Failure Of Concrete Structures Research Articles

Study on Prediction Method of Infrasound Waves for Concrete Structure Destruction in Underground Space

To study the characteristics of infrasonic wave response during the failure process of concrete samples and analyze the feasibility of infrasonic wave prediction for the failure of concrete structures in underground spaces, rock mechanics loading devices and infrasonic wave acquisition devices were used to carry out infrasonic wave test experiments on concrete samples during uniaxial loading. With the help of MATLAB numerical simulation software, the test results are processed and analyzed by constructing band-pass filtering program, wavelet denoising program and time–frequency analysis program. The analysis results show that: there is infrasound wave during the loading process of the concrete sample; During the loading process, the change of infrasonic wave presents stage characteristics, which can be divided into three stages: the initial stage when a certain amount of infrasonic events occur, the middle stage when there are few infrasonic events and the later stage when infrasonic events increase rapidly and reach a peak. These stages respectively correspond to the compaction deformation stage, elastic deformation stage, plastic deformation and later stage of concrete sample deformation, and there is a good corresponding relationship between them. When the concrete sample is damaged by the peak value, the frequency and amplitude of the infrasound wave have abnormal changes. Therefore, in the early stage of the failure of the concrete structure, when the local failure occurs, there is also an abnormal response of infrasonic wave and the failure of the concrete structure can be predicted based on the abnormal change. At the same time, the infrasound wave, as a kind of low-frequency wave, has the advantages of long propagation distance, small attenuation and flexible position arrangement and has stronger adaptability to the complex underground space environment. It is of great significance to improve the accuracy of underground space concrete structure failure prediction.

Efficient crack detection and quantification in concrete structures using IoT

ABSTRACT Now-a-days public transit in our country has a significant usage of bridges and tunnels. Maintaining the safety of such structures becomes the need of the hour. Cracking can invite sudden failures of concrete structures. Within recent years, there has been an increase in the use of image processing techniques as Non-Destructive Testing (NDT) method to detect defects and anomalies in such structures. Hence, this work presents an efficient image processing model for identifying and quantifying the cracks in common structures using two algorithms. The first algorithm uses pattern classification method to classify the identified specimens as crack or not. This pattern classification algorithm is tested and evaluated with the test specimens of structures having induced cracks. The second algorithm called morphological processing uses an efficient thresholding strategy to improve the detection accuracy of the cracks. Here the aim is to detect even the faintest of cracks and magnify them. Thus, any one of the algorithms can be adopted depending on the application. The developed algorithms have been tested in real field at the final stage and achieved a detection accuracy of nearly 96.37%and all the obtained images have been stored digitally on a web server.

Structure-modulated CaFe-LDHs with superior simultaneous removal of deleterious anions and corrosion protection of steel rebar.

The three anionic species; chloride (Cl−), sulfate (SO42−), and carbonate (CO32−), are typical chemical factors that environmentally accelerate failure of concrete structures with steel rebar through long-term exposure. Efficient removal of these deleterious anions at the early stage of penetration is crucial to enhance the lifespan and durability of concrete structures. Here, we synthesize CaFe-layered double hydroxide (CaFe-LDHs) by a simple one-step co-precipitation technique and structural modulation by calcination process. It is applied for the removal of Cl−, SO42−, and CO32− anions as well as corrosion inhibition on steel rebar in aqueous solutions. The synthesized CaFe-LDHs with phase transfer show notable improvement of removal capacity (Qmax) toward Cl− and SO42− over 3.4 times and over 5.69 times, respectably, then those of previous literatures. Furthermore, the steel rebar exposed to an aqueous solution containing the three anionic sources shows a fast corrosion rate (1876.56 × 10−3 mm per year), which can be remarkably inhibited showing 98.83% of corrosion inhibition efficiency when it is surrounded by those CaFe-LDHs. The novel adsorption mechanisms of these CaFe-LDHs-induced crystals and corresponding corrosion protection properties are elucidated drawing on synergy of memory effects and chemical reactions.

Multiscale modeling of distributed microcracking in concrete

AbstractConcrete is a quasi‐brittle material with a heterogeneous morphology across multiple scales, which also influences the evolution of damage in case of loading. Damage in concrete structures is initiated by growth of diffuse microcracks that is followed by damage localization eventually leading to structural failure. Thus, diffuse microcracking processes can be considered as failure precursors. Identification and characterization of these precursors can be applied in conjunction with structural health monitoring based on diffuse ultrasonic waves to develop early warning systems against catastrophic failure of concrete structures. To this end, a multiscale model for a simulation‐based description of diffuse damage in concrete is proposed. At the scale of the cement paste, microcrack growth is modeled by a combination of continuum micromechanics and linear elastic fracture mechanics [1]. The micromechanics model is incorporated into a reduced‐order Lippmann‐Schwinger based meso‐model for concrete [2], [3]. The mesoscale model is generated using Random Sequential Adsorption of realistic aggregates based on concave slicing of randomly cut polyhedrons. The influence of the microcrack morphology at the microscale on the diffuse microcracking and overall concrete stiffness degradation is presented.

