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This paper explores the influence of incorporating microencapsulated Phase Change Materials (MPCM) on the evolution of both mechanical behavior and meso-structural damage in mortars in response to prolonged freeze-thaw conditions, employing Differential Scanning Calorimetry (DSC) for thermal analysis, comprehensive mechanical performance experiments, and high-resolution X-ray Tomography (XRT) to assess internal damage evolution. The DSC results highlight the thermoregulatory effect of MPCM, which influences the performance of the mortars under freeze-thaw conditions. Mechanical experiments show a trade-off between initial strength and long-term durability, with MPCM-enhanced mortars demonstrating significantly reduced strength loss when exposed to extended freeze-thaw cycles compared to control mortars. XRT images further corroborate these outcomes, illustrating less pronounced meso-structural degradation in MPCM-containing samples when exposed to extended freeze-thaw cycles. Overall, the findings in this paper reveal that MPCM-infused mortars, particularly those with higher MPCM concentrations, exhibit significantly reduced internal damage and maintain better mechanical integrity compared to control samples. Collectively, these insights suggest that MPCM integration could be a pivotal strategy for designing more resilient and durable cementitious composites, paving the way for future advancements in construction practices tailored to withstand the challenges of freeze-thaw conditions. • MPCM-incorporation results in prolonged and consistent latent heat release in mortars. • MPCMs reduce ice formation during crystallization, mitigating freeze-thaw damage. • MPCM-integrated mortars show reduced strength loss over prolonged freeze-thaw cycles. • X-ray Tomography reveals less microstructural freeze-thaw damage in MPCM-mortars. [ABSTRACT FROM AUTHOR]

The size effect is a very important attribute of concrete fracture and damage. The classic Bažant size effect law is generally given based on the dimensionless parameter and transitional structure size. However, the determination of these parameters is still speculative, which causes directly the lack of consensus on concrete fracture modeling. The influence of concrete meso-structure geometrical characteristics on its splitting tensile strength and the corresponding size effect was investigated, based on the fractal dimension and meso-scale simulation method, in this study. The simulation results represented that the increased meso-structure's fractal dimension or increased coarse aggregate content would both cause the splitting tensile strength to decrease. A lower coarse aggregate content or a smaller meso-structure's fractal dimension would both cause a remarkable size effect. Furthermore, the dimensionless parameter and transitional structure size in size effect law introduced by Bažant were established quantitatively. This study contributes to the characterization of the geometric form of the concrete meso-structure and the understanding of its influence on the macro behavior of concrete. The advantage of the concrete meso-structure's fractal dimension was also demonstrated. • Splitting tensile strength decreases with increasing meso-structure fractal dimension. • Splitting tensile strength decreases with increasing coarse aggregate content. • A smaller meso-structure's fractal dimension cause a remarkable size effect. • A lower coarse aggregate content cause a remarkable size effect. • Dimensionless parameters in Bažant's size effect law are established quantitatively. [ABSTRACT FROM AUTHOR]

Meso-structure is one of the major sources of macro-performance in asphalt mixtures. The research on aggregate distribution state is of great significance for the further improvement of asphalt mixture macro-performance. However, the variations of research methods among prior works hamper the deduction of the holistic potential and promising directions of coarse aggregate distribution analysis from current research findings. This work comprehensively verified the quantifying ability of aggregate distribution state indices and their correlation with rutting performance under an advanced digital image processing technique and a wide range of asphalt mixture types, and aims to provide a reference of the holistic potential and promising directions of coarse aggregate distribution analysis for subsequent research. To this end, eleven typical asphalt mixtures' aggregate distribution state and rutting performance were measured, quantified, and correlated. The results show that K p e nears or more than 0.56 can be the sign of coarse aggregates effectively interlocked while it nears or less than 0.26 is the opposite; U a r e a nears or less than 2 % can be the sign of reaching a coarse aggregate distribution equilibrium; Δ o r i e n approaches 6.21 can be the sign of reaching a coarse aggregate orientation equilibrium; mixtures with a nominal maximum aggregate size of 10 mm are disabled in gathering contact chains. Moreover, these coarse aggregate distribution state quantifying indices proposed in existing research can indeed describe the meso-structural features of asphalt mixtures to a certain extent. However, these indices fail to capture the underlying meso-structural features relating to rutting performance and lead to limited applicability. Furthermore, the poor performance of these coarse aggregate distribution state quantifying indices in the global fitting mainly comes from their incompatibility with changes in nominal maximum aggregate size. • Meso-structural indices verification under the same conditions and various samples • The indices can reflect structural states but weakly correlate to macro-performance • The poor performance in correlation is mainly due to the variations in NMAS [ABSTRACT FROM AUTHOR]

Unlike synthetic elastomers, the structure of natural rubber (NR) evolves (dynamic structuring) and so do its properties during the storage before reaching an industrial mixer. In the rubber industry this is known as storage hardening. NR samples from three genotypes (GT1, RRIM600 and PB235) were subjected to different levels of structuring by varying the structuring time (t) on phosphorus pentoxide (0 < t < 28 h). Storage hardening (ΔP) of the samples was then determined by measuring the increase in Wallace plasticity (P) (macro-scale) and by analyzing their mesostructure (meso-scale) using asymmetrical flow field flow fractionation (A4F). Monitoring ΔP as a function of structuring time revealed a diversity of behaviors specific to the genotype from which the rubber originated. For example, NR samples from genotypes GT1 and PB235 exhibited different kinetics for t < 12 h, an increase in ΔP with structuring time, but reached the same final plateau (t > 12 h). An A4F analysis of the samples was used to quantify the fraction of microaggregates smaller than 1 μm (microgel <1μ). The microgel <1μ rate decreased with structuring time to varying extents depending on the genotype. A very significant negative relationship was found between ΔP and the microgel <1μ rate, indicating that the NR samples that hardened the most contained the lowest microgel <1μ rate, but the highest macrogel rate. • Storage hardening kinetics were monitored on a meso-scale (mesostructure) and macro-scale (Wallace plasticity). • Different size fractions of microaggregates were quantified by A4F. • The smallest microaggregates reacted together to build larger entities, with different kinetics and degrees depending on the genotype. • The more the sample hardened, the less was the fraction of microaggregates smaller than 1 μm (microgel <1μ) it contained. [ABSTRACT FROM AUTHOR]

