This paper presents a review on combining NDT techniques, such as rebound hammer and ultrasonic pulse velocity, for assessing concrete compressive strength. These methods, though being favorably not invasive and easy to be extended to a larger number of elements, are affected by many contingency factors. The SonReb technique suggests combining the two methods to partially offset their low reliability if considered separately. For years, this concept was introduced in order to improve the evaluation compared with the use of one NDT. In order to combine the ultrasonic pulse velocity and rebound hammer, many empirical, multiparametric models were proposed in the literature as linear, power, exponential, or polynomial. However, the variety of these models emphasizes that they can give a correct strength prediction only for the particular cases that they are derived for. Therefore, to assess concrete on site, the strength should be predicted using a calibration procedure due to the variability of existing concrete mixes. This paper presents a brief outline of the key aspects of strength assessment, including the different approaches used to build the SonReb model and a calibration procedure for assessing concrete strength. A comparison study between the different approaches is proposed, and a performance analysis using Monte Carlo simulations is discussed. Finally, the estimation capacity of the existing model identification approaches is investigated, and the effect of the “trade-off” is analyzed for different random sampling with varying the number of cores.

The compressive strength of concrete is one of the most important mechanical parameters in the evaluation of the mechanical performance of reinforced concrete structures. The recent methodology for the evaluation of the mechanical strength of concrete of an existing structure combines non-destructive testing (NDT) measurements, such as rebound measurement and ultrasonic wave propagation velocity measurement, with destructive measurements (sampling) in order to develop a conversion model, between mechanical strength and non-destructive measurements. The conversion model is then used to estimate the local value of the resistance at each location of the non-destructive measurements and thus to represent the spatial variability. The goal of this study is to propose a new methodology based on multi-objective optimization to predict the compressive strength of concrete and its variability based on NDT measurements. To this end, a large experimental and synthetic database of destructive and non-destructive tests was used. The conclusions drawn from the synthetic data will be compared with the results obtained on the real database in order to test the potential of the proposed methodology. This study shows the principle of the methodology and the first results of its effectiveness in predicting compressive strength and its variability.

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