Fresh Concrete Flow Research Articles

Comparative Study on the Mechanical Properties of Steel Fiber Reinforced Self-Compacting Concrete

Self-compacting concrete (SCC) is a flowable concrete which can consolidate under its own weight without the need of external vibration. The highly fluid nature of SCC makes it suitable for placing in difficult environments like congested reinforcement and thinner sections. Use of SCC can also help in decreasing noise pollution at worksites which is caused by vibration of concrete. SCC is used in bridges, buildings, and tunnel construction. The addition of small closely spaced and uniformly dispersed fibres to concrete would act as a crack resistor and would substantially improve its properties. This type of concrete is known as fibre reinforced concrete. In fact, the fibre reinforcement mechanisms can convert the brittle behaviour of this cement-based material into a pseudo-ductile behaviour up to a crack width that is acceptable under the structural design point-of-view. Fibre addition, however, increases the complexity of the mix design process, due to the strong perturbation effect that steel fibres cause on fresh concrete flow. In the present study, the effect of steel fibres on fresh and hardened properties are studied by adding steel fibres of different percentages such as 0%, 1% and 2% for M70 grade of concrete. An experimental investigation has been carried out to determine different properties like workability and strength of Fiber Reinforced Self Compact Concrete and Self- Compacting Concrete (SCC). For testing the properties of SCC and Fiber Reinforced SCC (FRSCC) in fresh state slump-flow, T50 Test, L-box, U-box, and V-funnel tests were conducted. Whereas for testing the properties in hardened state compressive strength, split tensile strength and flexural strengths are carried out. Detailed studies have revealed that the Steel Fiber Reinforced Self Compacting Concrete made with the Steel fibres displays a better performance. The investigations and results are presented from the study. Index Terms: Self compacting concrete, Steel fibre reinforced concrete, Super plasticizer, Silica fume, Fly ash, Steel fibre.

Image‐based analysis of fresh concrete flow ‐ determining the correlation between flow behavior and rheological properties

AbstractBesides compressive strength, the workability of fresh concrete is one of the most important characteristics of concrete. Only by adapting the rheology of the fresh concrete to the geometry of the element to be casted, the formation of air voids and damages can be avoided. This holds even more so true for 3D printable concrete. Currently, empirical test methods such as the slump test are used to determine rheological parameters. Rheometer tests, on the other hand, allow a much deeper insight into the rheological properties of concrete but are more challenging. Further, all currently available test methods can only be applied on a batch basis.In the paper at hand, a new approach for an automatic digital concrete quality control is presented using modern computer‐vision based analysis methods. Using a newly developed experimental setup, the flow of mortar down an inclined open channel is studied using a monocular camera setup. Differences in the mortar's rheology result in different flow behaviors which can be optically detected. Utilizing dense optical flow, rheological parameters are determined from the acquired monocular image sequences. The results shown in this paper prove that the computed flow behavior of the investigated mortars precisely correlates with their rheological properties, demonstrating the high potential of the method for an automated in‐line testing of fresh concrete e.g. during the discharge of a mixing truck.

CFD simulation of movement of fresh concrete in the chute during transporting

The movement behavior of fresh concrete greatly affects the change of concrete properties and the wear of pipelines during transportation. This paper aims to predict the movement of aggregates in fresh concrete during transporting on a mesoscopic scale. A dense discrete phase model (DDPM) was utilized to describe fresh concrete, which treats fresh concrete as a double-phase fluid composed of matrix mortar and dense spherical aggregate particles that had grading particle size, random distribution, and different densities from matrix mortar. The correctness of this method was verified by comparing it with the experimental results. Then, based on the Computational Fluid Dynamics (CFD) and the DDPM, the free flow of fresh concrete in the long-distance chute was simulated. Flow behavior of fresh concrete in the chute with different inclination angles and movement characteristics of fresh concrete with different viscosities at an optimal angle were investigated, respectively. Moreover, recommended parameters for the maintenance of concrete workability in the project were provided, and it is believed that a mortar viscosity of around 50 Pa·s can effectively suppress aggregate segregation, ensuring the consistency of concrete properties during transportation.

