207-INR : Interpretation of NDT results and assessment of RC structures

Technical Committee 207-INR

General Information

Chair: Prof. Denys BREYSSE
Deputy Chair: Dr Andrzej MOCZKO
Activity starting in: 2004
Cluster C

Subject matter

NDT methods are widely used in civil engineering for controlling new structures (quality control) as well as for assessing the level of damage of old structures and buildings whose behaviour is under question.
Many companies develop NDT equipment or offer their services to building managers but even if their skill is not questioned, the lack of internationally acknowledged reference texts is a heavy handicap:
- the choice of the best-fitted technique for a specific problem is not simple,
- the relevance of the measurement process is not guaranteed by any widely accepted guidelines,
- the question of how to cope with measurement results and how to finally assess the structural properties often remains unanswered.
On another hand, many institutes are involved in the improvement of techniques (developing innovative equipment or post processing of data, coupling measurements and numerical simulations, benchmarking their techniques on pilot sites...).
Until now, these efforts have been mainly undertaken at a national level (with many working groups or national research projects in Germany, Britain, France, USA, Japan...) but they have not resulted in the definition of general conclusions or proposals which could be accepted by the various actors involved in the field: building managers, contractors, regulators, NDT practitioners, consulting engineers...
It is considered that, due to the increasing need of validated NDT protocols (increasing need of structural assessment of ageing structures AND increasing need of quality control), it is time now to integrate - at an international scale - the huge amount of information and knowledge that has already been produced by many experts.

Terms of reference

Objectives of the RILEM-TC are:
(1) to write a state-of-the-art report dedicated to how NDT can be handled to answer the more common generic problems that (reinforced concrete) structures are faced with;
(2) to improve the calibration of techniques dealing with specific problems, through well-defined benchmarking on "model-problems" and quantifying the added value provided by the combination of methods;
(3) to establish recommendations for designing "international reference test sites" and qualification of techniques and/or operators for application in the building industry;
(4) to spread, via short courses and seminars (1-2 days), the synthetized knowledge the national communities of engineers and building managers.

Detailed working programme

These objectives can be achieved following some specific steps.

Aim 1: how to handle NDT for generic problems of structures
(a) Analysis of the most important questions that NDT would be helpful to answer in the RC structures field. This analysis would give a significant weight to the fact that, depending on the specific national constraints (like general state of buildings or overall level of economic development), the practically available equipment or the practical questions to answer can vary, thus modifying priorities in material / structural assessment;
(b) Definition of a limited number (3 to 7) of problems that the group will focus on;
(c) For each of these problems (indicative list: control of the thickness of a pavement, estimate of on-site compressive strength for early age concrete or old concrete, estimate of the residual lifetime of a corroded structure, delimitation of a spalling defect...), production of an inventory of the techniques which are used / can be used, assessing them in an objective way (sensitivity, limits of detection, uncertainty in the resulting assessment...);
(d) For each of these problems, write a synthetic paper with recommendations on how to handle it, from its definition by the building owner to the final assessment, through the protocol of measurement itself. These texts must focus on the fact that - even if correctly performed and problem relevant - a measurement cannot suffice if it is not interpreted. Even if a technique can detect and quantify a local variation of properties, it may remain unable to identify - among two or three possible causes - the relevant explanation (and, thus, it is not useful when one wants to forecast the problem evolution with time).

Aim 2: improve the calibration of techniques
While working on the above Aim 1, a need will emerge for more practical and undisputable information about the limits of some techniques faced with a given specific problem. Benchmarking, mainly based on "prototype-defects", will be the source of additional information.

Aim 3: recommandations for international reference test sites
As a secondary effect, an in-depth discussion on the advantages and shortbacks of existing sites with "prototype-defects" can lead to the development of recommendations for designers of such test-sites. Thus, it would be possible to design "international references", accepted by the international community of experts, and used for any future comparison/calibration...
Such references would serve as key elements for quantifying in an objective way the abilities of any new technique / equipment or the skillfulness of any operator handling a yet referenced technique.
Even if some problems appear to be material specific, some questions treated at this stage can be relevant for members of other TCs belonging to the same RILEM cluster, in the field of timber or masonry. Some work on the question of "international references test sites" can thus be done in common, and the advancement of this TC can be fruitful for the others.

Aim 4: spreading the knowledge
The organization of 1-2 day open seminars, in conjunction with the working (annual) meetings of the RILEM-TC, devoted to the practical use of NDT, is seen as a mean of ensuring some spreading of our "message" as well as a possible mean for raising some funds, making easier the travel of TC members and active scientific collaborations.
In addition, a conference will be held on an international basis at the end of the project, probably under the format of specific sessions in the framework of an already existing conference in the field of NDT in Civil Engineering. This conference could also be an opportunity for the "twin TCs" belonging to the same cluster, to spread their production on a wider basis.

In addition, the TC development could be accompanied by other efforts to increase the level of exchange in the international community of experts in the field of NDT in CE:
(a) Writing a proposal for a Network of Excellence in the frame of the 6th PCRD, which would make easier communication and benchmarking. (Task leader : Martin Krause, BAM, Germany)
(b) Analysis of what exists and what are the needs in teaching NDT at university level, trying to build (if needed) international Masters level courses or to develop exchange of students.

Technical environment

This TC intends to "replace" the TC NDE chaired by Pr. H. Wiggenhauser, who recently decided to withdraw with this TC. Some questions treated in the TC NDE will be accounted for in our TC, but with a slightly different view, since we will focus on use of NDT results for structural assessment and not on the technics themselves.
It is the reason why this new TC will be complementary with the TC 189-NEC chaired by Pr. Torrent (evaluation of surface concrete) and with a new TC which is to be proposed by Pr. Ohtsu (acoustical methods to detect cracks).

The proposal is also made with the idea to develop a methodology which will enable easily transfer to other building materials, like timber or masonry and, with the help of Pr. L. Binda, head of the relevant Cluster, and member of this TC, we intend to soon analyze all possibilities of tranfer, with the possible creation of "mirror TC" for the same kind of problems on other building materials.

Expected achievements

The following results are anticipated:
- state-of-the-art report dedicated to how NDT can be handled to answer the more common generic problems that (reinforced concrete) structures are faced with;
- RILEM recommendations for designing "international reference test sites" and qualification of techniques and/or operators for application in the building industry;
- dissemination of knowledge, via short courses and seminars (1-2 days) and via a final workshop and papers in Materials&Structures and other magazines of the NDT community.

Group of users

Experts in NDT practice and structural assessment, testing laboratories, structural managers, construction companies.

Specific use of the results

The economic impact is expected by a more rational and more efficient use of NDT technics on reinforced concrete strructures, helping the managers in developing long term strategies of maintenance and repair.