Non-Destructive Methods for the Detection of Delaminations in Concrete Bridge Decks

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

Detection of near-field, low permittivity layers with Ground Penetrating Radar: analytical estimation of the reflection coefficient

peer reviewedThe reflection coefficient of GPR waves encountering embedded thin layers is commonly estimated using a plane wave, far field approximation. But when the thin layer is situated in the near field of the antenna, the spherical nature of the waves and the possible propagation of a lateral wave into the layer may have a strong influence on the measured reflected amplitude. In this work, we studied through 2D FDTD simulations the behavior of a radar wave interacting with thin layers of different thicknesses. The snapshots and radargrams showed a large influence of the layer thickness on the wave propagation. For the very thin layers, the evanescent wave plays a major role and the plane wave approximation gives a good estimation of the reflection coefficient. For thicker layers, the specific inclination of each multiple reflection has to be taken into account, as well as the lateral wave propagation. On the basis of these observations, we determined which analytical method should be used for the analytical prediction of the reflection coefficient, as a function of the layer thickness

Surfology: concrete substrate evaluation prior to repair

peer reviewedThe 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

Optimizing vibration parameters of thick single-layer concrete pavements: results of the Belgian Monocrete project

peer reviewedThick single-layer concrete pavements are increasingly popular in Europe because they help tackle the increasing traffic loads on highways, airport taxiways, or industrial logistic platforms. They require less maintenance than other pavement materials, have a very long service life even under heavy loads, and can withstand static loads without permanent deformation. However, the environmental impact of such pavements is significant, due to the vast quantities of cement and inert materials required for each project. The MONOCRETE research project (March 2021-March 2024), funded by the Walloon GreenWin innovation cluster, brings together industrial partners (Eloy and Holcim) as well as research institutions (BRRC, CRIC-OCCN, and ULiège) with the aim of reducing this environmental impact by incorporating recycled concrete aggregates and an alternative, low-carbon cement. In addition to issues relating to concrete sustainability, the project studies the formulation and execution of thick concrete pavements. Indeed, a greater thickness will accentuate any compaction or vibration problem associated with a poor particle size distribution. The risk of bleeding or segregation is therefore increased. These issues are being studied through a combination of literature review, laboratory testing, and the execution of two test sections, implemented in fall 2022 and spring 2023. The purpose of this paper is to summarize the initial conclusions of this recent project on the vibration of thick concrete pavements.MonoCrete - Revêtement monocouche épais à base de liants alternatifs et de granulats recyclés11. Sustainable cities and communitie

The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data

We measure the Milky Way's rotation curve over the Galactocentric range 4 kpc <~ R <~ 14 kpc from the first year of data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We model the line-of-sight velocities of 3,365 stars in fourteen fields with b = 0 deg between 30 deg < l < 210 deg out to distances of 10 kpc using an axisymmetric kinematical model that includes a correction for the asymmetric drift of the warm tracer population (\sigma_R ~ 35 km/s). We determine the local value of the circular velocity to be V_c(R_0) = 218 +/- 6 km/s and find that the rotation curve is approximately flat with a local derivative between -3.0 km/s/kpc and 0.4 km/s/kpc. We also measure the Sun's position and velocity in the Galactocentric rest frame, finding the distance to the Galactic center to be 8 kpc < R_0 < 9 kpc, radial velocity V_{R,sun} = -10 +/- 1 km/s, and rotational velocity V_{\phi,sun} = 242^{+10}_{-3} km/s, in good agreement with local measurements of the Sun's radial velocity and with the observed proper motion of Sgr A*. We investigate various systematic uncertainties and find that these are limited to offsets at the percent level, ~2 km/s in V_c. Marginalizing over all the systematics that we consider, we find that V_c(R_0) 99% confidence. We find an offset between the Sun's rotational velocity and the local circular velocity of 26 +/- 3 km/s, which is larger than the locally-measured solar motion of 12 km/s. This larger offset reconciles our value for V_c with recent claims that V_c >~ 240 km/s. Combining our results with other data, we find that the Milky Way's dark-halo mass within the virial radius is ~8x10^{11} M_sun.Comment: submitted to Ap

Charactérisation par Géoradar de couches minces dans les bétons

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.Le Ground Penetrating Radar (GPR) est une méthode non destructive utilisée pour l'inspection des routes et des bâtiments, bien adaptée pour détecter les différentes couches constituant une structure. L'objectif de cette thèse est de développer une méthode pour une détermination rapide des propriétés d'une couche enfouie sur base des mesures GPR de surface. L'observation des ondes GPR dans des simulations numériques a mené au développement d'un modèle analytique, qui a pu être appliqué à la détermination expérimentale de structures multicouches de laboratoire

Détermination des propriétés de couches minces dans le béton à l’aide d’un géoradar commercial à hautes fréquences: approche pic-à-pic et analyse fréquentielle du coefficient de réflexion

peer reviewedLe Ground Penetrating Radar (GPR) est un outil efficace pour l’inspection non destructive de structures en béton. Il est largement utilisé pour détecter les armatures et les zones humides ou pour évaluer l’épaisseur des éléments. Mais lorsqu’un élément contient une couche mince, les ondes radar sont soumises à de multiples réflexions sur les interfaces et la couche apparait dans le radargram comme une unique réflexion, dont l’étude détaillée peut permettre de déterminer l’épaisseur et la permittivité de la couche mince. Deux approches ont été considérées dans cette étude. Dans la première, l’analyse est basée sur l’amplitude pic-à-pic de la réflexion. La seconde approche comporte une analyse fréquentielle du coefficient de réflexion, dont l’amplitude et la phase sont alors calculées pour différentes fréquences, ce qui permet en théorie de déterminer à la fois la permittivité et l’épaisseur de la couche. Les deux méthodes ont été validées numériquement, par simulations en différences finies, et testées expérimentalement sur des échantillons de béton contenant une lame d’air d’épaisseur variable. Nous avons montré que l’analyse fréquentielle permettait d’atteindre une précision plus élevée dans l’estimation des paramètres pour un faible coût de calcul supplémentaire. L’efficacité de la méthode dépend des conditions et est optimale pour les couches de permittivité élevée présentant un contraste important avec la matrice.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

Detection of Defects in Concrete With Ground Penetrating Radar

peer reviewedGround 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

Static Detection of Thin Layers into Concrete with Ground Penetrating Radar

peer reviewedGround 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

GPR detection of saturated areas into concrete in the presence of a water gradient

peer reviewedIn 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