Cemented granular materials play an important role in both natural and engineered structures, as they are able to resist traction forces. However, modeling the mechanical behavior of such materials is still challenging, and most of existing constitutive models follow phenomenological approaches that unavoidably disregard the microstructural mechanisms taking place on the bonded grains scale. This paper presents a multiscale approach applicable to any kind of granular materials with solid bonds between particles. Inspired from the H -model, this approach allows simulating the behavior of cemented materials along various loading paths, by describing the elementary mechanisms taking place between bonded grains. In particular, the effect of local bond failure process on the macroscopic response of the whole specimen is investigated according to the bond strength characteristics. [ABSTRACT FROM AUTHOR]

The deformation mechanism related to the initial relative density and uniformity of Cu W composite powders under quasi-static compression was investigated by multi-particle finite element method. The results show that under the same pressure, the relative density of powder increases with the increase of initial relative density or the uniformity of composite powders. The densification processes can be divided into three stages, namely particle rearrangement, Cu particle deformation and W particle deformation. Pores are mainly filled by the rearrangement of particles and the deformation of Cu particles. The rearrangement and deformation of particles are quantitatively characterized by introducing the mean rotation degree and the mean equivalent strain of powders. It is found that smaller voids formed in the initial denser powder are easily filled by the deformation of adjacent particles during compaction. Strong force chains formed by the contact of W particles severely hinder the compression, resulting in large porosity. Unlabelled Image • Multi-particle finite element models of Cu W composite powders are constructed. • Multi-scale analysis on the effects of initial packing structure is carried out. • Pores are mainly filled by particle rearrangement and Cu particle deformation. • Particle rotation and deformation are quantitatively characterized. • The deformation mechanisms of local packing structures are explored. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the geometric form of concrete meso-structure is important because it is associated with the complex and random mechanical behavior of concrete. In this study, the coarse aggregate content and fractal dimension were used to describe the geometric form of concrete at the meso-level. After validating the simulation results through a comparison with the experimental results, a group of meso-models of concrete with various fractal dimensions and coarse aggregate contents were simulated under compression. The simulation and experimental results suggested that the compressive strength increased with decreasing fractal dimension and increasing coarse aggregate content; the strain corresponding to the maximum stress decreased with decreasing fractal dimension and increasing coarse aggregate content. Also, increasing the fractal dimension can cause the elastic modulus to slightly decrease. The comprehensive consideration of the geometric form of meso-structure can provide a powerful tool for understanding the observed macroscopic behavior of concrete. Image 1 [ABSTRACT FROM AUTHOR]

The accurate characterization of the internal structure of asphalt mixture is significant to understand its mechanical behavior. Combining imaging with neutrons and X-rays is beneficial for investigations of asphalt mixture meso-structure as their different attenuation coefficients for the main components of the asphalt mixture. To compensate for the shortcomings of only using X-ray imaging to identify asphalt mixture meso-structure, this study aims to improve the identification of the meso-structure of asphalt mixture using the complementarity of neutron and X-ray tomography. Due to the lack of experience in using neutron imaging to test the asphalt mixture meso-structure, this paper studied the influencing factors of neutron imaging test on asphalt mixture. To obtain the fusion image, a registration method of the neutron image and X-ray image and an acquisition method of fusion image were proposed. The volume fractions and area fractions of three phases (air voids, aggregates and mortar) obtained from the fusion images were compared with those obtained from neutron and X-ray images. The proposed method was validated by comparing the volume fractions computed from images and the actual values. These efforts contribute to improving the identification of the internal meso-structure of asphalt mixture. • The influencing factors on neutron imaging testing of asphalt mixture were analyzed. • A registration and fusion method for neutron and X-ray images was proposed. • The meso-structure identification of asphalt mixture was improved by combined imaging. [ABSTRACT FROM AUTHOR]

Abstract In situ quantification of the meso-structural changes in block-in-matrix-soils (bimsoil) is crucial for stability predictions. While the macroscopic failure of bimsoil has been widely studied, the physical meso-scale mechanisms governing bimsoil deformation have not been well understood. Here, high energy X-ray computed tomography (CT) measurements were performed on a bimsoil sample with a rock block percentage (RBP) of 40% under uniaxial compression to collect three-dimensional data for the sample's meso-damage evolution. The 3D pattern of the sample deformation was imaged in real-time, and meso-structural changes are visualized by the rendered CT images. The data showed that cracks propagated by passing rock blocks, leading to a macroscopic fracture with a well-developed twisting characteristic. The crack rose diagram reveals the propagation path of the cracks, which are mostly parallel to the loading direction. In addition, interlocking occurs during the propagation of cracks, which determined the curved morphology of the fracture plane. Moreover, the fractal 3D digital image analysis quantifies the complexity of the crack distribution with increasing sample deformation. This work demonstrates the strong influence of local mechanical variations due to existing rock blocks on the crack propagation in bimsoil. Highlights • In situ 3D Visualization of meso-structural changes in bimsoil during uniaxial deformation. • Spatial well-developed tortuous cracks are influenced by the interlocking. • Stress dilatation caused by localization deformation is mainly controlled by the rock block motion. • 3D digital image analysis quantificationally indicates the complexity of crack distribution as deformation grows. [ABSTRACT FROM AUTHOR]

The shear band issue in frictional granular materials has attracted many concerns and perspectives at the micro- and meso-scale have been involved to analyze this problem. At the microscopic level, the contact sliding is associated with the plastic dissipation; while at the mesoscopic level, force chains and loops will change in geometry and topology as deviatoric loads are applied. This paper concerns the unstable behaviors from these two scales which could be regarded as loss of sustainability of internal structures, and tries to relate the microscopic sliding and the mesostructural evolutions. Firstly the heterogeneity generation is identified for the granular assembly subjected to the biaxial loading using DEM. Then the internal structure evolutions and interrelationships are investigated, leading to these main conclusions: sliding contacts are not within force chain structures but will be strongly influenced by the force chain buckling; exchanges within grain loops appear during the whole loading process and differ for domains inside and outside the shear band; the topological dilations are related to the higher probability of contact sliding. In brief, the microscopic dissipative behavior as the contact sliding plays an important role in the mesostructural organizations. [ABSTRACT FROM AUTHOR]

The effect of heterogeneity in meso level geometric and material properties on compressive strength and size effect in concrete cylinders is investigated. Crucial meso geometric parameters are identified by studying specimens belonging to three distinct gradations and spanning a range of sizes. A statistical analysis is used to account for dependencies between the parameters. Compressive strength and size effect are seen to depend on the degree of heterogeneity of critical meso parameters. For moderately sized specimens, major trends in the size effect are seen to be almost entirely explained by heterogeneity in the meso geometry; heterogeneity in meso level material properties is seen to be of comparatively less importance. [ABSTRACT FROM AUTHOR]

