Reliability Of Concrete Structures Research Articles

Improvement of crack detectivity for noisy concrete surface by machine learning methods and infrared images

In order to maintain serviceability and reliability of concrete structures, it is essential to assess their condition as concrete structures deteriorate in time. Cracks develop in concrete due to several reasons such as severe loading, environmental effects, chemical effects etc. and cause durability loss in the structure which may also lead to loss of stability. In this research, crack detection is realized by machine learning and an infrared image. The effects of infrared images on crack detection are confirmed by random forest algorithm to select useful explanatory features. Selected features are applied to random forest algorithm and neural network algorithm. Effective filters are selected as a feature selection technique to improve the accuracy. Crack detection is also conducted by U-Net with RGB and infrared images, and the detection characteristics are compared to conventional methods. The performance of two conventional machine learning methods, random forest and neural network, are evaluated based on F1 score and false positives. Applying selected features improves the accuracy of the crack detection from an infrared image. False positives decreased due to monitoring conditions and camera specifications in the infrared image. The most effective image processing filter is the blur filter for each algorithm. Comparing algorithms for crack detection using selected features, different accuracy values are obtained. U-Net enables more accurate crack detection compared to conventional methods. The number of false positives is reduced compare to conventional method. In the detection results by three algorithms, infrared image affects the balance of false negatives and false positives.

Optimization of the Composition of Cement Pastes Using Combined Additives of Alumoferrites and Gypsum in Order to Increase the Durability of Concrete

The reliability of concrete structures is closely related to the durability of the concrete materials stable under external environmental conditions. The present study is aimed at analysing the effect of a prospective hardening additive containing calcium alumoferrites and calcium sulfate (AFCS) as a substitute (5–15%) for Portland cement. The hardened cement pastes were characterized by water absorption, shrinkage, strength and corrosion resistance. It was shown that replacing a part of Portland cement with the AFCS additive results in an increase in the strength of fine-grained concrete and in the water resistance grade of concrete. The use of the AFCS additive in the mixed cements reduces the shrinkage of cement stone, resulting in shrinkage-free fine-grained concretes. The increased corrosion resistance of the hardened cement paste is caused by a chemical (saturation) equilibrium between corrosive medium and a cement stone. Penetration of sulphate ions from corrosive solution into the hardened cement paste is much lower, unlike Portland cement. Following saturation of the hardened cement paste with sulphate ions, their further penetration into the cement stone does not occur. Based on the results of the study, recommendations were developed for the use of the hardening alumoferrite-gypsum additive to Portland cement, which allows to improve the mechanical and corrosion characteristics of concrete.

Application of Alkali-Resistant Woven Fibre Mesh Confinement to Strengthen Lightweight Foamed Concrete

Lightweight foamed concrete (LFC) is a low-density concrete with numerous applications. However, because its weight is nearly half that of traditional concrete, its strength can also be expected to be reduced. This research investigates the possibility of using LFC reinforced with alkali-resistant woven fibre mesh to improve its mechanical properties. One of the key issues of reinforced lightweight concrete construction is the deterioration of reinforced steel, which has a considerable impact on the reliability of concrete structures. Because it is corrosion resistant, fibreglass netting can effectively solve the corrosion problem as an alternative to welded wire mesh. In this investigation, two densities of LFC (700 kg/m3 and 1400 kg/m3) were cast and tested with three different layers of fibreglass netting, one layer, two layers, and three layers. Compressive strength, flexural strength, and splitting tensile strength were determined. According to the findings, including woven fibre mesh in LFC improves flexural strength, compressive strength, and splitting strength. The addition of three layers of woven fibre mesh resulted in the best mechanical performance for all mechanical qualities studied in this study

Quality Control Method for the Service Life and Reliability of Concrete Structures

In the past few years, there has been an increasing societal and industrial demand for the reliable assessment and design of structural systems with service-life criteria of at least several decades. The life cycle characterisation of engineering structures in terms of an anticipated service life remains a significant aspect of sustainability in the construction industry. This requires special attention to the definition of structural performance under various actions, and to the implemented engineering materials and methods as well as to the inverse identification and monitoring of structural conditions. Subsequently, the focus remains on the development of a holistic performance-based design approach for new and existing structures and infrastructures. This paper presents the fundamental reliability concepts of performance-based design, with a focus on lifetime assessment. Case studies from actual structural components’ design are used to verify the proposed methodology and indicate the significance of quality assurance in the lifetime assessment of engineering structures. We also confirmed that reliability and quality assurance criteria are strongly connected. Therefore, a methodology for quality-based service life assessment is presented and elaborated in the case studies.