Effects of freezing conditions on the frost resistance and microstructure of concrete

Repeated freezing and thawing (F-T) cycles are the major reason for the frost damage and premature failure in concrete structures. Frost damage can be evaluated by its effects on formation of internal cracks and scaling at the surface of concrete. Both internal frost damage and surface scaling mechanisms depend on several environmental factors such as the rate of freezing, minimum temperature and the duration at the minimum temperature.The objective of this study is to investigate the effects of freezing conditions on the type and intensity of damage, and on microstructure of concrete. Investigations, within the scope of this research, indicated that freezing conditions significantly affect the F-T resistance assessment of the concrete mixtures. Microstructural examinations also revealed the severity of the scaling under slower freezing rate and longer exposure time at the minimum temperature. Therefore, examination of the local freezing and thawing regime is crucial for designing durable and sustainable concrete structures.

Experimental Investigation of Damage Evolution Characteristics of C50 Concrete under Impact Load

Impact loads widely exist in practical engineering and often cause cumulative damage and cracks or even fracture failure of concrete structures with their repeated long-term action. This experimental research is conducted on the damage evolution characteristics of concrete under impact loads by regarding C50 nonreinforced concrete as the research object and using a self-developed drop-weight device with electromechanical impedance measurement technology. Results show the following. (1) Under low-energy impact, concrete damage has long continuous development process and remarkable cumulative effects. An apparently sudden break characteristic appears before failure. Under high-energy impact, concrete damage accumulates rapidly, and piezoceramic patch signals grow linearly. (2) The root mean square deviation (RMSD) of the concrete increases exponentially with impact times. Particularly, when the RMSD exceeds 0.075, the concrete damage process enters the rapid development stage and approaches the critical failure state. (3) Under the experimental conditions in this study, the relationship between the ultimate impact times (damage life) and impact heights of the concrete samples shows the development trend of the power function. The above results can provide reference for the research on service life prediction methods of concrete structures under impact loads.

Numerical predictions of failures in concrete structures subjected to intense dynamic loadings using the Smooth Particle Hydrodynamics method

Typical failures such as cratering and spalling are frequently observed on the frontal and distal surfaces of concrete structures when subjected to blast and impact loadings. Numerical predictions of these failures call for an accurate material model and an appropriate algorithm, which is a topic of current research. In this paper, the inherent limitations of the frequently-used finite element method to predict dynamic failures in concrete with the aid of element erosion technique are firstly discussed. Motivated by the natural advantages of the meshfree method to describe the high deformation and large strain situations, the Smooth Particle Hydrodynamics (SPH) method is then combined with our recent KFCW material model to numerically predict dynamic failures in concrete structures. By comparing the numerical predicted failures with the post-test observations of two field tests, it is demonstrated that the SPH method combined with the new material model provides a promising way to predict the dynamic failures without introducing empirical and artificial parameters.

Research on durability evaluation of concrete in complex attack environment

In this study on concrete durability under a single environment, considering the meteorological data to determine the environmental correction coefficient, the computational model of concrete ultimate durability life under one environment is improved. Damage is defined as the ratio of service life to ultimate durability life, and it specifies the failure of concrete structures when the damage comes to 0.8. The Analytic Hierarchy Process (AHP) is modified by replacing the conventional fuzzy scale to the priority of every single environment determined by the ultimate durability life span of each environment. The weight of every environment is settled by modified AHP and is used to improve Miner linear cumulative criteria. Then, the computational model of concrete ultimate durability life under a complex environment based on damage is established, the applicability of which is verified by comparing the prediction results and field data in Tianjin and Yantai ports. This paper also improves set pair analysis by dividing the stability range with comprehensive index connectivity, and then, the evaluation of levels of concrete durability stabilization is developed.

A New 3D Empirical Plastic and Damage Model for Simulating the Failure of Concrete Structure

A new plastic–damage constitutive model based on the combination of damage mechanics and classical plastic theory was developed to simulate the failure of concrete. In order to explain different material behaviors of concrete under tensile and compressive loadings, the plastic yield criterion, the different kinematic hardening rule for tension and compressive and the isotropic flow rule were established in the effective stress space. Meanwhile, two different empirical damage evolution equations were adopted: one for compression and the other for tension. A multi-axial damage influence factor was also introduced to fully describe the anisotropic damage of concrete. Finally, the model response was compared with a wide range of experiment results. The results showed that the model could well describe the nonlinear behavior of concrete in a complex stress state.

