References of "Van der Wielen, Audrey"
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See detailCharacterization of thin layers into concrete with Ground Penetrating Radar
Van der Wielen, Audrey ULg

Doctoral thesis (2014)

The Ground Penetrating Radar (GPR) is a non-destructive method used for roads and buildings inspection: it is well adapted to detect the different layers constituting the structures. The objective of this ... [more ▼]

The Ground Penetrating Radar (GPR) is a non-destructive method used for roads and buildings inspection: it is well adapted to detect the different layers constituting the structures. The objective of this thesis is to develop a method for a fast determination of the properties of a buried layer on the basis of surface GPR measurements. The observation of the GPR waves propagation in numerical simulations led to develop an analytical model, which could be applied to the experimental determination of laboratory layered structures. [less ▲]

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See detailDétermination des propriétés de couches dans le béton à l'aide d'un géoradar commercial à hautes fréquences: approche pic-à-pic et analyse fréquentielle du coefficient de réflexion
Van der Wielen, Audrey ULg; Nguyen, Frédéric ULg; Courard, Luc ULg

in Annales du Bâtiment et des Travaux Publics (2014)

The Ground Penetrating Radar (GPR) is an efficient tool for the non-destructive inspection of concrete structures. It is widely used for the detection of rebars or humid zones or for evaluating the ... [more ▼]

The Ground Penetrating Radar (GPR) is an efficient tool for the non-destructive inspection of concrete structures. It is widely used for the detection of rebars or humid zones or for evaluating the thickness of elements. But when an element contains a thin layer, the radar waves are submitted to multiple reflections on the interfaces and the layer appears in the radargram as a single reflection, whose detailed analysis can allow determining the thickness and the permittivity of the thin layer. Two approaches were considered in this paper. In the first one, the analysis is based on the peak-to-peak reflection amplitude. The second approach uses a frequency analysis of the reflection coefficient, whose amplitude and phase can then be calculated for several frequencies. With this method, the thickness and permittivity of the layer can in theory be simultaneously determined. Both methods were numerically validated through finite difference simulations and experimentally tested on concrete samples containing an air layer of variable thickness. We showed that the frequency analysis allowed to reach a higher precision in the parameters estimation for a limited additional computing cost. The method efficiency depends on the conditions and is optimal for layers with a high permittivity presenting a large contrast with the matrix. [less ▲]

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See detailGPR detection of saturated areas into concrete in the presence of a water gradient
Louis, Arnaud ULg; Van der Wielen, Audrey ULg; Courard, Luc ULg et al

in 2012 14th International Conference on Ground Penetrating Radar (GPR) (2012, June)

In the concrete, saturated areas are most of the time limited by a transition zone, presenting a water gradient. This transition zone can affect the GPR wave’s reflection and decrease the reflection ... [more ▼]

In the concrete, saturated areas are most of the time limited by a transition zone, presenting a water gradient. This transition zone can affect the GPR wave’s reflection and decrease the reflection coefficient by comparison to the coefficient that would be obtained on a sharp interface. To quantify the impact of the water gradient on the reflection coefficient, we performed finite differences simulations. They showed that the reflection coefficient was reduced by 70% if the thickness of the transition zone was larger than 2/5 of the wavelength. Laboratory experiments, using hygrometric sensors for the water content control, confirmed this trend. [less ▲]

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See detailDetection of thin layers into concrete with static and CMP measurements
Van der Wielen, Audrey ULg; Courard, Luc ULg; Nguyen, Frédéric ULg

in 2012 14th International Conference on Ground Penetrating Radar (GPR) (2012, June)

Most concrete bridge decks contain a thin waterproofing layer, whose complex GPR signature can affect the detection of disorders or delaminations into the slab. In this study, we characterized the ... [more ▼]

