Failure Mechanism Of Concrete Research Articles

Effect of chloride binding and sulfate ion attack on the chloride diffusion in calcium sulfoaluminate-based material under seawater environment

The diffusion of chloride ions in reinforced concrete under the seawater environment will affect the physical or mechanical properties and durability. Sulfate ions also influence the diffusion of chloride ions by generating expansion products through physical and chemical reactions. Further research on the effects of chloride binding and sulfate ion attack on chloride ion diffusion will deepen the understanding of concrete failure mechanism. In this paper, a quaternary blend based on calcium sulfoaluminate (CSA) cement was prepared and laboratory immersion tests were conducted in artificial seawater with varying salt concentrations. Initially, chloride ion concentration measurements and XRD tests were conducted at different corrosion ages and salt concentrations. Subsequently, the chloride binding properties of CSA-based materials was quantified through the analysis of chloride ion concentration and the phases of hydration products. Meanwhile, the corrosive effect of sulfate ions on chloride ion diffusion was determined corresponds to the content of expansive hydration products. Furthermore, numerical simulations were employed to evaluate the impact of sulfate ion corrosion, chloride binding, and their combined effects on chloride ion diffusion, and the results were compared with free chloride ion concentration (Cf). The results indicate that the total chloride ion concentration (Ct) exhibits a linear relationship with increasing salt concentrations of seawater in CSA-based materials. Meanwhile, the bound chloride ion concentration (Cb) follows a logarithmic growth pattern. The chloride binding rate experiences a linear decline with the increase of chloride ion concentration in the artificial seawater. Additionally, the relationship between Cf and Cb or Ct can be described using different isothermal adsorption models for the CSA-based materials. Among these models, the Langmuir model is suitable for characterizing the relationship between Cf and Cb, while the Freundlich model is suitable for describing the relationship between Cf and Ct. Furthermore, it is noteworthy that sulfate ion attack and chloride binding exert nearly equivalent effects on the diffusion of chloride ions in CSA-based materials at short corrosion age and low chloride ion concentration. However, the corrosive impact of sulfate ions gradually evolves into the dominant factor in the progression of corrosion over time and the increase in seawater salt concentration.

Analysis of compressive failure mechanism of concrete and grouting cubes by Peridynamics

The structural failure forms and mechanisms of plain concrete, grout, and different aggregate concrete under the action of pressure have been puzzling the engineering and academic circles. To provide more favorable analytical means and theoretical support for structural damage and failure, this paper first adopts the experiments to analysis the compressive failure trend of cubic specimens of concrete and grout, and combines the results with the three-dimensional Peridynamics theory (PD) analyzed the damage trend and failure mechanism of the same tests with the same parameters under load. From the comparison, we can conclude that PD could truly analyze the failure mechanism of three-dimensional structures and was superior to the tests. Meanwhile, we also found that different number and position pebbles have a great influence on the failure path and damage mechanism of concrete.

Parameter calibration method of clustered-particle logic concrete DEM model using BP neural network-particle swarm optimisation algorithm (BP-PSO) inversion method

A high precision back propagation neural network-particle swarm optimization (BP-PSO) algorithm inversion method is proposed to calibrate the microparameters of the clustered-particle logic concrete discrete element method model. The calibration targets include initial damage, failure mode, and mechanical properties of the material. The research utilise 243 training datasets generated through orthogonal experimental design and conducted simulations to train the BP neural network. In addition, a parameter sensitivity analysis is employed on the trained BP neural network to quantify the impact level of each microparameter and guide future macroparameter fine-tuning. The results indicate that the mean absolute percentage error of the BP-PSO inversion method is only 3.79%. This research also study on the concrete failure mechanism by using a mesoscale model based on clustered-particle logic, which considered concrete as a three-phase composite composed of mortar matrix, aggregates, and interfacial transition zone. The crack initiation, propagation and coalescence of DEM model show a good agreement with the experimental results.

