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The ability to create realistic digital aggregates is the first step to computationally optimise civil engineering materials such as concrete, asphalt, or ballast, which are based on aggregates. A method to generate aggregates with realistic shapes has been created in a physics engine. The approach uses morphological properties of the aggregates as input parameters, such as the Perimeter, Area, and Weibull parameters of Minor Feret and Aspect Ratio, and consists of three major stages: (i) extraction of morphological information from real aggregates samples through digital image analysis; (ii) computational generation of 3D aggregates; and (iii) computational optimization of the aggregates via Differential Evolution methods. The efficiency of the method has been tested and validated by reproducing thousands of stones of 16 different types. The results indicate that the method can simulate aggregates, and a preliminary application indicates that these can be packed to obtain stone skeletons with realistic features.

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... This can be done by using imaging techniques, which capture the projection of aggregates to measure their shapes (Czajkowska et al. 2015). After, virtual geometries with shapes equivalent to rocks must be created (Garcia et al. 2020. Then, the rocks need to be compacted; see and the results compared to experiments, such as values from X-Ray Computed Tomography Scans (Yin et al. 2015, Yang et al. 2016. ...

... The diameter of one circle (x area ) which has the same area of that measured aggregate was also introduced to help describe aggregate's height (H v ). More details can be found in Garcia et al. 2020. ...

... Then, the prisms are deformed until their perimeter and area match those measured experimentally. The creation process is described clearly in (Garcia et al. 2020). Figure 1 shows an example of virtual granite aggre gates with a size of 14 mm. ...

... The minor Feret and aspect ratio are enough to characterise the dimensions of each particle projection [18]. The algorithm described in the previous section produces angular particles which minor Ferets and aspect ratios do not fit those of the actual aggregates. ...

... As it will be shown in the Results section, the aspect ratio and minor Feret of each aggregate type have been characterised using the Weibull distribution function, as it was done in [18]. This distribution is defined by two parameters, one of shape, k , and another one of scale, , which have been measured experimentally, see also Table 2. ...

... The minor Feret and Aspect Ratio data obtained from ImageJ have been analysed using the Anderson-Darling adjustment, which indicates the goodness-of-fit to a distribution curve; the closer the result is to zero, the better the fit of the curve to the data points [21]. Based on [18], a twoparameter Weibull distribution functions has been used to fit the minor Feret and Aspect Ratio. An example can be seen in Fig. 5, which shows the cumulative probabilities for the minor Feret of G1 aggregates. ...

An algorithm to re-create virtual aggregates with realistic shapes is presented in this paper. The algorithm has been implemented in the Unity 3D platform. The idea is to re-create realistically the virtual coarse and crushed aggregates that are normally used as a material for the construction of roads. This method consists of two major procedures: (i) to combine a spherical density function with a noise matrix based on the Perlin noise to obtain shapes of appropriate angularity and, (ii) deform the shapes until their minor ferret, aspect ratio and, thickness are equivalent to those wanted. The efficiency of the algorithm has been tested by reproducing nine types of aggregates from different sources. The results obtained indicate that the method proposed can be used to realistically re-create in 3D coarse aggregates.
Graphic abstract

... Several pieces of research have addressed this in the past. For example, [14,15] used a spherical harmonic function to create real-shaped aggregates based on reconstructed Computed Tomography (CT) scan images [16] assembled spheres to create realistic particles [17] used revolution solids to create particles [18] adjust the geometry of 2D projections obtained from CT scans until they matched aggregate distributions [19] adjust the geometry of a prism using a Perlin noise to produce realistic aggregate distributions. ...

