A Joint Inversion Approach of Capacitive and Resistive Measurements for the Estimation of Water Saturation Profiles in Concrete Structures

Concrete is a construction material that is well known for its durability. However, it is exposed to environmental attacks that lead to the penetration of aggressive agents such as water and chlorides, thus, threatening its durability and service life. Within this context and exploiting the sensitivity of the electromagnetic properties of concrete to its water content, the literature suggests determining water saturation profiles using non-destructive techniques. For instance, measuring the electrical resistivity at several points of the surface of the concrete structure can lead to an estimate of the resistivity depth profile. Then, after a calibration step, the water saturation depth profile can be obtained and the durability can be assessed. Similarly, the water depth profile can be assessed by dielectric permittivity measurements. In this paper, we propose a new inversion scheme based on the combination of both resistive and capacitive measurements: resistivity and permittivity measurements are inverted jointly to estimate the water saturation profile in concrete. Numerical experiments with simulated data show that information gathered from the two measurements enriches the inversion process, leading to the determination of more reliable water saturation profiles

Identification of inhomogeneous concrete cover by non-contact ultrasonic method

International audienceConcrete cover degradation is induced by aggressive agents in ambiance, chemicals, moisture, or temperature variations. Due to this degradation concrete becomes inhomogeneous and usually a thin surface layer appears with porosity and elastic modulus different than the properties of deeper sound concrete. Therefore the on-site nondestructive evaluation of concrete cover is important to monitor the integrity of concrete structures and prevent their irreversible damage. In this paper the methodology applied by the classical technique used for ground structure recovery called Multichannel Analysis of Surface Waves (MASW) is used as the NDT tool to characterize the thickness and elastic modulus of concrete cover. The procedure consists in generation and reception of surface waves within the required frequency band, using the non-contact transducers which scan evaluated profiles. Then the phase velocity dispersion characteristic V(f) is extracted, and concrete cover is characterized using as the proposed velocity gradient. The dispersion characteristics are exploited by the inversion software in order to obtain the variation of shear wave velocity as a function of depth

Towards the Determination of Chloride Profiles by means of Resistivity Measurements in Reinforced Concrete

Reinforced concrete (RC) structures, such wharfs or floating structures, are submitted to chloride ingress which can lead to rebar corrosion. Before the corrosion initiation, in a preventive point of view, engineers can be interested in non-destructive evaluation and inspection methods. In that way, electrical resistivity tomography is a promising tool to access to resistivity profiles then to chloride profiles in real RC structures in the future. We would like to present herein the advances in the necessary research developments to reach this goal, i.e. the resistivity profiles obtained in reinforced concrete slabs submitted to chloride ingress. The 4 slab dimensions are 90x70x13 cm. The specimens are cured, dried during 9 months then submitted to salted water imbibition during 4 months. Electrical resistivity tomography measurements are performed at short terms during 1 week of imbibition. The monitoring show that several phenomena influence the resistivity profiles such as the penetration of water and chloride ions. Meanwhile, steel rebar effect can be considered thus eliminated from electrical resistivity profiles following the method developed by (Alhajj et al. 2019)

Combining NDT tools for analysing the efficiency of repair techniques of wharves: the MAREO project

ISBN: 9780415669863Repair of structures in concrete is still a challenge, especially when access and environment offer a difficult context such as the case of wharves. Concerning the repair of concrete for marine structures, European standards give the requirements in predefined and standardised conditions. However, repair of wharves is performed in harsh conditions such as access, humidity and operator position. These conditions do not enable the direct application of standards. By accounting for these requirements, the repair technique consists in rebuilding the concrete cover and in some cases using protective coating for some beams. In this paper, we focus on the concrete repair techniques. The aim of MAREO project (French project of the National competitive cluster in Civil Engineering and Eco-Building) is to compare several repair techniques carried out in the most complex area for repair: the tidal zone. The project deals with initial performance, sustainability, cost of durability and concrete properties monitoring by Destructive Testing (DT) and Non-Destructive Testing (NDT) techniques. The studied NDT techniques are: impact-echo, surface waves, multi-offset radar, and capacitive method. Both, beams placed in natural exposure and slabs specimens placed in accelerated conditions in laboratory are considered. For all the beams, the contaminated concrete was removed using high-velocity water jets (hydro-demolition). The selected techniques are wet shotcrete, dry shotcrete, formed concrete and manual repair. This paper focuses on the ability of NDT techniques to evaluate the changes of properties related to the chloride ingress in concrete both on site and in accelerated laboratory conditions. The interest of each technique and its sensitivity to several physical factors are highlighted. The need of NDT-combination is illustrated

