Improving the reliability of on-site concrete strength estimation with non-destructive techniques

The non-destructive assessment of concrete strength in existing structures is a complex issue. While many standards exist addressing the way non-destructive measurements must be carried out, few exist for the strength assessment itself. Many questions remain unanswered, like for instance the reliability of the strength estimation, the possibility of estimating the concrete variability, or the advantages of combining several non-destructive techniques. These problems have been tackled by a recent RILEM committee (TC ISC 249) whose Guidelines and Recommendations are to be released soon. This paper details their main innovations and how they are expected to improve the engineering practice and the reliability of strength estimation in existing structures

Proposition d'une méthodologie de calibration de la vitesse de propagation des ondes radar pour la mesure de la teneur en eau du béton

Le radar de type GPR est très utilisé en Génie Civil pour le repérage des armatures de renforcement du béton. La technique s’est imposée face à des appareils d’un prix de revient plus faible grâce, d’une part à son rendement élevé et d’autre part à ses capacités d’investiguer des profondeurs importantes. Ce rendement élevé peut également être mis à profit pour la caractérisation physico-chimique du béton, en particulier pour la mesure de sa teneur en eau. Des travaux en laboratoire ont montré qu’un des observables les plus sensibles à la teneur en eau volumique, indépendamment de la salinité, est la vitesse de propagation du signal direct, qui se propage en surface. Une base de données conséquente entre cet observable et la teneur en eau a été constituée et elle devrait permettre de déterminer la teneur en eau à partir d’une mesure de vitesse. Sa mise en œuvre sur ouvrages réels a révélé les limites de cette approche. En effet, même si la teneur en eau est le paramètre le plus influent, la vitesse de propagation est sensible à d’autres facteurs, en particulier la nature des granulats. Il parait donc nécessaire de calibrer la mesure pour chaque ouvrage, de façon simple et rapide. Une méthodologie de calibration est proposée sur la base d’une mesure de la vitesse en transmission sur une carotte de béton prélevée dans l’ouvrage et conditionnée à différentes teneurs en eau. Un dispositif simple de mesure de la vitesse en transmission sur carottes est testé et son efficacité est démontrée. Les vitesses mesurées en transmission et en surface étant bien corrélées, il est possible d’établir le modèle de corrélation entre vitesse de l’onde transmise et teneur en eau volumique propre au matériau testé, qui pourra ensuite être utilisé pour la calibration des mesures réalisées en surface sur l’ouvrage réel

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

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

Waterfront Depth Analysis in Hardened Concrete by Means of the Nondestructive Ground-Penetrating Radar Technique

© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Durability of concrete structures depends mainly on the ease whereby water and any aggressive chemical agents dissolved therein can penetrate. Therefore, measuring water penetrability in concrete structures is crucial mostly when structures are in service. In this context, nondestructive techniques play an important role. In particular, the electromagnetic waves emitted by ground-penetrating radar (GPR) are very sensitive to the water content of the medium through which they propagate. This fact provides an interesting opportunity to analyze if the GPR technique allows the assessment of water penetrability in concrete with enough accuracy. In line with this, this paper describes the laboratory experiments and relevant analysis carried out to study the capability of GPR to assess water penetrability in hardened concrete. For this purpose, concrete specimens were fabricated and dried in an oven after 90 days of curing. They were then dipped into water and GPR measurements were taken at different intervals, based on coupling a 2.0 GHz antenna. The results showed that the agreement between velocity increments and the waterfront advance was excellent. In addition, a specific processing of the data acquired was developed. This process included the isolation of the reflection due to the waterfront, produced just before the reflection of the bottom of the samples. As a result of this processing, the in-depth waterfront location at different times was determined with high reliability.This work was supported by the Universitat Politecnica de Valencia (Spain) under the PAID-06-12 research plan through a project entitled: "Analisis de la durabilidad del hormigon por medio de la tecnica no destructiva del georradar."Rodríguez-Abad, I.; Klysz, G.; Martínez-Sala, RM.; Balayssac, JP.; Mene-Aparicio, J. (2016). Waterfront Depth Analysis in Hardened Concrete by Means of the Nondestructive Ground-Penetrating Radar Technique. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 9(1):91-97. https://doi.org/10.1109/JSTARS.2015.2449737S91979

