"Concrete Autopsy" Helps Strengthen the Pentagon

Kerry Hall
for National Geographic Today
July 9, 2002

Steve Wolter is one of the guys people call after disaster strikes.

As president of American Petrography Services in St. Paul, Minnesota, Wolter gets calls from people needing advice on whether they can salvage concrete that has been damaged or involved in a fire.

A geologist by training, Wolter performs autopsies—on concrete chunks. He tests concrete samples to ensure that buildings made out of the stuff will still be safe. But last year, Wolter was hired to study concrete that came from a building hit by the most extreme conditions that Wolter had ever seen.

The Pentagon.

"From a fire-damage standpoint, this was by far the worst, very intense, hot concentrated fire for a prolonged period of time," Wolter said.

Concrete Turned to Mush

The Pentagon was severely damaged on September 11, when the hijacked American Airlines flight 11 slammed into the building, killing all on board. The plane crashed through three of the Pentagon's five outer rings, destroying many structural columns and damaging dozens of others. The plane's jet fuel also exploded, starting an intense fire that burned for days.

American Petrography Services' task was twofold. The first challenge was to test the integrity of the Pentagon's remaining structures and tell engineers what needed to be replaced. The second task had broader implications: determine whether a stronger concrete mix could be made, such as one that could withstand not only pressure but also intense heat—or even a bomb.

Pentagon samples, pieces of Potomac River gravel mixed with sand, cement, and water, started arriving at the company's St. Paul, Minnesota, office almost immediately after Wolter landed the contract 11 days after the attack.

In all, the group received 170 pieces ranging in size from only a couple inches square to more than a foot long. Some samples arrived in such poor condition that scientists had to use Super Glue to piece them back together before they could study them.

Continued on Next Page >>


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