In this paper, an impulse-based Discrete Element numerical Method (iDEM) included in a physics toolbox, has been used to compact virtual aggregates. Firstly, geometrical properties, such as area, aspect ratio, perimeter, minor and major feret, circularity and roundness, of eleven types of coarse aggregates were measured. Then, a mass of each of these aggregates was compacted under vibration. The aggregate packings’ properties, such as aggregate segregation and orientation, porosity, pore -diameter, -tortuosity, -connectivity, -aspect ratio, -circularity, and -vertical distribution, were measured from Computed Tomography scans. Secondly, the aggregates were simulated using a Perlin noise in spherical primitives, which adjusted their geometry until they achieved realistic morphologies and gradations. iDEM detects contacts between complex shapes, including concavities, and computes the interaction between large amounts of complex objects. Results show that the properties from the packing experiments and simulations are highly comparable. This paper demonstrates the capacity of the physics toolbox to simulate granular materials effectively.

This chapter deals with the materials and design aspects of asphalt pavements. In the first part of the chapter, some of the upcoming technologies arising out of recent research, since the last decade or so, are highlighted. The immediate research challenges are also identified. In the second part, possible future directions are discussed briefly.

In this paper, a proof of concept of a method is presented for the study of granular materials, such as asphalt, based on the use of a physics engine. To begin with, virtual aggregates are generated with randomized 3D shapes and a size distribution based on a chosen gradation curve. Then, the aggregates are placed in a constrained volume and subjected to a simulated vibration until satisfactory compaction is reached. Finally, the packed stone assembly obtained is saved as a 3D model, so that the virtual aggregates can be used for further studies such as the analysis of the void space in the material. All the steps in the method are described and discussed, along with the approximations made. Furthermore, an analysis of the void space is performed to determine if the method is able to generate air pores with realistic features. The analysis is performed by comparing the void space of a computationally packed aggregate assembly to that of a real asphalt core with the same aggregate gradation. The preliminary results obtained show that the modelling approach is able to represent effectively the air pores, thus, suggesting that further studies to advance this proof of concept should be conducted.

This paper summarizes theoretical and applied studies of the structure of mixtures, formulated as the packing of spheres with different sizes. The effects of the particle size and the shape (fine or coarse) on the packing density are described. We discuss the relationships between the particle size distribution and the packing properties. We also sketch the major approaches, which can be usefully applied in nanotechnologies for the modeling of a material structure. Such a kind of analysis can be used both in the theoretical consideration of material engineering problems and in the chemical industry. Potential applications of these results include a synthesis of nanomaterials, adsorbents, catalyst carriers and packings for chromatographic columns.

A three-dimensional aggregate generation and packing algorithm applicable for modeling asphalt mixture with high content of graded aggregates is presented in this paper. In the algorithm, arbitrary-shaped polyhedra are used to model aggregates, so that the effect of aggregate shape on the mechanical performance of asphalt mixture can be considered. The algorithm consists of two steps: Aggregate generation and packing. Polyhedra are created by extending triangular fundaments and treated as visualized aggregates after passing through convex control and sharpness judgment. After that, graded aggregates are taken out from the aggregate base and randomly packed in a given cylindrical or cubical region one by one equiprobably. Overlapping between nearby aggregates is avoided by the help of Boolean partition operation in ANSYS. Finally, some asphalt mixture samples with a given gradation are modeled as examples, and their effective elastic properties and creep behaviors under uniaxial compression are simulated.

Truncated spherical harmonic expansions are used to approximate the shape of 3D
star-shaped particles including a wide range of axially symmetric ellipsoids, cuboids, and over 40 000
real particles drawn from seven different material sources. This mathematical procedure enables any geometric property to be calculated for these star-shaped particles. Calculations are made of properties such as volume,
surface area, triaxial dimensions, the maximum inscribed sphere, and the minimum enclosing sphere, as well
as differential geometric properties such as surface normals and principal curvatures, and the values are compared
to the analytical values for well-characterized geometric shapes. We find that a particle's Krumbein triaxial dimensions, widely used in the sedimentary geology literature, are essentially identical numerically to the length, width, and thickness dimensions that are used to characterize gravel shape in the construction aggregate industry. Of these dimensions, we prove that the length is a lower bound on a particle's minimum enclosing sphere
diameter and that the thickness is an upper bound on its maximum inscribed sphere diameter. We examine the ``true sphericity'' and the shape entropy, and we also introduce a new sphericity factor based on the radius ratio of the maximum inscribed sphere to the minimum enclosing sphere. This bounding sphere ratio, which can be calculated numerically or approximated from macroscopic dimensions, has the advantage that it is less sensitive to surface roughness than the true sphericity. For roundness, we extend Wadell's classical 2D definition for particle silhouettes to 3D shapes and we also introduce a new roundness factor based on integrating the dot product of the surface position unit vector and the unit normal vector. Limited evidence suggests that the latter roundness factor more faithfully captures the common notion of roundness based on visual perception of particle shapes, and it is significantly simpler to calculate than the classical roundness factor.

