Concrete Fracture Research Articles

Cause, Stability Analysis, and Monitoring of Cracks in the Gate Storehouse of a Flood Diversion Sluice

The cracks in a gate storehouse for a flood-diversion sluice of the Wangfuzhou Water Conservancy Project were studied to diagnose the structural safety. The study was based on an integrated method that involved the analysis of the cause of cracks, an assessment of the crack stability, online safety monitoring and diagnosis, and real-time monitoring and control. The results demonstrated that two dominant factors leading to cracks were the non-uniform settlement of the foundation of this gate storehouse structure combined with temperature drops in winter. By comparing crack-tip stress intensity factors at different cracking depths with concrete fracture toughness, the results showed that cracks at the gate storehouse would not continue to propagate, although some time-dependent components separated from the measuring point did not converge but tended to be closed. Therefore, the diagnosis suggests that the cracks at the gate storehouse are currently in a stable state. Additionally, the crack opening index estimated using the small probability method can be used for future real-time monitoring of crack behavior.

Review of Fracture Properties and Research Methods of Fiber Recycled Concrete

Aiming at the background of the application of fracture mechanics in fiber recycled concrete as well as the shortcomings of the current research, the relevant results and progress are summarized from three aspects, namely, the basic theory of fracture mechanics of fiber recycled concrete and the research progress of the fracture properties of fiber recycled concrete as well as the testing methods of the fracture of fiber recycled concrete, respectively. The development history of the application of fracture mechanics in concrete is described, three fracture forms, fracture process zones and three softening curve models of concrete are introduced, and it is proposed to combine the bilinear softening curve and the virtual crack zone model to construct the ontological relationship of the whole process of concrete cracking. The current research status of recycled brick aggregate concrete and polypropylene coarse fiber concrete is introduced. The incorporation of recycled brick aggregate adversely affects the workability, basic mechanical properties and fracture properties of concrete. The reinforcing effect of polypropylene fibers on concrete can effectively improve the adverse effects of brick aggregate on concrete, which opens up the research prospect of green concrete and has high research value. The applications of three-point bending test, four-point bending test and DIC technique in the study of concrete fracture characteristics are introduced.

Simulation of four-point bending tests for the viscoelastic fracture properties of concrete

Understanding the fracture properties of concrete, such as crack propagation behavior and fracture energy, is crucial for designing and evaluating concrete structures. Experimental results are insufficient and cannot be directly employed for a comprehensive analysis of the fracture behavior of concrete structures under load, particularly when considering concrete as viscoelastic with the presence of cracks. Recognizing the time and cost constraints of traditional experimental testing, this research leverages numerical simulations as a cost-effective alternative to determine viscoelastic material parameters. Thus, the critical evaluation of concrete fracture properties, fundamental for the design and assessment of concrete structures, is addressed. Employing a finite element method for four-point bending tests, the study systematically investigates parameters such as initial crack depth, displacement acceleration, and time step. The material properties of concrete are described using viscoelastic models. The findings provide valuable insights into crack propagation behavior and deformation characteristics, emphasizing the significant influence of the modulus of elasticity on both maximum load values and displacement. These findings contribute to a deeper understanding of the structure's response and underscore the importance of considering these parameters in similar simulations. The study highlights the importance of considering these parameters in simulations to enhance the understanding of concrete fracture behavior. The paper's contributions can extend to optimizing concrete mixtures, formulating repair strategies, and improving structural assessments. Further research is suggested to improve the accuracy of simulations and investigate material properties under various conditions.

The influence of fiber content and voltage on the impact resistance of carbon fiber reinforced concrete

The method of machine test was used in this study to analyze the influence of carbon fiber content and voltage strength on the impact resistance of carbon fiber concrete by recording the number of impacts to carbon fiber concrete fracture failure. The results show that as the volume content of carbon fiber increases, the impact resistance to the specimens increases first and then decreases. The impact resistance reaches maximum that the content of 0.24 %, and the calculation formula for the number of impacts to concrete beams under different carbon fiber content in the test is obtained. However, the impact resistance is in a state of overall reduction under the action of voltage, and the reduction range is obvious, indicating that the voltage effect has a negative impact on the impact resistance of carbon fiber concrete.

