Crack Propagation In Concrete Research Articles

Numerical Method for Mixed-Mode I–II Crack Propagation in Concrete

A crack-propagation criterion is proposed in this paper for mixed-mode I–II fracture in concrete. In this criterion, crack propagation is initiated when the difference between the stress-intensity factor at the crack tip caused by the external force and that by the cohesive stress satisfies the crack-initiation equation. On the basis of this criterion, a numerical method is developed to simulate mixed-mode I–II crack propagation in concrete. To verify the criterion, three sets of experimental data are selected: one is obtained from the self-conducted test and the other two are collected from the literature. The numerical results show that the calculated load versus crack-mouth opening and sliding displacement curves and crack trajectories are in good agreement with experimental results. Therefore, once the mode I initial cracking toughness, elastic modulus, fracture energy, possion’s ratio, and tensile strength of concrete are available, the whole mixed-mode I–II fracture process in concrete can be predicted with reasonable accuracy.

Implementation of Fictitious Crack Model Using Contact Finite Element Method for the Crack Propagation in Concrete under Cyclic Load

The mixed freedom finite element method proposed for contact problems was extended to simulate the fracture mechanics of concrete using the fictitious crack model. Pairs of contact points were set along the potential developing path of the crack. The displacement of structure was chosen as the basic variable, and the nodal contact force in contact region under local coordinate system was selected as the iteration variable to confine the nonlinear iteration process in the potential contact surface which is more numerically efficient. The contact forces and the opening of the crack were obtained explicitly enabling the softening constitutive relation for the concrete to be introduced conveniently by the fictitious crack model. According to the states of the load and the crack, the constitutive relation of concrete under cyclic load is characterized by six contact states with each contact state denoting its own displacement-stress relation. In this paper, the basic idea of the mixed freedom finite element method as well as the constitutive relation of concrete under cyclic load is presented. A numerical method was proposed to simulate crack propagation process in concrete. The accuracy and capability of the proposed method were verified by a numerical example against experiment data.

Measuring high speed crack propagation in concrete fracture test using mechanoluminescent material

Measuring crack length in concrete fracture test is not a trivial problem due to high speed crack propagation. In this study, mechanoluminascent (ML) material, which emits visible light under stress condition, was employed to visualize crack propagation during concrete fracture test. Three-point bending test was conducted with a notched concrete beam specimen. The cracking images due to ML phenomenon were recorded by using a high speed camera as a function of time and external loadings. The experimental results successfully demonstrated the capability of ML material as a promising visualization tool for concrete crack propagation. In addition, an interesting cracking behavior of concrete bending fracture was observed in which the crack propagated fast while the load decreased slowly at early fracture stage.

Calculating crack extension resistance of concrete based on a new crack propagation criterion

A crack propagation criterion was proposed for model I crack in concrete by using the initial fracture toughness KICini as an inherent material property. Based on this criterion, crack begins to propagate when the difference, between the stress intensity factors caused by the applied load KIP and that by the cohesive stress KIσ, exceeds KICini. Finite element analyses was then carried out to calculate the complete load vs. crack mouth opening displacement (P-CMOD) curve, the critical crack propagation length ΔaC and the unstable fracture toughness KICun for notched beams under three-point bending. It was found that numerical results showed a good agreement with the experimental ones. Based on this crack propagation criterion, crack extension resistance, in terms of stress intensity factor, KR being able to consider the variation of fracture process zone (FPZ) was employed for describing crack propagation in concrete. KR is composed of KICini and KIσ, which is actually equal to the driving action of crack extension. It was concluded that given the elastic modulus E, the uniaxial tensile strength ft, the fracture energy GF and KICini, the complete fracture process in concrete and the KR-curve of concrete can be calculated based on the numerical method. Finally, discussion was made on the effects of fracture process zone, GF and specimens geometries on KR-curve.

Study on Concrete Temperature Crack Based on Mesomechanics

A three-phase mesomechanics model was established to simulate the aggregate, cement mortar and the interface between them. In order to reflect the meso characters and heterogeneity of concrete, the parameters were randomly valued on the Weibull distribution. Then, by using this model the complete process of concrete crack propagation was analyzed based on the elastic brittle damage theory. This method was verified by simulation of uniaxial tension and three-point bend beam test. Finally, concrete structure cracking at early age during a cold snap was simulated under different surface insulation conditions. The results show that this method can simulate the crack initiation and propagation effectively and reflect the whole process of concrete crack under temperature load.

