Experimental study and modelling of shock-induced compaction of autoclaved aerated concrete through MHz X-ray radioscopy

Extreme scenarios related to sudden increase of stress states, such as mechanical impacts or collisions, can lead to severe physical damage on structures. However, through their compaction phase, porous materials absorb a part of mechanical energy and efficiently mitigate the shock wave induced damage. Autoclaved Aerated Concrete (AAC) is one type of cellular materials which exhibits such capability and also being non-flammable, which is of interest for most structures that must resist both impacts and fire. With good insulation properties and its low density, AAC is therefore a material of choice in protective design against shock loading.

It is however difficult to study in real time, especially because of the cloud of dust produced during compaction. In the present study, two AAC of respective densities of 550 kg/m³ and 115 kg/m³ are considered. Plate impact tests were performed at the European Synchrotron Radiation Facility (ESRF) and the compaction process was observed in-situ by ultra-fast X-ray phase-contrast radioscopy for impact velocities ranging from 250 to 400 m/s.

Through the records analysis, a compaction front is identified..The tracking of the compaction front and the initial velocity of the projectile provide a portion of the AAC compacted state. In line with the findings, an extended analysis extracting the mean pore size and the evolution of the densities and speed of sounds is conducted by the use of laser induced shock waves on samples pre-compacted. An analytical model is proposed to reproduce the compaction front dynamics, considering equivalent mass-spring systems.