Non destructive testing and numerical inversion for monitoring large structures – ContINuS
Nondestructive testing and numerical inversion for large structures' monitoring
ContINuS project aims to contribute to the evaluatition of large structures in Civil Engineering thanks to non-destructive measurements. On such structures many pathologies can be identified and both diagnosis and prediction of their development require knowledge of several parameters. One of these parameters is water content and more specifically its variation in depth. So the objective of ContINuS project is to characterise water content gradients of concrete in depth.
Supporting management of built heritage by determination of a significant parameter for predictive models, water content gradient of concrete in depth
The management of concrete built heritage has multiple aspects, technical, economic, administrative and is always an area of ??concern for researchers, engineers and project managers.<br />The assessment of the state of large structures is a major issue for at least two reasons. First for an economic reason because of the cost induced by the evaluation of a large structure can quickly become prohibitive for an owner if the heritage that it must manage is extensive and very old. Then for a social reason, because the trauma of an accident on such structures is such that it could result in the establishment of substantial investments to refurbishing the remaining heritage.<br />The concerned structures are varied. Transportation-related structures (bridges, tunnels, ...), to the production of energy (dams, cooling towers, ...) or containment (waste storage, enclosures of nuclear reactors, ...) are particularly affected.On such structures, pathologies can be numerous and therefore evaluation needs are important. An unmet need is about the characterization of water content gradients of concrete in depth. Indeed, concrete is a heterogeneous material due to its components but also to its exposure conditions, so its properties vary with depth. The assessment of the importance of this gradient is important especially if one wishes to predict the evolution of the concrete over several years. Furthermore, most reliable predictive models require not only knowledge of the properties of a finite volume of the material, but also how this property is distributed in the depth. Determining this water content gradient in depth for large structures is the main objective of ContINuS project.
The project aims to propose some inversion methods based on non-destructive electromagnetic and resistive measurements to determine water content gradients of concrete in depth.
In order to reach this objective, it is proposed to combine two techniques commonly used in non-destructive testing, radar and resistivity measurement. This study proposes to develop a new approach based on the inversion of numerical propagation models of electromagnetic waves in concrete emitted by GPR (Ground Penetrating Radar) on one hand and of an electric field generated by electrical resistivity measurement by using tomography on the other hand. This will allow to evaluate the permittivity and electrical resistivity at different depths of concrete and thus to evaluate the gradient.
Some models between electromagnetic or electric properties and water content of concrete will be developed by using homogenization methods. These models will then be used to evaluate water content gradients of concrete in depth from non-destructive measurements. The proposed approach consists in modeling the electric behavior (or electromagnetic) of the material for an elementary representative volume by finite element methods and / or analytical models ( Maxwell-Wagner, Le Pape, etc.).
The inversion results will be compared to measurements on laboratory samples of reinforced concrete conditionned to generate water content gradient of different natures.
Validation tests on a mock-up of a nuclear reactor named VERCORS built by EDF are also planned.
Too early
Too early
Too early
This industrial research project, a collaborative project in public-private partnership, aims to contribute to the assessment of large structures in reinforced concrete by determining moisture gradients in depth. On such structures damages are numerous and both diagnosis and prediction of their evolution require knowledge of many parameters. One of the most important needs relates to the characterization of the properties of concrete gradients in depth. Indeed, as concrete is a heterogeneous material both by its composition and by its exposure conditions, its properties vary with depth. The knowledge of the magnitude of this gradient is essential especially if one wishes to predict the evolution of material over decades. Furthermore, most of reliable predictive models require knowledge of the properties of a well-defined volume of the material (which is already difficult to quantify with conventional non-destructive tools), but also how this property is distributed in depth. In particular, to exceed a lifespan of 50 years provided at the design, the monitoring of aging phenomena, dependent on the amount of water and on its gradient in the material, is required: shrinkage, creep, internal swelling reactions (RSI and RAG ) or reinforcement corrosion , to mention only the best known. To achieve this objective, in this project, it is intended to combine two techniques commonly used in NDT which have shown a high sensitivity to water content in the concrete. These are a fast and global technique, Ground Penetrating radar (GPR), and another local but accurate, the resistivity measurement. A new approach based on the development of numerical propagation models of electromagnetic waves and of electric fields into reinforced concrete is proposed. The inversion of these models will allow the evaluation of permittivity and electrical resistivity at different depths of the material and then the assessment of the gradient form. For this project, a 3D inversion will be studied and developed. To do this, in the non-destructive process, it is planned to work by areas and therefore to only consider the inversion of a restricted 3D domain of the structure to be monitored. The size of this area and the number of measurements to be performed are parameters that we will seek to define. Various realistic environments will be modelled and it will be possible to develop the inversion procedure by comparing to actual measurements. Models will be developed to assess the physical properties of the material in order to link the gradient of water content and the permittivity or resistivity gradient. By knowing the concrete composition and by comparison with 0D models of homogenization used for mechanical properties, we propose to develop a 0D model of permittivity and electrical resistivity of concrete. The proposed methodology will be validated on a model of prestressed concrete containment of nuclear reactor. This model is equipped with embedded sensors for measuring moisture at different depths. Then it will be possible to compare the results provided by the inversion of non-destructive measurements with the values monitored by the embedded sensors.
Project coordination
gilles klysz (Laboratoire Matériaux et Durabilité des Constructions)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Partner
LMDC Laboratoire Matériaux et Durabilité des Constructions
ONERA Office national d'études et de recherches aérospatiales
EDF RECHERCHE ET DEVELOPPEMENT
ARKOGEOS
IECL Institut Élie Cartan de Lorraine
Help of the ANR 565,562 euros
Beginning and duration of the scientific project:
September 2014
- 42 Months