Experimental and numerical investigation of steel fiber concrete fracture energy

This research investigates the influence of steel fibers on the mechanical properties and behavior of concrete through a combination of numerical simulations and laboratory experiments. A series of numerical models were developed and validated against experimental results, employing circular-shaped aggregates to ensure model accuracy. The load-CMOD diagrams revealed that an increase in the percentage of steel fibers led to significant improvements in the tensile strength and energy absorption of the concrete specimens. The presence of steel fibers acted as an effective barrier, inhibiting crack propagation and enhancing the energy absorption capacity of the concrete. However, beyond a certain fiber percentage (approximately 4%), the increase in energy absorption became limited due to reduced bonding forces between the fibers and cement mortar, resulting in premature failure of the specimens. The numerical models provide valuable insights into the behavior of fiber-reinforced concrete, facilitating the optimization of concrete design for various engineering applications. This study contributes to a broader understanding of fiber-reinforced concrete behavior and underscores the significance of selecting the optimal fiber content and distribution for specific construction scenarios. Further research is encouraged to explore the complex mechanisms of fiber-matrix interaction in concrete for developing more resilient and durable concrete structures.

Fracture Simulation of Concrete Beams to assess softening behavior by varying different fractions of Aggregates

Simulating the concrete fracture unlike other elastic and brittle materials quite different due to its quasibrittleness. The present research focussed on assess softening behavior by varying different fractions of aggregates and cement matrix in micro details. Extended Finite Element Method (XFEM) for crack modeling implemented for simulating and visualizing crack propagation through Cement matrix, Interfacial Transition Zone (ITZ) and Aggregates . This approach permits the initializing crack by from enrichment zone and propagation of crack through element by traction separation law .The crack formation initiates when the maximum principal tensile stress reaches the tensile strength. The work involves creating python script for iterative process of random distribution of aggregates with in the matrix using Monte Carlo method and creating Cohesive zone element for zero thickness ITZ. introduces a finite element modeling technique for investigating multiscale fracture characteristics. This approach encompasses multiple levels of analysis, including the generation of aggregate particles using a Monte Carlo method implemented via a Python script. Additionally, we replicate the Interfacial Transition Zone (ITZ) between aggregate and mortar in the model. The load-deflection curves can be used to assess the softening behavior of concrete and suggest the realistic fraction of coarse aggregate in mix proportion to impart more ductility to beams.

Coupled hygro-thermo-mechanical peridynamic model for concrete fracture analysis at high temperature

Coupled hygro-thermo-mechanical peridynamic model for concrete fracture analysis at high temperature

A Cosserat peridynamic model with Bresler–Pister criterion and numerical simulation of concrete fracture

A Cosserat peridynamic model with Bresler–Pister criterion and numerical simulation of concrete fracture

Interaction between Groundwater and Rock Fractures under Stress and Seepage Based on Extractive Water Resource Utilisation

In the fragile mining areas of western China, the contradiction between coal mining and water resource protection coexists prominently. Facing this issue, it is necessary to understand the dynamic relationship between mining-induced shear stress and groundwater seepage, as well as the fracture morphology of the overlying strata. In this study, the seepage characteristics of rough fractures within the rock mass are thoroughly investigated, with an emphasis on studying the effects of shear stress and seepage erosion. This research is carried out through seepage experiments and 3D fracture morphology scanning, and the research results are mainly as follows: (a) Rocks with higher shear strengths show less fluctuation in changes in fracture morphology and seepage velocity. (b) The permeability of sandstone and concrete fractures is inversely proportional to the shear stress. The layering of coal greatly limits seepage through the fractures and the permeability of coal is about one-tenth of the permeability of sandstone and concrete under the same conditions. (c) The mechanism of erosion damage to the rock by water-force coupling is the result of the shear and extrusion generated by rock fractures and the transport of rock particles. Changes in fracture erosion and seepage characteristics brought about by the damage will mutually promote and intensify the erosive effect of water force. (d) The degree of change in fracture morphology (fracture damage) under the same conditions is coal > concrete > sandstone. There are differences in the response of different types of rock to the shear stress–seepage erosion, but all show obvious changes in fracture damage and seepage characteristics.

