Condition Assessment Of Concrete Structures Research Articles

Condition assessment of concrete structures using automated crack detection method for different concrete surface types based on image processing

In the inspection and diagnosis of concrete construction, crack detection is highly recommended in the earliest phases to prevent any potential risks later. However, the flaws in concrete surfaces cannot be reliably and effectively identified using traditional crack detection techniques. The suggested algorithm is a supportive tool for agents or authorities to use in crack detection mechanisms to monitor and assess the current condition of buildings or bridges. The researchers aim to establish an intelligent model for automatic crack detection on different concrete surfaces based on image processing technology. Three different concrete surfaces—bridge decks, walls, and concrete cubes—are used to test the model. A subset of the public dataset of bridge decks and walls from SDNET (2018) and 150*150*150 mm of concrete cubes taken from the material laboratory of the faculty of engineering at Ain Shams University are applied to the model. The model F1-score measures are 98.87%, 97.43%, and 74.11% for detecting cracks in bridges, walls, and concrete cubes, respectively. The validation of the applicability of the suggested novel approach is based on a comparison with recent methods for crack recognition. The contribution of this study is that it could be applied to detect cracks efficiently on three different types of concrete surfaces, including uneven concrete surfaces, random noise, voids, dents, colour changes, and stain marks. The proposed method is transparent in its workflow and has a lower computational cost compared with deep learning frameworks. Thus, the outcomes of this model demonstrate its effectiveness in concrete defect field investigation.

Non-destructive evaluation (NDE) methods used for condition assessment of concrete structures

As an integral part of the construction industry, concrete is an important part of the building materials industry, as well as an important material for infrastructure and engineering construction projects. It is widely used in various industries. In recent years, with the improvement of the quality awareness of the whole people, the engineering quality inspection has also received more attention. The previous concrete quality inspection methods have different degrees of damage to the original structure. This paper focuses on the state of concrete structure and its detection method, and introduces the EDN technology. At the same time, through comparison, practical experiment, theoretical research and other research methods to describe EDN technology. Based on the research results, it is concluded that ECN technology can provide a more comprehensive concrete quality report, which is beneficial to the maintenance, repair and restoration of Bridges and old buildings, and help engineers use.

ASSESSMENT OF CORROSION IN A PARKING DECK USING GPR

This research focused on finding the structural condition of a precast parking deck using a GPR. A GSSI SIR 4000 Bridge Scanner GPR was deployed for corrosiveness mapping of a precast deck. Small concrete slabs were prepared in the laboratory with fresh and corroded rebars to identify their differences in GPR scanned images. The GPR response from the slab indicated that the reflection amplitude obtained from the scan of the target rebar decreases with increasing depth. GPR B-scans from the fresh and corroded rebar indicated increase in corrosion. The field experiment was performed following the standard bridge deck survey procedures. Both numerical and image-based analysis methods were followed for developing the corrosiveness maps of the precast deck section. The corrosiveness map showed a few critical sections in the precast deck. A visual inspection of the precast deck matched the fault locations in the corrosiveness map. The present condition of a precast deck section was found satisfactory except for a few areas of serious cracking that need repairs to control the further growth of corrosion. GPR results showed higher accuracy with the field inspection outcomes demonstrating that a GPR can be used as a reliable non-destructive tool for the condition assessment of concrete structures.

Internal imaging of concrete fracture based on elastic waves and ultrasound computed tomography

The condition assessment of concrete structures belongs to the greatest challenges of non-destructive testing. Monitoring the fracture process of concrete and detecting cracks at the earliest possible stage is a vital aspect to ensure the safety of civil engineering objects. The use of ultrasound tomography enables imaging the internal structure of a tested element. This study aims at the visualization of fracture damage in concrete cubes. The tests are performed on samples made of plain concrete and concrete with fibres. The main contribution of this work is the study of the application of ultrasound transmission tomography to imaging cracks in concrete prisms before and after mechanical degradation in a wedge splitting test. A novel method of determination of the time-of-flight of a wave propagating from a transmitter to a receiver is introduced. The effectiveness of the imaging of fracture damage obtained using ultrasound tomography is proved by X-ray micro-computed tomography.