The greater part of asphalt mixtures is composed of aggregates. This means that particular features, such as shape and angularity, are the primary factors that affect the development of the mechanical performance of asphalt pavements. In order to investigate the combined effect of grain shape and angularity on the packing and stability of an aggregate's assembly for asphalt mixes, the authors have performed an experimental program using 3D Discrete Element Method. The results obtained from triaxial tests and from statistical analysis of the distribution of particle-particle contact forces show that the grain shape and angularity significantly affect the assembly behaviour.

Microfine rock aggregates, formed naturally or in a crushing process, pass a #200 ASTM sieve, so have at least two orthogonal principal dimensions less than 75 μm, the sieve opening size. In this paper, for the first time, we capture true 3-D shape and size data of several different types of microfine aggregates, using X-ray microcomputed tomography (μCT) with a voxel size of 2 μm. This information is used to generate shape analyses of various kinds. Particle size distributions are also generated from the μCT data and quantitatively compared to the results of laser diffraction, which is the leading method for measuring particle size distributions of sub-millimeter size particles. By taking into account the actual particle shape, the differences between μCT and laser diffraction can be qualitatively explained.

The convex hull of a set of points is the smallest convex set that contains the points. This article presents a practical convex hull algorithm that combines the two-dimensional Quickhull Algorithm with the general-dimension Beneath-Beyond Algorithm. It is similar to the randomized, incremental algorithms for convex hull and Delaunay triangulation. We provide empirical evidence that the algorithm runs faster when the input contains nonextreme points and that it uses less memory. Computational geometry algorithms have traditionally assumed that input sets are well behaved. When an algorithm is implemented with floating-point arithmetic, this assumption can lead to serious errors. We briefly describe a solution to this problem when computing the convex hull in two, three, or four dimensions. The output is a set of "thick" facets that contain all possible exact convex hulls of the input. A variation is effective in five or more dimensions.

Ballast is an essential layer of the railroad track structure, and provides primarily drainage and load distribution. In general, ballast aggregates are considered as uniformly graded, angular shaped with crushed faces. However, various ballast aggregate gradations and particle shapes are in use yet their effects on ballast performances remain unknown. In previous designs and modeling practices, railroad ballast has usually been treated as a homogeneous and continuous layer. This approach is not suitable to model the deformation behavior of the particulate nature railroad ballast aggregates under dynamic moving loads. Further, continuum solutions do not take into account realistically the morphological characteristics of aggregates such as particle size distribution and shapes. A combined digital image and Discrete Element Modeling (DEM) methodology has been developed in this PhD thesis to study effects of aggregate particle size and morphological characteristics on ballast performances. The approach has been calibrated using actual ballast aggregates through laboratory shear box texts and validated by further laboratory as well as field experiments. Using the DEM ballast model, individual effects of aggregate particle size distributions and shape properties on railroad ballast strength, lateral stability, and settlement potential were studied. From the DEM simulation results, it was found that aggregate particle size distribution and shape have significant impact on ballast performances. Ballast with broader size distribution was shown to yield less settlement potential than ballast with more uniformly graded aggregates. Also, ballast with angular aggregate particles were found from the DEM simulations to have higher strength as well as better lateral stability than ballast with rounded aggregate particles due to better stone on stone contact and aggregate interlock. In summary, the developed DEM ballast model has been proven in this PhD research to be a promising tool for studying railroad ballast load and deformation characteristics and could lead to the ultimate goal of designing better “engineered ballast.”

