Random Aggregate Model Research Articles

Investigation on statistical characteristics of asphalt concrete dynamic moduli with random aggregate distribution model

Finite element models generating the random aggregate have been used to predict the dynamic moduli of the asphalt concrete materials. The asphalt concrete is modeled as a triphasic medium composed of granular inclusions with linear elastic properties, interfacial transition zone (ITZ) with linear elastic properties, and a porous matrix of bituminous mastics exhibiting linear viscoelastic behavior at small strain level. The predicted complex moduli of asphalt mixes from numerical approach are found close to that from the dynamic modulus tests, resulting in a good agreement. Meanwhile, the size effort of dynamic modulus for asphalt concrete material is investigated through nearly 30,000 times numerical examples, and a theoretical statistic formula for describing the size effort of dynamic modulus is proposed. The simulation results reveal that the theoretical statistic formula provides a suitable description for the size effort of dynamic modulus for asphalt concrete.

Numerical simulation of fracture process of concrete under uniaxial compression via PFC2D

Simulation of cracks and cracking process is one of the difficult problems in the numerical simulation of concrete. In this paper, the discrete element method (DEM) was applied to the numerical simulation of concrete specimen under uniaxial compression and the whole process of crack generation and development were visualized. In order to simulate the three different components of aggregates, mortar and interfaces, the random aggregate model was used in the simulation. The strain-stress curves of concrete under uniaxial compression obtained from the simulation were in good agreement with experiments. These results show that the DEM can be well used to simulate the fracture process of concrete. Therefore, the study lay a foundation for the further study on the cracking mechanism of concrete members.

Multi-scale numerical simulation analysis for influence of combined leaching and frost deteriorations on mechanical properties of concrete

Purpose The multi-scale numerical simulation method, able to represent the complexity of the random structures and capture phase degradation, is an effective way to investigate the long-term behavior of concrete in service and bridges the gap between research on the material and on the structural level. However, the combined chemical-physical deterioration mechanisms of concrete remain a challenging task. The purpose of this paper is to investigate the degradation mechanism of concrete at the waterline in cold regions induced by combined calcium leaching and frost damage. Design/methodology/approach With the help of the NIST’s three-dimensional (3D) hydration model and the random aggregate model, realistic 3D representative volume elements (RVEs) of concrete at the micro-, the meso-, and the macro-scales can be reconstructed. The boundary problem method is introduced to compute the homogenized mechanical properties for both sound and damaged RVEs. According to the damage characteristics, the staggering method including a random dissolution model and a thermo-mechanical coupling model is developed to simulate the synergy deterioration effects of interacted calcium leaching and frost attacks. The coupled damage procedure for the frost damage process is based on the hydraulic pressure theory and the ice lens growth theory considering the relationship between the frozen temperature and the radius of the capillary pore. Finally, regarding calcium leaching as the leading role in actual engineering, the numerical methodology for combined leaching and frost damage on concrete property is proposed using a successive multi-scale method. Findings On the basis of available experimental data, this methodology is employed to explore the deterioration process. The results agree with the experimental ones to some extent, chemical leaching leads to the nucleation of some micro-cracks (i.e. damage), and consequently, to the decrease of the frost resistance. Originality/value It is demonstrated that the multi-scale numerical methodology can capture potential aging and deterioration evolution processes, and can give an insight into the macroscopic property degradation of concrete under long-term aggressive conditions.

Random aggregate model for mesoscopic structures and mechanical analysis of fully-graded concrete