Combining Active and Passive Stress Wave Monitoring Techniques: Opportunities for Condition Assessment of Concrete Structures

Condition monitoring of concrete structures has experienced increasing interest over the last decades, especially for bridges. In this presentation, a combined approach based on active and passive stress wave monitoring techniques is proposed and discussed. While from a wave propagation mechanics point of view, acoustic emission (AE) and ultrasonic monitoring are the same, they differ fundamentally in what the cause of the stress wave is. For the former, external stimuli such as overloading or temperature cause the spontaneous release of fracture energy in unknown locations. As a result, AE events cannot be repeated. For the latter, a known source at a known location is employed at a specified time. In contrast, this approach is highly controlled and repeatable. The presenter argues that a combination of these two techniques has the potential to provide a much more comprehensive picture of ongoing fracture processes as well as slowly occurring changes in the structure. An overview and comparison of the techniques is provided, along with observations and results from laboratory experiments and field tests that the presenter has been involved in over the last 15 years.

Validation of wireless impact echo prototype for condition assessment of concrete structures

A new wireless impact echo prototype was developed for the condition assessment of reinforced concrete slabs. The new system includes a wireless handheld sensing device which connects by Bluetooth to a tablet equipped with a user-friendly software for managing the testing grid, recording measurements, processing and transforming the data to a frequency domain, and presenting the results in real time. To validate the device, three large-scale concrete slabs of dimensions 2000 mm x 2000 mm x 300 mm were fabricated with artificial defects including voids, delamination, vertical cracks, and geometric discontinuities. The influence of slab boundaries, defect depth and location, overall thickness, steel reinforcement, and an internal conduit on the obtained measurements were investigated. The results were also compared with other commercial non-destructive testing devices including ground penetrating radar (GPR) and ultrasonic pulse velocity (UPE), and the advantages and disadvantages of each method are discussed. Overall, the results suggest that the impact echo technique using the new wireless prototype is able to accurately detect and characterise various defect types provided that the right size of impactor is used. Use of improper impactor sizes can result in alternative vibration modes depending on the slab thickness and defect depth; in that case, multiple readings may be required. The new system greatly improved the ease-of-use of the impact echo technique, although the inspector should be trained to properly interpret the results. Compared with the GPR technique, the impact echo system was not as rapid and unable to detect the location of steel reinforcement; on the other hand, it was better able to detect defects in the presence of steel bars which tended to obscure readings using GPR. UPE measurements were also faster than the impact echo tests and performed well for slab thickness measurements and detection of certain defect types; however, readings were found to be affected by the presence of steel reinforcement and in some cases were inconsistent. Overall, it may be concluded that each technique presents certain strengths and weaknesses that should be considered in the condition assessment strategy. The results obtained from each technique are complementary and may be used to develop a complete understanding of the internal state of the structure.

Environmental effects on condition assessments of concrete structures with ground penetrating radar

Reflection amplitude from rebar is the most commonly used parameter for condition assessment of concrete structures using Ground-Penetrating Radar (GPR). However, it was reported that such amplitudes might affect by several factors, including the chloride content, rust accumulated on the surface of steel bars due to corrosion, and the environmental conditions at the time of GPR data collection. The objectives of this study were to observe the change of GPR signals over time and to evaluate the effects of those factors on the reflection amplitude of steel bars. A series of six reinforced concrete slabs were fabricated with identical configurations but for different chloride contents. Two testing phases with the multiple GPR measurements were conducted both outside and inside an environmental chamber. In the first testing phase, the development of GPR signals was daily obtained from day one to day 90 in the laboratory conditions. In the second testing phase, the GPR data were collected inside the environmental chamber at an interval of 24 h. Relative Humidity (RH) was set at three levels of 55%, 70%, and 85%, respectively, while the temperature was varied between 5 °C and 40 °C. The test results from the first testing phase showed that the GPR signals developed at an exponential rate during the first three months. In addition, results from the second testing phase revealed that both the added chloride and the rust on the surface of steel reinforcement reduced the amplitude of rebar reflection. Regarding the effects of temperature, for sound (i.e., non-contaminated) concrete, the reflection amplitude decreased approximately 0.05 dB for every 1 °C increments. For the contaminated concrete, such ratio was found to increase proportionally to the chloride levels. Finally, the RH was observed to have insignificant effects on the amplitude of rebar reflection.