• The concept of continuous printing filament hypothesis is proposed through mesoscopic analysis. • A novel progressive failure model is established to predict the intra-layer failure process of FFF 3D printing GFRP. • Mechanical parameters of FFF 3D printing GFRP are determined by designing specific specimens and tests. • The distribution and regularities of intra-layer failure of FFF 3D printing GFRP are explored experimentally. The deficiency of failure analysis methods severely hinders the civil engineering application of Fused Filament Fabrication (FFF) 3D printing composites. In order to comprehensively investigate the failure process, this paper innovatively proposes the concept of continuous printing filament hypothesis based on mesoscopic analysis. This hypothesis serves to characterize the interconnection status between glass fiber reinforced polymer (GFRP) filaments during FFF 3D printing. Building upon this hypothesis, a progressive failure model is established, which can predict the intra-layer failure process under axial quasi-static load accurately. In the failure model, both Mode-2D and Mode-3D failure criteria are employed to pinpoint intra-layer damage initiation, while damage evolution is depicted using a stiffness reduction mode based on the fracture energy criterion. Simultaneously, the fundamental orthotropic mechanical parameters are examined, and 24 variations of printing laminates are meticulously designed. The ultimate tensile strengths (UTS), encompassing both cross-stacking (2/8, 4/6, 5/5) and angle-stacking (30°, 45°, 60°), are tested and simulated using the progressive failure method established during this study. Experimental results show that the lower layers of composites exhibit stronger ultimate resistance due to their layer-by-layer characteristics. Compared to the experimental results, all the relative errors of UTS predicted by Mode-3D are less than 15%. Therefore, the accuracy and predictive capacity of the progressive failure model are affirmed by the experimental data. [ABSTRACT FROM AUTHOR]

• The interaction between polymer and fiber on matrix strength is analyzed. • The bridging effect of fibers can slow down crack development and improve the integrity of the specimen at damage. • The polymer products bonding film between fiber and matrix is observed. • The increase of the number of cracks in the failure stage shows three stages of change. Insufficient adhesion of the fibers to the concrete matrix causes the fibers to be pulled out under load, making the fiber concrete unable to meet the support requirements of deep roadways. Basalt fiber (BF) and polymers were selected for the design of mechanical experiments and studied using CT scanning, scanning electron microscopy (SEM) and discrete element simulation. The results show that the fiber mainly affects the compressive and flexural strength of concrete, and the polymer has an effect on the splitting tensile strength of the fibers. From the fine viewpoint, the increase in BF admixture resulted in the conversion of medium pores to small pores within the concrete. Incorporation of polymers results in a smooth polymer film inside the concrete matrix and more hydration products on the surface of the BF to enhance the adhesion of the BF to the concrete matrix. In the discrete element simulation, the fracture evolution can be divided into three stages and the angle of the microscopic fracture is mainly distributed in the range of 60°∼130°. Under loading, BF shares the stress of the matrix and presents itself as a tensile force at its tip, and the increase in BF doping improves the integrity of the specimen at damage. [ABSTRACT FROM AUTHOR]

Concrete meso-structure significantly affects its mechanical property, as crack generally starts and develops basically along the interface between aggregate and mortar on the meso-scale. The cracking path is highly dependent on the interface structure, the main component of concrete meso-structure. Since the interface is formed due to aggregate distributing in mortar mix, the relation between aggregate surface area and interface perimeter could be considered as a representative index of concrete meso-structure. As it is too complicated to adopt traditional methods to represent this relation, in order to better understanding the influence of meso-structure change on mechanical property, fractal theory is introduced to explore the relationship, with the main focus on the characteristics of the concrete meso-structure and its influence on mechanical property. Results show that the specimen size has great impact on meso-structure and mechanical property, while the influence of aggregate volume fraction can be neglected. It is more obvious in larger specimen size that aggregate volume fraction increase could contribute a lot to bearing capacity improving and whole stress level descending. Besides, aggregate volume fraction increase could improve the local cracking stress, but reduce the cracking strain, resulting in cracking brittleness. [ABSTRACT FROM AUTHOR]

Mechanical pipe insulation systems are commonly used around cold pipes and play significant roles in maintaining the efficiency of building HVAC&R systems. However, thermal insulation systems normally become moist after years of service and various types of insulation are found to have different thermal performances even with the same amount of moisture ingress. Such inconsistencies are possibly caused by the internal structure of the materials and the location of water accumulation. In this paper, a full-scale fractal approach was proposed to simulate the thermal performance of closed-cell insulation by considering meso-structure parameters and moisture with different distribution patterns. Based on the validated model, sensitivity analysis was further discussed to determine the impacts of main meso-structure parameters and physical properties, such as fractal dimension, open porosity, size ratio of cells, thermal conductivity of gas and solid matrix, on the values of thermal conductivity ratio (TCR) with moisture ingress. [ABSTRACT FROM AUTHOR]

Non-obstructive Particle Damping (NOPD) is widely used as an effective passive damping technique. However, the understanding of the energy dissipation mechanism and meso-scale behavior of the granular system in NOPD is not sufficiently in-depth. In this paper, the damping effectiveness of NOPD, as represented by the contour plot of the loss factor, was analyzed in combination with the motion modes of the granular system, and the energy dissipation mechanism was illustrated at the meso-scale. The results show that the different motion modes of rheology behaviors and meso-structure contribute to the variations in the damping effectiveness. Generally, the NOPD has the optimal damping effectiveness in the buoyancy convection state. The purpose of this paper is to provide a better understanding and theory support for the design and application of NOPD. [ABSTRACT FROM AUTHOR]

• The real shape of particles was considered in the modeling process. • Analyze the effect of particles shape on the overall of the mixture skeleton and the particles themselves. • U 3 D is proposed to evaluate the particles distribution uniformity. Mixture skeleton is the main body bearing the load of asphalt mixture, and particle shape is an important factor affecting the meso -structure of mixture skeleton. Based on the minimum bounding box theory, obtain particles geometry by Digital Image Processing (DIP), and calculate the shape indices: angularity index (A 1) and flat-elongated index (F 1). By using discrete element method (DEM) software PFC3D , five mixture skeletons were built with different integrated angularity (A m) and flat-elongated particles content (F m). And analyzed air void, particles distribution and particle angle of mixture skeletons. The results show that A m has no obvious effect on the air void ratio, but increasing F m can increase the air void ratio. In addition, the index U 3 D was proposed to evaluate particles distribution on 3D scale, and found that small particles are more likely to have better distribution uniformity. And uniformity of particles distribution in mixture skeleton will increase with the increase of A m. For particles, angle will be increase with the increase of F 1. However, if F 1 is too large, particle angle will decrease due to the embedding effect. These studies and results analyzed that how can particles shape affect meso -structure of mixture skeleton. [ABSTRACT FROM AUTHOR]