Long-tern field test and numerical simulation of foamed polyurethane insulation on concrete dam in severely cold region

Abstract The environmental temperature is the key factor for cracking failure of mass concrete structures in severely cold regions. In this paper, field test and numerical calculation of long term insulation are carried out to prevent thermal cracks, and ensure the durability and safety of concrete arch dam. Firstly, an equivalent simulation element for concrete-polyurethane composite structure and its calculation method is proposed, based on the equivalence idea of heat emission coefficient for concrete layer and surface insulation layers with different thickness. Secondly, field tests are demonstrated on an 87.5 m height concrete gravity-arch dam, named Xianghongdian dam, from January 1, 2001 to May 30, 2017. Distributions laws, change laws of temperature field and horizontal displacement of the dam, before and after setting polyurethane insulation layer, are compared deeply. Then, the insulation effects of different thicknesses of foamed polyurethane layer are investigated upon the establishment of a FEM model of a concrete arch dam in northwest China. Consequently, stress fields under different broken conditions of polyurethane insulation layer with different typical temperature loads in severely cold region are calculated and analyzed. The results show that the polyurethane insulation layer generally decreases the temperature change range of concrete dam body over 30% in all conditions and even 90% at some locations. Accordingly, the horizontal displacement component, caused by dam temperature, decreases greatly from 10.80 mm to 2.34 mm and its contribution ratio to yearly horizontal displacement decreases from 75.11% to 36.23%. The insulation layer broken would result in a sharp increase of tensile stress of the corresponding area, with the combination influences of low temperature and cold wave. Under small broken condition, the tensile stress increases from 3.69 MPa to 7.57 MPa among broken area; while under large broken condition, the tensile stress increases to 8.68 MPa, which exceeds the maximum tensile stress of concrete material. In this case, a cracking failure of concrete structure would happen. As the dam concrete is an insulation material in some degree, the stress filed doesn’t change a lot in areas the insulation layer is unbroken.

Effects of SiO2 nanoparticles dispersion on concrete fracture toughness

Failure of concrete structures is usually accompanied by expansion of interior cracks due to stress concentration at the cracks tip. This phenomenon shows the importance of examination of the failure behavior of concrete structures. For this purpose, 4 types of concrete samples with different amounts of nano-SiO2 (0%, 0.2%, 0.5%, and 0.8%) were made to prepare some Central Straight-through Crack Brazilian Disk (CSCBD) specimens. The key focus of the investigation conducted was to investigate two assumptions. First, to check the pure mode I (tension) and pure mode II (shear) by compressing the standard discs with central cracks by an angle of 0° and 27° with respect to the loading axis; Second, to investigate the failure behavior of control and binary blended concrete using Acoustic Emission (AE) technique. The results show that the highest fracture toughness in both mode I and II was obtained at 0.5% of nano-SiO2 blended concrete. Also the behavior of micro cracks which transforms from tensile mode to shear mode could be sensible.

Time-and-Depth-Dependent Model of Chloride Diffusion Coefficient for Concrete Members Considering the Effect of Coarse Aggregate

AbstractChloride-induced reinforcement corrosion is one of the major causes of durability failure of concrete structures in a salty environment. Because concrete is a kind of heterogeneous material...

Categorization of Faults and Failures in Concrete Structures, Its Causes and Magnitude of Effects

Categorization of Faults and Failures in Concrete Structures, Its Causes and Magnitude of Effects

Three dimensional plastic-damage multidirectional fixed smeared crack approach for modelling concrete structures

A constitutive model to simulate the behaviour up to the failure of concrete structures subjected to multiaxial loading is presented. The proposed model is based on the combination of 3D multidirectional fixed smeared crack model to simulate the crack initiation and propagation, and a plastic-damage model to account for inelastic compressive behaviour of the intact concrete between cracks. The adopted smeared crack model considers the possibility of having more than one crack of different orientation in the same integration point and in different evolution of the cracking process. The plasticity part accounts for the development of irreversible strains and volumetric strain in compression, whereas the strain softening and stiffness degradation of the material under compression are controlled by an isotropic strain based damage model. The constitutive model was included in the 3D solid finite element of the FEMIX computer code, and the model appraisal is performed by simulating experimental tests with structural reinforced concrete (RC) elements. The numerical simulations have predicted with good accuracy the load carrying capacity, deformation, crack pattern, and plastic (compressive) zones of all analyzed tests. A parametric study is also performed to appraise the sensitivity of the numerical simulations to the values adopted for the model parameters.

