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A Smarter Slab for the Next Century

Tuesday, April 22, 2014

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A new concrete composite that can bend, repel water, self-monitor—and, oh yes, last more than 100 years—is taking shape at the University of Wisconsin-Milwaukee (UWM).

A new parking garage patching project equipped with monitors will determine whether the high-performance material can indeed pull off the 120-service life that researchers are hoping.

That would be about three times the current life span for concrete roads in Wisconsin. And that's an average. About 10 percent of reinforced bridge decks need replacement after just 30 years, the university says.

Scott Muzenski and Konstantin Sobolev
Troye Fox / UW-Milwaukee

Dr. Konstantin Sobolev (right) and doctoral student Scott Muzenski work on a sample of the "smart" concrete composite that they believe could last more than 120 years.

The new cement composite being developed in the lab of associate professor Konstantin Sobolev is a durable, water-resistant, malleable paving material with such a high degree of crack control that researchers say it may last 120 years or more.

SECC Slab

Sobolev's team is putting the hybrid material—officially, a Superhydrophobic Engineered Cementitious Composite (SECC)—to the test in a university parking structure.

A driveway of the structure had developed a large crack after many Wisconsin winters, making it the perfect testing ground for the material being developed in Sobolev's lab.

Last summer, civil engineering doctoral student Scott Muzenski led a crew of 25 students in laying down a 4-by-15-foot slab of their SECC material.

Because they expect the slab to outlive them, the researchers are equipping it with a self-monitoring system.

The students embedded electrodes in the concrete that are linked to a data acquisition system located behind an adjacent retaining wall, the university reported in a research announcement this week.

Tales of Water and Stress

“This is going to tell us whether water is getting into the material and how deep it goes,” Muzenski said in the announcement.

“It also detects the presence of chloride ions within the material, and senses load and stress as vehicles pass over it.”

UW-Milwaukee

Researchers at UW-Milwaukee offer a quick peek at their "concrete that's built to last."

When the software is completed later this year, the real-time data will be fed wirelessly to an online repository, where the team can "observe the performance of concrete as it happens, in real time,” says Sobolev.

Beading and Stretching

The material's secret? There are two, researchers say.

First, its superhydrophobic quality makes water bead up rather than sink into it. An additional tweak of the material at the molecular level gives the hardened concrete a microscopic spiky surface so that the water rolls off from the slightest angle.

Second, the composite's malleability allows it to bend without breaking. Although malleable concrete is not new, the university says Sobolev's lab has improved the material's ductility (stretchiness) by incorporating "super-strong unwoven polyvinyl alcohol fibers."

"When cracks begin, the fibers keep them from becoming larger tears," the university said.

Smaller Cracks

No, the university reports, the goal is not to prevent cracking. It is to force the load and stress across many tiny cracks that will not allow water in—unlike conventional, brittle concrete, where cracks get progressively worse with constant loading.

Cracked bridge
kingcounty.gov

Researchers suggest that the relatively expensive hybrid composite might be best used on areas like bridge approaches, where deterioration typically begins.

“Our architecture allows the material to withstand four times the compression with 200 times the ductility of traditional concrete,” says Sobolev.

Because the ductile concrete is more expensive than traditional concrete, Sobolev recommends that it be used strategically in places where deterioration begins, such as bridge approaches.

That’s where heavily reinforced concrete meets regular asphalt. The joint, says Sobolev, cannot withstand the continuous loading.

“The bridge and the road aren’t designed to work together,” he says. “You need something between them that has the durability to handle the stress.”

If the concrete proves as smart as researchers think, it could have other applications. Sobolev notes, for example, that remote monitoring would be possible at nuclear power plants and other high-risk facilities.

   

Tagged categories: Bridge/parking deck waterproofing; Concrete; Concrete defects; Concrete repair; Concrete slab waterproofing; Cracks; Maintenance programs; Research

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