• The meso‑structural model of unsaturated soils with three phases is reasonably reconstructed in a finite-element model based on the identified meso‑structure characteristics. • The wetting behavior between soil particles and water is effectively considered in the reconstructed meso‑structural model. • The finite-element method and the Monte Carlo simulation are coupled to account for the randomness in the characteristics of geomaterials. • Parametric analyses are conducted to investigate the effects of solid type, porosity, degree of saturation, and hydrophilia on the thermal conductivity of unsaturated soils. Unsaturated soils are three-phase porous materials that consist of the solid phase, the liquid phase and the gas phase. While accurate predictions to the thermal conductivity of unsaturated soils are crucial for the analysis and design of geothermal systems, the distribution characteristics of the different phases can also significantly affect the thermal performance. In addition, the fact that soils are heterogeneous materials also adds to the challenges in the evaluation of the thermal conductivity of unsaturated soils. In this paper, a methodology is proposed to calculate the thermal conductivity of unsaturated soils. This methodology starts from identifying representative soil parameters based on microscopy images of soil specimens. The meso‑structures that consist of the different phases are then reconstructed in a finite-element model based on the identified characteristics. The Monte-Carlo-based finite-element analyses are then carried out to calculate the thermal conductivity of unsaturated soils while considering the wetting behavior between the solid and liquid phases, which is characterized using the hydrophilia coefficient. After validating the methodology using both the experimental and numerical results reported in the literature, a parametric analysis is conducted. The results indicate that a high quartz content improves the heat transfer, but the quartz content does not affect the heat transfer skeleton. Furthermore, an increase in the solid content and degree of saturation results in an increase in the density of the heat transfer skeleton, which leads to enhanced heat transfer efficiency. A reduction in the hydrophilia coefficient and the formation of liquid-bridges have a similar effect. Last, the effects of wetting are more evident in soils with high porosity and a low degree of saturation. [ABSTRACT FROM AUTHOR]

• Investigation of the mechanical response of asphalt concrete patch structures at the meso -level. • Exploring the behavior mechanism of new and old asphalt concrete cracking after pothole patch through three-point bending test. • Simulation of viscoelasticity of asphalt mortar with cohesive units with a thickness of zero. • Analysis of the effect of aggregate and mortar on patching structural damage through simulation. Pothole is one of the most serious distresses of steel bridge deck pavement (SBDP). Due to the particular structural condition, severe environment, and heavy traffic load, patch failure has become very common in SBDP. To investigate the effects of different patch materials on the patched structures, this paper explored the behavioral mechanisms of new and old asphalt concrete cracking after pothole patching and the effects of the different types of patch materials through three-point bending (3 PB) tests and finite element (FE) simulation at the meso -level. The results show that changes in aggregate modulus, asphalt mortar modulus, and asphalt mortar bond strength affect the flexural-tensile property and crack location. Cracks are more likely to occur on the side with less asphalt mortar bond strength. When the mortar bond strength of patch material is much greater than that of old asphalt concrete, flexural-tensile strength will be improved, and the effect of the internal bond strength of the mortar is much more significant than that of the bond strength between the mortar and the aggregate. To improve flexural-tensile strength, priority should be given to changing the mortar modulus and its bond strength. [ABSTRACT FROM AUTHOR]

A constitutive model of concrete is proposed based on the mixture theory of porous media within thermodynamic framework. By treating concrete as a multi-phase multi-component mixture, we constructed the constitutive functions for elastic, interfacial, and plastic strain energy respectively. A constitutive law of concrete accommodating internal micro-cracks and interfacial boundaries was established. The peak stress predicted with the developed model depends primarily on the volume ratio of aggregate, and the results explain very well reported experimental phenomena. The strain-stress curve under uniaxial loading was found in a good agreement with experimental data for concrete with three different mixing proportions. [ABSTRACT FROM AUTHOR]

A discrete element method (DEM) numerical simulation is used as a tool to study the mechanical behavior of soil-rock mixtures (S-RM) in a landslide dam. A 2D random generation program (R-SRM 2D ) of the meso-structure of (S-RM) based on random polygonal rock blocks has been developed, and is used to generate the (S-RM) numerical model of the study area. A new multi-circle representation method of polygonal blocks has been developed, which can better model the mechanical properties and failure process of rock blocks. A DEM biaxial test method with a flexible confining stress boundary has also been developed, which can better model the side boundary conditions of the sample. The meso-parameters of the circular particles representing the soil and rock blocks of the (S-RM) have been obtained from laboratory tests and DEM numerical simulations of soil and rock samples. Based on the meso-parameters, a series of biaxial tests of (S-RM) sample have been conducted using the DEM numerical method. The shear strength, failure process and formation mechanism of shear zones in (S-RM) have been studied. With the increase of the confining stress, the rock blocks in or near the shear zones will be broken, changing the shape of the shear zones, and leads to the shear strength of the (S-RM) sample showing nonlinear characteristics. Furthermore, the strength envelope of (S-RM) sample can be fitted through a power law function in the p - q plane. [ABSTRACT FROM AUTHOR]

Modelling irregularly shaped aggregates in concrete uses advanced algorithms to describe complex geometric profile of, e.g, crushed gravels. Consequently, discretization of the complex geometry and computational convergence of the resulting mesh scheme are the bottlenecks that prevent wider application of mesoscopic fracture simulation of concrete with more realistic aggregates. In this paper, a novel modelling framework with simple pre-processing and good computational convergence is proposed based on the diffuse meshing technique and the coupled elasto-viscoplastic damage model. The proposed model discretizes concrete using only regular elements that may have different material components such as aggregates, mortar matrix and aggregate/matrix interface. The accuracy of the proposed model is validated by comparing with the full three-phase model that meshes aggregate, mortar and their interfaces separately. The proposed model is applied then to investigate the failure mechanism of concrete under uniaxial compression and tension. Furthermore, the effect of using simplified aggregate meso -structure is studied by comparing the results of using the complex shaped aggregate models and the spherical shaped aggregate model. The results show that the morphology of aggregate has a no-negligible influence on post-peak mechanical behavior, the orientation of aggregate affects crack initiation and propagation, and self-restraint stresses reduce the strength of concrete. [ABSTRACT FROM AUTHOR]