Most concrete bridge decks contain a thin waterproofing layer, whose complex GPR signature can affect the detection of disorders or delaminations into the slab. In this study, we characterized the detection limits of our 2.3 GHz antenna for the detection of thin layers, with static and CMP measurements. In this last configuration, we showed that the radiation pattern and the reflection coefficient estimation are key parameters to use the inversion of the amplitude versus offset (AVO) curves for the estimation of the layer parameters. The theoretical results were compared to the results of FDTD simulations, performed with GprMax2D, and to laboratory measurements, performed on concrete slabs or sand containing thin layers. [less ▲]

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See detailStatic Detection of Thin Layers into Concrete with Ground Penetrating Radar
Van der Wielen, Audrey ULg; Courard, Luc ULg; Nguyen, Frédéric ULg

in Restoration of Buildings and Monuments = Bauinstandsetzen und Baudenkmalpflege (2012), 18(3/4), 247-254

Ground Penetrating Radar (GPR) is a nondestructive technique particularly well adapted to the inspection of concrete structures and can help to determine the structure inner geometry or to detect damaged ... [more ▼]

Ground Penetrating Radar (GPR) is a nondestructive technique particularly well adapted to the inspection of concrete structures and can help to determine the structure inner geometry or to detect damaged areas. When the GPR is used on structures containing thin layers, for example the sealing layer of a concrete bridge deck or the void into a masonry wall, it is important for the radar user to know the minimum thickness required to detect and estimate the thickness of those layers. The theory of thin layer detection is based on a sine wave but, in reality, most commercial GPR systems emit a large frequency band wavelet, which undergoes attenuation into the layer. To analyze the influence of those realistic conditions on the reflection coefficient of a thin layer, we combined experimental measurements and numerical FDTD simulations. The experimental results matched the numerical predictions well, presenting a fast attenuation compared to the theoretical predictions. Nevertheless, for thicknesses inferior to λ/11, the reflection coefficient could still be considered as linearly dependent of the thickness to wavelength ratio. [less ▲]

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See detailDetection of Defects in Concrete With Ground Penetrating Radar
Van der Wielen, Audrey ULg; Courard, Luc ULg; Nguyen, Frédéric ULg

in ESPSC 2011: European Symposium on Polymers in Sustainable Construction (Czarnecki Symposium) (2011, September)

Ground Penetrating Radar (GPR) is a nondestructive technique particularly well adapted to the inspection of concrete structures and can help to determine the structure inner geometry or to detect damaged ... [more ▼]

Ground Penetrating Radar (GPR) is a nondestructive technique particularly well adapted to the inspection of concrete structures and can help to determine the structure inner geometry or to detect damaged areas. When the GPR is used on structures containing thin layers, for example the sealing layer of a bridge or the void into a masonry wall, it is important for the radar user to know the minimum thickness required to detect and estimate the thickness of those layers. The theory of thin layer detection is based on a sine wave but, in reality, the GPR emits a complicated pulse, which undergoes attenuation into the layer. To see the influence of those realistic conditions on the reflection coefficient of a thin layer, we combined experimental measurements and numerical FDTD simulations. The experimental results matched the numerical predictions well, presenting a fast attenuation compared to the theoretical predictions. Nevertheless, for thicknesses inferior to λ/11, the reflection coefficient could still be considered as linearly dependent of the thickness to wavelength ratio. [less ▲]

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See detailGPR Limits for Thin Layers in Concrete Detection: Numerical and Experimental Evaluation
Van der Wielen, Audrey ULg; Courard, Luc ULg; Nguyen, Frédéric ULg

in Progress In Electromagnetics Research Symposium Proceedings, Marrakesh, Morocco, March 20-23, 2011 (2011, March)

The Ground Penetrating Radar (GPR) is a nondestructive technique increasingly used in civil structures inspection. In those structures, thin layers, presenting a relatively small thickness compared to ... [more ▼]