The mechanical properties of concrete composites mainly depend on its ingredients and meso-structure, especially the shape, distribution, and grading of aggregates. Therefore, it is very important to establish realistic meso-scale models for concrete composites performance prediction and structural optimization design. However, there is only a few methods to generate models with high volume fraction in current studies. In this paper, a novel idea for numerical modeling, namely the aggregate expansion method, is used to establish more realistic 3D models with different volume fractions of convex and concave aggregates. The shrunken aggregates are first placed in an empty container, and then these aggregates are expanded to the predetermined sizes to obtain a numerical model. Using this approach can efficiently obtain a high volume fraction model with randomly distributed aggregates. In addition, realistic aggregates are generated according to the statistical data of actual aggregates shapes. A series of statistical data show that the randomness of aggregates in the space before and after expansion is still maintained. At last, the simulation results of 3D numerical models with different volume fractions under uniaxial tension are calculated. The consistency between the simulation results and experimental data verifies the good accuracy of the models.

This paper investigates the effects of air void topology on hydraulic conductivity in asphalt mixtures with porosity in the range 14%–31%. Virtual asphalt pore networks were generated using the Intersected Stacked Air voids (ISA) method, with its parameters being automatically adjusted by the means of a differential evolution optimisation algorithm, and then 3D printed using transparent resin. Permeability tests were conducted on the resin samples to understand the effects of pore topology on hydraulic conductivity. Moreover, the pore networks generated virtually were compared to real asphalt pore networks captured via X-ray Computed Tomography (CT) scans. The optimised ISA method was able to generate realistic 3D pore networks corresponding to those seen in asphalt mixtures in term of visual, topological, statistical and air void shape properties. It was found that, in the range of porous asphalt materials investigated in this research, the high dispersion in hydraulic conductivity at constant air void content is a function of the average air void diameter. Finally, the relationship between average void diameter and the maximum aggregate size and gradation in porous asphalt materials was investigated.

In this study, a two-dimensional Voronoi element based – explicit numerical manifold method (VE-ENMM) is developed as a new approach to investigate the acoustic emission characteristics during the failure process of intact rocks. The micro-granular structures of the intact rocks are approximated by the random Voronoi polygons and the interactions among rock grains are interpreted using a modified interface contact model. A new acoustic emission (AE) monitoring technique considering the clustering effect of micro-cracks is developed based on the explicit time integration scheme of numerical manifold method. With the newly developed approach, a series of numerical simulations are carried out. Firstly, numerical uniaxial compressive and Brazilian tests are conducted to validate the new approach on simulating micro-/macro-mechanical behaviors of granite samples. After that, the acoustic event properties, such as time evolution, spatial clustering and frequency-magnitude distribution of AE events during the failure process under uniaxial compression are studied in details. Simulation results show that the development of acoustic emissions is in good consistence with the damage evolution process of the numerical model, which may help to reveal the micro-fracturing mechanism of intact rocks in terms of seismic energy dissipation. To further illustrate the capability of the developed approach in monitoring the failure process as well as failure characteristics during TBM tunnel excavation, an additional numerical simulation is conducted and the fracturing behaviors as well as the related AE properties of the surrounding rock mass during TBM tunnelling are investigated.

To promote the use of unconventional coarse aggregates in cementitious materials, the authors carried out experiments on concrete mixtures containing 100% unconventional aggregates, either industrial by-products (sintered fly ash, crumb rubber and copper slag) or C&D waste (blue brick), as replacements for normal coarse aggregates in concrete and, to determine the mechanical performance and non destructive properties of concrete containing these aggregates. In addition, the micro-mechanical damage behaviour of the prepared mixtures under drop-weight impact loading were quantitatively analyzed using the X-ray computed tomography coupled with digital image analysis based on the changes in the air void distributions before and after the loading. It was proven that one effect of the aggregate on the resulting damage after impact loading is seen in the change in the porosity which is manifested in the level of pore connectivity from a micro-structure point of view. It was also concluded that the hydrophobic nature, softness, porosity and rigidity of the unconventional aggregates are of paramount importance for the performance and design of concrete with these aggregates.

