Hai Dang - One of the best experts on this subject based on the ideXlab platform.
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Study of the effect of the slip layer on the velocity profiles of pumped Concrete
2014Co-Authors: Le, Hai DangAbstract:La rhéologie du béton est un facteur d'influence direct sur la relation entre la pression de pompage et le débit. La rhéologie appliquée au béton est souvent caractérisée par une loi rhéologique à l'état stationnaire (indépendant du temps). Il s'agit d'un domaine assez pointu concernant principalement l'évolution de la contrainte de cisaillement en fonction du taux de cisaillement. Cette évolution du béton traditionnel est souvent caractérisée par le modèle de Bingham alors que pour un béton auto plaçant dont le rapport E/L est faible, l'évolution peut devenir non linéaire et peut suivre le modèle de Bingham modifié ou Herschel-Bulkley pour un fluide rhéo-épaississant. Pour ces modèles, on parle souvent d'un seuil de cisaillement au-delà duquel le béton commence à s'écouler, d'un indice de consistance (et un indice de puissance pour le cas d'une relation non linéaire) qui décrit l'intensité de l'évolution. En conséquence, la relation entre la pression et le débit peut être linéaire ou non linéaire en fonction du type du béton pompé. Comme les paramètres rhéologiques d'un béton participent directement à la prédiction de la pression de pompage, la mesure de ces paramètres fait l'objet un travail très exigeant au niveau de la précision.Comme les paramètres rhéologiques d'un béton ne sont pas des grandeurs physiques directement mesurables, les rhéomètres développés pour le béton frais ne sont capables de délivrer ces paramètres qu'à travers des mesures des autres grandeurs physiques de base comme la vitesse, le couple, la pression. Ensuite, plusieurs méthodes peuvent être appliquées pour reconvertir les grandeurs mesurées. Ces méthodes sont appelées la résolution du problème inverse. La méthode la plus efficace pour résoudre (ou confirmer la résolution du) le problème inverse concerne la calibration du rhéomètre avec des matériaux dont les propriétés rhéologiques sont connues. Plus le nombre de matériau utilisé pour la calibration est grand, plus la précision est meilleure. Cependant, pour les matériaux cimentaire, le nombre de matériau nécessaire pour bien couvrir les plages de valeurs des paramètres rhéologique est de l'ordre de quelques centaines de matériau. Cela demande un travail expérimental énorme et non rentable. Cependant, à la place de réaliser cette calibration expérimentalement, il est tout à fait possible de la réaliser en faisant des simulations numériques. Ces travaux numériques font partie du deuxième chapitre de la thèse.En complément de la rhéologie, la tribologie du béton est aussi un facteur déterminant du pompage. La tribologie permet de caractériser le comportement du béton à l'interface avec la paroi de la tuyauterie. Pour le cas de béton traditionnel dont le seuil de cisaillement est très important, l'écoulement du béton est dominé par l'effet de glissement du bloc de béton sur une couche limite de comportement lubrifiant. La couche limite est uniquement créée quand il y a une contrainte de cisaillement entre le béton et la paroi. Ce phénomène est présumé être la conséquence de la combinaison des trois phénomènes: l'effet géométrique de la paroi, la rupture structurelle interne et la ségrégation dynamique. Tous ces effets entrainent une diminution de la viscosité du matériau pompé sur une distance de quelques millimètres à la paroi. En conséquence, un écoulement non homogène est formé. Une vitesse de glissement à la paroi s'additionne à la vitesse engendrée par le cisaillement.Afin de caractériser le comportement du béton à la paroi, la tribométrie du béton voit le jour. Cela s'effectue avec les tribomètres qui simulent le mouvement relatif entre le béton et la paroi. Grace au mouvement, pour les bétons traditionnels dont le seuil de cisaillement est élevé, uniquement la couche limite est cisaillée mais pas le béton. Les paramètres délivrés sont un seuil d'interface, une constante visqueuse. Ces deux grandeurs permettent d'établir une relation linéaire entre la contrainte de cisaillement à l'interfThe rheological properties of Concrete are significantly influencing the relation between pumping pressure and discharge rate. The Concrete Rheology is often characterized by a rheological law in stationary conditions (time independent), giving the evolution of shear stresses as a function of shear rate. In case of traditional Concrete, this evolution is typically described by a Bingham model, while for a self-compacting Concrete with low water/powder ratio, the evolution often becomes non-linear and can be described by a modified Bingham or Herschel-Bulkley model, considering shear-thickening. In these models, a critical shear stress is typically considered above which the Concrete starts to flow. Furthermore, a consistency parameter is considered (and in case of non-linear behavior also an index) to describe the intensity of the evolution. As a consequence, the relation between pressure and discharge rate can be linear or non-linear, depending on the Concrete pumped. As the rheological parameters of the Concrete are directly relevant for the prediction of the pumping pressure, the accurate measurement of these parameters is a challenging task.As the rheological properties of Concrete cannot be directly measured as a physical quantity, Concrete rheometers can only be used to determine the rheological parameters in an indirect way, by measuring