Simulation numérique de l'écoulement du BAP dans des éléments de mur et de poutre en utilisant des modèles dynamiques d'écoulement

Abstract : Recently, there is a great interest to study the flow characteristics of suspensions in different environmental and industrial applications, such as snow avalanches, debris flows, hydrotransport systems, and material casting processes. Regarding rheological aspects, the majority of these suspensions, such as fresh concrete, behave mostly as non-Newtonian fluids. Concrete is the most widely used construction material in the world. Due to the limitations that exist in terms of workability and formwork filling abilities of normal concrete, a new class of concrete that is able to flow under its own weight, especially through narrow gaps in the congested areas of the formwork was developed. Accordingly, self-consolidating concrete (SCC) is a novel construction material that is gaining market acceptance in various applications. Higher fluidity characteristics of SCC enable it to be used in a number of special applications, such as densely reinforced sections. However, higher flowability of SCC makes it more sensitive to segregation of coarse particles during flow (i.e., dynamic segregation) and thereafter at rest (i.e., static segregation). Dynamic segregation can increase when SCC flows over a long distance or in the presence of obstacles. Therefore, there is always a need to establish a trade-off between the flowability, passing ability, and stability properties of SCC suspensions. This should be taken into consideration to design the casting process and the mixture proportioning of SCC. This is called “workability design” of SCC. An efficient and non-expensive workability design approach consists of the prediction and optimization of the workability of the concrete mixtures for the selected construction processes, such as transportation, pumping, casting, compaction, and finishing. Indeed, the mixture proportioning of SCC should ensure the construction quality demands, such as demanded levels of flowability, passing ability, filling ability, and stability (dynamic and static). This is necessary to develop some theoretical tools to assess under what conditions the construction quality demands are satisfied. Accordingly, this thesis is dedicated to carry out analytical and numerical simulations to predict flow performance of SCC under different casting processes, such as pumping and tremie applications, or casting using buckets. The L-Box and T-Box set-ups can evaluate flow performance properties of SCC (e.g., flowability, passing ability, filling ability, shear-induced and gravitational dynamic segregation) in casting process of wall and beam elements. The specific objective of the study consists of relating numerical results of flow simulation of SCC in L-Box and T-Box test set-ups, reported in this thesis, to the flow performance properties of SCC during casting. Accordingly, the SCC is modeled as a heterogeneous material. Furthermore, an analytical model is proposed to predict flow performance of SCC in L-Box set-up using the Dam Break Theory. On the other hand, results of the numerical simulation of SCC casting in a reinforced beam are verified by experimental free surface profiles. The results of numerical simulations of SCC casting (modeled as a single homogeneous fluid), are used to determine the critical zones corresponding to the higher risks of segregation and blocking. The effects of rheological parameters, density, particle contents, distribution of reinforcing bars, and particle-bar interactions on flow performance of SCC are evaluated using CFD simulations of SCC flow in L-Box and T-box test set-ups (modeled as a heterogeneous material). Two new approaches are proposed to classify the SCC mixtures based on filling ability and performability properties, as a contribution of flowability, passing ability, and dynamic stability of SCC.Résumé : Récemment, il y a un grand intérêt à étudier les caractéristiques d'écoulement des suspensions dans différentes applications environnementales et industrielles, telles que les avalanches des neiges, les coulées de débris, les systèmes de transport et les processus d’écoulement des matériaux. En ce qui concerne les aspects rhéologiques, la plupart des suspensions, comme le béton frais, se comportent comme un fluide non-Newtonien. Le béton est le matériau de construction le plus largement utilisé dans le monde. En raison de limites qui caractérisent le béton normal en termes de maniabilité et de capacité de remplissage de coffrage, il était nécessaire de développer une nouvelle classe de béton qui peut couler sous son propre poids, en particulier à travers les zones congestionnées du coffrage. Par conséquent, le béton autoplaçant (BAP) est un nouveau matériau de construction qui est de plus en plus utilisé dans les différentes applications. Étant donné sa fluidité élevée de BAP peut être utilisé dans certaines applications particulières, notamment dans la section densément renforcée. Cependant, la fluidité élevée rend le béton plus sensible à la ségrégation des gros granulats pendant l'écoulement (la ségrégation dynamique) et ensuite au repos (ségrégation statique). La ségrégation dynamique peut augmenter lorsque le BAP est coulé sur une longue distance ou en présence d'obstacles. Par conséquent, il est toujours nécessaire d'établir un compromis entre la fluidité, la capacité de passage, et la stabilité du BAP. Ceci doit être pris en considération afin de concevoir le processus de coulée et dosage des mélanges du BAP. Ceci est appelé la conception d'ouvrabilité du BAP. Une conception de maniabilité efficace et non coûteuse peut être achevée à travers la e prévision et l'optimisation de l'ouvrabilité des mélanges de béton pour les procédés de construction sélectionnés, notamment le transport, le pompage, la mise en place, le compactage, la finition, etc. En effet, les formulations de mélange doivent se confirmer à la qualité de la construction demandée, par exemple les niveaux exigés de fluidité, la capacité de passage, la capacité de remplissage, et la stabilité (statique et dynamique). Celui est nécessaire pour développer des outils théoriques afin d’évaluer dans quelles conditions les exigences de qualité de la construction sont satisfaites. Cette thèse est consacrée à la réaliser des simulations analytiques et numériques pour prédire la performance d'écoulement du BAP dans différents procédés de la mise en place du béton. L'objectif spécifique de cette étude consiste à simuler l'écoulement du BAP dans essais empiriques, notamment la boite en L et la boite en T pour évaluer la performance du BAP pendent la mise en place (la fluidité, la capacité de passage, la capacité de remplissage, et la ségrégation dynamique induite par cisaillement ou par gravité). Par conséquent, le BAP est modélisé comme matériau hétérogène. En outre, un modèle analytique est proposé pour prédire la performance à l'écoulement du BAP dans la boite en L en utilisant la théorie de Dam Break. D'autre part, les résultats des simulations numériques de l’écoulement du BAP dans une poutre renforcée sont comparés aux résultats expérimentaux par des profils de surface libres. Les résultats des simulations numériques de BAP coulée (modélisée comme un fluide homogène unique), sont utilisés pour déterminer les zones critiques correspondant à des risques plus élevés de ségrégation et de blocage. Les effets des paramètres rhéologiques, la masse volumique, le contenu des particules, la distribution de barres d'armature, et les interactions particule-barres sur les performances d'écoulement du BAP sont évaluées à l'aide de simulations MFN d’écoulement du BAP par les essais des L-Box et T-box (modélisée comme une matériau hétérogène). Deux nouvelles approches sont proposées pour classifier les mélanges du BAP sur la base de la capacité de remplissage, et les propriétés de performabilité, en fonction de la fluidité, la capacité de passage et de la stabilité dynamique du BAP

