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Concrete and Concrete Structures Monitored by Ultrasound

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: closed (10 April 2022) | Viewed by 15562

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Prof. Dr. Christoph Gehlen

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Guest Editor

Centre for Building Materials, Technical University of Munich, Franz-Langinger-Str. 10, 81245 München, Germany
Interests: concrete technology; durability of concrete constructions; corrosion of steel in concrete; service life design, protection, maintenance, and restoration of concrete structures; additive manufacturing
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Prof. Dr. Christian Große

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Centre for Building Materials, Technical University of Munich, Franz-Langinger-Str. 10, 81245 München, Germany
Interests: non-destructive testing in engineering materials

Special Issue Information

Dear Colleagues,

Major parts of our built environment today consist of reinforced concrete (RC) structures. Our lives, as with our mobility, the industrial performance and the functionality of modern society in general directly depend on the reliability and availability of these structures. Hence, cost-efficient preservation of the integrity of the RC infrastructure over the service life is of utmost importance, considering that RC structures, partly built some decades ago, has to meet increasing demands with regard to performance. The deterioration of concrete structures originates sometimes in the early age of fresh concrete and the actual condition of the completed structure is not always comprehensively known.

Ultrasonic methods have the potential to enhance the assessment of the safety and durability of engineering structures made from concrete, and can be applied efficiently by investigating the evolution of the setting and hardening process. Ultrasound can therefore cover the entire life cycle of concrete structures. In this Special Issue, we aim at scientific research referring to ultrasonic monitoring methods on the macro- as well as on the micro-structural level of concrete. Topics of interest include experimental progress, simulation of the material behavior related to elastic wave propagation, and advanced signal evaluation techniques. All topics should contribute to the central idea of monitoring concrete and concrete structures using ultrasound-based techniques, encouraging specifically the long-term condition assessment perspective.

We cordially invite you to submit your manuscript, original research paper or review article, on experimental analysis and/or theoretical studies.

Prof. Dr. Christoph Gehlen
Prof. Dr. Christian Große
Guest Editors

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Keywords

civil engineering
fresh and hardened concrete
hydration process
damage detection
non-destructive testing
structural health monitoring
ultrasound
elastic wave propagation

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Published Papers (6 papers)

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Research

15 pages, 5822 KiB

Open AccessEditor’s ChoiceArticle

Impact of External Mechanical Loads on Coda Waves in Concrete

by Fabian Diewald, Niklas Epple, Thomas Kraenkel, Christoph Gehlen and Ernst Niederleithinger

Materials 2022, 15(16), 5482; https://doi.org/10.3390/ma15165482 - 9 Aug 2022

Cited by 11 | Viewed by 1937

Abstract

During their life span, concrete structures interact with many kinds of external mechanical loads. Most of these loads are considered in advance and result in reversible deformations. Nevertheless, some of the loads cause irreversible, sometimes unnoticed changes below the macroscopic scale depending on the type and dimension of the impact. As the functionality of concrete structures is often relevant to safety and society, their condition must be known and, therefore, assessed on a regular basis. Out of the spectrum of non-destructive monitoring methods, Coda Wave Interferometry using embedded ultrasonic sensors is one particularly sensitive technique to evaluate changes to heterogeneous media. However, there are various influences on Coda waves in concrete, and the interpretation of their superimposed effect is ambiguous. In this study, we quantify the relations of uniaxial compression and uniaxial tension on Coda waves propagating in normal concrete. We found that both the signal correlation of ultrasonic signals as well as their velocity variation directly reflect the stress change in concrete structures in a laboratory environment. For the linear elastic range up to 30% of the strength, we calculated a velocity variation of −0.97‰/MPa for compression and 0.33%/MPa for tension using linear regression. In addition, these parameters revealed even weak irreversible changes after removal of the load. Furthermore, we show the time-dependent effects of shrinkage and creep on Coda waves by providing the development of the signal parameters over time during half a year together with creep recovery. Our observations showed that time-dependent material changes must be taken into account for any comparison of ultrasonic signals that are far apart in time. The study’s results demonstrate how Coda Wave Interferometry is capable of monitoring stress changes and detecting even small-size microstructural changes. By indicating the stated relations and their separation from further impacts, e.g., temperature and moisture, we anticipate our study to contribute to the qualification of Coda Wave Interferometry for its application as an early-warning system for concrete structures. Full article