Probabilistic assessment of the depassivation limit state of reinforced concrete structures based on inspection results

The aging of our concrete structures has led to a growing need to assess their actual condition, not only for maintenance purposes, but also to plan the extension of their service life. Today, only few methods that use inspection data can be found in the literature for performing that assessment, and are usually based on the Bayesian probability theory, which requires prior information on the structures condition and often demands specific statistical knowledge and software that are not familiar to most practitioners. In this article, a probabilistic methodology based on a frequentist approach is presented for assessing the limit state of depassivation of concrete structures, using inspection results on cover depth, carbonation depth and depth of critical chloride content. It introduces the concept of passivation curve, which depicts the confidence of the estimated percentage of passivated steel bars, providing a valuable tool for supporting the decision-making for the life-cycle management of concrete structures. Its application is demonstrated using the inspection data from five real structures up to 41 years old. This article also discusses the experimental and code requirements for the condition assessment of concrete structures and the physical interpretation of the probability of passivation in the context of inspection. The relevance of experimental conditions for the determination of the critical chloride content of concrete is highlighted, as well as the urgent need to get data on its in situ distribution.

Muon Tomography of the Interior of a Reinforced Concrete Block: First Experimental Proof of Concept

Quality assurance and condition assessment of concrete structures is an important topic world-wide due to the aging infrastructure and increasing traffic demands. Common topics include, but are not limited to, localisation of rebar or tendon ducts, geometrical irregularities, cracks, voids, honeycombing or other flaws. Non-destructive techniques such as ultrasound or radar have found regular, successful practical application but sometimes suffer from limited resolution and accuracy, imaging artefacts or restrictions in detecting certain features. Until the 1980s X-ray transmission was used in case of special demands and showed a much better resolution than other NDT techniques. However, due to safety concerns and cost issues, this method is almost never used anymore. Muon tomography has received much attention recently. Novel detectors for cosmic muons and tomographic imaging algorithms have opened up new fields of application, such as the investigation of freight containers. Muon imaging also has the potential to fill some of the gaps currently existing in concrete NDT. As a first step towards practical use and as a proof of concept we used an existing system to image the interior of a reference reinforced 600 kg concrete block. Even with a yet not optimized setup for this kind of investigation, the muon imaging results are at least of similar quality compared to ultrasonic and radar imaging, potentially even better. The data acquisition takes more time and signals contain more noise, but the images allowed to detect the same important features that are visible in conventional high energy X-ray tomography. In our experiment, we have shown that muon imaging has potential for concrete inspection. The next steps include the development of mobile detectors and optimising acquisition and imaging parameters.

Automated crack pattern recognition from images for condition assessment of concrete structures

Evaluating the appearance of cracks on concrete elements is necessary during condition assessment. Most imaging techniques related to crack identification focus on detecting cracks and measuring basic dimensions of cracks. However, condition assessment of an element from visible cracks requires further information, of which characterizing the crack pattern is necessary. To achieve this, this paper proposes an automated approach to recognize concrete crack patterns from images. By analyzing the characteristics of structural and non-structural cracks, a binary classification of crack patterns into isolated patterns and map patterns is proposed. The recognition of crack patterns is performed through similarity comparisons using DISTS index. Various parameters that may affect the performance are investigated through several experiments conducted using real-world images. According to the experimental results, the proposed method is shown to successfully recognize crack patterns with an accuracy of over 96%. Recommendations are further proposed to enhance the performance of the method.

Principal Component Thermography for Defect Detection in Concrete.

The goal of the condition assessment of concrete structures is to gain an insight into current condition of concrete and the existence of defects, which decrease durability and usability of the structure. Defects are quite difficult to detect using infrared thermography when concrete elements cannot be thermally excited with the Sun, together with unfavorable thermophysical properties of concrete structures. In this paper, principal component thermography (PCT) is applied as a post-processing method to a sequence of thermograms in order to enhance defect detectability in concrete structures. Defects are detected by analyzing a set of empirical orthogonal functions (EOFs), which were acquired by applying principal component analysis to a sequence of thermograms. The research was performed using concrete samples containing known defects, which were tested using a step heating thermography setup. The results of presented research show that PCT is an effective post-processing method to improve defect detection in concrete structures. By effectively improving the defect detection, PCT has a potential to improve the non-destructive testing (NDT) accuracy of using infrared thermography (IRT) on concrete structures, especially in shaded areas of such structures. The research also shows the defect detectability depending on concrete type thermal excitation setup and defect geometry.

