Optimization of cellular concrete microstructure for improved impact resistance

Engineered material arresting system (EMAS) is a cellular concrete material currently used as passive aircraft arresting system at airports around the U.S.A. and abroad. Its cellular structure crushes on impact, helping to absorb energy and create drag resistance. Energy absorbed during crushing is defined by the load–deformation response curve, in which a plateau is indicative of crushing behavior at a near-constant load. At the microstructural level, the energy absorbed from crushing is a combination of elastic buckling, plastic yield, and brittle fracture of the cellular microstructure. Therefore, optimization of the cellular structure (e.g., bubble size and distribution) is paramount to the overall performance of these systems. This study makes use of microstructural investigations, quasi-static indentation, and drop weight testing to investigate the performance of cellular concrete with varied microstructures. The results show that, while density (air content) has been considered the main predictor of overall performance, the nature of the cellular structure created by the use of different foaming agents can be a useful design tool. This adds another critical consideration in the design of impact-resistant infrastructure. Given this finding, a new set of design guidelines are presented in this paper. This work aims to inform better design of impact-resistant infrastructure by identifying cellular concrete microstructures that lead to optimal energy absorption in low-velocity impact events, such as aircraft overruns.