PolygamousRanchKid writes "Iran is an earthquake zone, so its engineers have developed some of the toughest building materials in the world. Ultra-high performance concrete (UHPC) could also be used to protect hidden nuclear installations from the artificial equivalent of small earthquakes, namely bunker-busting bombs. UHPC is based—like its quotidian cousins—on sand and cement. In addition, though, it is doped with powdered quartz (the pure stuff, rather than the tainted variety that makes up most sand) and various reinforcing metals and fibers. UHPC can withstand more compression than other forms of concrete. UHPC is also more flexible and durable than conventional concrete. It can therefore be used to make lighter and more slender structures. All of which is fine and dandy for safer dams and better sewers, which threaten no one. But UHPC's potential military applications are more intriguing—and for many, more worrying. Deep bunkers can be tackled in other ways. America's Defense Threat Reduction Agency (DTRA) has looked at what is known in the jargon as functional defeat, in other words bombing their entrances shut or destroying their electrical systems with electromagnetic pulses. They are also working on active penetrators—bombs which can tunnel through hundreds of meters of earth, rock and concrete. Development work is also under way on esoteric devices such as robot snakes, carrying warheads, which can infiltrate via air ducts and cable runs."