other physical values like speed, couple or pressure. Different methods can be applied in order to convert the measured physical values to obtain the rheological properties. The most direct method consist of calibrating the rheometers by testing materials with known rheological parameters. A higher precision in this approach can be obtained by testing a higher number of known materials. However, in order to cover the whole range of rheological properties of Concrete, a very high number of known materials would have to be tested, which would thus become very cumbersome. Instead of performing this calibration in an experimental way, it can be done in a numerical way. This kind of numerical calibration is the topic of chapter 2 of the doctoral thesis.Besides the Rheology of the Concrete, tribology is also an important factor determining the pumping characteristics. Tribology enables to characterize the behavior of Concrete in the interface with the surface of the pumping pipe. For traditional Concrete with high yield stress, the flow of Concrete in the pumping pipe is dominated by the slip layer or lubrication layer near the surface, while the bulk of the Concrete is flowing as a plug. This slip layer can only be formed due to shear stresses in this area, and is considered to be the consequence of three phenomenons: geometrical wall effect, structural breakdown, and dynamic segregation. These phenomenons induce a reduction of the viscosity of the Concrete within a layer of a few millimeter near the surface of the pumping pipe. As a result, a non-homogeneous flow is induced. Due to the occurrence of the slip layer, an additional speed component is added to the speed profile already induced by shear of the Concrete.In order to characterize the Concrete behavior near the surface, tribometers are being used, simulating the relative movement between Concrete and the surface. In case of traditional Concrete, with high yield stress, due to the relative movement only the slip layer is sheared, while the bulk Concrete is not sheared. In this case, the use of tribometers results in a yield stress and a viscous constant of the slip layer. These two parameters enable to define a linear relation between shear stress and shear rate in the interface. Meanwhile, in case of self-compacting Concrete, the Concrete is also sheared, leading to very complicated tribology measurements. For this reason, it is very difficult to characterize the behavior of self-compacting Concrete near the interface by means of a tribometer. This situations complicates the prediction of the relation between pumping pressur
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Etude de l'effet de la couche limite sur les profils de vitesses du béton pompé
HAL CCSD, 2014Co-Authors: Le, Hai DangAbstract:The rheological properties of Concrete are significantly influencing the relation between pumping pressure and discharge rate. The Concrete Rheology is often characterized by a rheological law in stationary conditions (time independent), giving the evolution of shear stresses as a function of shear rate. In case of traditional Concrete, this evolution is typically described by a Bingham model, while for a self-compacting Concrete with low water/powder ratio, the evolution often becomes non-linear and can be described by a modified Bingham or Herschel-Bulkley model, considering shear-thickening. In these models, a critical shear stress is typically considered above which the Concrete starts to flow. Furthermore, a consistency parameter is considered (and in case of non-linear behavior also an index) to describe the intensity of the evolution. As a consequence, the relation between pressure and discharge rate can be linear or non-linear, depending on the Concrete pumped. As the rheological parameters of the Concrete are directly relevant for the prediction of the pumping pressure, the accurate measurement of these parameters is a challenging task.As the rheological properties of Concrete cannot be directly measured as a physical quantity, Concrete rheometers can only be used to determine the rheological parameters in an indirect way, by measuring other physical values like speed, couple or pressure. Different methods can be applied in order to convert the measured physical values to obtain the rheological properties. The most direct method consist of calibrating the rheometers by testing materials with known rheological parameters. A higher precision in this approach can be obtained by testing a higher number of known materials. However, in order to cover the whole range of rheological properties of Concrete, a very high number of known materials would have to be tested, which would thus become very cumbersome. Instead of performing this calibration in an experimental way, it can be done in a numerical way. This kind of numerical calibration is the topic of chapter 2 of the doctoral thesis.Besides the Rheology of the Concrete, tribology is also an important factor determining the pumping characteristics. Tribology enables to characterize the behavior of Concrete in the interface with the surface of the pumping pipe. For traditional Concrete with high yield stress, the flow of Concrete in the pumping pipe is dominated by the slip layer or lubrication layer near the surface, while the bulk of the Concrete is flowing as a plug. This slip layer can only be formed due to shear stresses in this area, and is considered to be the consequence of three phenomenons: geometrical wall effect, structural breakdown, and dynamic segregation. These phenomenons induce a reduction