The realization of approximate practical aggregate models is a crucial link to the mesoscopic mechanical analysis for fully-graded concrete. This study systematically presents the establishment of mesostructure models of three-phase fully-graded concrete composed of anisotropic high-contented aggregates, cement paste, and interfaces bonding between them. A convex extension method is demonstrated in details to construct convex polygons and polyhedrons represented as crushed coarse aggregates in two- and three-dimensional spaces. The Walraven formula combined with the definition of an equivalent diameter is adopted to ensure the equivalence between the gradation and content of circle and spherical aggregates and that of the actual anisotropic geometric aggregates. We also propose a so-called “occupation and removal method (ORM)” to improve the efficiency of generating mesostructure models with a high aggregate content. Combining the ORM, the inter-particle overlap detection, and the random sequential packing scheme, random aggregate models (RAMs) of polygonal and polyhedral particles are realized to characterize the mesostructure models of concrete. Moreover, by the present RAMs applied, we implement a mesoscopic finite element simulation to investigate the flexural failure process of fully-graded concrete. The numerical results for dynamical flexural strength and dynamic increasing factors show a good in agreement with the experimental data reported in the literature. The proposed RAMs can simulate and explain qualitatively the effects of the mesoscopic structural properties on the macroscopic dynamic characteristics of fully-graded concrete.

Steady-state dynamic method: An efficient and effective way to predict dynamic modulus of asphalt concrete

This study presents two meso-mechanical methods of analyzing the asphalt concrete’s dynamic modulus, including the transient dynamic method (implicit dynamic method) based on the modified Newmark numerical differential algorithm and the steady-state dynamic method based on the perturbation theory. The results indicate that compared to the transient dynamic method based on the modified Newmark numerical differential algorithm, the steady-state dynamic method based on the perturbation theory is much more efficient in calculating dynamic modulus of asphalt concrete while maintaining similar accuracy. Furthermore, the random aggregate model of asphalt concrete coupled with the steady-state dynamic method is also employed to obtain the asphalt concrete’s dynamic modulus. The numerical solution was found in a good agreement with the corresponding experiment results, which indicates the proposed steady-state dynamic method an efficient and effective way to predict the dynamic modulus of asphalt concrete.

Numerical Simulation of Recycled Concrete Using Convex Aggregate Model and Base Force Element Method

By using the Base Force Element Method (BFEM) on potential energy principle, a new numerical concrete model, random convex aggregate model, is presented in this paper to simulate the experiment under uniaxial compression for recycled aggregate concrete (RAC) which can also be referred to as recycled concrete. This model is considered as a heterogeneous composite which is composed of five mediums, including natural coarse aggregate, old mortar, new mortar, new interfacial transition zone (ITZ), and old ITZ. In order to simulate the damage processes of RAC, a curve damage model was adopted as the damage constitutive model and the strength theory of maximum tensile strain was used as the failure criterion in the BFEM on mesomechanics. The numerical results obtained in this paper which contained the uniaxial compressive strengths, size effects on strength, and damage processes of RAC are in agreement with experimental observations. The research works show that the random convex aggregate model and the BFEM with the curve damage model can be used for simulating the relationship between microstructure and mechanical properties of RAC.

Damage Simulation of a Random Aggregate Model Induced by Microwave under Different Discontinuous Ratios and Exposure Times

A random aggregate algorithmic method and a numerical model for two-phase materials (composed of quartz and plagioclase) with different discontinuous ratios and irradiation times were studied based on the discrete element method using two-dimensional particle flow code (PFC2D). The results showed that this algorithm can simulate random irregular aggregate shapes. Furthermore, crack initiation and development and the coalescence process of microwave-induced material damage could be predicted using the discrete element method. After analysis of this study, the micro crack originated from the boundary of the high-absorption-phase plagioclase crystal and expanded around the plagioclase, extending into the quartz material. The crack morphology presented a radial network.

Mesoscopic Numerical Computation of Compressive Strength and Damage Mechanism of Rubber Concrete

Evaluations of both macroscopic and mesoscopic strengths of materials have been the topic of a great deal of recent research. This paper presents the results of a study, based on the Walraven equation of the production of a mesoscopic random aggregate structure containing various rubber contents and aggregate sizes. On a mesoscopic scale, the damage mechanism in the rubber concrete and the effects of the rubber content and aggregate-mortar interface on the rubber concrete’s compressive resistance property were studied. The results indicate that the random aggregate structural model very closely approximates the experimental results in terms of the fracture distribution and damage characteristics under uniaxial compression. The aggregate-mortar interface mechanical properties have a substantial impact on the test sample’s strength and fracture distribution. As the rubber content increases, the compressive strength and elastic modulus of the test sample decrease proportionally. This paper presents graphics of the entire process from fracture propagation to structural failure of the test piece by means of the mesoscopic finite-element method, which provides a theoretical reference for studying the damage mechanism in rubber concrete and performing parametric calculations.

