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Sherri Tombarge
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‘A Tough Little Engineering Phenomenon’

FullTextImage/img/@altMaj. Matt Swenty (left) and Josh Wells use the Demec gauge to measure concrete. -- VMI Photo by H. Lockwood McLaughlin.

Research Project on Rehabilitating Concrete Has Real-World Implications

LEXINGTON, Va., July 24, 2013 – A project currently under way in the civil engineering materials lab at VMI could have far-reaching implications for the construction industry.

Cadet Josh Wells ’14 is doing a summer undergraduate research project entitled, “The Rehabilitation of Old Concrete.” He’s trying to determine if rougher or smoother concrete will bond better to new concrete layers to minimize shrinkage cracking.

Shrinkage cracking occurs as concrete shrinks, explained Maj. Matt Swenty, assistant professor of civil engineering, who is supervising Wells’ research.

“Concrete just naturally wants to get smaller,” said Swenty. “That’s one of its material properties.”

He added that shrinkage cracking is a separate issue from load cracking. The latter occurs when too much weight is placed on a concrete structure.

In the real world, minimizing shrinkage cracking could speed up bridge building by allowing for greater use of prefabricated concrete parts. Currently, laying new concrete on top of old concrete usually doesn’t work, because the new concrete shrinks as it cures, and cracking can occur where new and old concrete meet. For example, Swenty said, precast girders work extremely well, but precast connections between them don’t work well at all.

That means a 100-percent precast bridge won’t meet design criteria because the connections won’t be durable, Swenty noted. Long-term durability is important when trying to meet a bridge design life of 50 years, 75 years or even longer.

“The more shrinkage you have on top, the more likely the interface is to crack,” explained Wells, a civil engineering major from Midlothian, Va.

“Cracking occurs at joints and connections, but if we roughen the surface a little bit, will that help us out?” asked Swenty. “A rougher texture might help us out, but it might not. The literature is very mixed, and there’s not much of it.”

Lending his expertise with the mathematical modeling of shrinkage is Lt. Col. Chuck Newhouse, associate professor of civil and environmental engineering. “It’s not an easy calculation to predict shrinkage,” said Newhouse, who wrote his doctoral dissertation on the shrinkage of concrete. “It’s a tough little engineering phenomenon to look at.”

To begin his summer project, Wells had to begin much earlier than his peers. Because new concrete shrinks rapidly, and takes several weeks to cure, Wells laid his first layer of concrete in early March.

By late June, that first layer had become “old” concrete, fully cured, so Wells laid a new layer of concrete on top of it, and began to measure the shrinkage of that new layer by using a Demec gauge, which can measure changes in length to ten-thousandths of an inch. He has been plotting the changes on a spreadsheet.

To control for environmental factors, Wells has kept the temperature in the concrete lab at a steady 72 degrees and humidity at 100 percent. “Concrete likes moisture,” said Swenty of the lab conditions. “If it doesn’t work here, it won’t work in the real world.”

Because both Swenty and Newhouse worked in industry before coming to teach at VMI, the two are very interested in encouraging civil engineering majors to get out of the classroom, and into the lab, which is located in the basement of the Nichols Engineering Building.

With that goal in mind, they are working toward establishing a separate structures lab to allow cadets to test structures for strength, flexibility, and deflection under applied loads. The current lab, where Wells is working, is designed for making and testing materials but lacks the capacity for significant application of loads.

For Swenty, lab work is a critical component of a student’s civil engineering education.

“Students who apply their knowledge to projects are able to see how knowledge from numerous classes meshes together in a realistic setting,” he noted. Speaking of Wells’ research, Swenty continued, “None of this is standard for an undergraduate course. He’s doing a great job.”

–Mary Price

-VMI-