Comparing investigation approaches and NDT methodologies for concrete strength estimation: an international benchmark

Strength assessment of concrete in existing structures is a key issue. Many NDT techniques are available which can provide information about the material condition and many models can be used to assess concrete strength from NDT results complemented by core tests, but currently there is no way to establish the level of accuracy/confidence of concrete strength estimates. Since the concept of “knowledge levels” (KL) was introduced in Eurocodes this issue has become more important. A benchmark has been carried out in order to compare (a) how experts define and carry out an NDT investigation programme and (b) how experts derive strength values from the NDT measurements. A third question was to build the relationship between the quality of the assessment and the methodology followed. The benchmark was based on synthetic simulations which reproduced a synthetic data set corresponding to a series of twenty 3m-high columns defining a building floor. On the basis of the contributions of benchmark participants, a model has been established of the investigation strategy, the main parameters of the strategy are identified and the results of each contributor have been analyzed. A companion paper will use Monte-Carlo simulations to analyze and quantify the efficiency of the investigation strategies regarding both average strength and strength variability assessment.