Evaluation of the predictive ability of the in situ concrete strength through core drilling and its effects on the capacity of the RC columns

Assessment of seismic performance of existing RC buildings is a difficult work. The concrete mechanical characteristics have a crucial role on the seismic performance of the buildings during a strong earthquake. The core test has become the most effective method to estimate directly the in situ compressive strength of concrete. Then, some Non-Destructive Tests (NDT) can be effectively used by setting reliable relationships with the core test results. In the past years, the core drilling has been widely studied. Many design codes or guidelines provide useful indication about the operative procedures in order to get no damaged samples. On the contrary, poor reference are available about the effects of core drilling on RC structure capacity. It should be remembered that, due to the increasing demand of utilization and rehabilitation of existing RC buildings, procedures in the evaluation and experimental tests on the constituent materials of these buildings should be improved. In fact, in poor quality concrete, the use of coring test method should take into account the potential negative impact on the safety of these structures. The peculiarities of this work are two: (1) the selection of samples and (2) the type of test. RC columns extracted from an existing old structure designed only for gravity loads have been considered and loading-unloading compression tests have been carried out on specimens. To this end, a wide description of the samples and their characterization has been considered as a fundamental step in order to properly design the experimental campaign. Non-destructive tests, core drilling and subsequent test have been carried out on RC columns extracted from an existing building. Monotonic loading-unloading compression tests on column specimens have been carried out. Comparison of test results highlights the effect on the strength of structural elements of core drilling and subsequent restoration.