Experimental investigation on the dynamic mechanical properties and energy absorption mechanism of foam concrete

For the construction of the deep-buried and super-long tunnels in an active tectonic zone, it is crucial to explore the dynamic mechanical properties and energy absorption mechanism of foam concrete (FC). In this study, splitting Hopkinson pressure bar (SHPB) tests were carried out with five different dry densities (DD) of FC. The influences of strain rate and DD on the dynamic mechanical properties of FC were analyzed based on the peak stress, stress-strain curve, energy absorption and failure mode. Finally, the energy absorption mechanism of FC and the influence of axial pre-stress on the energy absorption were discussed. The results show that the peak stresses of FC have a linear relation with strain rate. Furthermore, the dynamic stress-strain curve of FC has evident fluctuation characteristics, and the fluctuation is more prominent with a smaller DD. For FC with the same DD, the energy absorption rate (EAR) initially increases and then decreases with the increase of the incident energy. Whereas, the largest EAR of FC is achieved with the smallest DD. The energy absorption mainly depends on the compaction of pores for FC with the small DD, while the expansion of pores and new cracks is attained by FC with large DD. The pre-stress (less than 70% of the uniaxial compressive strength (UCS)) may enhance the EAR of FC. However, FC begins to release energy when the pre-stress reaches 90% of UCS.