Modeling of chloride-induced corrosion in reinforced concrete structures

A numerical procedure is presented in this paper for the prediction of chloride induced steel corrosion in reinforced concrete structures. Finite element analysis is introduced for the mechanical analysis of crack initiation and propagation due to the accumulation of corrosion products around the reinforcement, while the alternating direction implicit method is used to solve the transport equations of temperature, humidity, chloride ions and oxygen in concrete. Based on the assumption of a uniform distribution of corrosion products, a self-adaptation process for the variation of boundary conditions is proposed through a series of diffusion analyses together with crack propagation in concrete. Therefore, the interaction between the corrosion rate and the propagation of cracks in concrete is taken into account. Furthermore, a numerical program is developed and a case study involving bridge deck exposed to a marine environment in Hong Kong is investigated. The results show that interactive behavior has a significant effect on the corrosion rate of the reinforcement, and the non-cracking model significantly overestimates the service life of structures.

Use of Vibrating Wire Strain Gauges to Monitor Corrosion-Induced Deterioration of Concrete

Steel reinforcement corrosion is always one of the most significant incentives of concrete structure deterioration, especially under severe chloride erosion environment. In order to describe the whole process of concrete deterioration induced by reinforcement corrosion, the mechanism of rust expansion and crack propagation in concrete was analyzed from the perspective of elastoplastic mechanics and fracture mechanics firstly, and experimental study was carried out to use vibrating wire strain gauges for monitoring corrosion-induced concrete deterioration process. The mechanism analysis of corrosion-induced concrete deterioration indicates that the degradation process of cover concrete can be divided into aggressive medium transmission process, free corrosive expansion process, corrosive expansion stress development process, corrosive expansion crack generation and propagation process, and vibrating wire strain gauges can be used to monitor corrosion-induced cover concrete stress development, crack initiation and propagation process along with the procedure of reinforcement corrosion. The test curve seems to be generally consistent with that of the theoretic analysis, and the signals captured by vibrating wire strain gauges can successfully reflect the durability degradation process of reinforced concrete structure under severe erosion environment.

Fractal Analysis on Bond-Slip Behavior between Steel Shape and Concrete in SRC on Axial Pull-Out Test

Based on the experimental study of pull-out specimens on bond-slip behaviors between shaped steel and concrete in SRC (Steel Reinforced Concrete Structures), the graphic of the whole damage process are obtained. The crack propagation of concrete is fractal analyzed to calculate the fractal dimension. Relationships between fractal dimension and bond-slip behaviors of SRC are discussed. The main factors impact the bond-slip behaviors are studied to established the relationship with fractal dimension. Linear dependence relation of fractal dimension and bond-slip behaviors and the impact factors is discovered. Statistics formula is established to describe the relation of fractal dimension and ultimate bond strengths. All these may contribute to the further analysis of bond-slip performance and fractal behaviors in SRC composite structures.

Investigation on Cracks Creation and Propagation in Concrete Slab of Composite Beams

Analytical and experimental research have illustrated initiation of cracks in concrete deck immediately after its casting and placing on the upper flange of steel beams, especially prior to application of additional permanent load on composite element. Not only value of concrete shrinkage strain may influence creation and propagation of cracks in concrete. However ratio of deck reinforcement, cross-sectional area of reinforcement steel and strength of concrete can modify the process. Moreover, the ratio of steel beam flexural stiffness and flexural stiffness of concrete deck can be significant. Important shrinkage strains can occur at the lower concrete surface in the steel and concrete interface. Parametrical studies have provided the relationships illustrating impact of above parameters on crack aspect. The aim of the paper is to provide further details.

Prediction of Transient and Steady-State Flexural Fatigue Crack Propagation in Concrete Using a Cyclic R-Curve

Fatigue damage in plain portland cement concrete is a nonlinear process that exhibits two distinct crack stages: a deceleration stage (transient crack growth) and an acceleration stage (steady-state crack growth). In the past, either the transient crack growth stage was completely neglected or was described using a power law that used crack extension as its argument. This works well for constant amplitude loading and for one geometry. However, to extend the fatigue prediction to variable amplitude loading, and also account for size effect, a fatigue crack resistance curve should be obtained so that the bridging stresses behind the crack tip can be calculated. In this paper, a new method has been developed to determine the fatigue crack resistance curve from crack rate and stress intensity data obtained from three point bending single edge notched specimens. The results of this study suggest that the fatigue crack resistance curve has a similar shape to the quasi-static crack resistance curve. Primarily, the critical crack extensions are equivalent, and the maximum fatigue crack resistance value is approximately 40–45% of the quasi-static fracture toughness at the critical crack extension. In addition, the results suggest that the KIC in fatigue is larger than the KIC in quasi-static loading. The reason for this is that the quasi-static resistance continues to rise after peak load, which will tend to increase the fracture toughness in fatigue. Finally, it is shown that by using a fatigue crack resistance curve, a unique set of Paris parameters C and n can be defined for both the transient and steady-state crack stages, which can then be used to predict the fatigue life without having to separate the two crack stages.