A new perspective on measuring the corrosion rate of localized corrosion

AbstractMany corrosion phenomena are nonuniform, which means that anodic and cathodic locations are spatially separated. An example is macrocell corrosion of steel in concrete. Under these conditions, determining the corrosion rate from polarization resistance measurements and using the Stern–Geary equation is fundamentally not possible. We present a novel theoretical approach for the interpretation of galvanostatic pulse measurements, to make them applicable as a method for corrosion rate measurements in situations of localized corrosion. Experiments show that it is important to consider that (a) only a fraction of the applied current flows through the anode of the macrocell, and (b) this current is not constant over time. We propose an approach to quantify and consider these two effects, based on information generally accessible in condition assessment of concrete structures. Our results show that galvanostatic pulse measurements are a robust method to determine the corrosion current. With the traditional empirical approach, the measurement error was generally below factor 3, and occasionally up to factor 10. With the novel approach, this error could be reduced to a factor of maximum 2 in all cases.

Impulse response test for condition assessment of concrete: A review

The impulse-response test is one of the most versatile nondestructive test (NDT) methods for condition assessment of concrete structures. It is an elastic stress-wave propagation based low-strain and low frequency NDT method, which is widely employed in the NDT industry. Nevertheless, it is used mainly as a relative basis test, in which contour plots of the response parameter are used to distinguish between intact and anomalous regions in the test element. This article is the first to compile current published literature on the subject. A summary of the published case studies using impulse-response test is presented, followed by the current state-of-the-art of the fundamental theoretical understanding of the method. Current knowledge gaps are identified and recommendations are proposed to address these issues. The recommendations are aimed to move the impulse-response test from a qualitative NDT method to a quantitative condition assessment tool for concrete structures.

Infrared thermographic assessment of cement mortar porosity and strength

Noninvasive ways of condition assessment and quality control during construction are critically needed. In the study reported here, the possibility of using the infrared thermography (IRT) technique to estimate the total porosity and the compressive strength of cement mortar was investigated. To assess the cooling characteristics of specimens and the porosity detection limit of IRT, mortar mixtures with a constant aggregate volume fraction and varying water-to-cement ratios of 0.25, 0.35, 0.45, 0.55, and 0.65 were heated and subjected to four different cooling durations. Thereafter, the relationships between specimen cooling characteristics, measured porosity, and compressive strength were evaluated. The compressive strength prediction efficiency of the proposed IRT model was also compared to that of the commonly used ultrasonic velocity (UPV)-strength prediction models. Results indicate that the differences in the residual temperature of specimens during cooling became pronounced with decreasing w/c ratio. Although a generally good fit with the Newton’s Cooling function was obtained for all the cooling durations considered, 60 min was the best, giving a strong exponential relationship between thermal time constant and total porosity (R 2 value of 0.99). Furthermore, with R 2 values of 0.97–0.98 and standard error (SE) of 4.0–4.5 MPa, the compressive strength prediction accuracy of the IRT-strength models were superior to those of the UPV-strength models, which recorded 0.89–0.94 R 2 values and SE of 6.2–9.0 MPa for the same set of mixtures. These results suggest that besides serving as a quality control tool during new construction, the identification of delamination and appropriate area for core extraction during condition assessment of concrete structures are other inherent potentials of the IRT technique proposed in this study.

Optimization of Acoustic Methods for Condition Assessment of Concrete Structures

Extensive experimental studies were carried out to calibrate numerical models related to two acoustic nondestructive testing (NDT) methods: impact-echo (IE) and ultrasonic surface waves (USW). A detailed parametric study was performed to quantify the limitations of the IE and USW methods and to specify the degree of sensitivity of those methods to different parameters, including spatial discretization, overall dimension and material properties of the test object, boundary conditions, and delamination size and depth. Results from this study demonstrate that the effectiveness of the IE and USW methods is limited by their sensitivity to those parameters. This limitation makes the combination of the IE and USW results more effective in detecting and locating the defects within the concrete structures. Finally, the best testing setup, in terms of the spacing between the source and the receivers, was recommended to reliably estimate the slab thickness and to detect and locate the defects.