Homogenous Flow Performance of Steel Fiber-Reinforced Self-Consolidating Concrete for Repair Applications: Developing a New Empirical Set-Up

In this study, a new empirical Square-Box test was employed to evaluate the homogeneous flow performance of fiber-reinforced self-consolidating concrete (FR-SCC) under confined-flow conditions that are typical of repair applications. The Square-Box set-up consisted of a closed-circuit box, providing 2.4-m flow distance and a closed-surface cross section of 100-mm width and 200-mm height, equipped with 0 and 4 rows of reinforcing bar grids with 45-mm clear spacing. The flow performance was assessed in terms of dynamic stability and passing ability. The investigated mixtures were considered as diphasic suspensions of fiber-coarse aggregate (F-A \u3e 5 mm) in suspending mortars containing particles finer than 5 mm. According to the experimental results, the dynamic segregation and blocking indices of the investigated mixtures were found in good agreements with characteristics of F-A combination and rheology of mortar. The investigated mixtures exhibited significantly higher blocking indices through the Square-Box set-up compared to those obtained using the L-Box test. Furthermore, the characteristics of F-A and rheology of mortar showed opposite effects on dynamic segregation assessed using Square-Box and conventional T-Box set-ups. Under confined flow conditions, higher dynamic segregation led to more dissimilar compressive strength values at different flow distances through the proposed Square-Box set-up. A new filling ability classification was established based on the experimental dynamic stability and passing ability results of the proposed empirical test

Homogeneous Flow Performance of Steel-Fiber Reinforced Self-Consolidating Concrete for Repair Application: A Biphasic Approach

In this study, fiber-reinforced self-consolidating concrete (FR-SCC) was considered as a diphasic suspension of fiber and coarse aggregate (F-A ≥ 5 mm) skeleton in mortar suspension with solid particles finer than 5 mm. The coupled effect of the volumetric content of fibers, coarse aggregate particle-size distribution, and rheological properties of the mortar on the passing ability and dynamic stability of various FR-SCC mixtures was investigated. Nine high-strength and 10 conventional-strength FR-SCC mixtures for repair application were proportioned with water-to-binder ratios (W/B) of 0.35 and 0.42, respectively, and macro steel fibers of 0.1%–0.5% volumetric contents. The dosages of high-range water-reducer (HRWR) admixture were optimized to achieve a targeted slump flow of 680 ± 20 mm. The yield stress and plastic viscosity of the mortar mixtures varied between 4.6-17.7 Pa and 2.8–8.2 Pa s, respectively. Flow performance of the investigated mixtures were evaluated in terms of flowability (slump-flow test), passing ability (J-Ring and L-Box set-ups), and dynamic stability (T-Box test). According to the established correlations, the main influencing parameters on homogeneous performance of FR-SCC include W/B, paste volume, volumetric content-to-packing density of F-A (φ/φmax), HRWR dosage, fiber content, mortar rheology, and volume of excess mortar. The robustness analyses results revealed that homogeneous flow performance of FR-SCC is more sensitive due to variations of the φ/φmax and paste volume rather than mortar rheology, W/B, and HRWR dosage. The characteristics of the mixture constituents for FR-SCC mixtures with different strength levels were finally recommended to ensure acceptable homogeneous performance under restricted flow conditions of repair application