of the viscosity of the Concrete within a layer of a few millimeter near the surface of the pumping pipe. As a result, a non-homogeneous flow is induced. Due to the occurrence of the slip layer, an additional speed component is added to the speed profile already induced by shear of the Concrete.In order to characterize the Concrete behavior near the surface, tribometers are being used, simulating the relative movement between Concrete and the surface. In case of traditional Concrete, with high yield stress, due to the relative movement only the slip layer is sheared, while the bulk Concrete is not sheared. In this case, the use of tribometers results in a yield stress and a viscous constant of the slip layer. These two parameters enable to define a linear relation between shear stress and shear rate in the interface. Meanwhile, in case of self-compacting Concrete, the Concrete is also sheared, leading to very complicated tribology measurements. For this reason, it is very difficult to characterize the behavior of self-compacting Concrete near the interface by means of a tribometer. This situations complicates the prediction of the relation between pumping pressureLa rhéologie du béton est un facteur d'influence direct sur la relation entre la pression de pompage et le débit. La rhéologie appliquée au béton est souvent caractérisée par une loi rhéologique à l'état stationnaire (indépendant du temps). Il s'agit d'un domaine assez pointu concernant principalement l'évolution de la contrainte de cisaillement en fonction du taux de cisaillement. Cette évolution du béton traditionnel est souvent caractérisée par le modèle de Bingham alors que pour un béton auto plaçant dont le rapport E/L est faible, l'évolution peut devenir non linéaire et peut suivre le modèle de Bingham modifié ou Herschel-Bulkley pour un fluide rhéo-épaississant. Pour ces modèles, on parle souvent d'un seuil de cisaillement au-delà duquel le béton commence à s'écouler, d'un indice de consistance (et un indice de puissance pour le cas d'une relation non linéaire) qui décrit l'intensité de l'évolution. En conséquence, la relation entre la pression et le débit peut être linéaire ou non linéaire en fonction du type du béton pompé. Comme les paramètres rhéologiques d'un béton participent directement à la prédiction de la pression de pompage, la mesure de ces paramètres fait l'objet un travail très exigeant au niveau de la précision.Comme les paramètres rhéologiques d'un béton ne sont pas des grandeurs physiques directement mesurables, les rhéomètres développés pour le béton frais ne sont capables de délivrer ces paramètres qu'à travers des mesures des autres grandeurs physiques de base comme la vitesse, le couple, la pression. Ensuite, plusieurs méthodes peuvent être appliquées pour reconvertir les grandeurs mesurées. Ces méthodes sont appelées la résolution du problème inverse. La méthode la plus efficace pour résoudre (ou confirmer la résolution du) le problème inverse concerne la calibration du rhéomètre avec des matériaux dont les propriétés rhéologiques sont connues. Plus le nombre de matériau utilisé pour la calibration est grand, plus la précision est meilleure. Cependant, pour les matériaux cimentaire, le nombre de matériau nécessaire pour bien couvrir les plages de valeurs des paramètres rhéologique est de l'ordre de quelques centaines de matériau. Cela demande un travail expérimental énorme et non rentable. Cependant, à la place de réaliser cette calibration expérimentalement, il est tout à fait possible de la réaliser en faisant des simulations numériques. Ces travaux numériques font partie du deuxième chapitre de la thèse.En complément de la rhéologie, la tribologie du béton est aussi un facteur déterminant du pompage. La tribologie permet de caractériser le comportement du béton à l'interface avec la paroi de la tuyauterie. Pour le cas de béton traditionnel dont le seuil de cisaillement est très important, l'écoulement du béton est dominé par l'effet de glissement du bloc de béton sur une couche limite de comportement lubrifiant. La couche limite est uniquement créée quand il y a une contrainte de cisaillement entre le béton et la paroi. Ce phénomène est présumé être la conséquence de la combinaison des trois phénomènes: l'effet géométrique de la paroi, la rupture structurelle interne et la ségrégation dynamique. Tous ces effets entrainent une diminution de la viscosité du matériau pompé sur une distance de quelques millimètres à la paroi. En conséquence, un écoulement non homogène est formé. Une vitesse de glissement à la paroi s'additionne à la vitesse engendrée par le cisaillement.Afin de caractériser le comportement du béton à la paroi, la tribométrie du béton voit le jour. Cela s'effectue avec les tribomètres qui simulent le mouvement relatif entre le béton et la paroi. Grace au mouvement, pour les bétons traditionnels dont le seuil de cisaillement est élevé, uniquement la couche limite est cisaillée mais pas le béton. Les paramètres délivrés sont un seuil d'interface, une constante visqueuse. Ces deux grandeurs permettent d'établir une relation linéaire entre la contrainte de cisaillement à l'inter
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Etude de l’effet de la couche limite sur les profils de vitesse du béton pompé
