Advanced measuring technique for the dynamic testing of concrete

Concrete is a widely used material in civil and defense constructions. When exposed to shock, explosions or impacts, concrete structures are subjected to complex confined compression and severe dynamic tensile forces that lead to intense damage modes. In order to build up relevant numerical models able to simulate the dynamic behaviour of concrete, the use of advanced and well instrumented experimentations is essential to improve the accuracy of the measurements. Among the techniques used to characterise the dynamic tensile strength of concrete, the so called “spalling technique” figures prominently. The principle of this technique is the generation of a dynamic tensile loading by impacting a concrete sample with a projectile launched by a propeller. This technique allows to apply controlled high loading-rates and obtain high velocity damage. Leveraging the spectacular progress in ultra-high speed imaging, the present project aims at developping a novel processing method based on the full-field measurement of displacements. Recent cameras provide images of increased quality with interframes reduced to 0.2µs, giving access to the full field measurements of strain at unprecedented sensitivity levels.

In this project, the development of new algorithms and the manipulation of experimental parameters enables us to explore a wider range of loading rates. The processing being previously validated on calibrated standard samples of concrete, new experiments are performed on several grades of concrete and the results compared with the data given in the literature. In that way, the key parameters involved in the increase of strength with strain-rates of concrete should be clarified. In a last part, post-mortem analysis will be considered by means of X-ray Computed Tomography. The whole set of experimental data will be used to develop continuous or mesoscopic modelling of the dynamic tensile behaviour of concrete.