Investigation of Ultrahigh-Performance Concrete Fracture Characteristics with Different Steel Fiber Fractions Based on Acoustic Emission

Investigation of Ultrahigh-Performance Concrete Fracture Characteristics with Different Steel Fiber Fractions Based on Acoustic Emission

An ultrasonic approach for characterising subsurface fractures in concrete

ABSTRACT An ultrasonic Rayleigh wave detection method is proposed to determine the geometrical characteristics of subsurface small-scale fractures in concrete. A three-dimensional observation system, including an inclined wedge ultrasonic device, is used to obtain the Rayleigh wave wide-angle data to exhibit the azimuth-dependent scattered wave field. The anisotropic characteristics of Rayleigh wave transmission coefficient are used to determine the distribution range and dip angle of fractures. Fracture models in concrete with different dip angles are designed, and the dip angle is correlated with the degree of attenuation (transmission coefficient) anisotropy. The transmission coefficient characteristics are presented in a random observing system. A focusing approach can be adopted to distinguish the subsurface fracture and to verify the reliability and flexibility of the surface wave approach in practice. The tendencies of experimental results are consistent with patterns obtained from numerical simulation. The proposed method has important application prospects for the non-destructive testing of complex invisible fractures in concrete.

Investigation of driving forces in a phase field approach to mixed mode fracture of concrete

Concrete, with its heterogeneous internal structure of cement mortar and grains, exhibits complex quasi-brittle cracking where a gradual decrease in the material integrity is observed. In practical engineering, concrete structures are commonly under loading conditions that cause complex mixed mode fracture patterns. Hence, the prediction of failure mechanisms and patterns in concrete is a demanding task. In the past decades, computational fracture modeling of concrete has proven to be a suitable substitute for costly experimental testing. Among many fracture models, the phase field approach, owing to its ability to capture various crack phenomena without a need for ad hoc criteria, has gained significant attention. Although there exist phase field models applied to various failure mechanisms ranging from brittle to ductile fractures, only a limited number of them deal with the quasi-brittle cracking observed in concrete. Hence, in this work, a thermodynamically consistent phase field approach for quasi-brittle fracture is presented, and its performance for capturing the mixed mode failure patterns of concrete is investigated. Starting from a purely geometric approach, the evolution of fracture is associated with a constitutive crack driving functional. The crack driving force is related to an equivalent effective stress measure leading to a simple, yet versatile, framework in which various failure criteria can be implicitly incorporated into the framework. In particular, equivalent effective stresses based on the Rankine, Drucker–Prager, modified von Mises, and three-parameter failure criteria are derived. A unified form of the equivalent effective stress encompassing all the models is also proposed, which offers flexibility in choosing an appropriate driving force, and allows a simple implementation into a finite element framework. Utilizing this unified form, the effectiveness of the aforementioned driving forces in capturing complex mixed mode cracking in concrete is investigated by comparing the results obtained from computational simulations to existing experimental data. In particular, the load–displacement curves and the crack propagation paths are compared with the corresponding experimental observations, and a systematic study of the performance of different driving forces is detailed in this study.

Recycled Fine and Coarse Aggregates' Contributions to the Fracture Energy and Mechanical Properties of Concrete.