Université de Cergy-Pontoise. UFR de Sciences et Techniques. Génie civil ; Université de Gand. Faculté de Sciences d'ingénierie et d'Architecture, 2014Co-Authors: Le, Hai DangAbstract:The rheological properties of Concrete are significantly influencing the relation between pumping pressure and discharge rate. The Concrete Rheology is often characterized by a rheological law in stationary conditions (time independent), giving the evolution of shear stresses as a function of shear rate. In case of traditional Concrete, this evolution is typically described by a Bingham model, while for a self-compacting Concrete with low water/powder ratio, the evolution often becomes non-linear and can be described by a modified Bingham or Herschel-Bulkley model, considering shear-thickening. In these models, a critical shear stress is typically considered above which the Concrete starts to flow. Furthermore, a consistency parameter is considered (and in case of non-linear behavior also an index) to describe the intensity of the evolution. As a consequence, the relation between pressure and discharge rate can be linear or non-linear, depending on the Concrete pumped. As the rheological parameters of the Concrete are directly relevant for the prediction of the pumping pressure, the accurate measurement of these parameters is a challenging task. As the rheological properties of Concrete cannot be directly measured as a physical quantity, Concrete rheometers can only be used to determine the rheological parameters in an indirect way, by measuring other physical values like speed, couple or pressure. Different methods can be applied in order to convert the measured physical values to obtain the rheological properties. The most direct method consist of calibrating the rheometers by testing materials with known rheological parameters. A higher precision in this approach can be obtained by testing a higher number of known materials. However, in order to cover the whole range of rheological properties of Concrete, a very high number of known materials would have to be tested, which would thus become very cumbersome. Instead of performing this calibration in an experimental way, it can be done in a numerical way. This kind of numerical calibration is the topic of chapter 2 of the doctoral thesis. Besides the Rheology of the Concrete, tribology is also an important factor determining the pumping characteristics. Tribology enables to characterize the behavior of Concrete in the interface with the surface of the pumping pipe. For traditional Concrete with high yield stress, the flow of Concrete in the pumping pipe is dominated by the slip layer or lubrication layer near the surface, while the bulk of the Concrete is flowing as a plug. This slip layer can only be formed due to shear stresses in this area, and is considered to be the consequence of three phenomenons: geometrical wall effect, structural breakdown, and dynamic segregation. These phenomenons induce a reduction of the viscosity of the Concrete within a layer of a few millimeter near the surface of the pumping pipe. As a result, a non-homogeneous flow is induced. Due to the occurrence of the slip layer, an additional speed component is added to the speed profile already induced by shear of the Concrete. In order to characterize the Concrete behavior near the surface, tribometers are being used, simulating the relative movement between Concrete and the surface. In case of traditional Concrete, with high yield stress, due to the relative movement only the slip layer is sheared, while the bulk Concrete is not sheared. In this case, the use of tribometers results in a yield stress and a viscous constant of the slip layer. These two parameters enable to define a linear relation between shear stress and shear rate in the interface. Meanwhile, in case of self-compacting Concrete, the Concrete is also sheared, leading to very complicated tribology measurements. For this reason, it is very difficult to characterize the behavior of self-compacting Concrete near the interface by means of a tribometer. This situations complicates the prediction of the relation between pumping pressure and discharge rate. In order to characterize and quantify the effect of the slip layer, an experimental method enabling the measurement of the velocity profile in the flowing Concrete in an open pipe has been developed. By measuring the velocity profile, it is possible to determine the thickness of the slip layer and the velocities in the slip layer. An experimental research program studying the effect of the mix design on the slip layer thickness has been carried out. An experimental method to sample the material of the slip layer has been developed in order to determine its rheological properties. This study, performed on self-compacting Concrete, enables to relate the Rheology of the slip layer to the Rheology of the bulk Concrete. Finally, the experimental results are implemented in a numerical simulation method. The results of the numerical simulation enable to validate the experimental methods and the obtained experimental results. Based on the available rheological models like the Bingham model, modified Bingham model or Herschel-Bulkley model, it is possible to predict the relation between the pressure gradients and the discharge rate, considering the Poiseuille formula for a laminar flow in a circular pipe. Knowing the thickness of the slip layer and the relation between rheological properties of slip layer and bulk Concrete, it is possible to predict the relation between pumping pressures and discharge rates. A numerical application has been performed in order to compare the numerical results with the experimental results obtained within a series of previously performed pumping tests available in literature
Robert J. Flatt - One of the best experts on this subject based on the ideXlab platform.