SGBEM for Cohesive Cracks in Homogeneous Media

In this paper, the Symmetric Galerkin Boundary Element Method for Linear Elastic Fracture Mechanics is extended to non-linear cohesive cracks propagating through homogeneous linear elastic isotropic media. The cohesive model adopted is based on the concept of free energy density per unit undeformed area. The corresponding constitutive cohesive equations present a softening branch which induces a potential instability. Thus, a suitable solution algorithm capable of following the growth of the cohesive zone is needed, and in the present work the numerical simulation is controlled by an arc-length method combined with a Newton-Raphson algorithm for the iterative solution of nonlinear equations. The Boundary ElementMethod is very attractive for modeling cohesive crack problems as all nonlinearities are located on the boundaries of linear elastic domains. Moreover a Galerkin approximation scheme, applied to a suitable symmetric boundary integral equation formulation, ensures an easy and efficient treatment of cracks in homogeneous media and an excellent convergence behavior of the numerical solution. The cohesive zone model is applied to simulate a pure mode I crack propagation in concrete. Numerical results for three-point bending test are used to check the numerical results for mode I and are compared with some numerical results obtained by FEM analysis found in the literature.

11 From benchside to byteside: what we can learn from computational modelling

The need for mechanistic constitutive models to evaluate the complex interaction between concrete crack propagation, geometry and soil foundation in concrete- and composite pavement systems has been recognized. Several models developed are either too complex or designed to solve relatively simple problems, e.g. limited to one type of load configuration or test set-up. In order to develop a general and mechanistic modeling framework for non-linear analysis of low-cycle damage in cemented materials, this paper presents a cracked-hinge model aimed at the analysis of the bending fracture of the cemented material. The model is based on the fracture mechanics concepts of the fictitious crack model. The proposed hinge is described in a general and consistent format, allowing for any type of stress-crack opening relationship and unloading- reloading formulation. The functionality of the proposed hinge model is compared to numerical- and experimental results. The proposed hinge shows good performance and seems promising for the description of low-cycle fracture behavior in cemented materials.

Fracture mechanical behavior of concrete and the condition of its fracture surface

In this research project, a series of uniaxial, deformation controlled tensile tests were performed in order to study the fracture mechanical behavior of concrete. The parameters under investigation were the strength of concrete, curing conditions, concrete temperature and loading rate. The fracture surfaces of the tested specimens were investigated in detail and their condition was quantified using the fractal geometry. The evaluation of the experimental results and the results of the fractological investigation displayed correlations between the shape of the stress–crack opening relation of concrete and the values of the roughness as well as the fractal dimension of its fracture surface for all parameters under investigation. Relationships were drawn between the individual material as well as test parameters and the degree of concrete heterogeneity, which proved to be decisive for the formation and propagation of cracks in concrete. It was concluded that the roughness of the fracture surfaces might be considered as a representative replica of the crack system correlating directly with the concrete heterogeneity.

Modelling multiple cohesive crack propagation using a finite element–scaled boundary finite element coupled method

This paper presents an extension of the recently-developed finite element–scaled boundary finite element (FEM–SBFEM) coupled method to model multiple crack propagation in concrete. The concrete bulk and fracture process zones are modelled using SBFEM and nonlinear cohesive interface finite elements (CIEs), respectively. The CIEs are automatically inserted into the SBFEM mesh as the cracks propagate. The algorithm previously devised for single crack propagation is augmented to model problems with multiple cracks and to allow cracks to initiate in an un-cracked SBFEM mesh. It also addresses crack propagation from one subdomain into another, as a result of partitioning a coarse SBFEM mesh, required for some mixed–mode problems. Each crack in the SBFEM mesh propagates when the sign of the Mode-I stress intensity factor at the crack tip turns positive from negative. Its propagation angle is determined using linear elastic fracture mechanics criteria. Three concrete beams involving multiple crack propagation are modelled. The predicted crack propagation patterns and load–displacement curves are in good agreement with data reported in literature.

Simulation of reinforcement-corrosion-induced crack propagation in concrete by acoustic emission technique and boundary element method analysis

Corrosion of reinforcement is one of the major causes of deterioration in reinforced concrete structures. Various crack patterns are nucleated around reinforcement in concrete due to expansion of corrosion products. Crack kinematics of locations, types, and orientations are quantitatively determined by the acoustic emission (AE) – simplified Green’s functions for moment tensor analysis (SiGMA) procedure in association with laboratory tests conducted on concrete specimens simulating corrosion-induced damage. These kinematic outcomes are obtained as three-dimensional (3-D) locations and vectors, and are thus visualized in 3-D by using virtual reality modeling language (VRML). Numerical analysis is conducted by the boundary element method (BEM) based on the concept of linear elastic fracture mechanics (LEFM) to clarify the mechanisms of corrosion-induced crack extension. Relationships between dimensionless stress intensity factors and cracking types are studied by BEM. Contributions of mode I and mode II failures are dependent on the cracking types. It is found that the process of crack propagation due to corrosion of reinforcement in concrete is mostly a mode I fracture with mixed-mode and, in a few cases, mode II fracture.Key words: acoustic emission, moment tensor, corrosion cracking, stress intensity factor.