Abrasion resistance of concrete under coupled debris flow and freeze-thaw cycles

In cold regions, the coupled actions of freeze-thaw cycles and debris flow abrasion cause severe deterioration of concrete structures. The effects of freeze-thaw cycles (0, 10, 30, 50, 70), debris flow velocities (2.5 m/s, 3.0 m/s, 3.5 m/s), and abrasion modes (abrasion-freeze, freeze-abrasion) on the abrasion resistance are investigated in this study to enhance the anti-abrasion performance of concrete. Abrasion rate, abrasion depth, abrasion morphology, and abrasion failure mechanism of concrete are discussed. The results show that the abrasion resistance of concrete decreases with the increase of debris flow velocities and freeze-thaw cycles. The abrasion failure degree of concrete is exacerbated by freeze-thaw cycles. The abrasion rate of the reference concrete (R) increases by 62.5–117.7% after 70 freeze-thaw cycles, compared to the unfrozen concrete. Furthermore, the freeze-abrasion mode loses more strength and mass loss than the abrasion-freeze mode, particularly at high freeze-thaw cycles. When compared to the mass loss caused by freeze-thaw cycles, abraded mass loss is the primary cause of concrete mass loss under coupled freeze-thaw cycles and debris flow abrasion. Due to improved mechanical strengths, steel fibre-reinforced concrete performs well under coupled freeze-thaw cycles and debris flow abrasion conditions.

Strain rate effect on the fracture parameters of concrete three-point bending beam with a small span-to-height ratio

The fracture properties of concrete are greatly affected by strain rate, and changes in fracture parameters can reflect the crack resistance and failure mechanism of concrete. In this study, fracture tests were carried out on samples of concrete three-point bending beam (TPB) by considering 3 small span-to-height ratios (2, 2.5 and 3) and 4 strain rate grades (10−5/s, 10−4/s, 10−3/s and 10−2/s), in order to examine the strain rate effect on the fracture parameters of TPB. From the test data, the crack propagation rate, fracture toughness, length of fracture process zone (FPZ) and determination of damage scale were calculated. The results showed that the fracture parameters of TPB with a small span-to-height ratio were subjected to an obvious strain rate effect. With the increase of span-to-height ratio, the strain rate effect on the crack propagation rate, fracture toughness and determination of damage scale was gradually weakened, while that on the length of fracture process zone (FPZ) was gradually strengthened. Overall, changes in strain rate can significantly affect the fracture parameters of TPB with a small span-to-height ratio. This paper provides a reference for further research on the strain rate effect and failure mechanism of TPB with a small span-to-height ratio.

Experimental study on cracking behavior of concrete containing hole defects

Cavity often exists in the mass concrete when insufficient vibration occurs. These defects play an important role in the failure mechanism of concrete. Cracking behavior of surface flaws in concrete is widely investigated, while research on failure mechanism of internal flaws is limited because it is difficult to cut internal flaws in specimens and cannot capture the cracking processes of internal flaws through direct observations. In this study, a novel method for preparing concrete samples with embedded flaws is first proposed by volatilization of camphor. AE and CT techniques are adopted to investigate the internal damage failure behavior of hollowed concrete. Experimental results demonstrate that internal hole defects result in a reduction of strength and deformation properties of concrete materials. The peak strength, crack initiation stress, and deformation properties of hollowed concrete specimen decrease with the cavity diameters. Since hole defects induce high stress concentration which exacerbates crack initiation, AE events of specimen with an internal cavity occurred much earlier than the case of intact specimen. The ultimate failure modes of concretes are dominated by tension failure. For intact specimens, tension cracks mainly happen near to the boundaries of specimens. While for hollowed specimens, tension cracks initiated at the cavity perimeter, which then propagated to the boundaries of specimens.

The investigation into the failure criteria of concrete based on the BP neural network

This paper proposes a method for modelling the failure criteria of concrete through the back propagation (BP) neural network. The mappings between the inputs and outputs are constructed through the mechanical analyses based on two types of failure mechanisms of concrete. The influences of the number of neurons and the activation functions in the hidden layer on the modelling results are studied by tuning the hyperparameters of the neural network. The BP neural network is trained systematically with the hidden layer of different numbers of neurons to construct the failure criteria based on the octahedral shear stress and various failure modes of concrete, respectively. The models are examined by comparing the mean square errors (MSEs) and coefficients of determination (R2). And the geometrical characteristics of the failure surfaces, the tensile and compressive meridians and the envelope features on the deviatoric plane are analyzed to evaluate the failure criteria models. The optimal configuration of the BP neural network is selected through the comparative analyses including the number of neuronal nodes, the activation functions in the hidden layer, and the input and output variables. Compared with the Ottosen failure criterion, the failure surfaces obtained through the BP neural network achieve higher accuracy, being consistent with the morphological characteristics of the failure surfaces described by previous experiments and the classical hypotheses.