This paper investigates the fracture mechanical properties of concrete, using crushed concrete aggregates (CCA) and granulated blast furnace slag (GGBS) for partial cement replacement. CCAs made from prefabricated concrete replace 100% of the fine and coarse fractions in concrete recipes with w/c ratios of 0.42 and 0.48. Two pre-treatment methods, mechanical pre-processing (MPCCA) and accelerated carbonation (CO2CCA), are investigated for quality improvements in CCA. The resulting aggregates show an increased density, contributing to an increase in the concrete's compressive strength. The novelty of this paper is the superposition of the effects of the composite parts of concrete, the aggregate and the cement mortar, and their contributions to concrete fracture. Investigations are directed toward the influence of fine aggregates on mortar samples and the influence of the combination of coarse and fine aggregates on concrete samples. The physical and mechanical properties of the aggregates are correlated with mortar and concrete fracture properties. The results show that CCA concrete achieves 70% of the fracture energy values of concrete containing natural aggregates, and this value increases to 80% for GGBS mixes. At lower w/c ratios, MPCCA and CO2CCA concretes show similar fracture energies. CO2CCA fine aggregates are the most effective at strengthening the mortar phase, showing ductile concrete behavior at a w/c ratio of 0.48. MPCCA aggregates contribute to higher compressive strengths for w/c ratios of 0.42 and 0.48. Thus, mechanical pre-processing can be improved to produce CCA, which contributes to more ductile concrete behavior.

Modeling tensile failure of concrete considering multivariate correlated random fields of material parameters

This paper presents a novel approach for modeling the tensile failure of quasi-brittle materials by incorporating a multivariate random field to represent material parameters in the phase field model. The aim is to characterize and propagate uncertainties in the behaviors of materials, taking into account the spatial variability and probabilistic dependence. Copula theory is employed to investigate the probability distributions and dependence configuration of the parameters. The proposed framework combines the generation approach for the multivariate random field with the phase field model, resulting in a complete numerical analysis methodology. The governing equations of the deterministic phase field model for quasi-brittle solids are outlined, followed by a description of the multivariate random field for quasi-brittle media and its uncertainty characterization procedure using copula theory. A numerical approach for generating samples of the multivariate random field is introduced. The numerical analysis procedure for the tensile fracture of concrete is presented, and the effects of material uncertainties on failure patterns and macroscopic responses are discussed. The results demonstrate that the developed methodology effectively captures the random damage and fracture processes in concrete specimens. The interaction between the correlation length of the random field and the characteristic length scale of the phase field significantly influences the probabilistic characteristics of the random responses. The research findings emphasize the importance of determining the correlation length values accurately. This study contributes to the field of structural reliability analysis by providing a comprehensive framework for modeling the stochastic behavior of quasi-brittle materials. The integration of a multivariate random field and copula theory allows for the realistic representation of material uncertainties and their probabilistic dependence. The proposed methodology, combined with the probability density evolution method (PDEM), offers a powerful tool for analyzing and predicting the probabilistic evolution of material behaviors under tensile loading conditions.

Experimental and Numerical Study of Concrete Fracture Behavior with Multiple Cracks Based on the Meso-Model.

In this paper, a series of experimental and numerical studies were carried out to investigate the effect of multiple cracks on concrete fracture behavior. Seven groups of double-crack concrete three-point bending (TPB) experiments with different crack lengths and different crack distances were carried out. The experimental results showed that the bearing capacity of double-crack specimens was slightly larger than the standard specimen with one central crack. Additionally, with an increase in the second crack length or with a crack distance reduction, the concrete's bearing capacity increased correspondingly. Based on the experiments, a numerical meso-model was developed based on applying cohesive elements. The aggregate, mortar, interface transition zone (ITZ), and potential fracture surfaces were explicitly considered in the model. In particular, cohesive elements were used to characterize the mechanical behavior of the ITZ and potential fracture surfaces. A modified constitutive concrete model was developed by considering the potential fracture surfaces' damage relation and friction effect. The accuracy of the developed meso-model was validated through a comparison between simulation and experiments. Based on meso-models, the influence of multiple cracks on the concrete bearing capacity was investigated by analyzing the energy evolution. The analysis results showed that the bearing capacity has a linear relation with the proportion of mode II energy consumption during the fracture process, which explains why specimens with multiple cracks have a slightly larger bearing capacity than the standard specimens. In summary, this study has found that in three-point bending fracture tests primarily characterized by mode I fractures, the presence of multiple cracks near the main crack slightly enhances the load-bearing capacity of the specimens. This is attributed to a slight increase in internal energy dissipation associated with the presence of these multiple cracks.