Experimental Determination of Concrete Fracture Properties with Modified S-FPZ Model

Modified singular fracture process zone(S-FPZ) model is proposed in this paper to determine a fracture criterion for continuous crack propagation in concrete. The investigated fracture properties of the proposed fracture model are strain energy release rate at a micro-crack tip and the relationship between crack closure stress(CCS) and crack opening displacement(COD) in the FPZ. The proposed model can simulate the actual fracture energy of experimental results fairly well. The results of the experimental data analysis show that specimen geometry and loading condition did not affect the CCS-COD relation. However, the strain energy release rate is a function of not only specimen geometry but also crack extension. The strain energy release rate remained constantly at the minimum value up to the crack extension of 25 mm, and then it increased linearly to the maximum value. The maximum fracture criterion occurred at the peak load for specimens of large size. The fracture criterion remained at the maximum value after the peak load. The variation of the fracture criterion is caused by micro-cracking and micro-crack localization. The fracture criterion of strain energy release rate can simply be the size effect of concrete fracture, and it can be used to quantify the micro-cracking and micro-crack localizing behavior of concrete.

Study on the Average Fracture Energy for Crack Propagation in Concrete

Fracture energy represents the average total energy consumption during a complete crack propagation process. The use of one fracture property, the RILEM fracture energy, on its own is not sufficient to characterize the fracture behavior during crack stable and unstable propagation periods. In this paper, two fracture energy quantities, the stable fracture energy and unstable fracture energy, are introduced to predict energy consumption for those two crack extension periods. Wedge splitting tests were carried out on concrete specimens with different ligament length to identify all three fracture energy quantities. The experimental results show that the stable fracture energy remains almost a constant irrespective of specimen size, while the unstable fracture energy increases with increasing ligament length. A similar size dependency is observed in the RILEM fracture energy. An explanation is offered for this size dependency by considering the boundary effect of the specimen.

Self-structural Health Monitoring Function of RC Structures with HCFRP Sensors

In this article, the self-structural health monitoring (SHM) function of reinforced concrete (RC) structures is studied with the application of a novel type of hybrid carbon fiber-reinforced polymer (HCFRP) sensors that are characterized by broad-based and distributed sensing capabilities. The HCFRP composite sensors are designed and fabricated to consist of three types of carbon tows, wherein the active materials are carbon tows by virtue of their electrical conductivity and piezoresistivity. Two types of HCFRP sensors, with and without pretreatment, are fabricated. First, the sensing properties of these two types of sensors are tested under uniaxial tension. Then, the HCFRP sensors are bonded with epoxy resins on the bottom concrete surface of RC beams to monitor the strain, the yielding of reinforcing steel bars, and the initiation and propagation of cracks in concrete. The experimental results show that the pretreatment can enhance the change in electrical resistance more than 100 times, especially in a low-strain range before the rupture of carbon tows. With the application of HCFRP sensors, the structural health, including the average strain amplitude, the yielding of reinforcing steel bars, the deformation of the beams, and the initiation and propagation of cracks in RC structures, can be monitored in a real-time manner.

Residual flexure capacity of corroded reinforced concrete beams

This work presents results from an experimental investigation which correlated flexure capacity loss with steel cross-section loss due to generalized corrosion of the embedded steel in a humid environment. Concrete beams (100×150×1500 mm) cast with chlorides were used in this investigation. Further acceleration of the corrosion process was achieved by applying a nominal 80 μA/cm 2 constant anodic current for approximately 50–180 days. The specimens were subsequently tested in flexure under three-point loading. The average corrosion penetration, x AVER , the maximum concrete surface crack width, CW MAX, and the maximum rebar pit depth, PIT MAX, were estimated for each corroded beam using gravimetric metal loss procedure. The results obtained showed: (1) the corrosion-induced concrete crack propagation was enhanced if dry rather than wet environment is used during the accelerated corrosion stage; (2) wet environment during corrosion acceleration enhanced pit formation at the rebar surface; (3) a decrease of as much as 60% in the flexure load capacity values was observed with only 10% of x AVER / r 0 , where r 0 = rebar radius ; and (4) PIT MAX, not the x AVER / r 0 ratio, was the most important parameter affecting flexural load capacity reduction in corroded beams.

Confinement-shear lattice CSL model for fracture propagation in concrete

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.