Concrete Use Gets
Even Cooler in Texas

by Eileen Schwartz

Researchers at the University of Texas at Austin's Construction Materials Research Group have been studying the effects of liquid nitrogen on concrete since 2004.

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Their investigation, sponsored by the Texas Department of Transportation, is focusing on the safety implications of liquid nitrogen applications; its effects on mixing equipment, cement hydration and microstructural development; and its effects on concrete properties and performance including fresh properties, strength, dimensional stability and durability.

"The research is being done so that TxDOT will feel comfortable recommending more extensive use of the technique," said Maria Juenger, assistant professor in the Department of Civil, Architectural and Environmental Engineering. The goal is to be able to recommend optimal liquid nitrogen delivery devices and methods with regard to human and equipment safety.

Juenger said the initial prognosis is good. "Any changes to the concrete properties that we have seen are minimal," she said. "I think the technique will become much more widespread because of the convenience of use compared to traditional techniques such as crushed ice."

Mixing Cement in Texas

In Texas, where the summers are anything but cool, liquid nitrogen as a cement-mix coolant to replace ice and chilled water in the warmer months, is especially attractive.

In addition to a potential cost savings, benefits include fewer nighttime pours and longer distances ready-mix can be transported. And since liquid nitrogen is a waste product of the liquid oxygen industry, it keeps the price low and carries the potential environmental benefit of utilizing a waste product.

"It saves time, labor and often money," Juenger said. "It also allows concrete to be cooled to a lower temperature."

Liquid nitrogen proved a cool solution on the recently completed State Highway 45 project in Austin. General contractor Austin Bridge & Road of Dallas opted to use liquid nitrogen extensively to cool concrete to 75 ° Fahrenheit, which TxDOT requires for mass placements of anything with a least dimension of 5 ft.

Joe Dan Johnson, quality control manager with Dallas-based TransitMix, the concrete supplier for the job, said he was aware of liquid nitrogen, and thought it was a good option for the job as opposed to ice because of the "great deal of mass placements."

"We decided to stop fighting ice we go with liquid nitrogen," Johnson said.

Johnson and William Beaver of PBS&J, the project's construction manager, went to El Paso to tour Jobe Readymix, which had a system for liquid nitrogen installed at their plant.

"They were the only company that had been using liquid nitrogen in ready-mix operations on a regular basis for certain jobs," Johnson said. "We watched what they did to get an idea of what it took to get a system going."

Johnson said that setting up such a system can be expensive. "The capital investment is high," he said. "So there has to be enough yards of at a certain price to justify a system."

"Currently it is cost effective on big projects," Juenger said. "The biggest investment is in the delivery devices and storage containers-not in the nitrogen itself."