The purposes of this work were: (i) to understand how erosive wear is affected by the random meso structure of concrete, and (ii) to develop a model for erosive wear of concrete structures due to the action of sediment bearing water loads. An aggregate generation algorithm with certain novel features is used to generate a database comprising 400,000 aggregates with varying levels of angularity and flakiness. Using these aggregates, a probabilistic model for mass loss due to aggregate erosion was formulated. A Monte Carlo simulation is used to obtain the time to failure for single aggregates; these were used to obtain an estimate of slurry erosive loss from the concrete structure, where successive layers of aggregates are assumed to satisfy the ergodicity assumption. The mass loss estimates were compared with experimental results for a sediment bearing water jet. A good qualitative match was observed, with both experimental results and probabilistic estimates exhibiting very similar dependence on meso geometry. [ABSTRACT FROM AUTHOR]

Triaxial tests on three types of soil–rock mixture (S-RM) samples with the same rock block content, but different grain size distributions, were performed in this study. To better understand the meso-mechanical behavior of soil–rock mixtures, one set of samples containing “oversized rock blocks” was designed. The oversized rock blocks in the other two sets were handled using the equivalent weight replacement method and the similar translation method. On this basis, the effect of the grain size distribution on the mechanical properties of the soil–rock mixtures was explored. The interlocking and the breakage of the large rock blocks were found to be two of the controlling factors of the mechanical properties of soil–rock mixtures. The deviator stress and the volumetric strain correlated well with the uniformity coefficient of the particle size distribution curve and performed differently under different confining pressure levels. Based on X-ray computed tomography (CT) slices of samples taken during the triaxial tests, the interaction of the internal rock blocks and the evolution of the sample meso-structure in the loading process were observed and analyzed; the present analysis provides explanations for the macroscopic mechanical behavior of soil–rock mixtures. [ABSTRACT FROM AUTHOR]

An analysis of the structural features of high and room temperature liquids is proposed, which attempts to explain the differences in disorder between these two types of systems by the particles shape and the ratio of the molecular size to the temperature. This is achieved by the study of different types of models, by computer simulations and liquid state integral equation techniques. The comparative study of the correlation functions and structure factors explains the origin of the pre-peak observed in room temperature ionic liquids, and clarifies the respective roles of the electrostatic and neutral part of the various atom–atom interactions. The study equally clarifies the differences between the fluctuations, and in particular critical fluctuations, and the structural micro-heterogeneity. The excellent agreement between the theory and the simulations, as opposed to the poorer agreement often observed in case of associated molecular liquids (such as water and alcohols), illustrates the conceptual difference between free and bound charges, ionic and molecular liquids. It is argued herein that different forms of disorders are associated to this underlying difference. [ABSTRACT FROM AUTHOR]

Turfy soil is a special soil with numerous undecomposed plant fibers and humus, which can be considered a soil-fiber mixture. In this paper, the macro-mesoscopic dynamic responses of turfy soil subjected to multilevel cyclic loading with different waveforms (triangular, square, sinusoidal) were investigated employing the discrete element method (DEM). The microscopic parameters of the DEM model were confirmed by laboratory tests and calibration procedures. The hysteresis between the applied and measured stress on the loading plates was discussed to determine the appropriate frequency before simulation. Macroscopically, the discrepancies, including the velocity of the loading plates, the deformation of the specimen, and sample size effect were investigated under these three waveform loadings. Microscopically, the differences in energy, coordination number, average normal contact force between pure and turfy soil, internal force alternation and bending degree of fibers in turfy soil were studied to disclose the discrepancies in macroscopic behaviors with different waveforms. Simulation results illustrate that square waveforms can excite the support of the soil matrix by plant fibers in turfy soil to a greater extent. This study is beneficial for further understanding the mechanical behaviors of soil-fiber mixtures under the action of different forms of cyclic loads in safety engineering. [ABSTRACT FROM AUTHOR]

The design of protein particles with tailored properties has received an increased attention recently. Several approaches, from simple heat treatment in dilute systems to the combination of heat and mechanical treatments in concentrated protein solutions, have been used to obtain protein particles with varying functional properties. Control of particle size, morphology, surface- and internal properties is crucial for obtaining protein particles with the necessary properties for emerging applications. The latter include not only the use of protein particles in foods, where they can improve the stability of foods at high protein content, but also as food-grade particles for the delivery of bio-actives. By tuning the morphology and size of protein particles, protection or controlled release of various bio-active components may be obtained. We review the various methods that have been used to prepare protein particles and discuss the behavior of the particles in dispersed systems and their possible applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] The real time loading and monitoring system for coal or rock were established. [•] CT images show that the raw coal is a kind of heterogeneous material. [•] Fractures happen between skeleton and matrix or on the weak region. [•] 3D reconstruction images were conducted under the different stress status. [Copyright &y& Elsevier]

• Capture optimal models of hierarchical materials of different asphalt mixtures. • Analyze the effect of coarse aggregate meso-structure on the thermal contraction of asphalt mixtures. • Improve the prediction accuracy of thermal contraction of asphalt mixture. The thermal contraction characteristics of asphalt mixture are closely associated with the low-temperature cracking of pavement. As for the research on the thermal contraction characteristics of asphalt mixture, it focuses mainly on the method of meso-theoretical prediction, which did not further analyze the impact of meso-structure characteristics of asphalt mixture. In this paper, a hierarchical prediction was made to analyze the effect of coarse aggregate meso-structure on the asphalt mixture. Experiments were conducted to obtain the thermal contraction strain of asphalt and asphalt mixture in steady heat transfer and to determine the meso-structure characteristics of asphalt mixture through industrial X-ray computed tomography (CT) and image processing. Given the matching degree of four meso-prediction models and asphalt-based materials and different meso-structure characteristics, the interaction term between inclusions in the meso-prediction model formula was clarified, and the impact of meso-structure on the thermal contraction of asphalt mixture was quantified. By analyzing the relationship between meso-structures and meso-prediction models, the Mori-Tanaka model was confirmed as optimal, and the model parameter of the interaction terms was adjusted using the test values of asphalt mixtures with different meso-structures, which further improves prediction accuracy for the thermal contraction of asphalt mixture. This paper provides a theoretical reference for the design of asphalt mixture materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] Three-dimensional Voronoi structure was generated to model metallic foams. [•] Contact between cell walls was considered under compression deformation. [•] Damage and failure of cell walls were considered under tensile deformation. [•] The deformation characteristics are due to the formation of plastic bands. [•] Pore irregularity was introduced to quantify the heterogeneous structure. [ABSTRACT FROM AUTHOR]