Study on stage characteristics of hydraulic concrete fracture under uniaxial compression using acoustic emission

ABSTRACT Acoustic emission (AE) can monitor and evaluate the cracking situations of hydraulic structures for it is real-time and non-destructive. However, a current challenge of this approach is to accurately identify the various stages during the cracking process. The innovation of this paper lies in the application of AE data in analyzing the stage characteristics during the whole process of hydraulic concrete fracture. First, the slope changing of the cumulative ringing count curve was used to determine the cracking stages of hydraulic concrete. Second, the function of inter-event times (denoted as F-function) was used to further investigate the AE characteristics proximity to the final fracture. Last, the spatial-temporal-energy evolution of cracks was studied. The results show that: (1) The whole process of hydraulic concrete failure shows an obvious stage characteristic from the perspective of AE feature and it can be distinguished to five stages by the slope change of the cumulative ringing count curve; (2) The F-function can be used to identify the last two cracking stages, and it is capable of early warning the macroscopic cracking in ahead of b-value; (3) The spatial-temporal-energy distribution of cracks helps to better understanding the generation and evolution for cracks inside hydraulic concrete.

Real Time Assessment of Smart Concrete Inspection with Piezoelectric Sensors

Utilization of an Electromechanical impedance (EMI) technique with Piezoelectric (PZT) sensors has showed potential for Structural Health Monitoring (SHM). The changes in mechanical structure via flexural bending and cracking can be detected by monitoring the deviations in electrical impedance signals recorded with embedded PZT sensors. This paper has conducted a comprehensive study on the potential of an EMI technique with embedded PZT sensors with 3D Concrete Printing (3DCP) structures subjected to flexural bending test until plastic failure. The impact of different Piezoelectric housing methods and materials has been studied comprehensively through the monitoring of EMI signals. Experimental results indicate that material housing types and thickness affect the sensitivity of EMI readings but also performed as a reinforcement when a load is directly applied. The embedded PZT sensors with the EMI technique have shown strong potential to address the cost and lifecycle challenges posed by traditional construction methods as the insertion of PZT sensors seamlessly functions with 3DCP workflows. Further developmental work can be carried out to address the sensitivity of the sensor, performance as a reinforcement, and installation automation. The results proved that the coated sensors could detect fractures in 3DCP concrete with decreased sensitivity on thicker coating layers through the variance in materials and coating thickness in the paper.

Models of nonlinear deformation of concrete in a triaxial stress state and their implementation in the PRINS computational complex

Modern construction standards and regulations prescribe to carry out calculations of concrete and reinforced concrete structures in a nonlinear formulation with account of the real properties of concrete and reinforcement. However, the most of finite-element program complexes cannot perform such calculations in a nonlinear formulation with account of plastic deformations of concrete and reinforcement. To solve this problem, a methodology has been developed and a solid finite element adapted to the PRINS computing complex has been created, which made it possible to perform calculations of reinforced concrete structures considering their actual work. The aim of the study - development and implementation of a method for calculating reinforced concrete structures under conditions of a three-dimensional stress state, considering both brittle fracture and elastic-plastic deformation of concrete. A finite-element methodology, algorithm, and program for calculation of massive reinforced concrete structures with account of plastic deformations of concrete have been presented. The methodology is based on the modified Willam and Warnke strength criterion supplemented with the flow criterion. Two models of volumetric deformation of concrete have been regarded: the elastic model at brittle failure and the ideal elastoplastic model. An eight-node finite element with linear approximating functions of displacements implementing the mentioned deformation models is created. Verification calculations of a massive concrete structure in three-axial compression testify to the accuracy and convergence of the developed finite elements. The PRINS can be effectively used by engineers of designing and scientific organizations to solve a wide class of engineering problems related to calculations of building structures.

