It looks something like a baby carriage, but this little stroller only delivers critical information to help keep bridges safe.

Known as "HollowDeck" and used to inspect the condition of concrete bridge decks, the portable monitor is the brainchild of scientists at Mississippi State's Diagnostic Instrumentation and Analysis Laboratory. A three-wheel, walk-behind prototype recently produced at the university is being tested by the state Department of Transportation.

"Concrete bridges are constructed with a mesh of reinforced steel within the deck," said DIAL research engineer Mark Henderson. "Over time, water and other corrosive agents can cause the steel to deteriorate.

MSU researchers stroll with HollowDeck on a Starkville bridge.

"When this happens," he added, "portions of the bridge may separate into layers and eventually lead to problems ranging from an annoying pothole to serious structural damage."

Ground-penetrating radar and other high-tech equipment can be used to check for structural problems in bridges, but these methods are expensive and time consuming.

The simple, economical and time-honored way to tell if separation has occurred involves the use of a metal chain dragged across the concrete. While solid concrete produces a clear, ringing sound, areas with separations cause the moving links to yield a dull and hollow rattle.

Henderson, leader of a research team that includes MSU graduate and undergraduate students, said the traditional chain technique works fine as long as the person doing the testing can distinguish the sounds.

"Traffic and other road noise, or even an operator's sinus problems, often can affect the interpretation," he said.

HollowDeck takes the old chain process and wheels it into the 21st century. As a series of chains attached to a metal bar drag across the concrete surface, a microphone and amplifier send sound-generated data to a computer also housed in the 'carriage.' The computer then produces a 'map' of the bridge.

With a clear representation of areas where unseen damage is occurring, MDOT crews immediately can begin repair work.

"HollowDeck enables bridge inspections to be done faster and more economically," Henderson said. "That's important when you consider that federal and state laws require the approximately 500,000 bridges in this country to be inspected at least once every two years."