Mesoscale modeling of fracture in cement and asphalt concrete (original) (raw)
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Meso-scale studies in fracture of concrete: A numerical simulation
Computers & Structures, 2011
The fracture behaviour of concrete is complex due to highly heterogeneous nature of the material. The heterogeneity of concrete manifests itself at various scales. At mesoscale, the presence of aggregates influences the strength of concrete by developing a zone of weakness in the form of aggregate-matrix interface. These lead to an increased distributed micro-cracking and enhances the energy absorption capacity of the material. The energy absorption capacity of structure is dependent not only on material properties but also on structural geometry and loading conditions. The present work attempts to identify the material and structural parameters that influence the overall behaviour, by using discrete numerical modelling of the material at mesoscale. Lattice modelling, a technique to model the heterogeneity using lattice elements is used to study the fracture behaviour of the material. Effect of aggregate volume fraction, specimen thickness and depth on the global behaviour is studied.
Effects of Meso-scale Modeling on Concrete Fracture Parameters Calculation
Periodica Polytechnica Civil Engineering
Mechanical fracture brings about considerable financial and living costs to various communities. Since the early twentieth century, the issue has been scientifically under scrutiny. Hence, it is of necessity to explore the failure of various materials including concrete as one of the most widely used materials in the construction industry. In examining the concrete structures, while it is assumed that concrete is a homogeneous material, it consists of several components such as cement paste, an aggregate of sand, gravel, and air, and the components play an essential role in determining correct concrete behavior. Hence, in the present research, to calculate the concrete fracture parameters under the three-point bending experiment, 100 distributions of aggregates and cement matrix were considered, and fracture factor and integral J were investigated, and contrary to expectations, the second and third fracture modes were also created. Besides, energy release ratio distribution along th...
Monte Carlo simulations of mesoscale fracture modelling of concrete with random aggregates and pores
A procedure is devised to generate mesoscale concrete samples with random multi-phases. Complex crack initiation and propagation is realised using cohesive interface elements. Samples in tension fail with 1 or 2 cracks, regardless of aggregates' and pores' shape and fraction. The effects of aggregate shape and porosity should not be neglected in meso-modelling. a b s t r a c t A procedure for generating two-dimensional heterogeneous meso-scale concrete samples is developed, in which the multi-phasic features including the shape, size, volume fraction and spatial distribution of aggregates and pores are randomised. Zero-thickness cohesive interface elements with softening traction–separation relations are pre-inserted within solid element meshes to simulate complex crack initiation and propagation. Extensive Monte Carlo simulations (MCS) of uniaxial tension tests were carried out to investigate the effects of key multi-phasic features on the fracture patterns and load-carrying capacities. It is found that the fracture behaviour and stress-displacement responses of the numerical specimens are highly dependent on the random mesostructures, especially the post-peak softening responses. The specimens fail with either one or two macro-cracks, regardless of the shapes and volume fractions of aggregates and pores. Assuming that the aggregate–mortar interface is weaker than the mortar, using polygonal rather than circular or elliptical aggregates, or increasing the aggregate volume fraction will reduce the tensile strength of specimens. The porosity is found to have severely adverse effects on the specimen strength and cannot be neglected in mesoscale fracture modelling of concrete.
Computer simulation of fracture processes of concrete using mesolevel models of lattice structures
Cement and Concrete Research, 2004
Mesolevel simulations were used to describe fracture processes in concrete. A new stochastic -heuristic algorithm was developed for generating the composite structure of concrete in 3-D space, producing specimens with comparably high aggregate content and realistic distribution. Aggregate particles were described as ellipsoids, allowing control in shape and size distributions. The continuum was discretised into lattices of linear elements, in structural analyses. For 2-D analyses, slices from the 3-D specimen were idealised as planar trusses/frames, while for the 3-D analyses the specimens were idealised as space structures. Fibre-reinforced concrete (FRC) was also modelled by introducing additional linear elements interconnecting distant nodes of the lattice. Compression, direct tension and wedge-splitting tests were simulated. Parametrical study was carried out to investigate the effect of different material properties and proportions in concrete admixtures. Simulation results are in agreement with experimental observations. Applicability and enhancements for such models are discussed and future research directions are proposed. D
Numerical simulation of dynamic mechanical properties of concrete based on 3D mesoscale model
This paper attempts to disclose the mechanical properties of concrete under dynamic load. To this end, concrete was considered as a three-phase composite of mortar, aggregate and interfacial transition zone (ITZ) on the mesoscale. In light of the dynamic constitutive relation of concrete, the dynamic response of concrete specimens was numerically simulated on a 3D meso-mechanical model. Then, the authors discussed how the loading speed, aggregate volume content, and aggregate particle size affect the dynamic mechanical properties of concrete. The simulation results show that the damage morphology of concrete under dynamic load agrees well with that of theoretical analysis; the peak stress of concrete increased with the loading speed, revealing an obvious strain rate enhancement effect; the peak stress of concrete also increased with aggregate volume content; however, the peak stress of concrete gradually decreased with the increase in aggregate particle size under the constant volume content and grading of aggregate. The research findings shed new light on anti-impact design of concrete structures.
