DEM study of fresh concrete under surface vibration: based on the optimized elastic vibration structure of a leveling machine

Toward Development of Self-Compacting No-Slump Concrete Mixtures

This study addresses a key limitation in meso-scale discrete element modeling (DEM) of ultra-high performance concrete (UHPC). Most existing DEM frameworks rely on extensive macroscopic calibration and do not provide a clear, transferable pathway to derive contact law parameters from measurable micro-scale properties, limiting reproducibility and physical interpretability. To bridge this gap, we develop and validate a micro-indentation-informed, poromechanics-consistent calibration framework that links UHPC phase-level micromechanical measurements to a flat-joint DEM contact model for predicting uniaxial compression, direct tension, and flexural response. Elastic moduli and Poisson’s ratios of the constituent phases are obtained from micro-indentation and homogenization relations, while cohesion (c) and friction angle (α) are inferred through a statistical treatment of the indentation modulus and hardness distributions. The tensile strength limit (σₜ) is identified by matching the simulated flexural stress–strain peak and post-peak trends using a parametric set of (c, α, σₜ) combinations. The resulting DEM model reproduces the measured UHPC responses with strong agreement, capturing (i) compressive stress–strain response, (ii) flexural stress–strain response, and (iii) tensile stress–strain response, while also recovering the experimentally observed failure modes and damage localization patterns. These results demonstrate that physically grounded micro-scale measurements can be systematically upscaled to meso-scale DEM parameters, providing a more efficient and interpretable route for simulating UHPC and other porous cementitious composites from indentation-based inputs.

In this study, the experimental tests for the direct tensile strength measurement of Ultra-High Performance Concrete (UHPC) were numerically modeled by using the discrete element method (circle type element) and Finite Element Method (FEM). The experimental tests used for the laboratory tensile strength measurement is the Compressive-to-Tensile Load Conversion (CTLC) device. In this paper, the failure process including the cracks initiation, propagation and coalescence studied and then the direct tensile strength of the UHPC specimens measured by the novel apparatus i.e., CTLC device. For this purpose, the UHPC member (each containing a central hole) prepared, and situated in the CTLC device which in turn placed in the universal testing machine. The direct tensile strength of the member is measured due to the direct tensile stress which is applied to this specimen by the CTLC device. This novel device transferring the applied compressive load to that of the tensile during the testing process. The UHPC beam specimen of size 150 × 60 × 190 mm and internal hole of 75 × 60 mm was used in this study. The rate of the applied compressive load to CTLC device through the universal testing machine was 0.02 MPa/s. The direct tensile strength of UHPC was found using a new formula based on the present analyses. The numerical simulation given in this study gives the tensile strength and failure behavior of the UHPC very close to those obtained experimentally by the CTLC device implemented in the universal testing machine. The percent variation between experimental results and numerical results was found as nearly 2%. PFC2D simulations of the direct tensile strength measuring specimen and ABAQUS simulation of the tested CTLC specimens both demonstrate the validity and capability of the proposed testing procedure for the direct tensile strength measurement of UHPC specimens.

Blocking analysis of fresh self-compacting concrete based on the DEM

Fiber reinforced self-compacting concrete (SCC) has several advantages compared to normal concrete. It has higher tensile strength and better flowability to fill the gaps and voids in mold. Fiber distribution and orientation are the most important factors for the mechanical performance of the fiber reinforced SCC. In this paper a numerical framework consisting computational fluid dynamics (CFD) and discrete element method (DEM) is suggested to model the casting process of the fiber reinforced SCC. First the casting procedure for fresh concrete is modeled as non-Newtonian fluid by computational fluid dynamics (CFD), and the CFD simulations are validated against the slump and LCPC test. Then the fiber movement and rotation are simulated with discrete element method (DEM). The results showed that the proposed framework could be utilized to model casting process of the fiber reinforced SCC and the simulation results have a good agreement with the test data from literature.

Based on production practice, it is known that the mixing scraper is an important mechanical part that the planetary mixer directly contacts with the concrete. Its structural shape will directly affect the mixing effect of the mixer, and the inclination angle of the mixing scraper is one of the most important factors affecting the mixing efficiency of the mixer. In this paper, based on the discrete element numerical analysis method, a three-dimensional simulation model of the vertical axis planetary concrete mixer is established, and the concrete mixing process is simulated, and the inclination angle of the mixing scraper is optimized based on the simulation results. An automatic precast concrete mixing experiment platform was built, and the simulation results were verified experimentally. The research results show that the experimental data and the simulation results are very consistent, which verifies the accuracy of the discrete element dynamics simulation model. It can be seen from the simulation and experimental results that the mixing efficiency of the mixer is the highest when the inclination angle of the mixing blade is 45°, and the number of collisions between different types of material particles in the mixing tank is the highest.

