Roger Chen, professor of civil and environmental engineering at West Virginia University, has recently received a research grant from the West Virginia Department of Transportation for the second phase of a project studying thermal cracking of concrete in bridges.
“Concrete is brittle,” explained Chen. “When the water and cement mix, the chemical reaction gives off heat, making the internal temperature very hot while the external temperature is cool. The inside will expand while the outside contracts, causing the concrete to crack.”
Specifically, Chen is analyzing temperature differential in the concrete bridge caps and piers. These structures undergo a great deal of stress, but the greatest source of stress comes from temperature differential.
In the first phase of the project, Chen tested the thermal behaviors of concrete structures that use class B concrete, which is commonly used in highway construction in West Virginia. It uses large amounts of cement and produces a lot of internal heat.
Chen, in phase two, is studying thermal-friendly mixes that reduce the internal thermal temperature and the cracking potential. These mixtures substitute fly ash, the residue left from burning coal, or slag, the waste leftover from creating steel, into the mixture. These additives give off less heat during the chemical reaction.
“Right now, we have progressed to using 30 percent fly ash replacement in our mixture,” said Chen. “We are now up to 45 to 50 percent slag.”
This solution may also be more economically efficient. Fly ash and slag are readily available waste products to West Virginian construction companies.
The second phase is funded for 27 months. The first phase of the project, also funded by the WVDOT, investigated the new Ices Ferry Bridge that spans Cheat Lake, just east of Morgantown. Chen and two of his doctoral students, Yun Lin and Alper Yikici, monitored this bridge, along with five other bridges across the state. Chen’s group developed computer models to predict thermal stress development in newly placed concrete structures and their cracking potential.
“We want our concrete structures to last longer,” said Chen. “Cracking will allow water to penetrate inside concrete and corrode the steel reinforcement. The corrosion of the steel reinforcement will damage the structures and the structures will become unattractive and deteriorate faster.”
Chen said he feels “very satisfied” to be able to advance academic knowledge and make it applicable to improve the infrastructure of the state. “I am very grateful for the support from the WVDOT engineers, especially the project monitors Mike Mance, Ryan Arnold and the head of research and special studies, Donny Williams.
“This problem is important everywhere, even in different states and countries. Other people can use these methods to analyze temperature differential and stress development,” he explained.
To Chen, applicable research is another step toward improving the reputation of WVU.
CONTACT: Mary C. Dillon, Statler College of Engineering and Mineral Resources
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