Abstract: Recent developments in the Rigid-Body-Spring Network (RBSN) modeling of concrete are presented, with candid assessments of research needs for the modeling of pre-critical crack growth under multi-axial stress conditions. Fracture of micro-concrete specimens is investigated through the combined use of such discrete (lattice) models, X-ray tomography, and imaging techniques. The specimens contain small amounts (10–50wt.% fraction) of spherical glass aggregates. Acid-etching of the glass aggregate surfaces is done to vary the bond properties of the matrix–aggregate interface. Tomographic images of the unloaded specimens provide the initial configurations of the three-dimensional lattice models, which are based on a three-phase representation of the material meso-structure: fine-grained mortar matrix, glass aggregate inclusions, and matrix–aggregate interfaces. The numerical and physical test results agree well with respect to peak loads and the associated crack patterns. Material structure and interface properties affect pre-critical cracking, in accordance with expectations. Dependence of composite strength on aggregate content and arrangement is studied through simulations of large sets of nominally identical models, which differ only in random positioning of the aggregates. [Copyright &y& Elsevier]

Abstract: A polymer-modified cementitious composite which is used as the cover layer of bridges and highways is designed based on the multiscale material design theory. A meso-scale lattice model is employed to predict the primary mechanical properties and the crack paths of the designed cementitious cover layer. The modeling is done based on the meso-structure of concrete captured through a micro-CT (micro-focus computational tomography). Further, the prediction results of the modeling are compared by the experimental results. The results show that the raw materials of the polymer-modified cementitious cover layer can effectively be selected and optimized by the multiscale material design theory and the lattice model. [Copyright &y& Elsevier]

Abstract: In this paper, a statistical second-order two-scale (SSOTS) method is presented for predicting heat conduction performances of the structures of composite materials with inconsistent random distribution. Firstly, the meso-scopic configuration for the structure with inconsistent random distribution is characterized. Secondly, the SSOTS asymptotic formulation for predicting the heat conduction parameters and the temperature fields of the heat conduction problems of the structure is given by means of construction way. Then the heat conduction properties for the functional gradient materials (FGM) with varying volume fraction are predicted by the SSOTS method. The numerical results are compared with experimental data and theoretical results. Finally, macroscopic heat conduction properties for the structures with varying probability distribution models including size, location and orientation distributions of grains are calculated. The numerical results show that the SSOTS method in this paper is valid to predict heat conduction performances of composite structures with inconsistent random distribution. [Copyright &y& Elsevier]

Meso-structure of soil-rock mixture (SRM) has a great influence on its hydraulic conductivity. However, the potential relationship between them has not been systematically studied. In order to reveal the effect of meso-structure on seepage characteristics of soil-rock mixtures (SRMs), the pore seepage model based on the finite-discrete element method (FDEM) is used to predict the effective hydraulic conductivity (k eff) of soil-rock mixtures in this paper. Firstly, the model is verified through a simple example. Then, the effects of rock size, content, shape, angle, distribution, and mixed two different shapes of rock blocks on k eff of SRMs are investigated. Finally, the seepage failure pattern of soil-rock mixtures is predicted according to the seepage flow velocity obtained by the simulation results. The approach in this study provides a new quantitative tool for determining the effective hydraulic conductivity of soil-rock mixtures and has a wide range of engineering application prospects. [ABSTRACT FROM AUTHOR]

Abstract: The cohesive crack model is, nowadays, widely used for the analysis of propagating cracks in concrete and other quasi-brittle materials. So far the softening curve, which gives the stress transmitted between two adjacent crack surfaces as a function of the crack opening, has been considered a material property and the parameters defining that curve, the tensile strength , the initial fracture energy G f (area under the initial tangent of the softening curve) and the total fracture energy G F (total area under the softening curve), have been identified by testing relatively small laboratory specimens. In this study typical experimental procedures used for the characterization of the fracture behavior of concrete, namely single notched specimens subjected to tensile loading, three-point bending tests, bending of unnotched specimens, and splitting (Brazilian) tests are analyzed on the basis of the Confinement-Shear Lattice (CSL) model, recently developed by the authors. A two-scale procedure is outlined in order to infer an equivalent macroscopic cohesive crack law from the meso-level response. The analysis of the lattice model response is analyzed in order to define the actual macroscopic material properties of concrete fracture. The results show that the tensile strength and the initial fracture energy are material properties and that they can be identified from the analysis of laboratory specimens. On the contrary, the total fracture energy identified from usual experiments is size-dependent and boundary-condition-dependent. [Copyright &y& Elsevier]

Abstract: A previously developed lattice model is improved and then applied to simulations of mixed-mode crack propagation in concrete. The concrete meso-structure is simulated by a three-dimensional lattice system connecting nodes which represent the centers of aggregate particles. These nodes are generated randomly according to the given grain size distribution. Only coarse aggregates are taken into account. Three-dimensional Delaunay triangulation is used to determine the lattice connections. The effective cross-section areas of connecting struts are defined by performing a three-dimensional domain tessellation partly similar to Voronoi tessellation. The deformations of each link connecting two adjacent aggregate pieces are defined in the classical manner of Zubelewicz and Bažant in which rigid body kinematics is assumed to characterize the displacement and rotation vectors at the lattice nodes. Each strut connecting adjacent particles can transmit both axial and shear forces. The adopted constitutive law simulates fracture, friction and cohesion at the meso-level. The behavior in tension and shear is made dependent on the transversal confining strain, which is computed assuming a linear displacement field within each tetrahedron of Delaunay triangulation, and neglecting the effect of the particle rotations. A mid-point explicit scheme is used to integrate the governing equations of the problems. General procedures to handle the boundary conditions and to couple the lattice mesh to the usual elastic finite element mesh are also formulated. Numerical simulations of mixed-mode fracture test data are used to demonstrate that the model is capable of accurately predicting complex crack paths and the corresponding load–deflection responses observed in experiments. [Copyright &y& Elsevier]

