Protective effect of graded density aluminium foam on RC slab under blast loading – An experimental study

[Display omitted] •Static compressive tests were conducted on different aluminium foams.•Graded density foam shows more potential than homogenous foam.•Unordered density foams yield unstable stress–strain curves.•Protective effects of different foams on RC slabs were tested in blast test.•The direction of linear density foam influences its protective performance. In recent decades, bomb incidents have significantly increased due to various blast accidents and growing terrorist threats. Therefore, the protection of important infrastructures against blast loading has never been more important. Aluminium foam, which is often used as a protective layer to absorb impact energy, has demonstrated its ability to mitigate blast effect in several studies. The outstanding energy absorption capacity of aluminium foam is mainly resulted from its long-lasting plateau-stress region which allows it to only transmit a small stress (which is equal to the plateau stress) to the protected structure while absorbing the rest by self-compaction. For aluminium foam that is manufactured by the same method, the overall energy absorbing capacity per unit volume increases proportionally with mass density; however, the plateau stress also increases with mass density which means a larger stress would be transmitted to the protected structure. Therefore, there is a trade-off between the mass density and the transmitted stress. In order to increase the overall energy absorbing capacity of aluminium foam while keeping the transmitted stress at a reasonably low magnitude, the idea of density-graded foam has been proposed which is simply a foam structure with various densities along its thickness. In this paper, the effectiveness of density-graded foams has been investigated. A number of static compressive tests are conducted on different types of aluminium foams including aluminium foams with uniform density, density-graded aluminium foams with linear gradient as well as density-graded aluminium foams with unordered gradient. In addition, a blast test program is also carried out to investigate the blast mitigation effect of graded density foams on reinforced concrete (RC) slabs.