Application of Base Force Element Method to Mesomechanics Analysis for Concrete

The base force element method (BFEM) on damage mechanics is used to analyze the compressive strength, the size effects of compressive strength, and fracture process of concrete at mesolevel. The concrete is taken as three-phase composites consisting of coarse aggregate, hardened cement mortar, and interfacial transition zone (ITZ) on mesolevel. The random aggregate model is used to simulate the mesostructure of concrete. The mechanical properties and fracture process of concrete under uniaxial compression loading are simulated using the BFEM on damage mechanics. The simulation results agree with the test results. This analysis method is the new way for investigating fracture mechanism and numerical simulation of mechanical properties for concrete.

Simulation of Numerical Test of Concrete Microscopic Structure by Second-Order Manifold Method

To simulate the numerical test of concrete, the random aggregate model according to the Monte Carlo method and Fuller Graded Formula is carried out based on the assumption that the concrete is a multi-phases composite material composed of matrix. By adding the function of tracing the propagation of cracks,the Numerical Manifold Method proposed by Shi Genhua is developed which can simulate both the discontinuity of block system and the tensile or shear failure of intact block. The random aggregate model according to the Monte Carlo method and Fuller Graded Formula is carried out, and the concrete fracture process is simulated by the NMM. The strength and failure pattern are in good agreement with the experimental data, which shows that the method put forward and the program developed in this paper can effectively simulate the fracture process of concrete composed of multi-cracks.

A Simple Method of Coarse Aggregate Generation Based on PFC2d

To establish an appropriate random aggregate model at meso-level is the basis for successfully simulating the meso-mechanical behaviors of concrete. This paper proposes a new simple method to generate random aggregates of concrete by PFC2d. And the distribution of aggregate in the two-dimensional concrete specimen cross-section is determined by Walraven formula. The results show that the numerical aggregate distribution matches well with the theoretical grading curve.

IMPROVED RANDOM AGGREGATE MODEL FOR NUMERICAL SIMULATIONS OF CONCRETE ENGINEERING SIMULATIONS OF CONCRETE ENGINEERING

In numerical simulations, concrete is usually considered as a three-phase material consisting of an aggregate, a cement matrix, and an interfacial transition zone (ITZ). Three-dimensional modeling of concrete usually requires extremely large computational requirements. In this study, an improved random aggregate model for numerical simulations of concrete is developed, which can minimize the number of elements, optimize the ITZ thickness, and create internal cracks and holes. Numerical investigations on the cracks form as well as deflection and tensile strength are also conducted based on three-point bending tests. The simulation results agree well with the experimental results.

Application of Base Force Element Method to Mesomechanics Analysis for Recycled Aggregate Concrete

The base force element method (BFEM) on potential energy principle is used to analyze recycled aggregate concrete (RAC) on mesolevel. The model of BFEM with triangular element is derived. The recycled aggregate concrete is taken as five-phase composites consisting of natural coarse aggregate, new mortar, new interfacial transition zone (ITZ), old mortar, and old ITZ on meso-level. The random aggregate model is used to simulate the mesostructure of recycled aggregate concrete. The mechanics properties of uniaxial compression and tension tests for RAC are simulated using the BFEM, respectively. The simulation results agree with the test results. This research method is a new way for investigating fracture mechanism and numerical simulation of mechanics properties for recycled aggregate concrete.

