Pothole-Proof Roads: Purdue's concrete testing labs - Part 2

If you have been on any of the new span of U.S. 31, you may have noticed it is made of concrete.

Concrete is stronger than asphalt and more pothole resistant, but also more expensive.

The researchers at Purdue University continue to improve the quality of concrete to make it last longer in our Midwest climate.

"From a mechanical perspective, we are trying to make sure the concrete can resist the forces or the load that's applied to it," explains Dr. Jason Weiss, Professor of Civil Engineering at Purdue University.

Weiss heads the concrete testing labs at Purdue. He doesn't want our roads -- and especially our bridges -- developing large cracks. This allows water into the concrete.

"From a durability perspective, what we want to do is make sure the concrete can resist water, or de-icing salts or sea water going in, as well as resist the pressures that are generated when chemical reactions occur, or when there is freezing and the water begins to expand and push," Weiss explains.

The longer we keep the water and chemicals out, the longer our concrete roads and bridges will last. Most concrete has steel bars inside, called rebar, which will begin to rust when water gets in there.

"One of the things we are interested in is the durability of a bridge deck: how long it takes deicing salts, chloride ions, to get from the surface down to the reinforcing bar to start the corrosion process," Weiss says. "This is a process where we wait for the concrete to age. It takes about three months to get a lot of the reaction to take place."

During that long curing process, concrete will crack, although it's designed to do so along the grooves that are built in. Some of the cracks, though, begin where they are not seen at first.

Water causes particular trouble because it expands about nine percent when it freezes.

Obviously, testing a small sample in a laboratory is different than doing it outdoors, so one of the things Purdue can do is bring a thirty foot sample of concrete in to a lab, where they can regulate the moisture and the temperature. It can go from 120 degrees to -20.

"We can actually place small microphones on the concrete to listen to those cracks as they start to form, so we can develop better models to predict how these concretes will crack when they have de-icing salts and freezing going on at the same time," Weiss explains.

Researchers have been in the lab for the past seven years and have developed a concrete that is expected to double or triple the service life of regular concrete pavement deck.

Last year, the process was used on the State Road 933 bridge in Saint Joseph County that crosses over Baugo Creek on Lincolnway in Osceola.

"We are working on techniques where we can internally cure the concrete by placing pockets of water in the concrete," Weiss reveals. "The idea is to use water inside light-weight aggregates that is mixed into the concrete that is fresh, so we can get a nice dense microstructure, but that water can be there to hydrate all of the cement and reduce the potential for cracking. So when people are talking about internally cured concrete, this is what they are talking about, and Indiana has been a leader in this."

Engineers hope that, by using these new techniques, concrete road surfaces could last 75 years.

That saves taxpayers money and keeps us from having to drive around construction.


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