The Ground Penetrating Radar (GPR) is a nondestructive technique increasingly used in civil structures inspection. In those structures, thin layers, presenting a relatively small thickness compared to their area, are common and induce a complex multiple reflection scheme of the GPR waves on the two interfaces limiting the layer. The theoretical relationships predicting the reflected amplitude are based on multiple simplifying assumptions that are not matched by most commercial GPR impulse machines. In the first part of this study, we confronted the theoretical curves with numerical finite difference simulations performed with GprMax2D, with both a continuous sine wave and a realistic pulse derived from measurements. In the second part, we performed experiments on two concrete slabs, separated with an air space of variable thickness. The measured amplitude appeared to be different from the predictions, probably due to surface noise. [less ▲]

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See detailRecherche dans le domaine du béton à l'Université de Liège (2009-2010)
Dotreppe, Jean-Claude ULg; Franssen, Jean-Marc ULg; Somja, H. et al

Scientific conference (2010, October 21)

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See detailUtilisation du GPR pour la détection des discontinuités dans les tabliers de ponts
Van der Wielen, Audrey ULg; Nguyen, Frédéric ULg; Courard, Luc ULg

Scientific conference (2010, August 27)

Le Ground Penetrating Radar (GPR) est une technique non destructive utilisée depuis des décennies dans l’auscultation des sols. Depuis quelques années, l’apparition sur le marché d’antennes à hautes ... [more ▼]

Le Ground Penetrating Radar (GPR) est une technique non destructive utilisée depuis des décennies dans l’auscultation des sols. Depuis quelques années, l’apparition sur le marché d’antennes à hautes fréquences a permis d’appliquer cette méthode à des structures de moindre épaisseur, et notamment aux tabliers de ponts en béton. A l’Université de Liège, des travaux sont menés afin d’améliorer la détection des discontinuités dans les tabliers de ponts en béton. Dans une première étude expérimentale, 12 échantillons en béton contenant des défauts simulant des délaminations ont été réalisés et scannés par radar. Nous avons ainsi pu représenter les défauts en 3D et constater que leur visibilité était dépendante de leur épaisseur. Actuellement, une seconde étude théorique et expérimentale porte sur la détermination exacte de la limite de détection des couches minces. [less ▲]

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See detailFrom defects to causes: pathology of concrete and investigation methods.
Courard, Luc ULg; Van der Wielen, Audrey ULg; Darimont, Anne ULg

in Startegjia Izvedbe Sanacij Objektov (2010, May 19)

The proper planning of investigations before carrying out repair works is important if optimum use is to be made of the test data. A major step needs to be taken from knowing, for example, that chloride ... [more ▼]

The proper planning of investigations before carrying out repair works is important if optimum use is to be made of the test data. A major step needs to be taken from knowing, for example, that chloride is present in the concrete, to select the best methods for repair. Engineers require guidance on both the techniques available for the condition assessment of structures and the methods for data interpretation. Two major stages are usually recommended for such an operation: the first stage is based on a rapid-scan visual assessment, often including limited sampling in areas obviously damaged, from which areas can be selected for more detailed investigations. The second stage contains a detailed diagnostic survey that relies on destructive and non destructive testing techniques. Non destructive techniques are more and more utilized not only for the evaluation of the concrete strength but also for the detection of cracks and delaminations. Moreover, the interest for techniques able to evaluate concrete permeability is rising, due to the importance of this factor for durability evaluation. The paper will discuss the assessment of concrete structures and describe the main destructive and non destructive techniques with regard to specific pathologies. [less ▲]

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See detailOn the relation between bond quality and impact-echo frequency spectrum
Piotrowski, Tomasz; Garbacz, Andrzej; Van der Wielen, Audrey ULg et al

in Proceedings of the 13th International Congress on Polymers in Concrete ICPIC 2010 (2010)

According to EN 1504-10 and ACI Concrete Repair Manual, bond strength and interface quality are the main features of repair system necessary to be assessed. Pull-off test is most commonly used for bond ... [more ▼]