ПРОГНОЗИРОВАНИЕ ДОЛГОВЕЧНОСТИ БЕТОННЫХ КОНСТРУКЦИЙ С УЧЕТОМ МАССОПЕРЕНОСА И КОЛЬМАТАЦИИ ПОР ПРИ КОРРОЗИИ

The object of research is the corrosion process of destruction of concrete and reinforced concrete structures in aggressive media. The purpose of the investigation is to establish a set of relationships and ratio between the characteristics of this process and various external and internal factors that affect the growth of corrosion. To solve the tasks set on the basis of the obtained experimental data, the method of mathematical modeling of corrosion processes was applied. The theories of physical and chemical transformations and heat and mass transfer laws suggest that different stages of corrosion can be simulated by differential equations of interrelated heat and mass transfer with boundary conditions. They are defined by arbitrary functions of initial transfer potentials and nonlinear boundary conditions of all known types. The possibilities of developed physical and mathematical models of mass transfer in the processes of studying corrosion of various types are demonstrated. They allow to evaluate the concentration of the transported component throughout the thickness of the concrete structure and in the biofilm itself at any time, as well as the concentration of "free" calcium hydroxide in the liquid phase. As a result, it is succeeded to predict the durability and reliability of concrete structures with a minimum error. The proposed author's model of the destruction of cement concretes, taking into account the colmatation of pores and capillaries, ensures the adequacy of judgments about the kinetics of mass transfer processes during corrosion of the II type.

Copula-Based Quantification of Probabilistic Dependence Configurations of Material Parameters in Damage Constitutive Modeling of Concrete

The constitutive model of concrete is the key basis for nonlinear analysis of concrete structures under disastrous dynamic actions, e.g., earthquakes. The material parameters of the constitutive model of concrete are essentially probabilistically dependent. However, in practice, it is mostly assumed that these parameters are either independent or perfectly dependent. In the present paper, the quantification of probabilistic dependence configurations between random material parameters and their effects on stochastic structural responses are investigated. Based on the ample amount of data from tested complete curves of compressive stress-strain relationships of concrete with different strength grades, the parameters in the damage constitutive model of concrete are samplewise identified. Further, the probabilistic dependence configurations are studied based on copula theory, which is also considered as a data-mining tool. The complete constitutive curves of concrete are generated according to the obtained dependence configurations and marginal distributions. Then, combined with the probability density evolution method, the stochastic response analysis of concrete structures is carried out. The analysis results show that the dependence among the strength, peak strain, and the parameter of the descendent segment cannot be ignored. Due to the constraint of dependence configurations, the distribution characteristics of the generated point set are substantially consistent with the tested results, and the generated complete stress-strain curves agree well with the tested curves at both the level of sample and the level of second-order moments. In addition, no abnormal complete stress-strain curves, e.g., those with low strength and sharp descendent segment, which are unlikely to occur in the test, are generated. The dependence configuration of the parameters of concrete has considerable effects on the response and reliability of concrete structures, and may even lead to the change of overall structural failure mode. Consequently, ignoring the probabilistic dependence of material parameters may yield misleading results for decision making. Problems to be further studied are also discussed.

A stochastic model considering heterogeneity and crack propagation in concrete

The heterogeneity of concrete results in the uncertainties of its fracture properties which usually affect the actual load bearing capacity and reliability of concrete structures. However, in existing studies of the heterogeneity of concrete, little research has been reported that considers the randomness of crack initiation. The current study presents a stochastic model for predicting the crack growth process of concrete by introducing a mixed-mode I - II crack propagation criterion with initial fracture toughness. Some routine tests are conducted to determine the statistical parameters of the presented model. The effects of the heterogeneity of the concrete on the load versus crack mouth opening displacement (P-CMOD) curve, the fracture process zone (FPZ) length LFPZ and the crack growth trajectory are studied. It is found that compared with the P-CMOD curve based on the homogeneous model, the predicted results based on the stochastic model show obviously discrete changes that reasonably display the discreteness of concrete, and this is more scientific and accurate for describing the actual performance of concrete. During the crack propagation, the heterogeneity of the concrete has little influence on LFPZ before LFPZ reaches a maximum, and thereafter LFPZ is greatly affected by the heterogeneity of the concrete. In comparison with the crack growth trajectory predicted by the homogeneous model, the tortuous trajectories based on the stochastic model are more realistic and show reasonable agreement with the experimental observations obtained from the literature. Additionally, the envelope of these paths can be obtained. The analysis of the values of the predicted peak load Pmax of the stochastic model statistically indicates that they follow the normal distribution, which can be used for the reliability analysis of concrete structures.