Numerical Simulation of Uniaxial Compression Performance for Recycled Concrete Using Micromechanics

Recycled Aggregate Concrete (RAC) is referred to as Recycled Concrete (RC). In this paper, the compression performance of recycled concrete was researched using the micromechanics. The recycled concrete was taken as a five-phase composite material consisting of recycled coarse aggregate, old hardened cement paste, new hardened cement paste, the old interfacial transition zone (Old ITZ) and the new interfacial transition zone (New ITZ) on meso-level. A random aggregate model was used to simulate the meso-structure of recycled concrete. The propagation process of cracks and the mechanical properties of uniaxial compression specimens of recycled concrete were simulated using finite element method (FEM) with damage model. The numerical simulation results agree well with the corresponding experimental results. The results show that the specimen usually damaged along the old interfacial transition zone and the new interfacial transition zone.

Numeric Analysis of Size Effect on Mesol Concrete Random Aggregate Model

In order to research that statics properties of concrete cylinder sample are influenced by micro-concrete material heterogeneity, by random aggregate models generated by different random number were established. By fixed aggregate size and constantly changing of the sample size, the concrete numerical model was simulated and Strength change of concrete samples was analyzed .So that strength influence of the aggregate location of the concrete random sample was study. Calculation shows that: the strength of concrete has been little effect by the aggregate random location, the size effect on concrete has been changed regularly, with the size effect ratio coefficient of aggregate and sample gradually increasing, the error square sum of strain was reduced and the brittlness of the samples becomes obvious.

Numerical Dynamic Simulation for Three Phase Random Aggregate Model of Concrete

In this paper the concrete under impact load and failure mechanism was studied. Concrete was considered as a three-phase composite material: aggregate, cement mortar and interfacial transmission zone (ITZ).The simulation was based on random polyhedron aggregate model. Mortar and the transition zone were considered as the brittle fracture model material, and the aggregate was considered as plastic material. LS-DYNA finite element program was used to simulate concrete in SHPB experimental device under the impact damage process. It was showed that the reason of the final macro failure was the development of the microcrack, aggregate shape on concrete failure has a certain impact on the failure process.

The Impact of Aggregates Distribution on Concrete Failure

As the key component, the aggregates have a significant impact on the concrete’s mechanical properties and fracture modes. To study the impact of aggregates distribution on concrete failure, the extended finite element method (XFEM) is adopted to simulate the mesostructure failure process by virtue of random aggregate model under uniaxial tension. The result shows that aggregates distribution has little effect on the concrete mechanical properties, but aggregates distribution effect fracture modes.

Numerical Simulation of Meso-Damage Process of Concrete under Dynamic Load and CT Experiment Verification

In mesoscopic level, concrete was taken as three-phase composites consisting of aggregate, bond and mortar. Use the Monte Carlo methods, establish random aggregate model of concrete and apply the concrete damage plasticity model. Judge the failure based on the load-displacement curve and then doing the numerical simulation to the specimen on the impact loads. Through CT test, get the CT images of various force stages of the concrete. Compare the damage process picture of the numerical simulation with CT test. Find the failure process of the numerical simulation is similar to the CT test. The results show that the model is right to simulate the damage and fracture of concrete which is under the dynamic load. It is established that the model of the method is feasible.

The Concrete Fracture Performance Response to the Interface Transition Zone Parameters Based on Mesoscopic Simulation

The interface transition zone (ITZ) has a significant impact on the concrete’s mechanical properties and fracture modes. For the influence of ITZ’s strength and elastic modulus, the extended finite element method (XFEM) is adopted to simulate the mesostructure failure process by virtue of random aggregate model under uniaxial tension. The results show that ITZ’s strength and elastic modulus have a certain effect on the mechanical properties and fracture modes. With the tensile strength of ITZ increasing, the fractured modes transit from single coalescent crack to multiple non-coalescent cracks and the fracture energy increases, the ductility of concrete is enhanced. With the elastic modulus of ITZ increasing, the concrete’s elastic modulus increases, the tensile strength and the fracture energy decrease.

Numerical Simulation of Splitting Tensile Strength for Concrete

The random aggregate model was used to simulate the structure of concrete, and microscopic damage and crack of concrete in splitting tensile tests were simulated by Finite Element Method. The process of splitting tensile damage for concrete was studied. The result shows that the method of numerical simulation based on random aggregate model is mainly feasible, and the surface between concrete aggregate and mortar is the weak part