Study on Durability of Concrete under Alkali-Aggregate Reaction

The alkali-aggregate reaction has always had a great impact on the safety and durability of concrete projects. Therefore, the study of concrete failure mechanism under alkali-aggregate reaction has become a hot topic in the engineering field. This paper takes the Longtanqing debris flow ditch concrete treatment project as the background. Based on the alkali-aggregate reaction inhibition test under different conditions, regression analysis and trend surface analysis were used to study the correlation between fly ash content, expansion rate of concrete specimens, and curing age. And the engineering measures are put forward to effectively inhibit the alkali-aggregate reaction: (1) the optimum amount of fly ash appears at 30%-40%, fly ash has the strongest ability to inhibit alkali-aggregate reaction; when the content of fly ash is less than 20%, the fly ash ability to inhibit alkali aggregate reaction is weak. (2) To lower the height of the alkali content of concrete, there is 35% of the grade I class F coal ash as concrete admixture.

Concrete failure simulation method based on discrete element method

This paper improves the method of high-efficiency calibrating the meso-parameters considering the concrete aggregate gradation, and carries out numerical simulations of four-point bending strength test and direct shear strength test on concrete beams. Firstly, unconfined uniaxial compression test carried out to calibrate the meso-parameters of C40 concrete based on DEM. Secondly, the accuracy of the numerical model is verified according to the stress-strain curve and failure morphology of concrete prism. Finally, the crack propagation and load-displacement curves of concrete beams under four-point bending strength test and direct shear strength test were analyzed. The result show as follow: ① The DEM numerical model which take into account the concrete as a three-phase composite material can well realize the mechanical property of concrete. The display of force chains and micro-cracks greatly contributes to the concrete failure mechanism. ② The numerical model is generated by the random distribution of particles, which shows the characteristics of concrete heterogeneity, and defines the contact model between particles with parallel bond model (PBM). Compared with the numerical simulation and experiment results, the error is within 10.4%; ③ In four-point bending strength test, the crack initiates from the bottom edge of the beam and propagates upward. With the increase and coalescence of micro-cracks, only one concentrated, wide and long macro-crack is formed; In direct shear strength test, however, the high shear stress of two shear surfaces resulted in the generation of cracks. With the one side crack coalescence, the other side of crack initiate follow, and finally two coalescence macro-cracks are formed.

High fidelity 3D mesoscale modeling of concrete with ultrahigh volume fraction of irregular shaped aggregate

High fidelity mesoscale modeling techniques are of vital importance for exploration of mechanical behaviors and failure mechanisms of concrete. This paper presents an innovative approach in construction of 3D mesoscale models of concrete with ultrahigh volume fraction of randomly distributed irregular-shaped aggregate. The new modeling method combines Voronoi diagram-based method with take-and-place strategy. In this method, a database of irregular-shaped aggregate models is built based on computed tomography (CT) scan of real aggregates. Then the geometric models of concrete are constructed with the coarse aggregates generated by shrinking Voronoi cells and the fine aggregates packed through a modified take-and-place procedure. 3D mesoscale models of 50 mm × 50 mm × 50 mm concrete specimens are created by the proposed method and proven to bear a close resemblance to the real ones. Ultrahigh aggregate volume fraction up to 66.2 vol% is achieved in the model following the Fuller gradation. To demonstrate the reliability of the generated models, the results of finite element analysis for the epoxy polymer concrete under uniaxial compression is compared with the experimental data. The simulation well reproduces the mechanical behaviors of the epoxy polymer concrete.

Meso-concrete modeling based on laser scanning technology

<p indent="0mm">This contribution focuses on the construction of a 3D or 2D mesoscopic concrete model using laser scanning technology and the state dot-matrix method of aggregate placement. First, a 3D laser scanner was used to collect geometry information from real aggregates to create an aggregate library. The aggregates were then randomly selected from the aggregate library and placed according to the Fuller grading curve in order of reduction to produce a 3D mesoscopic concrete model. By cutting the 3D geometry model, a simplified two-dimensional plane geometry model was obtained. One of the benefits of laser scanning technology is that it ensures the realistic morphology of various aggregates while ensuring that the aggregate library perfectly meets the fundamental requirement for the construction of mesoscopic concrete models. Furthermore, the current aggregate placement algorithm allows for the efficient and rapid establishment of a concrete geometry model with microstructure. Finally, combined with the laboratory experiments of concrete, the influence of aggregate distribution on the failure mechanism of concrete was studied by the finite element method with the cohesive zone model under uniaxial compressions.