Novel Tri-Viscous Model to Simulate Pumping of Flowable Concrete through Characterization of Lubrication Layer and Plug Zones

In this study, computational fluid dynamics (CFD) was employed to simulate the pipe flow of 18 self-consolidating and four highly workable concrete mixtures in a 30-m long pumping circuit. Pressure loss (ΔP) in 100- and 125-mm diameter (DP) pipelines was measured under low (1.2–6.2 l/s) and high (8.1–16.4 l/s) flow rates (Q). The numerical simulation was successfully carried out using a two-fluid model and a new variable-viscosity single-fluid approach, namely double-Bingham and tri-viscous models, respectively. The radial variation of rheological properties of the concrete across the pipe section, representing the plug flow, sheared concrete, and lubrication layer (LL) zones was successfully simulated based on a total of 404 pipe flow experiments. The relative LL viscous constant (ηLL) values obtained using numerical simulations-to-those obtained experimentally using a tribometer ranged between 30% and 200%. Moreover, the coupled effect of the characteristics of different flow zones, DP, and Q on ΔP was evaluated

Coupled Effect of Fiber and Granular Skeleton Characteristics on Packing Density of Fiber-Aggregate Mixtures

The addition of fiber to cementitious materials enhances mechanical performance but can reduce workability of the fiber-reinforced concrete (FRC) mixtures. This can be due to the negative effect of fibers on packing density (PD) of the fiber-coarse aggregate (F-A) combination. The performance of FRC, as a diphasic suspension, is dependent on the characteristics of both F-A (suspended-solid skeleton) and mortar (suspending liquid) phases. PD can reflect the voids within the F-A skeleton to be filled with mortar. An adequate optimization of the characteristics of the F-A skeleton can modify the performance of FRC in fresh and hardened states. The F-A skeleton can be characterized in terms of particle-size distribution, volumetric content, and morphology of the coarse aggregate, as well as size, rigidity, and content of fibers. In this study, a comprehensive investigation was undertaken to identify the coupled effect of the characteristics of fibers and coarse aggregate on the PD of F-A combination used without any cement paste/mortar. The solid components play a key role in the overall performance of the concrete produced. This study was carried out to optimize the F-A combination and enhance the workability design of FRC. Various types of steel, polypropylene, and polyolefin fibers having different sizes and rigidities were investigated. Moreover, four combinations of three different classes of coarse aggregate were used to proportion F-A mixtures. Test results showed that shorter length, smaller diameter, and more flexible fibers can lead to higher PD of F-A systems. Moreover, the coarser aggregate skeleton with larger interparticle voids led to more available length for fibers to be deformed, hence improving the PD of F-A mixtures. New empirical models were proposed to predict the packing density of F-A combinations given the characteristics of coarse aggregate and fibers, as well as the level of compaction. The established models were employed to propose a new proportioning approach for fiber-reinforced self-consolidating concrete mixtures to achieve the targeted workability

Discrete-Element Modeling of Shear-Induced Particle Migration during Concrete Pipe Flow: Effect of Size Distribution and Concentration of Aggregate on Formation of Lubrication Layer

The Paper Seeks to Better Understand the Particulate Mechanics Giving Rise to the Lubrication Layer (LL) in Flows with Wide Particle-Size Distributions (PSD) Typical of Concrete Pumping Applications. the Study Uses a Soft-Sphere Discrete Element Method (DEM) to Simulate the Shear-Induced Particle Migration (SIPM) Mechanism of Formation of the LL. to Provide Realistic Understanding of SIPM and Rheological Heterogeneity of Concrete, Three Wide PSDs (Fine, Medium, and Coarse) and Three Different Concentrations (10 %–40 %) of Five Spherical-Particle Subclasses (1–17 Mm Diameter) Were Investigated. the Radial Evolution of Concentration and Particle Distribution Was Simulated over Time and the LL Formation Was Successfully Simulated. the Predicted LL Thicknesses Compared Well with Experimental Values. the Coupled Effect of PSD, Concentration, and Mean Diameter of Particles on Wall Effect, SIPM, and Rheological Heterogeneities Across the Pipe Was Evaluated. Higher Rheological Heterogeneity Across the Pipe Was Obtained for Higher Concentration and Coarser Particle Size Distributions

