Energy absorption of foamed concrete from low-velocity impacts

Foamed concrete has existing uses as an energy absorber for large-scale and low-cost applications, such as explosion prevention in mines and military engineering projects and aircraft arresting systems. However, there is little information enumerating the energy absorption characteristics of different foamed concretes; this paper describes a study that determined these using low-velocity impact tests. A range of foamed concretes were tested with plastic densities varying from 500 to 1400 kg/m³, which are typical of those produced commercially. The tests used hemispherical projectiles with a range of masses from 1·2 to 8·4 kg, dropped from a fixed height of 4·7 m. The resulting ‘damage' was measured and related to the impact energy imparted to the test specimen. A classification, using five different failure modes, was established and the mode in which the test specimen neither caused ‘rebound' of the projectile nor itself fractured was selected as representing ‘ideal' energy absorption behaviour. Making the assumption of no energy losses and using the conservation of energy law, the energy absorption capacity of foamed concrete was calculated and was found to vary from 4 to 15 MJ/m³ for different mixes. The optimum energy absorption was noted for the 1000 kg/m³ mix at water to cement (w/c) ratios from 0·6 to 0·7, which allowed a debris field of crushed foamed concrete to form and be pushed into the concrete bubble space ahead of the nose of the projectile, without fracturing.