Experimental investigation on blast response of cellular concrete

• Cellular concrete with entrained porosity undergoes compaction produced by crushing of the cellular structure and subsequent densification of the material.
• A compaction front is produced in the foam when the blast pressure amplitude is higher than the crushing strength.
• There exists a critical length of cement foam, Lcr, such that when L > Lcr, the compaction wave diminishes before reaching the solid substrate and a rectangular stress pulse is transmitted at the target end.
• When L < Lcr, the magnitude of the transmitted stress increases above the initial rectangular-shaped stress pulse.
• If the length of the foam is significantly smaller than the required Lcr, the compaction in the material produces densification and the stress enhancement is higher than the applied blast pressure amplitude.

A test setup consisting of a shock-tube with an instrumented short rod is developed for investigating the blast response of cellular concrete foams. In the shock tube facility, blast pressure wave is generated by the rupture of a notched aluminum membrane. An instrumented rod is calibrated for measuring transmitted stress from the cellular foam. Experiments are conducted on brittle cellular concrete foam, which exhibits non-linear stress–strain behavior associated with crushing of the cellular structure and subsequent densification. Crushing is initiated when the stress exceeds the crushing strength and continued crushing produces an upward concave stress–strain curve leading to densification of the material. Foams with two different crushing strengths are evaluated. The influence of the length of the foam is investigated. For an applied blast pressure amplitude, which is higher than the crushing strength of foam, the wave structure in the foam consists of an elastic precursor wave followed by a compaction front that produces crushing of the cellular structure of the material. From the experimental investigation, the existence of a critical length for completely attenuating the applied blast pressure wave is established. For a given blast pressure loading, when the length of foam is larger than the critical length, the applied blast pressure wave is transmitted as a rectangular pulse of nominally constant magnitude, which is slightly higher than the crushing strength of the foam. The foam is compacted without significant densification. The critical length depends on the crushing strength of the foam and the blast pressure amplitude and duration. If the length of the foam is smaller than the critical length, there is an enhancement in the transmitted stress amplitude. If the length of foam is significantly smaller than the critical length, the transmitted stress is enhanced to a magnitude higher than the applied blast pressure amplitude and the compaction of foam leads to significant densification of the material.