Asphalt mixture usually needs compaction prior to servicing in field. Traditionally, finite element methods cannot simulate the compaction of asphalt mixture in field. Although discrete element methods (DEM) are able to describe such a process, the intrusion among aggregates always exists and influences the calculation accuracy. Additionally, the central difference method used in DEM requires very fine elements, which significantly jeopardizes the calculation efficiency. This study proposed an innovative systematic method to generate virtual asphalt mixture based on random aggregate modeling method and virtual physics engine theory. The aggregates were virtually generated with random aggregate modeling methods and imported into the virtual physics engine, where the movements of aggregates in asphalt concrete during compaction was simulated. The coordinates of aggregates after compaction were extracted, which were incorporated into the Convex Hull Algorithm to determine the new locations of aggregates after compaction. The original contribution of this study is that a pre-processing method of generating virtual asphalt concrete was proposed, which can successfully introduce compaction of asphalt mixture into finite element models and solve the intrusion problem of aggregates. The dynamic modulus of asphalt concrete simulated in finite element method (FEM) based on this modeling method was found much closer to the experimental results, comparing to the traditional analytic methods. It indicates the proposed method valid in generating virtual asphalt concrete in FEM.

This study evaluates the influence of morphological properties of aggregates on the mechanical behavior of bituminous mixtures. For that, two aggregates with different characteristics, i.e., round river gravel and crushed gneiss, were used in the research. Laboratory tests were conducted to characterize morphological properties of the aggregates following traditional methodologies and using a modern image analysis system, AIMS 2. Six asphalt mixtures containing different proportions of gravel and crushed gneiss were designed according to the Superpave methodology and evaluated in mechanical performance tests. The results obtained indicated that aggregate morphological characteristics, especially those of coarse particles, are strongly correlated with the resistance to rutting of the asphalt mixtures. In addition, AIMS 2 was shown to provide more direct and scientific measurements of aggregate morphological characteristics that present higher correlations with the mixture performance than traditional methodologies. Finally, the results also demonstrated that the aggregate surface texture is highly correlated to the performance of the mixtures and should be carefully considered in aggregate and asphalt mixture specifications.

Aggregate skeleton in asphalt concrete mixtures plays a significant role in the pavement performance. However, the mechanical roles for different-sized particles in the aggregate skeleton have not been fully revealed due to the limitations of physical techniques. This study utilizes a numerical simulation approach to evaluate aggregate structure characteristics and their resistance to deformation. Using the discrete element method (DEM), a three-dimensional (3D) aggregate blend was generated with due consideration of the gradation. The blend was employed to simulate the penetration test of aggregate blends with different friction coefficients of 0.1, 0.2, 0.3, 0.4 and 0.5, respectively. The determination of the friction coefficient and the validation of DEM model were further conducted by laboratory experiments. Using the validated DEM model, penetration tests of five uniform blends and nine graded blends were simulated. External applied force (i.e., penetration force), penetration displacement, contact force, contact number and force taken by aggregate particles of different sizes were calculated using the DEM simulation to explore the mechanical characteristics of aggregate particle. This study demonstrated that the aggregate size plays an important role on the mechanical performance of aggregate skeleton. The results of this research can be applied to optimize the mix design of asphalt concrete and to further improve the aggregate gradation design.

This paper presents a study of the micromechanical behaviour of crushable soils. For a single grain loaded diametrically between flat platens, data are presented for the tensile strengths of particles of different size and mineralogy. These data are shown to be consistent with Weibull statistics of brittle fracture. Triaxial tests on different soils of equal relative density show that the dilatational component of internal angle of friction reduces logarithmically with mean effective stress normalized by grain tensile strength. The tensile strength of grains is also shown to govern normal compression. For a sample of uniform grains under uniaxial compression, the yield stress is related to the average grain tensile strength. If particles fracture such that the smallest particles are in geometrically self-similar configurations under increasing macroscopic stress, with a constant probability of fracture, a fractal geometry evolves with the successive fracture of the smallest grains, in agreement with the available data. A new work equation predicts that the evolution of a fractal geometry gives rise to a linear compression line when voids ratio is plotted against the logarithm of macroscopic stress, in agreement with published data.