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Concrete Rheology: A basis for understanding chemical admixtures
Science and Technology of Concrete Admixtures, 2016Co-Authors: A. Yahia, Sara Mantellato, Robert J. FlattAbstract:Abstract Concrete Rheology is affected by many factors. The effect of admixtures takes place at the paste level, and propagates through length scales to be felt at the macroscopic level of Concrete. Thus studies on paste can provide correct relative properties at the Concrete level for different admixed Concrete, but cannot directly provide the absolute rheological properties of Concrete. Concrete behaves as a material with a yield stress fluid, and the yield stress plays an essential role in many applications. Its viscosity and possible shear thickening must also be taken into account in a significant number of cases, particularly in formulations with low water–cement (w/c). Concrete can exhibit a thixotropic behaviour and, depending on the rate of structural build-up, this must be taken into account and possibly also exploited. Over recent years much progress has been made in understanding Concrete Rheology from a practical and a fundamental point of view.
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Towards a prediction of superplasticized Concrete Rheology
Materials and Structures, 2004Co-Authors: Robert J. FlattAbstract:The Rheology of Concrete is influenced by water content, the amount, size and size distribution of all the solid components as well as by the dispersion of the finer particles through the addition of superplasticizers. In addition, the rheological behariour over time ovolves as a result of cement hydration. Consequently the a-priori prediction of Concrete Rheology is a complex task. In this article, models that have been and are being developed to achieve this task are discussed. The key role of the degree of dispersion will be underlined. A treatment of interparticle forces and a yield stress model integrating these will be presented. Such work is necessary to integrate the dispersion efficiency of superplasticizers based on their dosage and molelar, structures into existing models for predicting Concrete Rheology. La rhéologie du béton est influencée par la teneur en eau, la quantité, la taille et la distribution de taille de tous les matériaux granulaires ainsi que du degré de dispersion qui peut être obtenu par l'ajout de superplastifiant. De plus, le comportement rhéologique de ce matériau évolue dans le temps à cause de l'hydration du ciment. Il en résulte que la prédiction de la rhéologie du béton est particulièrement complexe. Dans cet article, des modèles existant et en cours de développment dont le but est précisément d'atteindre cet objectif sont discutés L'importance du degré de dispersion sera soulignée. Un traitement des forces interparticulaires et de leur lien au seuil d'écoulement est présenté. Le but d'un tel travail est de pouvoir en fin de compte inclure l'effet du dosage et de la structure moléculaire de superplastifiants dans les modèles existants pour la prédiction de la rhéologie du béton.