Four-Way CFD-DEM Coupling To Simulate Concrete Pipe Flow: Mechanism Of Formation Of Lubrication Layer

This study introduced a four-way CFD-DEM coupling approach to simulate the shear-induced particle migration (SIPM) mechanism leading to formation of the lubrication layer (LL) during concrete pumping. The CFD-DEM simulations considered the coupled effect of concentration (10 %–40 %) and wide size distribution (1–17 mm) of aggregate and rheology of the mortar for forces between the suspending matrix and the particles (and vice versa), as well as force transmission directly between particles (and the pipe wall). The formation of the LL was successfully simulated through a more realistic understanding the SIPM mechanism and rheological evaluation across the pipe with comparable calculation times compared to the one-way coupled DEM approach, especially for high concentrations. The simulated LL thicknesses of 0.8–2.7 mm compared well with experimental values. The flow rate and rheological heterogeneity of pumped concrete, and rheology of the LL, were found mostly controlled by the granular-skeleton characteristics rather than the suspending-matrix rheology

Modeling of Flow Performance of Self-Consolidating Concrete using Dam Break Theory and Computational Fluid Dynamics

The main objective of this study is to evaluate the applicability of Dam Break Theory to analytically simulate the flow profile of self-consolidating concrete (SCC) in a modified L-Box set-up. SCC mixtures with relatively low to high stability levels are cast in the vertical compartment of a modified L-Box apparatus at heights of 50 and 110 cm in order to evaluate the effect of gravitational force on flow conditions into the horizontal section of the L-Box following the opening of the sliding gate. The effect of static segregation on flow profiles was also evaluated for three different rest times of 1, 5, and 15 min. A computational fluid dynamics software was used to numerically simulate the free surface flow of the SCC that have linear and non-linear flow properties that can be described using the Bingham and Herschel-Bulkley rheological models, respectively. The results of the analytical models, based on the Dam Break Theory, and the numerical models showed accurate prediction of flow profiles that were observed in the SCC in modified L-Box apparatus. Considering the inertial and frictional forces, as well as the presence of bars in the L-Box set-up, the numerical simulations are shown to provide greater accuracy of predicting flow profiles than the analytical models. The Herschel-Bulkley rheological model led to better analytical prediction of the flow profile than the Bingham model

Numerical Simulation of Self-Consolidating Concrete Flow as a Heterogeneous Material in L-Box Set-Up: Effect of Rheological Parameters on Flow Performance

A computational fluid dynamics (CFD) software was used to simulate the effect of rheological parameters on the heterogeneous performance properties of self-consolidating concrete (SCC) in the horizontal and vertical directions of the L-Box set-up. These properties consist of flowability, blocking resistance, and dynamic segregation. Different suspending fluids having five plastic viscosity values (10–50 Pa.s), three yield stress values (14–75 Pa), two fluid densities (2000 and 2500 kg/m3), and two shear elasticity modulus values (100 and 1000 Pa) were considered. The suspensions consisted of a number of 135 in total spherical particles with 20-mm in diameter and 2500 kg/m3 density. The results of 25 simulations in total are found to correlate well with the rheological parameters of the suspending fluid. Plastic viscosity of the suspending fluid was shown to be the most dominant parameter affecting flow performance of SCC in the L-Box test. A new approach was also proposed to classify SCC mixtures based on the filling ability properties

Numerical Simulation of Self-Consolidating Concrete Flow as a Heterogeneous Material in L-Box Set-Up: Coupled Effect of Reinforcing Bars and Aggregate Content on Flow Characteristics

A computational fluid dynamics software was employed to simulate the coupled effect of reinforcing bar spacing and coarse aggregate content on the blocking resistance and shear-induced segregation of self-consolidating concrete (SCC) along the horizontal channel of the L-Box apparatus. The rheology of the modelled suspending fluid, which corresponds to the stable and homogeneous portion of the mixture, consists of plastic viscosity value of 25 Pa s, yield stress values of 75 Pa, fluid density of 2500 kg/m3, and shear elasticity modulus value of 100 Pa. Two different values of 20-mm spherical particles (135 and 255 particles in total), as well as three bar arrangements consisting of 0, 3, and 18 bars distributed along the horizontal channel of the L-Box were considered in the numerical simulations. A new approach is proposed to evaluate the coupled effect of reinforcing bar arrangements and the number of spherical particles on the flow performance of SCC