In current practice of mixture design, volumetric properties such as voids and binder content along with mechanical properties such as modulus or rutting resistance are used as the main quality indicators. Visualisation is an important tool that has not been widely used in asphalt mixtures. As part of the Reunion Internationale des Laboratoires et Experts des Materiaux activities, the aggregate structure has been identified as a possible important mixture characteristic in need of measuring and quantifying. This paper is a report on part of this effort. Software for processing and analysing two-dimensional images of asphalt concrete mixtures to provide information about the aggregate structure within a mix was developed. Images with accompanying volumetrics and gradation information can be processed with the software and a virtual sieve analysis of aggregates within the image is performed to verify a match with known measured gradations. Once images were successfully processed, analysis is performed to determine the number of contact points between aggregates as well as radial distribution and orientation of each aggregate. Segregation of aggregates within each specimen was also determined. Mixtures with a broad range of variables were compacted in the laboratory, using a number of compaction methods of various countries. In addition, mixtures with various nominal maximum aggregate sizes, aggregate type (limestone or gravel) and design ESALs (E-3 or E-10) were compacted in the US gyratory compactor, using two pressures (600 and 300 kPa) and two temperature levels (120°C and 60°C). Results indicate that the aggregate structure is affected by compaction methods and conditions although volumetrics are very similar. The results show that a fresh look at evaluating the aggregate structure within mixtures is required.

The microfabric discrete element modeling (MDEM) approach is used herein to predict the asphalt mixture complex modulus in extension/compression across a range of test temperatures and load frequencies. The method allows various constitutive models to be employed to describe particle and interface properties, such as normal and shear stiffness and strength. An uncalibrated two-dimensional (2-D) model was developed, and complex modulus predictions were compared to theoretical bounds on moduli. As expected, the uncalibrated 2-D model underestimates the significant stiffening effects of the coarse aggregate skeletal structure and predictions are found to be near the lower theoretical bounds, well below experimentally determined moduli. A technique was developed to calibrate the MDEM model to experimental results by dilating aggregates to create additional aggregate contact, which is believed to be more representative of the actual three-dimensional behavior. This method is shown to provide better modulus estimates across a range of test temperatures and load frequencies compared to more traditional calibration methods. As future modeling efforts are extended to three dimensions, the degree of model calibration required should be greatly reduced.

Granular materials occur almost everywhere in nature, and are actively studied in many fields of research, from food industry to planetary science. One approach to the study of granular media, the continuum approach, attempts to find a constitutive law that determines the material's flow, or strain, under applied stress. The main difficulty with this approach is that granular systems exhibit different behavior under different conditions, behaving at times as an elastic solid (e.g. pile of sand), at times as a viscous fluid (e.g. when poured), or even as a gas (e.g. when shaken). Even if all these physics are accounted for, numerical implementation is made difficult by the wide and often discontinuous ranges in continuum density and sound speed. A different approach is Discrete Element Modeling (DEM). Here the goal is to directly model every grain in the system as a rigid body subject to various body and surface forces. The advantage of this method is that it treats all of the above regimes in the same way, and can easily deal with a system moving back and forth between regimes. But as a granular system typically contains a multitude of individual grains, the direct integration of the system can be very computationally expensive. For this reason most DEM codes are limited to spherical grains of uniform size. However, spherical grains often cannot replicate the behavior of real world granular systems. A simple pile of spherical grains, for example, relies on static friction alone to keep its shape, while in reality a pile of irregular grains can maintain a much steeper angle by interlocking force chains. In the present study we employ a commercial DEM, nVidia's PhysX Engine, originally designed for the game and animation industry, to simulate complex granular flows with irregular, non-spherical grains. This engine runs as a multi threaded process and can be GPU accelerated. We demonstrate the code's ability to physically model granular materials in the three regimes mentioned above: (1) a static and steep granular pile; (2) granular flow with a complex velocity field; and (3) an agitated granular pile resulting in size based segregation. We compare our simulations to laboratory experiments in the first and third regimes, and to a known empirical constitutive law (Jop et al. 2006) in the second. We discuss application of this code in studies of several planetary systems, including analysis of the tensile strength of comets from evidence of tidal disruption, and bulking and banding on rubble-pile asteroids, as an indication of their seismic history.

