Description of the general outlines of the French project SENSO – Quality assessment and limits of different NDT methods

The management and maintenance of the built heritage is one of the main concerns of the owners of concrete structures. Engineers wish to obtain quantitative information about concrete properties and their variability. Non-destructive testing (NDT) is very popular in this context as it quickly provides relevant information on the integrity and ageing of the material, but several kinds of indicators representative of the concrete condition need to be evaluated. Combining NDT methods is currently considered as one of the most appropriate ways to improve the quality of the diagnosis of concrete structures. This paper describes a French project named SENSO (Strategy of non-destructive evaluation for the monitoring of concrete structures) devoted to developing a methodology for the non-destructive evaluation of concrete based on a multi-technique approach. The main objective of the project was to define the sensitivity of the techniques (ultrasonics, radar, capacitive and resistivity) and the variability of the evaluation for each indicator concerned. To achieve this, a large experimental programme, involving a representative range of concretes and several indicators, was carried out. A database linking the measured values by NDT and the indicators allowed the different measurements to be distinguished in terms of quality (linked to the variability) and in terms of relevance for the characterisation of each indicator. The added value of the combination of techniques was obtained by means of data fusion. The methodology developed in laboratory conditions, involving both evaluation of the indicators and data fusion, was tested on full-scale models in which the indicators were not fully controlled.