2D mesoscale model for concrete based on the use of interface element with a high aspect ratio
International Journal of Solids and Structures, 2016
The mesostructure of concrete plays a very important role in the process of initiation and propagation of cracks. Microcracks tend to start in the Interfacial Transition Zone (ITZ) and propagate toward the mortar matrix until a macrocrack formation. Seeking to better understand the influence of the concrete mesoscopic structure, translated macroscopically in the form of loss of stiffness and energy dissipation, this work proposes a 2D mesoscale model in which the concrete is modeled as a heterogeneous three-phase material composed of coarse aggregates, mortar matrix and ITZ. The coarse aggregates are generated from a grading curve and placed into the mortar matrix randomly. Interface solid finite elements with a high aspect ratio are used to represent the ITZ and the crack process based on a mesh fragmentation technique. These interface elements present the same kinematics as the Continuum Strong Discontinuity Approach (CSDA), which allows the use of a continuum constitutive relation to describe their behavior. Thus, an appropriate continuum tension damage model is adopted to describe the complex nonlinear behavior of concrete due to the crack phenomenon. Initially, the proposed mesoscale approach is applied in uniaxial tensile tests to study the influence of the size, volume and distribution of the coarse aggregates within the mortar matrix. Then, three-point bending beams are simulated in mesoscale and the results compared with the experimental ones. The results showed that the proposed 2D mesoscale model presents the same kinds of characteristics that real 3D concrete shows, considering the effects of the mesostructure constituents.
Cement and Concrete Research, 2016
The computational power allows nowadays the development of mesoscopic models of concrete, based on finite element or lattices approaches, which represent the contribution of inclusions to the behavior of concrete. However, the smallest heterogeneities are often removed to these simulations for decreasing the computation time. In this paper, the effect of aggregate classes on the fracture behavior of a plain concrete is studied. Different simulations are performed from a mesoscopic model based on a diffuse meshing technique and Fichant's damage model, in which the smallest aggregates are successively removed from the granular skeleton to the benefit of a homogenized continuous mortar. The effects of these simplifications are then evaluated by comparing the fracture behaviors obtained to the one of the reference concrete. The results show the relevance of modeling all classes of aggregates in order to obtain an accurate description of the failure behavior of concrete.
Mesoscale models for concrete: Homogenisation and damage behaviour
Finite Elements in Analysis and Design, 2006
In this paper three-dimensional geometrical models for concrete are generated taking the random structure of aggregates at the mesoscopic level into consideration. The generation process is based upon Monte Carlo's simulation method wherein the aggregate particles are generated from a certain aggregate size distribution and then placed into the concrete specimen in such a way that there is no intersection between the particles. For high volume fractions of aggregates, new algorithms for generating realistic concrete models are proposed.
Fracture of model concrete: 2. Fracture energy and characteristic length
Cement and Concrete Research, 2006
The specific fracture energy G F was measured in six types of simple concrete: all from the same matrix. The aggregates were spheres of the same diameter (strong aggregates, that debonded during concrete fracture, and weak aggregates, able to break); three kinds of matrix-aggregate interface (weak, intermediate and strong) were used. All in all, 55 test results are reported. These results are intended to be used as an experimental benchmark for checking numerical models of concrete fracture. A meso-level analysis of these results showed a correlation between the measured G F values and the properties of the matrix, aggregates and interfaces, particularly with the actual area of the fracture surface. The strength of the matrix-aggregate interface correlates quite well with G F , and concrete ductility, measured by means of the characteristic length, correlates also with the strength of the matrix-aggregate interface.
Size effect in concrete under tension is studied by Monte Carlo simulations of mesoscale finite element models containing random inclusions (aggregates and pores) with prescribed volume fractions, shapes and size distributions (called meso-structure controls). For a given size and a set of controls, a number of realisations with different spatial distribution of inclusions are simulated to produce statistical data for macroscopic load/stress-strain curves. The complex meso-crack initiation and propagation is captured by pre-inserted cohesive interface elements. The effects of specimen size and meso-structure controls on macroscopic strength and toughness are analysed, and empirical size-effect laws for their dependences are proposed by data regression. It is also shown that the mesoscale porosity affects both strength and toughness and should not be ignored in size effect studies of concrete.