Different from fine-grained sedimentary reservoirs such as sandstone and shale, glutenite reservoir is rich in gravel. Its physical and mechanical properties are affected by gravel content and gravel size and are related to the cementation and support pattern between the matrix and gravel. Characterizing the meso-structure of glutenite reservoirs and its influence on the physical and mechanical properties is of great significance for the evaluation, exploration and development of glutenite reservoirs. Thus, an experimental study on ultrasonic characteristics was conducted on glutenite of different meso-structures. Measurements were performed along different travel paths in each sample to study the effect of gravel. Combined with the meso-structure of samples, the scattering effect on ultrasonic waves by gravel was analyzed. The results show that (1) Gravel content, gravel size and the support pattern between the matrix and gravel have an important influence on the ultrasonic waveform, frequency spectrum and velocity. The higher gravel content or larger gravel size is, the more severe waveform disturbance is. And the wave velocity decreases with the increase of gravel content or gravel size. (2) In glutenite, the scattering of waves by gravel is responsible for the ultrasonic characteristics. The higher the gravel content or larger the gravel size is, the stronger the scattering effect is. (3) Because the gravel size and wavelength in glutenite are approximately the same, the effective medium theory does not work on ultrasonic propagation in glutenite. (4) Thus, we established the velocity heterogeneity model to evaluate the meso-structure of glutenite. The rise of the velocity heterogeneity reflects the increase of gravel content, gravel size and meso-heterogeneity, and the transition of support pattern from matrix-support to gravel-support. This approach is more concise and effective and may potentially realize downhole meso-structure characterization by logging. • Experimental study on ultrasonic characteristics was carried out on glutenite with different meso-structures. • Gravel content, gravel size and the support pattern influence the waveform, frequency spectrum and velocity. • Scattering by gravel was found to be the dominant behavior when ultrasonic travels in glutenite. • The velocity heterogeneity model was built and applied to characterize the meso-structure of glutenite. [ABSTRACT FROM AUTHOR]

• A framework is proposed to recognize and measure meso-structure of cellular concrete. • U-Net is best to recognize the meso-characteristics of concrete splitting surface. • Porosity, size and distribution of pores are verified to affect the splitting-tensile strength. • Correlation between splitting-tensile strength and pore-structure is investigated. Properties of cellular concrete are significantly influenced by the mesoscopic pore structures, but the porosity-property relationships are still unclear. This paper tried to understand the pore effect on the splitting-tensile strength of cellular concrete by the specially prepared specimens with controlled additions of porosity. A series of cellular concrete specimens with different mix design were carefully prepared and subjected to splitting-tensile tests at a specified loading rate of 1 mm/min. Then, an integrated framework was developed for recognizing and measuring meso-structure based on the deep-learning model. The meso-characteristics of pores on splitting surfaces directly related to the splitting-tensile strength were captured and quantified automatically, and the relationship between meso-characteristics of pores and splitting-tensile strength was discussed in details. It was found that the splitting-tensile strength decreases as the porosity or pore size increases, accompanied by the variability of other pore characteristics such as uniformity coefficient and fractal dimension. At last, pore size and surface porosity on the splitting surface were identified as the main factors for splitting-tensile strength, and an empirical model was suggested to predict it with the above main factors. The findings in this paper further improve the understanding of the influencing mechanism for pores on the splitting-tensile strength, which can be used to optimal design of cellular concrete. [ABSTRACT FROM AUTHOR]

• The open-hole tensile properties of M3D woven composites are evaluated. • A macro-meso coupling and full-scale analysis model of OH-M3D specimen is proposed. • The failure mechanisms of OH-M3D specimen are analyzed using Micro-CT measurement. • Simulation of progressive damage evolution for OH-M3D woven composites is performed. In the present work, the multiaxial 3D (M3D) woven composites and 3D layer-to-layer (3D LTL) interlock woven composites were designed and manufactured. Both unnotched and notched specimens of two composites were tested in quasi-static tension, and the macro mechanical behavior characteristics of all specimens were monitored using the digital image correlation (DIC) technique. Based on the meso -structure characteristics of the M3D woven composites, a macro-meso coupling and full-scale analysis model for the centrally notched specimens was proposed. Furthermore, the progressive damage analysis was performed to simulate the damage evolution processes of the open-hole (OH) specimens, and the failure mechanisms were revealed in cooperation with the CT measurement. The study concluded that the reduction in tensile strength for the OH-M3D composites was about 19.8% compared to the unnotched strength, which was significantly lower than the 3D LTL case. Besides, the strain field in the loading direction uniformly distributed on the surface of the OH-M3D specimen, and the notched plate failed along the + 45° and −45° directions, exhibiting a diamond like fracture behavior. The interwoven structure of M3D specimen with the + 45° and −45° yarns influenced the stress distributions in the vicinity of the hole and damage mode. [ABSTRACT FROM AUTHOR]

• The effect of early-age loading on the mechanical properties of concrete is related to meso-structure. • The mechanical properties of concrete deteriorate with the increase of early-age loading. • The pore structure characteristics of concrete were obtained by nuclear magnetic resonance. • A constitutive behavior which can reflect the initial compaction stage is established. To explore the influence of early-age loading on the mechanical properties and internal structures of concrete, loads equivalent to 10%, 25%, and 40% of the concrete current compressive strength were applied to 1 day and 3 days specimens. The results of mechanical properties and mesoscopic scanning tests show that the development of uniaxial compression damage of concrete affected by early-age loading is divided into three stages. With an increase in early-age loading, the elastic modulus decreased and the Poisson's ratio first increased and then decreased. When the loading was 10% of current compressive strength of specimens, the number of macropores and cracks would decrease, and the subsequent mechanical properties of concrete would not be affected considerably. A continuous increase in early-age loading, the proportion of mesopores and cracks increased considerably, the cementitious structure loosened, and the mechanical properties of concrete deteriorated in the subsequent stage. By analyzing the relationship between the total deformation and the deformation of primary flaws and skeleton, the concept of void strain ratio was proposed. Accordingly, a constitutive behavior that reflects the nonlinear characteristic of primary flaws compaction stage during uniaxial compression process was established, the theoretical calculation is in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The reuse of coarse aggregate (CA) on clay-based materials is a sustainable and cost effective solution to minimize the extraction of natural farmland resources and reinforce the mechanical behaviour of impervious materials. However, limited knowledge is available regarding the compactability and permeability of CA-clay mixtures and their intrinsic connections. This study reports the results of a series of modified dynamic compaction tests and triaxial permeability tests performed on impervious clay materials reinforced with various contents of CA. Results demonstrate that compaction behaviour of CA-clay mixtures changes significantly with coarse aggregate content (C g). A peak value of global maximum dry density is achieved at C g = 70%, while the fine clay matrix is compacted to its densest state when C g <30%. The permeability, as a good indication of meso-structure in CA-clay mixtures, is significantly dominated by coarse aggregate content as well as the clay matrix void ratio. From the perspective of preferential flow path concept, permeability reaches a lowest value at C g = 30%. Due to the clay bridge effect induced by the heterogeneous density field, the larger the coarse particle size is, the smaller the permeability coefficient will become. [Display omitted] • Compaction and permeability are investigated on coarse aggregate-clay composites. • Effect of coarse aggregate content on compatibility and permeability is discussed. • Compacted global and clay matrix void ratio are compared and highlighted. • Meso-structure and clay matrix void ratio together control permeability behaviour. • Permeability evolution is interpreted via a concept of preferential flow paths. [ABSTRACT FROM AUTHOR]