A Linear Elastic Fracture Mechanics Analysis of the Pre-Cracked Concrete Failure Mechanism Under Modes I, II, III, and IV Loading Conditions

A Linear Elastic Fracture Mechanics Analysis of the Pre-Cracked Concrete Failure Mechanism Under Modes I, II, III, and IV Loading Conditions

A Study on Fatigue Behaviors of Concrete under Uniaxial Compression: Testing, Analysis, and Simulation

Abstract The fatigue damage of concrete is an important reason for cracking and failure. To comprehensively study fatigue behaviors of concrete under uniaxial compression, cylindrical specimens with two different strength levels were made for cyclic loading tests. The evolution of fatigue process was detected via sensors, strain gages, and an X-ray computed tomography (CT) scanner. Parameters of fatigue life, deformation, internal cracks, and strength under different stress levels are analyzed based on measurements. The stress-cyclic number (S-N) equation is also given. Then, the fatigue damage parameter D is used to evaluate the status of damage. Additionally, a finite element modeling approach is developed based on the CT images to simulate the evolution of fatigue cracks within concrete specimens. With results of both macroscopic and microscopic analysis, the fatigue failure mechanism of concrete is expounded. The analysis results of this paper can provide a basis for the safety assessment for concrete structures.

Crack propagation studies in strain hardened concrete using acoustic emission and digital image correlation investigations

The crack formation, propagation and failure mechanism of concrete are very complex. Incorporation of fibers complicates it further, alters the damage characteristics of concrete. There is a consistent effort to impart the strain hardening properties, for which the special type of chemical fibers (Polyvinyl alcohol, PVA) is found to be very promising. Presently, an attempt has been made to understand the damage mechanisms of PVA fibers incorporated concrete (with three fibre dosages (0%, 1%, 2%) subjected to flexural loading using both contact (Acoustic Emission, AE) and noncontact (Digital Image Correlation, DIC) techniques. The advantages of AE which provides information on internal cracking and DIC which provides surface crack characteristics information are suitably exploited in this study. It was found that the combined use of both techniques has the potential to investigate the crack bridging phenomenon, to analyse the damage progression during loading, and to identify the critical failure mechanism and damage classification.

Microscopic Multiple Fatigue Crack Simulation and Macroscopic Damage Evolution of Concrete Beam

Microcracks in concrete can coalesce into larger cracks that further propagate under repetitive load cycles. Complex process of crack formation and growth are essentially involved in the failure mechanism of concrete. Understanding the crack formation and propagation is one of the core issues in fatigue damage evaluation of concrete materials and components. In this regard, a numerical model was formulated to simulate the thorough failure process, ranging from microcracks growth, crack coalescence, macrocrack formation and propagation, to the final rupture. This model is applied to simulate the fatigue rupture of three-point bending concrete beams at different stress levels. Numerical results are qualitatively consistent with the experimental observations published in literature. Furthermore, in the framework of damage mechanics, one damage variable is defined to reflect stiffness reduction caused by fatigue loading. S-N curve is subsequently computed and the macroscopic damage evolution of concrete beams are achieved. By employing the combined approaches of fracture mechanics and damage mechanics, made possible is the damage evolution of concrete beam as well as the microscopic multiple fatigue crack simulation. The proposed approach has the potential to be applied to the fatigue life assessment of materials and components at various scales in engineering practice.

Meso-Scale Simulation of Concrete Uniaxial Behavior Based on Numerical Modeling of CT Images.

It is important to study the failure mechanism of concrete by observing the crack expansion and capturing key structures at the mesoscale. This manuscript proposed a method for efficiently identifying aggregate boundary information by X-ray computed tomography technology (CT) and a discrete element modeling method (DEM) for equivalent random polygon aggregates. This method overcomes the shortcomings of the Grain Based Model (GBM) which is impossible to establish a mesoscopic model with a large difference in grain radius. Through the above two methods, the CT slice images were processed in batches, and the numbers of edges, axial length, elongation of the aggregate were identified. The feasibility of the method was verified by the comparison between experimental and simulating results. Three mesoscopic models for different porosities were established. Based on aggregate statistics, this manuscript achieved the meso-model recovery to the maximum extent. The test results show that the crack appeared at the tip of the aggregate firstly, and then the broken boundary was applied in the direction of the applied load and around the pores. Finally, the crack was selectively expanded under the axial force. During the loading process, the minor principal stress was normally distributed. As the porosity and loading time increased, the heterogeneity increased.