Condition assessment of concrete structures using a new analysis method: Ground-penetrating radar computer-assisted visual interpretation

Many transportation authorities in the United States and Canada require condition assessments of concrete bridge decks and roadways as part of scheduled rehabilitation and maintenance programs. Nondestructive test (NDT) methods and laboratory studies are commonly used by engineering consultants to perform these evaluations. Amongst typical NDT methods, ground-penetrating radar (GPR) is one of the best suited to accomplish this task. Unfortunately, reported test results are oftentimes ambiguous, due to the current numerical analysis approach to evaluate the data. This paper describes some of the shortcomings of numerical analysis of GPR profiles and it introduces an alternative method developed by the authors. Several examples of actual field investigations are described, where the computer-assisted visual interpretation of GPR profiles was used to validate and eventually improve this new analysis approach. The authors’ project experiences on several structures indicate that mapping defects by visual identification of corrosion-induced anomalies in concrete is a much more accurate way of mapping defects. The results obtained from the field applications suggest that use of the computer-assisted visual interpretation of GPR data is an efficient and reliable approach that can be used by experienced GPR analysts.

Condition assessment of concrete structures at nuclear power plants by state of the art non-destructive testing

The approach combining Non Destructive Examination (NDE) with Finite Element Analysis (FEA) methods is both workable and necessary in order to accurately determine and predict the condition of Nuclear Power Plant (NPP) containment structures. This approach was introduced in the European 5th Framework Project with acronym CONMOD [1]. The current paper presents some of the work performed after the CONMOD project combining the on-site investigation at nuclear power plant (NPP) stations in Sweden and Finland. Several non-destructive techniques were chosen for the investigations described in this paper. The MASW (Multi Channel Analysis of Surface Waves) and Impact Echo (IE) techniques have been used for evaluation of thickness and stiffness of concrete and also for location of possible defects. The above-mentioned techniques have been applied under investigations of concrete containments. Additionally reinforcement corrosion was investigated in cooling water channels by means of the Galvanostatic Pulse technique allowing determination of corrosion rate. Further, following the CONMOD concept, the coupling between the non-destructive measurements on site and finite element method is established. As the result of this coupling, the information about the status of concrete structures in nuclear power plants is obtained. In the ongoing research & development project CONSAFESYS (Concrete Containment Condition Status & Ageing Examination System) the qualification and validation of investigative methods and diagnostic tools and analysis for reactor containments are further developed. One unique benefit with the CONSAFESYS project is the possibility of introducing artificial defects and anomalies into a decommissioned reactor containment structure.

Investigation of a management framework for condition assessment of concrete structures based on reusable knowledge and inspection

Managing and reusing knowledge in engineering and construction sectors can lead to greater competitive advantage, improved designs, and more effective management of constructed facilities. The use of Information Technology (IT) in design and construction can exploit strategic opportunities for new ways of integration, sharing and facilitating information and knowledge in any field of engineering. The integrating of separate areas of IT can be used to bring a group of experts and specialists in any field of engineering closer together by allowing them to communicate and exchange information and expertise that facilitate knowledge capture, sharing, and reuse. A lack of an advisory management system and a need to marshal all available data in a common format has indicated the need for an integrated engineering computing environment to investigate concrete repair problems. The research described in this paper is based upon an evaluation management system (EMS) which comprising a database management system (REPCON) alongside visualisation technologies and evaluation system (ECON) is developed to produce an innovative platform which will facilitate and encourage the development of knowledge in educational, evolution and evaluation modes of concrete repair. This allows us to create assessment procedures that will allow the current condition of the concrete structure and its components to be expressed numerically using a confidence level (CL) so as to take the best course of action in the repair and maintenance management. The explained rating system, which is related to structural integrity and serviceability of the structure, allows the confidence level to be determined by visual inspection and the descriptive information and pictures taken from an available REPair of CONcrete (REPCON) database.

Imaging of concrete structures

Demand for the development of non-destructive testing (NDT) techniques for concrete structures has increased with the growing concern about the deteriorating condition of the World's infrastructure. Efficient and accurate imaging techniques are needed for a reliable evaluation of safety and serviceability of concrete structures. Although, presently, imaging is routinely used in various fields, implementation of these technologies in NDT of civil engineering systems, especially of concrete structures, offers many challenges and requires additional development due to the composite nature of the concrete material and the complexities of reinforced or prestressed concrete systems. This paper presents the basic principles of various imaging techniques associated with several NDT methods applicable to concrete structures. The techniques considered are radiography, radioactive computerized tomography, infrared thermography, radar imaging and acoustic imaging. Special considerations regarding the applicability and accuracy of these techniques for the condition assessment of concrete structures are discussed, and examples of imaging applications are given.