Structural dynamics analysis of spatial robots with finite element approach

When a powder bed is vibrated, the particles may move like a fluid, and various flow patterns and surface shapes can exist, depending on the vibration conditions — particularly the frequency and amplitude. A two-dimensional (2D) bed is often used so that the flow pattern in a vibrated powder bed can be directly visualized. Because three-dimensional (3D) fluidization phenomena are complicated, 2D observation is not sufficient. However, it is difficult to observe the internal flow of a 3D fluidized bed. A unique method for doing this is positron emission particle tracking (PEPT), a technique derived from the same physical phenomena as in positron emission tomography (PET). In the most common version of the PEPT technique, the flow in a bed is analyzed by following the behavior of a single radioactively labeled particle. We adopted the PEPT technique to analyze flow patterns in a cylindrical vibrated powder bed. From the particle trajectory data obtained with PEPT, some characteristic internal flow structures that cannot be understood from observing surface particle motion were successfully obtained. However, it is difficult to clarify the detailed mechanisms driving such flow patterns from experimental data alone. Therefore, we also carried out numerical simulations based on the discrete element method (DEM). Because the DEM is a Lagrangian method, its computational time depends on the number of particles, so that simulations were restricted to 2D. In order to compare the simulated results to the experimental ones, the average speeds of particles were obtained. Consequently, it was found that the simulated average speed of particles depends only on the amplitude of the applied vibration. In general, good agreement between simulated and experimental results was obtained, but agreement became poorer under conditions of high frequency and low vibration strength.

Filling capacity analysis of self-compacting concrete in rock-filled concrete based on DEM

A discrete element method (DEM) has widely been used to simulate asphalt mixture characteristics, and DEM models can consider the effect of aggregate gradation and interaction between particles. However, proper selection of model parameters is crucial to obtain convincing results from DEM‐based simulations. This paper presents a method to appropriately determine the mechanical parameters to be used in DEM‐based simulation of asphalt concrete mixture. Splitting test specimens are prepared by using asphalt mixture, and the splitting test results are compared with simulation results from two‐dimensional (2D) DEM and three‐dimensional (3D) DEM. Basing on the DEM results, the effects of contact model parameters on the simulation results are analyzed. The slope of the load‐displacement curve at the beginning stage is mainly affected by the stiffness parameters, and the peak load is mainly determined by using the value of the bond strength. The laboratory splitting test of AC‐20 and AC‐13 specimens were performed at different temperatures, namely, −10°C, 0°C, 10°C, and 20°C, and the load‐displacement relationships were plotted. According to the real load‐displacement curve’s slope at the beginning stage and peak load applied, the range of DEM bond model parameters is determined. On the basis of DEM results of the splitting test, the relationships between simulation load‐displacement curve’s characteristics and bond model parameters are fitted. The values of the parameters of the DEM contact bond model at different temperatures are obtained depending on the actual load‐displacement curve’s initial slope and peak load. Lastly the DEM and laboratory test results are compared, which illustrates that the parallel bond model can well simulate the behavior of asphalt mixture.

DEM simulation of SCC flow in L-Box set-up: Influence of coarse aggregate shape on SCC flowability

Experimental and numerical investigation on fracture characteristics of self-compacting concrete mixed with waste rubber particles

Rockslides are among the most dangerous geohazards. The discrete element method (DEM) has been increasingly used to simulate the emplacement process of rockslides. However, few studies have modeled the fragmentation of jointed rock masses during movement via DEM simulations and verified the reliability of the results through comparison with the results of laboratory experiments and field events. In this paper, a series of DEM simulations based on PFC3D5.0 was conducted to replicate laboratory experiments in which breakable blocks with different structural forms impact and slide on a horizontal plane and experience fragmentation. The results show that the DEM model provides first-order estimates that are comparable with the results of experiments in terms of the kinetic features and depositional characteristics of rockslides, including crack propagation, velocity distribution, preservation of source stratigraphy, progressive fragmentation, and spreading of fragments. Conversely, the normalized horizontal runout and degree of fragmentation are poorly represented in the DEM model. A theoretical analysis is further conducted to discuss the causes of travel distance discrepancy between the DEM model and experiments. It is found that the inconsistency of fragment interactions caused by the defect of the fragmentation process in DEM simulation may take primary responsibility. An alterable restitution coefficient method based on the rock mass fragmentation process is proposed for application to the fragmenting rock mass movement in DEM simulation, with the utilization of additional laboratory experimentation as the calibration benchmark. Further verification of our method needs to be performed in the future.

Self-compacting barite concrete has good radiation resistance and flow performance. Can adapt to most nuclear power projects; Many projects expect concrete to have good radiation resistance and a clean water effect. However, the research on the effect of auxiliary vibration on the surface porosity of self-compacting barite concrete has not been carried out. To effectively explore the influence of auxiliary vibration on the porosity on the surface of self-compacting barite concrete, 300mm*250mm*100mm self-compacting barite concrete test blocks under different vibration states were prepared by changing the vibration time and frequency. After curing, digital cameras were used to take photos of the surface of concrete test blocks to obtain the surface image of concrete. In addition, Image analysis software Image-Pro Plus was used to analyze and process the surface porosity of concrete, to obtain the surface porosity variation characteristics of concrete under different vibration modes. Analysis results show that the self-compacting concrete barite surface parameters such as the number of maximum pore size, surface area, and porosity increase with auxiliary vibrating time and frequency of the change of the first, increase with the decrease of the average pore diameter of concrete surface porosity along with the change of auxiliary vibrating time and frequency has been reduced, when the auxiliary vibration voltage of 70 v, when time is 8 s concrete surface blowhole best.

Dynamic behaviors assessment of steel fibres in fresh Ultra-High Performance Concrete (UHPC): Experiments and numerical simulations