According to EN 1504-10 and ACI Concrete Repair Manual, bond strength and interface quality are the main features of repair system necessary to be assessed. Pull-off test is most commonly used for bond strength evaluation but growing interest in nondestructive techniques (NDT) is recently noted. Impact-echo (IE) is treated as the most promising one for this purpose. The aim of this paper is to analyze an effect of bond quality on stress wave propagation in repair systems. A group of samples has been prepared in order to obtain repair systems of different bond quality. Prior to repair, quality of concrete substrates has been characterized according different techniques: compressive strength, superficial cohesion, surface roughness index and cracking quantification. Than a polymer-modified repair mortar has been applied. Af-ter hardening, IE signals have been recorded and pull-off bond strength determined. The rela-tionships between parameters characterizing surface quality, bond strength, IE frequency spec-trum and results of wavelet analysis of IE signal have been analyzed. [less ▲]

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See detailRelation between bond quality and impact-echo frequency spectrum
Piotrowski, Tomasz; Garbacz, Andrzej; Van der Wielen, Audrey ULg et al

in Restoration of Buildings and Monuments = Bauinstandsetzen und Baudenkmalpflege (2010), 16(4/5), 303-314

According to EN 1504-10 and ACI Concrete Repair Manual, bond strength and interface quality are the main features of repair system necessary to be assessed. Pull-off test is most commonly used for bond ... [more ▼]

According to EN 1504-10 and ACI Concrete Repair Manual, bond strength and interface quality are the main features of repair system necessary to be assessed. Pull-off test is most commonly used for bond strength evaluation but growing interest in nondestructive techniques (NDT) is recently noted. Impact-echo (IE) is treated as the most promising one for this purpose. The aim of this paper is to analyze an effect of bond quality on stress wave propagation in repair systems. A group of samples has been prepared in order to obtain repair systems of different bond quality. Prior to repair, quality of concrete substrates has been characterized according different techniques: compressive strength, superficial cohesion, surface roughness index and cracking quantification. Than a polymer-modified repair mortar has been applied. After hardening, IE signals have been recorded and pull-off bond strength determined. The relationships between parameters characterizing surface quality, bond strength, IE frequency spectrum and results of wavelet analysis of IE signal have been analyzed. [less ▲]

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See detailOn the relation between bond quality and impact-echo frequency spectrum
Piotrowski, Tomasz; Garbacz, Andrzej; Van der Wielen, Audrey ULg et al

in Restoration of Buildings and Monuments = Bauinstandsetzen und Baudenkmalpflege (2010), 16(4/5), 303-314

According to EN 1504-10 and ACI Concrete Repair Manual, bond strength and interface quality are the main features of repair system necessary to be assessed. Pull-off test is most commonly used for bond ... [more ▼]

According to EN 1504-10 and ACI Concrete Repair Manual, bond strength and interface quality are the main features of repair system necessary to be assessed. Pull-off test is most commonly used for bond strength evaluation but growing interest in nondestructive techniques (NDT) is recently noted. Impact-echo (IE) is treated as the most promising one for this purpose. The aim of this paper is to analyze an effect of bond quality on stress wave propagation in repair systems. A group of samples has been prepared in order to obtain repair systems of different bond quality. Prior to repair, quality of concrete substrates has been characterized according different techniques: compressive strength, superficial cohesion, surface roughness index and cracking quantification. Than a polymer-modified repair mortar has been applied. After hardening, IE signals have been recorded and pull-off bond strength determined. The relationships between parameters characterizing surface quality, bond strength, IE frequency spectrum and results of wavelet analysis of IE signal have been analyzed. [less ▲]

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See detailWykorzystanie impact-echo i radaru do wykrywania defektow ukladu naprawczego nie zawierajacych warstwy powietrza
Garbacz, Andrzej; Harassek, Piotr; Van der Wielen, Audrey ULg et al

in 39th Polish Conference on Non destructive Testing Methods, Szczyrk 26-28 October, Zeszyty Problemowe. Badania nieniszczące (2010)