Effect of fibre diameter and tensile strength on the mechanical, fracture, and fibre distribution properties of eco-friendly high-strength self-compacting concrete

The development of Steel Fibre-Reinforced Self-Compacting Concrete (SFR-SCC) is a complex task with significant practical implications for the construction industry. However, the absence of established design guidelines and recommendations, and the limited availability of design methodologies, present a significant challenge. Achieving the targeted rheological and mechanical properties while simultaneously minimising production costs requires a comprehensive understanding of the optimal blend of fibre type and quantity and the coarse aggregate content. This paper addresses the impact of steel fibre properties on the rheological and fundamental mechanical properties of eco-friendly high-strength self-compacting concrete (HSSCC), using 40% ground granulated blast furnace slag (GGBS) as a cement replacement. The research focused on 30 mm long hooked-end steel fibres with tensile strengths of 1345 MPa and 3070 MPa, and diameters of 0.55 mm and 0.38 mm, respectively. In addition, the study investigated the combined effect of coarse aggregate content and steel fibre type on the performance of eco-friendly HSSCC. The fresh properties of eco-friendly HSSCC were assessed using the slump flow and J-ring tests. Furthermore, mechanical and fracture properties such as compressive strength, splitting tensile strength, elastic modulus, four-point flexural strength, and three-point flexural strength on notched prisms were also evaluated. The distribution and alignment of steel fibres in the HSSCC were assessed using image analysis techniques, which showed that the steel fibre diameters were a crucial factor in the fibre dispersion. The results demonstrated that using steel fibres with higher tensile strength and smaller diameter significantly enhanced the splitting tensile strength, flexural strength, and fracture energy, compared to steel fibres with larger diameters and lower tensile strengths. Additionally, the study indicated that the elastic modulus and fracture energy of eco-friendly HSSCC reinforced with both types of steel fibre are highly dependent on the content of coarse aggregate used. The study highlighted that the coarse aggregate proportion and the steel fibre characteristics were two vital factors that influenced the rheological and mechanical properties of HSSCC and must be considered during the mix design process to optimise the desired properties while also minimising production costs.

Studying the rheological features, mechanical properties and flexural toughness of the WSFRSCC by varying the coarse aggregate volume

The low tensile strength of concrete structures requires studying the effects of fibers on the performance of fresh and hardened concretes where finding the right amount of coarse aggregates is a challenge in the concrete industry. This study has addressed the effects of increasing the volumes of wavy steel fibers (0.15, 0.3 and 0.45%) and coarse aggregates (30, 40, 50 and 60%) on fresh concrete parameters and Self-Compacting Concrete (SCC) strength and fracture characteristics. Results have shown that using wavy steel fibers has negative effects on the properties of the fresh SCC because its efficiency and flowability are reduced, and increasing the coarse aggregate volume has positive effects because the rheological properties are improved. On the other hand, increasing the wavy steel fiber volume will improve the compressive strength in concretes containing 50 and 60% coarse aggregates. Only in 60% coarse-aggregate concretes, increasing the fiber volume from 0.15 to 0.45% will slightly reduce the wavy steel fiber reinforced self-compacting concrete (WSFRSCC) tensile strength. Increasing the coarse aggregate volume (30% – 60%) will improve the elasticity modulus of specimens with fixed percent fiber. Comparison of ASTM C 1609, JSCE SF-4 and JG/T 472-2015 methods revealed that the latter could well provide a thorough understanding of the variations of the flexural toughness of the WSFRSCC due to the demarcation of the pre- and post-peak load areas.