On the macro- and micro-scale of dilute suspensions: A particle-based numerical investigation

We consider the micro- and the macro-scale to investigate the motion of single grains in a dilute suspension under shear flow and Poiseuille flow to analyze effects like shear-wall migration and rolling of grains as observed in physical experiments. To be able to simulate the behavior of fresh concrete or mud flow, as realistically as possible, we are taking into account a non-Newtonian Bingham–Papanastasiou rheology for the carrier fluid. Due to a surface coupled approach, Smoothed Particle Hydrodynamics (SPH) gives the opportunity to consider both, the motion of a solid particle, by tracking its center of mass and also surface points, and the interaction and influence on the near field of the velocity field in the fluid phase. We show an independence of the motion of solid grains from the surrounding carrier fluid. While the macroscopic flow reaches a stationary flow field quite fast, the motion of the solid grains still oscillates between parts of the fluid that flow with different velocities and does not show a stable steady state. Providing a comparison between the motion in a Newtonian and a non-Newtonian fluid, we point out the differences and thus the importance of the choice of the material model for the carrier fluid in numerical simulations.

Numerical simulation of fresh concrete flow in the L-box test using computational fluid dynamics

Concrete remains a widely used material in construction. As structures become more optimised, a deeper understanding of the rheology of the concrete mixture is necessary. This paper aims to numerically simulate the flow of fresh concrete in the L-box apparatus, with the objective of gaining insights into its rheological behaviour and predicting its properties. The fresh concrete flowing through the L-box test is simulated from the moment that the gate is lifted until the stoppage and the material takes its final shape. The flow in this tool occurs on a free surface. In this work, a three-dimensional model has been developed using the computational fluid dynamics technique for simulation. The flow behaviour of fresh concrete was assumed to be non-Newtonian following the Bingham law, characterised by a non-linear shear stress–shear rate ratio, yield stress and plastic viscosity. A set of numerical simulations by varying workability were conducted. Furthermore, a parametric study was conducted to examine the impact of introduced parameters in the concrete flow, including the effect of yield stress, viscosity and density.

Analysis of the relationship between the L-box test and the yield stress of fresh concrete: an analytical approach

The objective of this work was to study fresh concrete flow in the L-box test, predict the final deposit shape after flow stoppage and estimate the yield stress. This is very useful for controlling concrete casting in real structures, detecting problems and developing solutions on time. Concrete rheometers used for measuring the rheological parameters of concrete are expensive, not always available and can lead to measurement disparity. To overcome these issues, an effective method is to analyse concrete flow phenomena physically and solve the problem analytically based on L-box measurements. In the first part of this work, fresh concrete was considered as a homogeneous yield stress fluid moving under the effect of its self-weight. By developing momentum equations for an incompressible fluid, a theoretical approach was used to study three probable final shapes depending on the concrete rheology. Expressions were established for predicting the final shape and the yield stress. In the second part, the results obtained were compared with those of previous models and good agreement was found, thus validating the proposed approach. This study provides a consolidation of rheometer results, allowing evaluation and perhaps a calibration to reinforce their validity.

CFD Comparison of the Influence of Casting of Samples on the Fiber Orientation Distribution

The main goal of this research is to show that even a small deviation from the prescribed casting method EN 14651 causes a difference in fiber orientation distribution in sample beams. A further goal is to investigate the difference in the fiber orientation between bottom and side layers, which would carry the tensile load in the in-situ situation (bottom layer) compared to testing according to EN 14651 (side layer). Nowadays, the development of the proper numerical simulations that aim to visualize the casting process of the fresh concrete flow is a promising challenge in the construction industry. To be able to predict the orientation and spatial distribution of the short fibers using numerical tools may significantly simplify the investigations of the fibered composite materials. This paper compares simulations of different casting methods of the fiber concrete mixture with various flowabilities. The casting of the testing specimen was simulated in different ways: the filling of the formwork according to EN 14651, from the center only and from one edge of the formwork using computational fluid dynamics. The influence of different casting methods in combination with four specific sets of the rheological parameters on the final fiber orientation distribution is discussed. The presented outcomes of the simulations demonstrate that even a minor change in the casting procedure can significantly alter the final characteristics of the material.

Relation between Shear Stresses and Flexural Tensile Stresses from Standardized Tests of Extracted Prismatic Specimens of an SFRC Bridge Girder.