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See detailNondestructive Detection of Delaminations in Concrete Bridge Decks: A First Experimental Study
Van der Wielen, Audrey ULg; Courard, Luc ULg; Nguyen, Frédéric ULg

in Proceedings of the XIII International Conference on Ground Penetrating Radar (2010)

To detect delaminations in concrete bridge decks, nondestructive techniques (NDT) permit a frequent and large inspection of the slabs without damaging structures. This research was devoted to detect ... [more ▼]

To detect delaminations in concrete bridge decks, nondestructive techniques (NDT) permit a frequent and large inspection of the slabs without damaging structures. This research was devoted to detect simulated defects in twelve repaired concrete slabs. These were scanned with high frequency ground penetrating radar (GPR) with the common offset (CO) and common midpoint (CMP) methods. The electromagnetic waves speed was determined from CMPs. A 3D visualization program was also created to display the CO measurements. The visibility of the inserted defects revealed to be dependent on their lateral extension, their thickness and their constitutive material. [less ▲]

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See detailNon-Destructive Methods for the Detection of Delaminations in Concrete Bridge Decks
Van der Wielen, Audrey ULg

Master's dissertation (2009)

To detect delaminations in concrete bridge decks, the non-destructive techniques (NDT) permit a frequent inspection of the slabs without damaging the structures. Within this study, twelve samples were ... [more ▼]

To detect delaminations in concrete bridge decks, the non-destructive techniques (NDT) permit a frequent inspection of the slabs without damaging the structures. Within this study, twelve samples were realized, presenting diverse horizontal defects simulating delaminations. They were scanned with high frequency GPR with the common offset (CO) and common mid point (CMP) methods. The electromagnetic waves speed and defects depth were determined from the CMPs. A 3D visualization program was also created to display the CO measurements. The visibility of the inserted defects revealed to be dependent on their lateral extension, their thickness and especially their constitutive material. [less ▲]

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See detailSurfology: concrete substrate evaluation prior to repair
Courard, Luc ULg; Michel, Frédéric ULg; Schwall, Damien ULg et al

in Mammoli, A.; Brebbia, C. A. (Eds.) Materials Characterization: computational methods and experiments IV (2009)

The study of adhesion of repair materials on concrete structures implies a good knowledge of the influence of concrete surface treatment. The effects of surface preparation technique are rarely clearly ... [more ▼]

The study of adhesion of repair materials on concrete structures implies a good knowledge of the influence of concrete surface treatment. The effects of surface preparation technique are rarely clearly described and parameterised: it is consequently difficult to point out the real influence of roughness on adhesion results. A large research project has been realized with regards to the influence of concrete substrate strength and preparation technique efficiency. The surface roughness of concrete has been quantified by means of the projection “Moiré” technique, which is an interferometrical measurement method. Comparison between polished, scrabbled and hydro-jetted surfaces evaluation is presented. [less ▲]

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See detailRecherches menées à l'Université de Liège dans le domaine du béton en 2008-2009
Dotreppe, Jean-Claude ULg; Franssen, Jean-Marc ULg; Somja, Hugues et al

Conference given outside the academic context (2009)

Composite steel-concrete columns made of CFSHS filled with self compacting concrete under ambaint temperature and in the fire situation. Design equation for the buckling of high strength concrete columns ... [more ▼]

Composite steel-concrete columns made of CFSHS filled with self compacting concrete under ambaint temperature and in the fire situation. Design equation for the buckling of high strength concrete columns subkected to compression and bending. Improvement of the textural quality of concrete with hydraulic binders. Influence of the reutilisation of OSB panels shuttering on the colour and texture of concrete surfaces. Non destructive methods for the detection of delamination in the decks of concrete bridges [less ▲]

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