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The Rheology of Cementitious Materials
MRS Bulletin, 2004Co-Authors: Robert J. Flatt, Nicos Martys, Lennart BergströmAbstract:The introduction of a new generation of dispersants in Concrete allow this material to exhibit self-compacting properties in its fresh state and high durability and mechanical strength in its hardened state. These properties translate into many practical advantages for the construction field.Two of the most important are reducing the ecological impact of this sector of industry and reducing the labor-intensive work associated with placing ordinary Concrete by vibration. In this article, it will be shown that knowledge of colloidal science has proven essential in the development of this new generation of dispersants for Concrete. Indeed, the polymer molecules used in these dispersants are specifically designed to induce steric repulsion between cement particles, reducing their agglomeration and allowing high workability of fresh Concrete prior to setting. While the linkage between interparticle forces and the rheological behavior of cement pastes is still only semiquantitative, recent advances in the modeling of Concrete Rheology show very promising results in terms of handling aggregates with a wide distribution of particle sizes and shapes. However, accurate modeling requires reliable input on the interaction of the dispersant with the hydrating cement at the molecular level, which is identified as a future research challenge.
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Towards a prediction of superplasticized Concrete Rheology
Materials and Structures, 2004Co-Authors: Robert J. FlattAbstract:The Rheology of Concrete is influenced by water content, the amount, size and size distribution of all the solid components as well as by the dispersion of the finer particles through the addition of superplasticizers. In addition, the rheological behariour over time ovolves as a result of cement hydration. Consequently the a-priori prediction of Concrete Rheology is a complex task. In this article, models that have been and are being developed to achieve this task are discussed. The key role of the degree of dispersion will be underlined. A treatment of interparticle forces and a yield stress model integrating these will be presented. Such work is necessary to integrate the dispersion efficiency of superplasticizers based on their dosage and molelar, structures into existing models for predicting Concrete Rheology.
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The Rheology of Cementitiousterials
2004Co-Authors: Robert J. Flatt, Nicos Martys, Lennart BergströmAbstract:The introduction of a new generation of dispersants in Concrete allow this material to exhibit self-compacting properties in its fresh state and high durability and mechanical strength in its hardened state. These properties translate into many practical advantages for the construction field. Two of the most important are reducing the ecological impact of this sector of industry and reducing the labor-intensive work associated with placing ordinary Concrete by vibration. In this article, it will be shown that knowledge of colloidal science has proven essential in the development of this new generation of dispersants for Concrete. Indeed, the polymer molecules used in these dispersants are specifically designed to induce steric repulsion between cement particles, reducing their agglomeration and allowing high workability of fresh Concrete prior to setting. While the linkage between interparticle forces and the rheological behavior of cement pastes is still only semiquantitative, recent advances in the modeling of Concrete Rheology show very promising results in terms of handling aggregates with a wide distribution of particle sizes and shapes. However, accurate modeling requires reliable input on the interaction of the dispersant with the hydrating cement at the molecular level, which is identified as a future research challenge.
Romildo Dias Toledo Filho - One of the best experts on this subject based on the ideXlab platform.
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Rheological and mechanical behavior of High Strength Steel Fiber-River Gravel Self Compacting Concrete
Construction and Building Materials, 2017Co-Authors: Marco Antônio Da Silva, Marco Pepe, Rodolfo Giacomim Mendes De Andrade, Michèle S. Pfeil, Romildo Dias Toledo FilhoAbstract:Abstract This study reports the results of a comprehensive experimental campaign aimed at demonstrating the feasibility of using river gravels in substitution of ordinary crushed aggregates for the production of high strength Steel Fiber-River Gravel-Self Compacting Concrete (SFRGSCC). Due to geomorphological reasons, the river gravels represent the most common type of aggregates used in Amazon region for ordinary structural Concrete production but only few researches focused on the use of this kind of raw material for the production of high performance cement-based composites. In fact, the river gravels present different intrinsic characteristic in comparison with crushed rocks such as, higher density and elastic modulus, rounded shape with a smoother surface and a more brittle behavior. As a consequence, when embedded in a cement-based matrix they can significantly affect the Rheology and mechanical performance of both self-compacting Concrete matrices (RGSCC) and Fiber Reinforced Concrete (SFRGSCC). In this context, the present study firstly analyzes the physical and mechanical properties of the alternative aggregates and then, investigates how the complete replacement of crushed aggregate by river gravel can influence the flowability, segregation potential, yield stress and plastic viscosity of the RGSCC and SFRGSCC in the fresh state as well as the stress-strain behavior under compression, direct tension and bending in the hardened state. The results highlight as the river gravel aggregates shape and surface roughness have relevant effects on the Concrete performance as they improve the Concrete Rheology increasing the Concrete flowing and reducing the corresponding yield stress and entrapped air while, on the other hand, reduce the strain capacity of the matrix resulting in a more fragile mechanical response under compression, tension and bending. The addition of steel fiber to the RGSCC resulted being more beneficial than to the reference crushed aggregate SCC. The reinforcement significantly enhanced the RGSCC toughness being this improvement even more pronounced when the samples were submitted to direct tension and bending loads.