Comparison of durability indicators obtained by Non Destructive Testing methods to monitor the durability of concrete structures

International audienceThis paper deals with the use of non destructive testing methods (NDT) to assess indicators of concrete durability and mechanical properties of reinforced concrete structures. On site, NDT methods based on electromagnetic or ultrasonic wave propagation (such as radar, impact echo, ultrasonic transmission deviceÉ) are used because they are more or less sensitive to water content and mechanical properties depending on the method. It has been shown, in a former project [1, 2], that the NDT results called Òobservablesî are linked to mechanical and durability indicators (YoungÕs modulus, compressive strength, porosity and saturation degree). Meanwhile, the relationship between observables and indicators depends on the concrete mix design. A calibration protocol is then proposed to get this relationship for the right mix of the reinforced structure studied by using a minimal number of cores. The cores are non-destructively characterised in laboratory or used to determined reference indicators by standardised destructive methods. The aims of this paper are first to present the ND calibration protocol on cores and then to validate this proposed calibration protocol. To achieve this goal, some NDT results obtained on site and on the corresponding core are compared and durability indicators deduced from NDT calibration are compared with reference durability indicators

Evaluation de la durabilité du béton armé vis à vis des ions chlorure à l'aide de capteurs noyés dans le béton versus des auscultations en parement

GC'2019, le Génie Civil au coeur des mutations technologiques et numériques , CACHAN, FRANCE, 20-/03/2019 - 21/03/2019L'évaluation du processus de corrosion de structures en béton armé en milieu chloruré a été étudiée en utilisant deux approches complémentaires : l'auscultation non destructive (ND) du béton d'enrobage et la corrosion des armatures. Différentes méthodes d'évaluation non destructives basées, soit sur de l'instrumentation avec des capteurs noyés dans le béton armé, soit sur des auscultations réalisées en parement, ont été utilisées afin de caractériser la phase d'incubation puis la phase de propagation de la corrosion. Dans cette première phase d'étude, les différents objectifs étaient les suivants : 1) Etudier des bétons différents formulés avec du ciment Portland ou des laitiers, en termes de réaction de transfert dans le béton et de réactions électrochimiques armature/béton/environnement, 2) Analyser les résultats des capteurs noyés dans le béton armé (formulé avec du ciment Portland ou des laitiers) qui permettent de suivre en continu l'évolution des phénomènes, 3) Comparer les résultats entre les capteurs noyés et les mesures réalisées sur parement, 4) Démontrer l'intérêt du Corrosion Health Monitoring sur ouvrages neufs et/ou réparés en termes de surveillance (système d'alerte plutôt qu'alarme) dans le temps. Les différentes méthodes basées sur des mesures de résistivité (capteurs noyés et auscultation en surface) permettent d'accéder à des profils traduisant la pénétration d'eau de mer par imbibition. Des méthodologies d'inversion et de calibration ont été consolidées. Une expérience sur les capteurs de corrosion a été capitalisée. Enfin, de nouvelles méthodes ont été explorées (SUSI, radar de fréquence,...) et certaines sont prometteuses. Les interprétations des résultats peuvent s'avérer délicates et il convient de bien énoncer les hypothèses et les limites notamment dans une prise de décision (maintenance et/ou réparation par ex). Enfin, il est nécessaire de poursuivre cette étude sur du plus long terme afin d'affiner les résultats et les applications fortes pour la gestion du parc d'ouvrages vieillissants

Implementation of an Embedded Sensor Based on Electrical Resistivity to Monitor Drying in Thick Concrete Structures

Electrical resistivity is a parameter sensitive to several properties of concrete, including water content, which is one of the key parameters governing concrete long-term durability. In this paper, the monitoring of the concrete water content profile throughout its entire thickness is discussed using an electrical approach as a measurement method. This is very relevant to applications requiring a centimeter resolution over a large thickness. The aim of this paper is to implement a multi-electrode embedded sensor in a concrete slab to determine the resistivity profile over concrete depth in order to monitor its drying. The sensor, designed as a printed circuit board (PCB), is integrated in two 30 cm thick concrete slabs. Different measurement configurations are presented. Following qualification in laboratory and controlled conditions, the study focuses on characterizing the sensor‘s response during the drying of the slabs. The results demonstrate the capability of the sensor to monitor concrete drying by measuring the resistivity profiles with a spatial centimetric resolution