Application of ground-penetrating radar technique to evaluate the waterfront location in hardened concrete

The long-term performance of concrete structures is directly tied to two factors: concrete durability and strength. When assessing the durability of concrete structures, the study of the water penetration is paramount, because almost all reactions like corrosion, alkali-silica, sulfate, etc., which produce their deterioration, require the presence of water. Ground-penetrating radar (GPR) has shown to be very sensitive to water variations. On this basis, the objective of this experimental study is, firstly, to analyze the correlation between the water penetration depth in concrete samples and the GPR wave parameters. To do this, the samples were immersed into water for different time intervals and the wave parameters were obtained from signals registered when the antenna was placed on the immersed surface of the samples. Secondly, a procedure has been developed to be able to determine, from those signals, the reliability in the detection and location of waterfront depths. The results have revealed that GPR may have an enormous potential in this field, because excellent agreements were found between the correlated variables. In addition, when comparing the water-front depths calculated from GPR measurements and those visually registered after breaking the samples, we observed that they totally agreed when the waterfront was more than 4 cm depth.The authors are grateful to COST - European Cooperation in Science and Technology (www.cost.eu) for funding the Action TU1208 "Civil engineering applications of Ground Penetrating Radar" (www.GPRadar.eu). The authors also thank the Laboratorio de Materiales de Construcion of the Escuela Tecnica Superior de Ingenieria de la Edificacion de la Universitat Politecnica de Valencia technical team for the valuable collaboration.Rodríguez Abad, I.; Klysz, G.; Martínez Sala, RM.; Balayssac, JP.; Mené Aparicio, J. (2016). Application of ground-penetrating radar technique to evaluate the waterfront location in hardened concrete. Geoscientific Instrumentation, Methods and Data Systems. 5(2):567-574. doi:10.5194/gi-5-567-2016S56757452Klysz, G. and Balayssac, J. P.: Determination of volumetric water content of concrete using ground-penetrating radar, Cement Concrete Res., 37, 164–117, https://doi.org/10.1016/j.cemconres.2007.04.010, 2007.Klysz, G., Balayssac, J. P., and Ferrières, X.: Evaluation of dielectric properties of concrete by a numerical FDTD model of a GPR coupled antenna-Parametric study, NDT&E Int., 41, 621–631, https://doi.org/10.1016/j.ndteint.2008.03.011, 2008.Lai, W. L., Kou, S. C., Tsang, W. F., and Poon, C. S.: Characterization of concrete properties from dielectric properties using ground penetrating radar, Cement Concrete Res., 39, 687–695, https://doi.org/10.1016/j.cemconres.2009.05.004, 2009.Laurens, S., Balayssac, J. P., Rhazi, J., Klysz, G., and Arliguie, G.: Non-destructive evaluation of concrete moisture by GPR: experimental study and direct modelling, Mater. Struct., 38, 827–832, 2005.Martínez-Sala, R., Rodríguez-Abad, I., and Del Val, I.: Effect of penetration of water under pressure in hardened concrete on GPR signals, Proceedings of the International Workshop on Advanced Ground Penetrating Radar (IWAGPR 2013), Nantes, France, 237–242, 2013.Martínez-Sala, R., Rodríguez-Abad, I., Mené-Aparicio, J., and Fernández Castilla, A.: Study of the waterfront advance in hardened concrete by means of energy level increment analysis, Proceedings of the 8th International Workshop on Advanced Ground Penetrating Radar (IWAGPR), Firenze, Italy, https://doi.org/10.1109/IWAGPR.2015.7292695, 2015.Otieno, M. B., Alexander, M. G., and Beushausen, H. D.: Corrosion in cracked and uncracked concrete – influence of crack width, concrete quality and crack reopening, Mag. Concrete Res., 62, 393–404, 2010.Pérez Gracia, V.: Radar del subsuelo. Evaluación en arqueología y patrimonio histórico-artístico, PhD doctoral thesis, Universitat Politècnica de Catalunya, Spain, 2001.Rodríguez-Abad, I., Martínez-Sala, R., Mené, J., and Klysz, G.: Water penetrability in hardened concrete by GPR, Proceedings of the 15th International Conference on Ground Penetrating Radar, Brussels, Belgium, 862–867, 2014.Rodríguez-Abad, I., Klysz, G., Martínez-Sala, R., Blayssac, J. P., and Mené, J.: Waterfront depth analysis in hardened concrete by means of the nondestructive ground penetrating radar, IEEE J. Sel. Top. Appl., 9, 91–97, 2016a.Rodríguez-Abad, I., Klysz, G., Balayssac, J. P., and Pajewski, L.: Assessment of waterfront location in hardened concrete by GPR within COST Action TU1208, European Geosciences Union (EGU) General Assembly 2016, Vienna, Austria, EGU2016-18427, 2016b.Sbartaï, Z. M., Laurens, S., Balayssac, J. P., Ballivy, G., and Arliguie, G.: Effect of concrete moisture on radar signal amplitude, ACI Mater. J., 103, 419–426, 2006.Senin, S. F. and Hamis, R.: Ground penetrating radar wave attenuation models for estimation of moisture and chloride content in concrete slab, Constr. Build. Mater., 106, 659–669, https://doi.org/10.1016/j.conbuildmat.2015.12.156, 2015.Soutsos, M. N., Bungey, J. H., Miljard, S. G., Shaw, M. R., and Patterson, A.: Dielectric properties of concrete and their influence on radar testing, NDT&E Int., 34, 419–425, 2001.Tosti, F. and Slob, E.: Determination, by Using GPR, of the Volumetric Water Content in Structures, Substructures, Foundations and Soil, Civil Engineering Applications of Ground Penetrating Radar, 1, Benedetto, A., Pajewski, L., Springer International Publishing, Switzerland, 163–194, https://doi.org/10.1007/978-3-319-04813-0, 2015.UNE-EN 12390-2:2009/1M:2015, Testing hardened concrete. Part 2: Making and curing specimens for strength test, AEN/CTN83-Hormigón, AENOR, 2015