Simplified structural deterioration model for reinforced concrete bridge piers under cyclic loading

Deterioration due to reinforcement corrosion represents a significant cause of damage to reinforced concrete bridges all over the world. Although numerous studies have identified the substantial influence that corrosion can have on the failure of concrete structures under seismic loads, there has been comparatively less work done on the modelling of structural vulnerability due to corrosion. Accurate and computationally efficient structural modelling of corrosion deterioration is an essential prerequisite for structural reliability or fragility prediction, or life cycle cost and impact estimation. In this paper, a simplified approach for modelling reinforced concrete bridge columns that have undergone deterioration due to chloride-induced reinforcement corrosion is presented. While several models of increasing complexity are evaluated, a simplified non-linear analytical model that accounts primarily for the reduction in the steel cross-section due to corrosion is the central focus of the paper. The accuracy of the simple model is validated by comparing analytical results with experimental tests on reinforced concrete columns subjected to accelerated corrosion. The model results show excellent agreement with the experimental tests, making it particularly suitable for applications in vulnerability or reliability analysis where numerous non-linear dynamic analyses are necessary, or for further downscale or upscale integration with materials-level or system-level models.

Electrochemical process to improve the durability of concrete structures

Chloride induced corrosion of steel in concrete is a major threat to the construction industry leading to the premature failure of concrete structures. Electrochemical injection of corrosion inhibitor (EICI) into concrete is a promising technique for existing concrete structures, which can serve as a rehabilitative measure to retard or reduce rebar corrosion. An attempt has been made to evaluate the effectiveness of a hybrid inhibitor formulation injected into chloride contaminated concrete. The optimised current density of 0.5A/m2 was found to be a minimum requirement with maximum efficiency. During EICI, the amount of free chloride removed from cover concrete was also tested. The mechanism of inhibitive action was established through FTIR, SEM, EDAX and MIP studies.

Adaptive concurrent three-level multiscale simulation for trans-scale process from material mesodamage to structural failure of concrete structures

A new multiscale method is developed to simulate the trans-scale process of concrete structures from material mesodamage to structural failure with three-level model which, respectively, describe nonkey, key, and damaged regions. Adaptive level change criteria coupled in the method ensures level change due to evolving damage without user intervention in the computation. As a case study, the trans-scale damage process of a concrete cantilever beam and reinforced concrete (RC) frame structure is simulated. It shows that the method can be used to reveal the failure mechanisms of concrete structures from the view of mesoscale with lower cost.

Prediction of the residual strength for durability failure of concrete structure in acidic environments

According to the results of accelerated tests of acidification corrosion depth and compressive strength of concretes subjected to sulfuric acid environments, the acidification depth laws of concretes were predicted based on the grey system theory. Thus, the remaining compressive strength was calculated when the acidification depth reached the protection layer thickness of concrete structures, which indicates that the limit state of durability failure can be defined based on strength degradation, and the calculation process was illustrated by an example. The calculated results show that the remaining compressive strength values in the durability failure limit state for the concrete structures exposed to pH=2 and 3 sulfuric acid water environments and wet-dry cyclic sulfuric acid environment with pH=2 are 74%, 72%, and 80% of initial strength, respectively. The method provides references for the durability evaluation of concrete structure design under the acidic environments.

Adaptive mesh refinement FEM for seismic damage evolution in concrete-based structures

In order to study the seismic damage mechanisms of concrete-based structures, a adaptive multi-grid method is developed to simulate the process from evolving damage to structural failure in concrete structures under seismic loading. The theory of multi-grid FEM coupled evolving damage is developed on the basis of the improved variational principle, in which the elements in each sub-domain with different grid sizes are under the different state of damage. Meanwhile the FE elements can be refined adaptively with the accumulation of its damage for lower cost, without user intervention in the computation. As a case study of the method, the failure process of reinforced concrete column under seismic loading is simulated, the results show that, the simulated results fit well with the experiment, and the developed method can be used to reveal the seismic damage mechanism of concrete-based structures by considering the process from material damage to structural failure; the adaptive multi-grid method can give satisfactory result with lower cost by compared with experiment.

NATURAL CORROSION INHIBITORS FOR STEEL REINFORCEMENT IN CONCRETE — A REVIEW

Reinforced concrete is one of the widely used construction materials for bridges, buildings, platforms and tunnels. Though reinforced concrete is capable of withstanding a large range of severe environments including marine, industrial and alpine conditions, there are still a large number of failures in concrete structures for many reasons. Either carbonation or chloride attack is the main culprit which is due to depassivation of reinforced steel and subsequently leads to rapid steel corrosion. Among many corrosion prevention measures, application of corrosion inhibitors play a vital role in metal protection. Numerous range of corrosion inhibitors were reported for concrete protection that were also used commercially in industries. This review summarizes the application of natural products as corrosion inhibitors for concrete protection and also scrutinizes various factors influencing its applicability.