Mesoscopic Numerical Simulation of Fracture Process and Failure Mechanism of Concrete Based on Convex Aggregate Model

To investigate the fracture process and failure mechanism of concrete subjected to uniaxial compressive loading, a new finite element method—the base force element method (BFEM)—was adopted in the modeling of numerical simulation. At mesoscale, concrete is considered as a three-phase heterogeneous material composed of aggregate particles, cement mortar, and the interfacial transition zones between the two phases. A two-dimensional random convex aggregate model was established using the principle of the area equivalence method. A multistage linear damage constitutive model that can describe nonlinear behavior of concrete under mechanical stress was proposed. The mechanical properties of concrete mesoscopic components are determined. The numerical simulation results indicate that the base force element method can be applied to predict the failure pattern of concrete under compressive loading, which have a good accordance with the available experiment data. The stress contour plots were given and used to analyze the failure mechanism of concrete. The effects of specimen size on the strength of concrete material were studied. It is found that compressive strength of concrete decreases as the specimen size increases. In addition, the influences of aggregate distribution, coarse aggregate content, and end friction on concrete performance are explored.

Prediction of cracking, yield and ultimate strengths based on the concrete three-phase micromechanics model

On a microscopic scale, concrete was regarded as a three-phase composite consisting of coarse aggregate, cement mortar and interface transition zone (ITZ). The coarse aggregates and their peripheral ITZ were equated with equivalent particles blended in cement mortar through two equivalent processes. Taking the effects of ITZ, aggregate gradation, maximum aggregate size and the interactions among equivalent particles into consideration, the average stress of microscopic phase of concrete was calculated based on a micromechanics model, and the stress concentration within ITZ phase was further solved. Adopting the Drucker-Prager criterion to decide the failure of the microscopic phases, the cracking strength, yield strength and ultimate strength of the concrete were calculated respectively when the ITZ cracking, the ITZ failure and the mortar failure occurred. The results were compared with test data to verify the effectiveness and reliability of the model. Based on the model, the influence of the elastic modulus of coarse aggregate, the coarse aggregate content and the elastic modulus of ITZ on the yield strength and ultimate strength are discussed. This paper presents an approach to explore the connection between macroscopic strength and microscopic phase strength, which provides a theoretical reference for studying the failure mechanism of concrete.

Numerical simulation of the effect of bedding layer geometrical properties on the shear failure mechanism using PFC3D

In this research the effect of bedding layer angle and bedding layer thickness on the shear failure mechanism of concrete has been investigated using PFC3D. For this purpose, firstly calibration of PFC3d was performed using Brazilian tensile strength. Secondly shear test was performed on the bedding layer. Thickness of layers were 5 mm, 10 mm and 20 mm. in each thickness layer, layer angles changes from 0 to 90 with increment of 25. Totally 15 model were simulated and tested by loading rate of 0.016 mm/s. The results shows that when layer angle is less than 50, tensile cracks initiates between the layers and propagate till coalesce with model boundary. Its trace is too high. With increasing the layer angle, less layer mobilize in failure process. Also the failure trace is very short. It\'s to be note that number of cracks decrease with increasing the layer thickness. The minimum shear test strength was occurred when layer angle is more than 50. The maximum value occurred in 0. Also, the shear test tensile strength was increased by increasing the layer thickness.

Simulating Tensile and Compressive Failure Process of Concrete with a User-defined Bonded-Particle Model

A user-defined bonded-particle model (UBM) which is based on the modified parallel bond was established in this paper to investigate the tensile and compressive failure mechanism of concrete on the three-dimensional (3D) level. The contact constitutive relation and the failure criterion of the UBM can be added to the commercial discrete element software PFC^{3D} by compiling them as a dynamic link library file and loading it into PFC^{3D} whenever needed. In addition, the aggregate particles can be generated according to the volume fraction and the shape of each aggregate is irregular. Then, by comparing the results of numerical simulation with the results of laboratory tests, it is found that this bonded-particle model can simulate the tensile and compressive failure process of concrete well to a certain extent. Specifically, the two have basically similar failure patterns and stress–strain responses no matter under tension or compression loading condition. All results indicate that this UBM is a promising tool in understanding and predicting the tensile and compressive failure process of concrete.