An effective computer generation method is presented in this paper to more perfectly and rapidly generate the random distribution domains with large numbers of grains (pores). At first, the geometries of heterogeneous grains and the stationary random distribution model with large numbers of grains are defined. Second, the effective computer generation method, including compactness algorithm and selection algorithm, is described in detail. Then the effectiveness of the generation method and the comparison with the take-and-place method are given, and some examples with different geometries of grains in 2- and 3-dimension cases are illustrated. The computer generation method in this paper has been applied to the computation of effective heat transfer behavior for the composites of the random distribution with large numbers of grains, and some numerical results are demonstrated. The generation method in this paper is able to make the generated samples hold better stochastic property, and it is also suitable to generating samples subjected to non-uniform probability model.

The properties of composites made by placing inclusions in a matrix are often controlled by the shape and size of the particles used. Mathematically, characterizing the shape of particles in three dimensions is not a particularly easy task, especially when the particle, for whatever reason, cannot be readily visualized. But, even when particles can be visualized, as in the case of aggregates used in concrete, three-dimensional (3-D) randomness of the particles can make mathematical characterization difficult. This paper describes a mathematical procedure using spherical harmonic functions that can completely characterize concrete aggregate particles and other particles of the same nature. The original 3-D particle images are acquired via X-ray tomography. Three main consequences of the availability of this procedure are mathematical classification of the shape of aggregates from different sources, comparison of composite performance properties to precise morphological aspects of particles, and incorporation of random particles into many-particle computational models.

Porous materials due to their complex geometry are difficult to be examined by FEM-based approaches and usually are simulated by simplified geometrical models. In the present paper a novel procedure for describing the solid geometry of open-cell foams is introduced, facilitating the establishment of a corresponding FEM model for simulating the material behavior in micro-tension. Open-cell Al-foams were fabricated using the polymer impregnating method. A serial sectioning image-based process is described to capture, reproduce and visualize the exact three-dimensional (3D) microstructure of the examined foam. The generated 3D geometry of the Al-foam, derived from the synthesis of digital cross sectional images of the foam, was appropriately adjusted to build a FE model simulating the deformation conditions of the Al-foam under micro-tension loads. The obtained results render possible the visualisation of the stress fields in the Al-foam, allowing for a full investigation of its mechanical behavior.

Physical particle packing is becoming a hot topic in concrete technology as more and more types of granular materials are used in concrete either for ecological or for engineering purposes. Although various analytical methods have been developed for optimum mixture design, comprehensive information on particle packing properties is still missing, e.g. on the impact of the packing method on such properties. Computer simulation therefore provides a promising perspective for particle packing simulation. However, developing flexible algorithms for simulation of arbitrary shaped particle packing still remains a challenge for concrete researches. This study aim offers a solution for these problems. The strategy of simulating particles of arbitrary shape is based on an experimental approach to this problem. The simulation strategies are thereupon implemented into a DEM-based dynamic concurrent algorithm-based simulation (CAS) approach for particle packing. Finally, influences of particle shape, particle size and packing method on packing density are evaluated and discussed. This methodology renders possible producing virtual concrete on meso-level. In combination with FEM, the influence of particle packing on mechanical properties of concrete has been assessed in this way. In the same way the simulation of cement particle packing can be realized on micro-level. Upon simulation of hydration, the capacity of self-healing of cracks due to unhydrated cement is assessed by a DEM-based simulation system for different cement types and packing densities.

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