First-passage probability analysis of Wiener process using different methods and its applications in the evaluation of structural durability degradation

The first-passage probabilities in stochastic processes are important for the evaluation of structural reliability. In this work, Wiener process’s first-passage probability was analysed using different methods. First, the Poisson process method was used to analyse the first-passage probability of the Wiener process, and it was found this method cannot calculate the first-passage probability of the Wiener process. Then, the symmetry and Markov property of the Wiener process were used to derive equations for calculating the first-passage probability of a Wiener process. The results indicate analytical expressions for the first-passage time probability distribution function of the Wiener process can be derived either through the symmetry or Markov property of the process. Neither of the analytical expressions requires the use of assumptions in their derivations. The analytical method based on the symmetry of the Wiener process yields fully exact solution, whereas the analytical method based on the Markov property of the Wiener process produces highly accurate solution. Finally, the Wiener process is used to represent the time-varying amount of structural degradation at any point in time, leading to a non-stationary stochastic model for the degradation process, which will provide a basis for an estimation of the durability and reliability of concrete structures.

Evaluate the Expressions of Compression Strength and UPV Relationship

Ultrasonic pulse velocity method UPV has been commonly implemented to examine the mechanical properties and reliability of concrete structures. The principle of UPV is the speed of propagation of waves that depends on the density and the modulus of elasticity of the concrete. UPV is a simple and easier method of non-destructive testing (NDT) for evaluating the structures and material. The results can be rapidly achieved and data can be periodically collected from the same test points. This paper aims to find a general formula will apply for all types of concrete, wide range of ages and compressive strength. The current formulae assimilate limited numbers of experimental tests. This is because of the formula produced of these data is limited to the specimens were tested only. In this study, 575 different experimental tests between 3 and 180 days for compressive strengths ranging from about 20 to 100 MPa were collected and summarized. Moreover, the current equations have been developed to give an accurate correlation between Compressive strength and UPV. In addition, a contemporary design formula was presented.

Development of compositions of modified concrete with improved water-repellent properties for underground parts of buildings

In building of various underground structures, one of the main tasks is to ensure the durability and reliability of concrete structures, as well as the resistance to ground and aggressive water, which, in its turn, should be taken into account in the development of concrete compositions. The wastes from the chemical and processing industry are used as additives to concrete to regulate various properties of composites. This study shows that the use of a modifier from the organic fraction of oil waste make a material with improved characteristics for its use in underground parts of structures. When solving the problem of selecting the composition of a sulfate-resistant composite with water-repellent properties, the methodology of mathematical design of the experiment was used on the basis of a polynomial model linking the optimization parameter of the compressive strength limit with independent technological factors having three levels of variation. The analysis of the results of the experiment made it possible to determine the admissible limits of the oscillations of the independent variable factors, which ensure that the optimization parameter is found not only at the extreme point, but also in the region of given values.

Experimental Study of Nondestructive Geophysical Methods for Evaluating the Condition of Concrete Structures

It is often necessary to evaluate the integrity and reliability of concrete structures that are exposed to extreme environmental conditions over a long period of time. This paper presents a range of nondestructive geophysical methods, including Ultraseismic, Parallel Seismic, and Impulse Response techniques that use elastic-wave properties to inspect concrete-foundation structures. These approaches depend on basic waveform properties such as wave speed, amplitude, and frequency. The goal of this research is to obtain an appropriate test procedure and identify parameters for i) verifying the wave reflected from internal concrete defects, and ii) identifying the effective depth of a pre-built test foundation. To do so, we have established an experimental laboratory to calibrate and check the reliability of the measured data and understand the wave properties for different concrete conditions (i.e., fractures). It is often necessary to evaluate the integrity and reliability of concrete structures that are exposed to extreme environmental conditions over a long period of time. This paper presents a range of nondestructive geophysical methods, including Ultraseismic, Parallel Seismic, and Impulse Response techniques that use elastic-wave properties to inspect concrete-foundation structures. These approaches depend on basic waveform properties such as wave speed, amplitude, and frequency. The goal of this research is to obtain an appropriate test procedure and identify parameters for i) verifying the wave reflected from internal concrete defects, and ii) identifying the effective depth of a pre-built test foundation. To do so, we have established an experimental laboratory to calibrate and check the reliability of the measured data and understand the wave properties for different concrete conditions (i.e., fractures). We concluded that the aforementioned geophysical approaches could provide vital information for quality control and rehabilitation purposes.