• Square region segmentation algorithm was proposed for CT image segmentation. • Zwikiker-Kosten model of rigid skeleton porous material was improved. • Parameters for road design dominated by small vehicles were recommended. In order to further reveal the influence of voids on sound absorption performance of porous asphalt pavement, more factors were considered to improve an acoustic model (Zwikiker-Kosten) and structural optimization design of porous asphalt concrete (PAC) based on meso-structure was conducted in this paper. Based on the Otsu algorithm, a square image segmentation algorithm was proposed through comparative analysis to obtain the meso-structure characteristic parameters of voids in porous asphalt concrete. Combined with the effect of airflow velocity on the flow resistance and the measured sound absorption spectrum, the relationship between void length and pavement thickness was quantified, and the Zwikiker-Kosten model of rigid skeleton porous material was improved and verified for the prediction of sound absorption performance of PAC. Besides, the influence of void parameters on the sound absorption performance of PAC was analyzed, the structural optimization design was carried out for the road dominated by small vehicles, and proposing pavement design parameters at last. The results show that the two-dimensional air voids obtained by square region segmentation algorithm have high accuracy, which can be used for the recognition and segmentation of voids in CT images; According to the comparative and correlation analysis, the improved Zwikiker-Kosten model can accurately predict the sound absorption performance of PAC; The peak sound absorption coefficient (SAC) of PAC is mainly affected by air voids, while its corresponding frequency is mainly affected by the length of voids. Moreover, the road dominated by small vehicles was recommended to adopt the following design parameters: void equivalent diameter, air void and pavement thickness should be limited to about 3 mm, 18% and 30 mm, respectively. [ABSTRACT FROM AUTHOR]

• Fractal dimension of concrete does not influence its tensile mechanical behavior. • Elastic modulus increases with increasing coarse aggregate content. • Tensile strength decreases with increasing coarse aggregate content. • Strain at the maximum stress decreases with increasing coarse aggregate content. The coarse aggregate content and fractal dimension were used to describe the geometric form of concrete at the meso-level. After the simulation results were validated, several meso-models of concrete with various fractal dimensions and coarse aggregate content were simulated under tension using Random Fractal Modeling. With increasing coarse aggregate content, the elastic modulus increased, and the tensile strength and the strain corresponding to the maximum stress decreased. The fractal dimension did not obviously influence the tensile mechanical behavior. The comprehensive consideration of both fractal geometry and classical Euclidean geometry can aid in predicting the macroscopic behavior of concrete. [ABSTRACT FROM AUTHOR]

• An approach to establish two kinds of mesoscale models synchronously for fully-graded concrete is presented. • The main cracking mode of mixed-mode fracturing in fully-graded concrete is visualized. • Batch embedding technique of cohesive elements is illustrated and developed by a Python script. • Uniaxial compressive and tensile experiments are conducted with 2D and 3D meso-structures of fully-graded concrete. Complicated fracture modes of fully-graded concrete are investigated at mesoscale with the proposed numerical method in this study. A generation method for two kinds of meso-structures, which gets the randomness of the appearance and distribution of aggregates involved, is proposed based on the mesoscopic features of fully-graded concrete. Cohesive elements are globally inserted to the mesoscale models to capture the fracture propagation with batch embedding technique, and the description and visualization of main cracking mode of fractures are realized based on relative energy proportions. Uniaxial compressive and tensile experiments are conducted with 2D and 3D models to validate the proposed method for simulating fracturing behavior, and the numerical outputs show high consistency with the experimental results and demonstrate that the proposed method is feasible to characterize the fracturing features of fully-graded concrete at mesoscale eventually. [ABSTRACT FROM AUTHOR]

• Mechanical properties of CGFB with cracks under seepage were studied. • Seepage and prefabricated cracks aggravate the damage and degradation effect of CGFB. • Damage mechanism of CGFB with cracks under seepage-stress coupling was analyzed. Seepage and cracks are two important factors affecting the stability of the cemented gangue-fly ash backfill (CGFB, a mixture of coal gangue, fly ash, cement and water). In this study, the CGFB samples with a 45° single crack were prepared and the mechanical properties of CGFB with cracks under different seepage water pressures were studied. Based on the theory of damage mechanics, the damage variable which can evaluate the seepage effect and crack effect was introduced, and the damage evolution law of CGFB with cracks under the seepage-stress coupling was discussed. The research hat: The mechanical properties of CGFB with cracks under seepage-stress coupling are mainly determined by the seepage water pressure, prefabricated crack and their coupling effects. Seepage and crack aggravate the attenuation of the peak strength and elastic modulus of CGFB, but with the increase of seepage water pressure, the deterioration effect of the crack weakens. Seepage and crack have significant effects on the damage of CGFB. Finally, based on the discrete element software, damage mechanism of CGFB with cracks under seepage-stress coupling was analyzed from a microscopic perspective. The research results can lay a foundation for the long-term stability analysis and instability prediction of CGFB with geological defects such as joints and cracks in water-rich mines. [ABSTRACT FROM AUTHOR]

A 3D multi-phase meso-scale model is proposed to analyse the evolution of damage and transport properties in concrete. This model includes five phases: aggregates, mortar, voids, cracking and interfacial transition zones (ITZs) between aggregates and mortar. They are generated using measurable characteristics, such as shape, size and volume fraction of aggregates and voids. Mechanical part of the model is validated through comparing the predicted and experimental stress-strain curves and cracking patterns. Transport part of the model is validated by the comparison of predicted and experimental diffusivities of chloride ions in concrete. A new interface element type is also proposed to represent cracking in transport analysis which can simulate transport not only in normal directions but also in tangential directions. The effects of parameters relevant to aggregates, voids, ITZs and cracking patterns on the mechanical and transport responses of concrete are also analysed. The derived qualitative understanding of the relation between meso-structural features and macroscopic properties will help future advances in modelling and formulation of experimental programmes to improve the calibration and validation of meso-scale models. The proposed sequential mechanical-transport coupling model is applicable to a large class of composite materials with appropriate selection of phases and their properties. [ABSTRACT FROM AUTHOR]