Experimental research on the direct shear behavior of fiber-reinforced concrete is often carried out using prisms molded with specific dimensions for a standardized test. However, the flow of fresh concrete in these molds can be different than in the case of a full-scale structural element. This is important considering that the flow direction highly influences the distribution and orientation of fibers. In addition, most of the studies did not relate their shear results to other mechanical properties. In contrast, this study attempted to deepen the experimental knowledge of the crack propagation of a steel fiber-reinforced concrete (SFRC) used in a full-scale prototype of a bridge box girder built in the laboratory. Prismatic specimens were sawn from webs and top flanges of this prototype. Serving as references, additional specimens were molded in wooden boxes. In a previous study of our research group, both had been tested under a three-point notched bending configuration maintaining test conditions proportional to the EN14651 specifications. From each of the previously flexurally tested specimens, two prismatic specimens suitable for the Fédération Internationale de la Précontrainte (FIP) shear test setup were extracted by adopting a cutting methodology that avoided the damage induced by the flexural tests to be part of the FIP specimens. These FIP specimens were tested in almost pure shear loading conditions for assessing the performance of SFRC. Computer tomography images and photos of the shear failure faces were used to determine the distribution and density of fibers. The results demonstrated that the peak loads were proportional to the fiber density at the shear failure section. Assuming that the SFRC conditions of the webs were representative of a common batching procedure in the construction industry, the results from the tests in specimens extracted from these webs were adopted to establish shear stress/flexural tensile stress ratios vs. crack mouth opening displacement curves. The curves belonging to cross-sections of a similar fiber density in the shear and flexural cases allowed for the proposal of a normalized crack-dilatancy relation composed of three stages of the crack propagation. In addition, a trilinear crack width-slip relation was established using the same set of specimens. The relevancy of this proposal is that the shear response can be estimated from a widely accepted standardized flexural test, which demands a simpler instrumentation and is also easier to execute than the shear setup.

Numerical flow simulation of fresh concrete in mixing truck

The structure of concrete truck not only affects the homogeneity of fresh concrete but also influences the construction efficiency. The repeatability of fresh concrete's test is worse and its cost is high. With this in mind, the simulation of fresh concrete flowing in concrete truck was conducted. The effects of screw pitch and height of blade on discharging speed were analyzed. The numerical results shown that increasing the screw pitch of blade at posterior cone can significantly promote the discharging speed. The discharging uniformity was also investigated. It is shown that increasing the height of blade or decreasing the screw pitch of blade can improve the homogeneity. Fig. 1. Discharge speed and increase percentage of series 1–6. Fig. 2. Discharge uniformity and increase percentage of series 1–6. • A numerical method was developed to simulate flow of fresh concrete in mixing drum. • The screw pitch and height of blade have an effect on discharge uniformity. • Increasing the screw pitch of blade at the posterior cone can increase discharge speed.

Benchmark Simulations of Dense Suspensions Flow Using Computational Fluid Dynamics

The modeling of fresh concrete flow is still very challenging. Nevertheless, it is of highest relevance to simulate these industrially important materials with sufficient accuracy. Often, fresh concrete is assumed to show a Bingham-behavior. In numerical simulations, regularization must be used to prevent singularities. Two different regularization models, namely the 1) Bi-viscous, and 2) Bingham-Papanastasiou are investigated. Those models can be applied to complex flows with common simulation methods, such as the Finite Volume Method (FVM), Finite Element Method (FEM) and Smoothed Particle Hydrodynamics (SPH). Within the scope of this investigation, two common software packages from the field of FVM, namely Ansys Fluent and OpenFOAM, COMSOL Multiphysics (COMSOL) from FEM side, and HOOMD-blue.sph from the field of SPH are used to model a reference experiment and to evaluate the modeling quality. According to the results, a good agreement of data with respect to the velocity profiles for all software packages is achieved, but on the other side there are remarkable difficulties in the viscosity calculation especially in the shear- to plug-flow transition zone. Also, a minor influence of the regularization model on the velocity profile is observed.

Computational Analysis of Concrete Flow in a Reinforced Bored Pile Using the Porous Medium Approach

In this paper, the flow of concrete in a reinforced bored pile is analysed using computational simulations. In order to reduce the computational time, a porous medium that equally mimics the presence of the reinforcement is used. Experimental measurements are used as bounds on the material parameters describing the flow of fresh concrete. The influence of rheological properties of fresh concrete and the thickness of the porous medium that represents the reinforcements is analysed with a classical U-box simulation. Finally, casting of a bored pile is analysed using computational simulation implementing a porous medium representing the reinforcement cage. The concrete flow behavior and especially the filling of the concrete cover zone is analyzed for casting scenarios with different concretes varying in their rheological behavior. Simulations using the porous medium approach is 10x faster than simulations that explicitly model the reinforcements. Simulation results show that a good workability (low viscosity and low yield stress) of the initial batches of concrete must be maintained throughout pouring to avoid the risk of defect formation in the cover zone.