Reliability Analysis for Transverse Crack of Concrete Structure

According to the national standard "Code for Design of Concrete Structure", the reliability index for the structural members of reinforced concrete have not been given, which are controlled by serviceability limit states. A methodological framework was proposed, which made use of fuzzy invalidation rule for reliability analysis of reinforced concrete members. Firstly, A membership function was chosen. Secondly, A equivalent function was established to deal with the fuzzy reliability of concrete structure by traditional JC method. Finally, the fuzzy reliability index of transverse crack of reinforced concrete structure was obtained.

Effect of Fiber-Reinforced Polymer Configuration on Reliability of Flexurally Strengthened Concrete Beams

External bonding of composite materials in the form of strips, plates, and laminates to add tensile capacity in deficient zones has proved to be an efficient strengthening technique. The performance of composite materials in strengthening ailing infrastructure components has made them a mainstream alternative in some applications such as strengthening concrete structures. The technique is mature enough that design standards have been published. Few researchers have investigated the reliability of concrete structures strengthened with fiber-reinforced polymer (FRP). The results of these reliability investigations were incorporated in some of the recently published design guidelines. It is a well-known fact that FRP debonding is the dominant mode of failure. Nevertheless, the impact of different FRP configurations on the reliability of strengthened concrete beams in flexure has not yet been investigated. An analytical study is presented of the reliability of FRP-strengthened concrete beams in two of the most popular configurations: U-wrap and soffit-only. Material, fabrication, and model uncertainties are accounted for in a strength limit state function to analyze the reliability of strengthened reinforced concrete beams by using the first-order reliability method. Results from this study show that the reliability of U-wrap configurations is higher than that of soffit-only configurations. This finding can be used in establishing different resistance factors for each case such that the use of more materials in the U-wrap configuration is rewarded by the ability to predict its performance better.

최대 밀도 이론을 이용한 고성능콘크리트의 배합 설계

In recent years the field application of high performance concrete has been increased to improve the quality and reliability of concrete structures. The mix design of the high performance concrete includes the 2 set-off mixture theory of mortar and coarse aggregate and that of paste and aggregate. The 2 set-off mixture theory of mortar and coarse aggregate has a problem of having to determine its value through repeated experiments in applying the rheological characteristics of mortar. The 2 set-off mixture theory of paste and aggregate has never been applied to high performance concrete since it doesn't take into account the relationship between optimum fine aggregate ratio and unit volume of powder nor does it consider the critical aggregate volume ratio. As the mixture theory of these high performance concretes, unlike that of general concrete, focuses on flowability and charge-ability, it does not consider intensity features in mix design also, the unit quantity of the materials used is determined by trial and error method in the same way as general concrete. This study is designed to reduce the frequency of trial and error by accurately calculating the optimum fine aggregate ratio, which makes it possible to minimize the aperture of aggregate in use by introducing the maximum density theory to the mix design of high performance concrete. Also, it is intended to propose a simple and reasonable mix design for high performance concrete meeting the requirements for both intensity and flowability. The mix design proposed in this study may reduce trial and error and conveniently produce high performance concrete which has self-chargeability by using more than the minimum unit volume of powder and optimum fine aggregate with minimum porosity.

Updating Performance and Reliability of Concrete Structures Using Discrete Empirical Bayes Methods

When performing a probabilistic assessment of the reliability of deteriorating structures, we often need to integrate the results of different inspections in time, within the models used to analyze the progress of deterioration. A new framework is described in this paper. It rests on a special case of the empirical Bayes method where the non-observable parameter is a discrete random variable with a relatively small number of outcomes. Various likelihood functions are derived. They are based on mixtures of deterioration scenarios. It is shown how the method can be used to calibrate the response of a stochastic deterioration model and to merge with a time-dependent reliability analysis. Examples relating to the long-term chloride corrosion in a reinforced concrete slab are presented in the paper.