A few weeks back, the Air Force detonated out its mostpowerful bunker-buster yet. But a new Iranian super-strong concrete might make it almost useless before it reaches service.

I owe this story to DANGER ROOM reader Jay Sappington, a civil engineer in Fort Worth. He graduated with his masters from the University of Texas at Arlington (UTA), where he had participated in a student competition organized by the American Concrete Institute. The challenge was to make a 2”x2” concrete cube with the highest possible compressive strength. Among the competitors at this internationally diverse school was a team from the University of Tehran. Jay takes up the story.

*"I designed a 2”x2” concrete cube with a compressive strength of 16,000 psi [pounds per square inch] at 28-days, a relatively high strength as standard concrete is on the order of 3,000 psi, typically. Now, The University of Tehran made several cubes between 50,000 to 60,000 psi, and possible stronger! I thought the aggregate to be made from quartz, and I also remember some steel fibers in the mix. These cubes exploded at failure, finally damaging the compression machine on the third or fourth cube (that machine was substantial, made for much larger samples). So, keep in mind this is unreinforced concrete (save the steel fibers) at an early age. Concrete becomes stronger, sometimes by orders of magnitude, over time. *

Jay Googled the sponsoring professor of the Iranian students, and found that he has an extensive resume in the fields of ultra high strength concrete and nuclear reactors. So it’s far from impossible that the Iranian nuclear industry has access to some pretty advanced technology in this area – and given the repeated threats to bomb nuclear installations, we can expect them to be well protected.

To give you some idea of just how tough we are talking, rock of over 10,000 psi is considered hard. The strongest granite is about 30,000 psi. How well would the MOP deal with ultra-tough concrete?

According to Globalsecurity.org, the Air Force's new, 30,000-pound, bunker-busting Massive Ordnance Penetrator "is expected to penetrate as much as 60 meters [200 feet] through 5,000 psi reinforced concrete. It will burrow 8 meters into the ground through 10,000 psi reinforced concrete."

That’s quite a reduction between 5,000 and 10,000 psi. Something several times stronger could degrade performance a lot more. I asked Rex Swenson, Public Affairs Liaison of the Air Force Research Laboratory’s Munition Directorate, about this. He answered:

Unfortunately, we can not discuss the actual capabilities of the MOP due to security concerns. Suffice to say that the numbers on the Global Security website were not provided by DTRA [Defense Threat Reduction Agency] or the AFRL/MN.

The bottom line is that any highly reinforced target might withstand one strike from a MOP, but even a bunker roof made of 60,000 psi concrete can be chipped away at until it finally fails to protect what's underneath.

Personally, I’d guess that advanced concrete could severely limit the effectiveness of the blunt instrument/brute force approach embodied by MOP. You really don’t want to be dropping bombs at intervals against the same spot, especially when an aircraft can only carry one.

The answer has to lie in smarter weapons with more advanced payloads. The Air Force is looking at more sophisticated ways to defeat a bunker complex – earthquake bombs and robot cockroaches being among the more extreme. Beating your head against an ultra-hard concrete wall may not be the answer.