Numerical approach to pipe flow of fresh concrete based on MPS method

As a fundamental study of concrete pumping, this study developed a numerical method to simulate the flow and segregation of fresh concrete in pipes, based on the improved MPS (Moving Particle Semi-implicit) that has complete implicit algorithm, hereafter called I-MPS. The slip layer (LL) near the pipe inner wall was treated by the macroscopic approach, which estimates the slip resistance and the volumetric flow rate of LL from the apparent slip velocity of LL. Two constituent models were used to describe fresh concrete, called single-phase & mono-particle (SPMP) model and double-phase & multi-particle (DPMP) model, respectively. In the former, fresh concrete is considered as a single-phase granular fluid, but in the latter, fresh concrete is regarded as two-phase granular fluid with different particle shapes and sizes of coarse aggregate and matrix mortar. By comparing the numerical and theoretical pumping pressures of three concretes having slump from 13 cm to 21 cm, it was found that by using the macroscopic approach of LL and either of the constituent models, the numerical approach can predict properly the pumping pressure and velocity profile of fresh concrete in pipes. Moreover, if using the DPMP model, the segregation behavior of coarse aggregate particles during the pipe flow can also be simulated.

Effects of the sole or combined use of chemical admixtures on properties of self-compacting concrete

Chemical additives are very important in determining the behavioral characteristics of self-compacting concrete. For this reason, determining the building materials that make up the chemical structure of self-compacting concrete and the interactions of these materials is of great importance. The present study pertains to the effects of the use of different chemical admixtures (high-range water-reducing, i.e., superplasticizer, hydration accelerating, air-entraining, shrinkage reducing, and hydration heat reducing admixtures) on the fresh and hardened properties of self-compacting concrete. The influence of using a single one or a hybrid combination of the air-entraining, hydration-accelerating, heat-reducing, and shrinkage-reducing admixtures on the mechanical properties of fresh and hardened SCC was investigated through a set of tests. For this purpose, sixteen different SCC mixtures with different combinations of chemical additives were prepared and tested. The properties of fresh concrete were examined as well as the compressive and tensile strengths of the mixtures. SCC mixtures with shrinkage-reducing admixtures were evaluated in terms of shrinkage development. The effect of the use of admixtures was found to be more pronounced on the early-age concrete strength. The use of any type of additive in addition to the shrinkage-reducing admixture increased the speed of flow of fresh concrete.

Effect of elevated temperatures on mechanical properties of lightweight geopolymer concrete

This study aims to examine the effect of high temperatures on lightweight geopolymer concrete (LWGC) and lightweight ordinary concrete (LWOC) made of natural pumice and lightweight expanded clay aggregate (LECA) with the addition of trapped air. To this end, a geopolymer concrete matrix has been synthesized by the alkali-activation of fly ash (FA) and granulated blast furnace slag (GBFS). The geopolymer concrete samples were cured for 24 h at a temperature of 80 °C. To study the properties of fresh concrete, slump and slump flow tests and unit weight were applied. The mechanical properties were also measured by the compressive strength, splitting tensile, flexural strength, and elastic modulus tests. High temperatures of 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, and 800 °C were applied on the geopolymer concrete samples to obtain the residual compressive strength. In general, pumice and LECA can be used as an alternative to the dolomite aggregate to produce LWGC and LWOC. The mixture F-50D50P-A achieved the lowest of unit weight of 1660 kg/m, a slump flow of 555 mm, and compressive strength of 32.9 MPa at 91-days. Lightweight geopolymer concrete containing 50 % fly ash and 50 % GBSF achieved the best compressive strength test results. The results showed a similarity in the behaviour of LWGC with LWOC under the influence of all the variables applied in this study.

Measurements of unconfined fresh concrete flow on a slope using spatial filtering velocimetry

Fluidity of fresh concrete is an important performance, and it can be evaluated by concrete flow process. Before the experiments, the theory of the lateral spread and accumulation were assumed. Then, the velocity and spread characteristics of concrete with different water content on an inclined plane were studied. Spatial filtering velocimetry (SFV) was used to measure the free-surface spreading evolution of concrete of a fixed volume slowly released onto a slope. The velocity gradients along the flow direction were calculated in the steady zone and the results showed that the velocity gradient was a reasonable indicator to assess concrete fluidity. Based on these analysis and results, the flow depth during the flow process was estimated too.