(This article belongs to the Special Issue Concrete and Concrete Structures Monitored by Ultrasound)

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17 pages, 14844 KiB

Open AccessArticle

Correlation of Load-Bearing Behavior of Reinforced Concrete Members and Velocity Changes of Coda Waves

by Felix Clauß, Niklas Epple, Mark Alexander Ahrens, Ernst Niederleithinger and Peter Mark

Materials 2022, 15(3), 738; https://doi.org/10.3390/ma15030738 - 19 Jan 2022

Cited by 12 | Viewed by 2309

Abstract

The integral collection of information such as strains, cracks, or temperatures by ultrasound offers the best prerequisites to monitor structures during their lifetime. In this paper, a novel approach is proposed which uses the collected information in the coda of ultrasonic signals to infer the condition of a structure. This approach is derived from component tests on a reinforced concrete beam subjected to four-point bending in the lab at Ruhr University Bochum. In addition to ultrasonic measurements, strain of the reinforcement is measured with fiber optic sensors. Approached by the methods of moment-curvature relations, the steel strains serve as a reference for velocity changes of the coda waves. In particular, a correlation between the relative velocity change and the average steel strain in the reinforcement is derived that covers 90% of the total bearing capacity. The purely empirical model yields a linear function with a high level of accuracy (

R^{2} = 0.99,

R M S E \approx 90 μ

strain). Full article

(This article belongs to the Special Issue Concrete and Concrete Structures Monitored by Ultrasound)

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15 pages, 5950 KiB

Open AccessArticle

Damage Detection at a Reinforced Concrete Specimen with Coda Wave Interferometry

by Stefan Grabke, Felix Clauß, Kai-Uwe Bletzinger, Mark Alexander Ahrens, Peter Mark and Roland Wüchner

Materials 2021, 14(17), 5013; https://doi.org/10.3390/ma14175013 - 2 Sep 2021

Cited by 18 | Viewed by 2394

Abstract

Reinforced concrete is a widely used construction material in the building industry. With the increasing age of structures and higher loads there is an immense demand for structural health monitoring of built infrastructure. Coda wave interferometry is a possible candidate for damage detection in concrete whose applicability is demonstrated in this study. The technology is based on a correlation evaluation of two ultrasonic signals. In this study, two ways of processing the correlation data for damage detection are compared. The coda wave measurement data are obtained from a four-point bending test at a reinforced concrete specimen that is also instrumented with fibre optic strain measurements. The used ultrasonic signals have a central frequency of 60 kHz which is a significant difference to previous studies. The experiment shows that the coda wave interferometry has a high sensitivity for developing cracks and by solving an inverse problem even multiple cracks can be distinguished. A further specialty of this study is the use of finite elements for solving a diffusion problem which is needed to state the previously mentioned inverse problem for damage localization. Full article

(This article belongs to the Special Issue Concrete and Concrete Structures Monitored by Ultrasound)

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16 pages, 5433 KiB

Open AccessEditor’s ChoiceArticle

Sensitivity of Ultrasonic Coda Wave Interferometry to Material Damage—Observations from a Virtual Concrete Lab

by Claudia Finger, Leslie Saydak, Giao Vu, Jithender J. Timothy, Günther Meschke and Erik H. Saenger