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

Non Destructive Evaluation of Containment Walls in Nuclear Power Plants

Two functions are regularly tested on the containment walls in order to anticipate a possible accident. The first is mechanical to resist at a possible internal over-pressure and the second is to prevent leakage. The reference accident LLOCA (Large Loss of Coolant Accident) is the rupture of a pipe in the primary circuit of a nuclear plant. In this case, the pressure and temperature can reach 5 bar and 180°C in 20 seconds. The national project ‘Non-destructive testing of the containment structures of nuclear plants’ aims at studying the non-destructive techniques capable to evaluate the concrete properties and its damaging or progression of cracks. This 4-year-project is segmented into two parts. The first consists in developing and selecting the most relevant NDEs (Non Destructive Evaluations) in the laboratory to reach these goals. These evaluations are developed in conditions representing the real conditions of the stresses generated during ten-yearly visits of the plants or those related to an accident. The second part consists in applying the selected techniques to two containment structures under pressure. The first (technique) is proposed by the ONERA (National Office for Aerospace Studies and Research of France) and the second is a mock-up of a containment wall on a 1/3 scale made by EDF (Electricity of France) within the VeRCoRs program. Communication bears on the part of the project that concerns the damaging and cracking follow-up. The tests are done in bending on 3 or 4 points in order to study the cracks’ generation, their propagation, as well as their opening and closing. The mostly ultrasonic techniques developed concern linear or non-linear acoustic: acoustic emission [1], LOCADIFF (Locating with diffuse ultrasound) [2], energy diffusion, surface waves velocity and attenuation, DAET (Dynamic Acousto-Elasticity Testing) [3]. The data contribute to providing the mapping of the parameters searched for, either in volume, in surface or globally. Image correlation is an important additional asset to validate the coherence of the data. The spatial normalization of the data allows proposing algorithms on the combination of the experimental data. The tests results are presented and they show the capacity and the limits of the evaluation of the volume, surface or global data. A data fusion procedure is associated with these results