Rami Khatib - One of the best experts on this subject based on the ideXlab platform.
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How do Concrete Rheology, tribology, flow rate and pipe radius influence pumping pressure?
Cement and Concrete Composites, 2016Co-Authors: Dimitri Feys, Kamal H. Khayat, Rami KhatibAbstract:Abstract Finding the critical factors that influence the pressure during pumping of Concrete has been investigated for years. From fluid mechanics, the relationship between pressure and flow rate, radius or viscosity is known. In the practical guidelines for pumping of conventional vibrated Concrete (CVC) the viscosity term is replaced by the Concrete yield stress. However, recently, the influence of viscosity on pumping pressure has been reevaluated for self-consolidating Concrete (SCC). In this paper, the influence of Concrete Rheology, tribology, flow rate and pipe radius on pumping pressure are discussed, based on full-scale pumping tests. The Concrete mixtures varied from pumpable CVC to segregating SCC. The influence of flow rate and viscosity on pumping of Concrete has been confirmed. It is also shown that with a 20% decrease in pipe radius (from 125 to 100 mm), the pumping pressure can be roughly doubled. An increase in yield stress also increases the pumping pressure, but its influence is only visible when the viscosity is approximately constant. The total flow resistance in the tribometer also appears to correlate well with the pumping pressure, proving that the developed tribometer mimics quite well the flow of Concrete in a pipe.
Kamal H. Khayat - One of the best experts on this subject based on the ideXlab platform.
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Variations in surface quality of self-consolidation and highly workable Concretes with formwork material
Construction and Building Materials, 2020Co-Authors: Wael A. Megid, Kamal H. KhayatAbstract:Abstract The effect of the forming materials on surface quality of the self-consolidating and highly workable Concretes was experimentally evaluated. Several mixtures having wide ranges of workability and Rheology were investigated. The mixtures were placed in a Z-shaped mold. No mechanical consolidation was applied at all. The sides of the mold were built up using plywood, PVC, steel, and permeable formwork liner using a polyester filter. The Concrete surface quality was evaluated in terms of the voids, bleeding, segregation, and insufficient self-consolidation, using an image processing technique. The surface diameter and area of the voids found on the formed Concrete surfaces were statistically correlated to the Concrete Rheology. The permeable lined formwork was shown to produce Concrete surfaces with better quality compared to impermeable formwork materials. The same outcome was also noticed for the Concrete mixtures having insufficient self-consolidation and even the unstable mixtures that manifested signs of bleeding. The permeable lined formwork was shown to provide an effective way for the entrapped air/water bubbles and the bleed water to escape. The maximum surface dimension of the voids found on the Concrete surfaces was limited to 3, 6, 7, and 10 mm for the mixtures cast using the permeable liner, steel, PVC, and plywood formwork materials, respectively.
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How do Concrete Rheology, tribology, flow rate and pipe radius influence pumping pressure?
Cement and Concrete Composites, 2016Co-Authors: Dimitri Feys, Kamal H. Khayat, Rami KhatibAbstract:Abstract Finding the critical factors that influence the pressure during pumping of Concrete has been investigated for years. From fluid mechanics, the relationship between pressure and flow rate, radius or viscosity is known. In the practical guidelines for pumping of conventional vibrated Concrete (CVC) the viscosity term is replaced by the Concrete yield stress. However, recently, the influence of viscosity on pumping pressure has been reevaluated for self-consolidating Concrete (SCC). In this paper, the influence of Concrete Rheology, tribology, flow rate and pipe radius on pumping pressure are discussed, based on full-scale pumping tests. The Concrete mixtures varied from pumpable CVC to segregating SCC. The influence of flow rate and viscosity on pumping of Concrete has been confirmed. It is also shown that with a 20% decrease in pipe radius (from 125 to 100 mm), the pumping pressure can be roughly doubled. An increase in yield stress also increases the pumping pressure, but its influence is only visible when the viscosity is approximately constant. The total flow resistance in the tribometer also appears to correlate well with the pumping pressure, proving that the developed tribometer mimics quite well the flow of Concrete in a pipe.