Materials 2021, 14(14), 4033; https://doi.org/10.3390/ma14144033 - 19 Jul 2021

Cited by 10 | Viewed by 2819

Abstract

Ultrasonic measurements are used in civil engineering for structural health monitoring of concrete infrastructures. The late portion of the ultrasonic wavefield, the coda, is sensitive to small changes in the elastic moduli of the material. Coda Wave Interferometry (CWI) correlates these small changes in the coda with the wavefield recorded in intact, or unperturbed, concrete specimen to reveal the amount of velocity change that occurred. CWI has the potential to detect localized damages and global velocity reductions alike. In this study, the sensitivity of CWI to different types of concrete mesostructures and their damage levels is investigated numerically. Realistic numerical concrete models of concrete specimen are generated, and damage evolution is simulated using the discrete element method. In the virtual concrete lab, the simulated ultrasonic wavefield is propagated from one transducer using a realistic source signal and recorded at a second transducer. Different damage scenarios reveal a different slope in the decorrelation of waveforms with the observed reduction in velocities in the material. Finally, the impact and possible generalizations of the findings are discussed, and recommendations are given for a potential application of CWI in concrete at structural scale. Full article

(This article belongs to the Special Issue Concrete and Concrete Structures Monitored by Ultrasound)

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14 pages, 6009 KiB

Open AccessArticle

Single-Station Coda Wave Interferometry: A Feasibility Study Using Machine Learning

by Erik H. Saenger, Claudia Finger, Sadegh Karimpouli and Pejman Tahmasebi

Materials 2021, 14(13), 3451; https://doi.org/10.3390/ma14133451 - 22 Jun 2021

Cited by 8 | Viewed by 2562

Abstract

Coda wave interferometry usually is applied with pairs of stations analyzing the signal transmitted from one station to another. A feasibility study was performed to evaluate if one single station could be used. In this case, the reflected coda wave signal from a zone to be identified was analyzed. Finite-difference simulations of wave propagation were used to study whether ultrasonic measurements could be used to detect velocity changes in such a zone up to a depth of 1.6 m in a highly scattering medium. For this aim, 1D convolutional neural networks were used for prediction. The crack density, the crack length, and the intrinsic attenuation were varied in the considered background material. The influence of noise and the sensor width was elaborated as well. It was shown that, in general, the suggested single-station approach is a possible way to identify damage zones, and the method was robust against the studied variations. The suggested workflow also took advantage of machine-learning techniques, and can be transferred to the detection of defects in concrete structures. Full article

(This article belongs to the Special Issue Concrete and Concrete Structures Monitored by Ultrasound)

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13 pages, 5390 KiB

Open AccessArticle

Assessment of the Deterioration State of Post-Installed Bonded Anchors Using Ultrasonic

by Oliver Zeman, Michael Schwenn, Martin Granig and Konrad Bergmeister

Materials 2021, 14(8), 2077; https://doi.org/10.3390/ma14082077 - 20 Apr 2021

Cited by 2 | Viewed by 1929

Abstract

The assessment of already installed anchorages for a possible exceeding of the service load level is a question that is gaining more and more importance, especially in building maintenance. Bonded anchors are of particular interest here, as the detection of a capacity reduction or load exceedance can cause damage to the concrete-bonded mortar behavior. This article investigates the extent to which ultrasonic methods can be used to make a prediction about the condition of anchorages in concrete and about their load history. A promising innovative assessment method has been developed. The challenges in carrying out the experimental investigations are the arrangement of the transducers, the design of the test set-up and the applicability of direct, indirect or semidirect ultrasonic transmission. The experimental investigations carried out on a test concrete mix and a bonded anchor system show that damage to the concrete structure can be detected by means of ultrasound. The results indicate the formation of cracks and therefore a weakening of the response determined by means of direct, indirect and semidirect ultrasonic transmission. However, for application under non-laboratory conditions and on anchors with unknown load history, the calibration with a reference anchor and the identification of the maximum load is required. This enables a referencing of the other loaded anchors to the unloaded conditions and allows an estimation of the load history of individual anchors. Full article

(This article belongs to the Special Issue Concrete and Concrete Structures Monitored by Ultrasound)

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