Numerical method for predicting flow and segregation behaviors of fresh concrete

Current meshless particle methods are able to simulate the flow of fresh concrete, but fail to predict the segregation since fresh concrete is regarded as homogeneous fluid. This study aims to develop a numerical approach to predict the segregation of coarse aggregate (CA) in fresh concrete together with the flow behavior. A double-phase & multi-particle (DPMP) model was proposed to describe fresh concrete, which treats fresh concrete as a double-phase fluid composed of matrix mortar and the CA particles that had random shapes, size distribution, and different density from matrix mortar. Each CA particle was formed by the element particles, of which number was dependent on the size and shape of described CA particle. Three types of inter-particle interaction, including CA-CA particles, CA-mortar particles, and two mortar particles, were investigated, respectively. Then, based on the complete implicit MPS (I-MPS) method and the DPMP model, the L-box flow of two series of high fluidity concrete were simulated. The ability of the proposed numerical approach to simultaneously simulate the flow and segregation behaviors of fresh concrete was confirmed. Moreover, this numerical method can analyze the changes of localized rheological parameters of segregated concrete.

Study on hydrodynamic properties of a common building material

The efficient self-leveling ability of self-compacting concrete is widely used in various industries and structures, but the influence mechanism and law on its flow performance have not been quantified, so it is urgent to find a suitable explanation method. Water film thickness is considered to be one of the key factors affecting the flow performance of mortar and cement paste, but there is a lack of research in concrete. In this paper, relevant experimental studies are carried out based on the theoretical innovation of water film thickness. In order to further improve the flow performance of self-compacting concrete, according to a certain gradient, 24 fresh self-compacting concrete flow performance tests and filling density measurement tests were carried out to observe the relationship between water film thickness and concrete flow performance. The results show that there is a strong correlation between the flow performance of concrete and the thickness of water film, and there is a positive correlation between them. the addition of talc powder can improve the flow performance of self-compacting concrete, and the flow performance is the best when 5% talc powder is added to replace cement.

Numerical simulation of fresh concrete flow: insight and challenges

Recent developments in concrete technology are advancing into a scientific-based approach, where both experimental and numerical simulations are utilised to achieve an optimum mix design and an effective placement into formwork at the jobsite. Since the load carrying capacity and service life of concrete structures is fully dependent on the success of the placement process, researchers all over the world have started to work on casting prediction tools using different numerical software. However, a lot of work is still to be done in order to properly model the large-scale flow processes. This is because fresh concrete is a very complex material and its simulations involve complex material models and extensive computations. An exact material model of fresh concrete does not exist, and the researchers use diverse approximations to depict concrete flow. In this paper, we identify the main challenges for modelling fresh concrete and review the existing simulation methods. The advantages, disadvantages and application fields are discussed, including future perspectives for having numerical tools for practical use.

A SPH simulation method for opening flow of fresh concrete considering boundary restraint

When fresh concrete flows through opening, such as steel bars, blockage may occur due to segregation or insufficient fluidity. Insufficient fluidity may be attributed to the increase of deformation resistance because of opening’s boundary restraint. In this paper, opening flow behavior of fresh concrete was analyzed by Smoothed Particle Hydrodynamics. We proposed a boundary restraint stress model to treat opening’s boundary restraint to the flow, which clarified that normal stress acting on the shear plane of fresh concrete increases during opening flow. The parameters in the model were obtained by matching the experimental and numerical results of V-funnel flow test. Then, the flow of fresh concrete in L-box with steel bars was simulated. The numerical results indicated that the restraint of opening’s boundary has considerable effect on the flow behavior when fresh concrete has larger average particle contact angle and average particle friction angle, or the opening is narrow.

A REVIEW OF DEM-BASED SIMULATION OF FRESH CONCRETE FLOW

Recently, there has been growing research interest in simulation on the flow behaviors of fresh concrete, because these properties have significant effects on construction quality of casting and forming process, and also the properties of hardened concrete. The behaviors of fresh concrete are usually described by workability, consistency, flowability, mobility, pumpability, shootability, compactibility, and finishability. While various numerical simulations for concrete flow are available, District Element Method (DEM) has been applied widely due to its unique advantages of both macro and micro analysis i.e. the flow of the concrete mixture as a whole and particulate behavior of individual constituents in a mixture. This paper first presents a brief overview on the rheological models of fresh concrete, followed by a detailed review on simulating the fresh concrete flow using the DEM method. Moreover, recommendations for future work and directions will be provided.