Content area
Full Text
A new high-performance material known as frangible concrete was developed with the goal of eliminating the potential for lethal-sized fragments of broken concrete when a structure is impacted by a dynamic load, such as the blast force from a terrorist vehicle bomb. Based on a strategy of developing concrete with moderate, quasi-static, load-bearing properties and high frangibility under dynamic loading conditions, the investigation made use of the shrinkage and fracture properties of cement and slag binders, along with the proper choice of aggregate and aggregate gradations. The development process included designed experiments to optimize mixture proportions against compressive strength and laboratory-scale impact tests followed by the manufacture of concrete masonry units (CMUs) for testing a wall under full-scale field blast conditions.
Keywords: aggregate gradation; dynamic loading; frangible concrete; frangibility index; ground-granulated blast-furnace slag; high performance; microcracking.
INTRODUCTION
While typically associated with high strength, high-performance concrete is defined as any concrete that meets the needs and performance requirements for special conditions in which conventional concrete mixtures would not suffice. In this study, the authors describe the development of a new type of high-performance concrete that is optimized for frangibility rather than strength, where the term "frangible" refers to a material that breaks into small pieces when it fractures.
In the wake of terrorist vehicle bombing events, such as the Khobar Towers bombing in Dhahran, Saudi Arabia, and the Murrah Federal Building in Oklahoma City, OK, the U.S. Army sought solutions to restrict vehicular access to such facilities. One such solution was to install standoff barrier walls made of concrete to limit vehicles from close access to the structure. However, the wall would become part of the problem if a vehicle bomb was exploded outside the wall because the concrete would break into large pieces, becoming lethal projectiles hurled at the facility and its occupants. Therefore, the question was asked: instead of strengthening concrete to resist a blast, could concrete be designed to break into small pieces? On an equal mass basis, smaller fragments will lose more energy to air resistance than larger fragments. Thus, frangible concrete will absorb energy, both through the process of fracturing and by loss into the atmosphere, better than normal concrete. This study describes the development of such a concrete through...