Nov. 10, 1997 ROLLA, MO. -- A glass-and-asphalt paving material invented nearly 30 years ago at the University of Missouri-Rolla is now being used in a new way to pave airport runways and taxiways.
For the first time, "glasphalt," which paved the way for recycling waste glass into roads and parking lots, is being used to pave an airport runway, parking apron and taxiway. The project, at a general aviation airport in Rolla, Mo., was completed in November 1996. One year later, the material is holding up exceptionally well, says Dr. Delbert E. Day, Curators' Professor of ceramic engineering at UMR and one of the inventors of glasphalt.
Ozark Rivers Environmental Inc., a not-for-profit corporation, used a grant from the Missouri Environmental Improvement and Energy Resources Authority to demonstrate how waste glass can be easily and economically substituted for some of the rock and sand used in ordinary asphalt paving, and in paints used to mark airport runways and taxiways.
"The purpose of the demonstration project is to show how some of the approximately 10 million tons of waste glass in the U.S. that cannot presently be recycled into new glass products can be disposed of in a low-cost and beneficial way that avoids the costly disposal fees now being paid to put waste glass in landfills," Day says.
Three faculty members from UMR provided technical help in paving the runway, taxiway and parking apron at the Rolla Downtown Airport, a small general aviation airport.
After paving the 3,000-foot-long runway with four inches of glasphalt that contained 10 percent broken glass, it was painted with a paint that also contained waste glass as part of the pigment.
According to Day, about 450 tons of waste glass, crushed to 1/4-inch and smaller, that would otherwise have been buried in landfills, was used in place of some of the rock and sand in the glasphalt paving material.
"One of the advantages of glasphalt is that no special equipment is needed, and glass of any color and type from bottles, windows, glass used for baking, and tableware can be used," Day says. The glasphalt was prepared in a commercial asphalt plant close to Rolla, and then placed using the same equipment used for laying ordinary asphalt paving.
"Glass recycling is difficult throughout Missouri since there are only a few glass plants in the state which will purchase scrap glass or cullet," Day says. "In addition, the buyers of scrap glass are often long distances -- 100 miles or more -- from the communities where the scrap glass is recovered, so transportation costs can exceed the value of the glass."
All of the glass used in the airport project was collected from community recycling programs in south central Missouri.
"Glasphalt offers the advantages of being able to use those types of waste glass which would otherwise be buried in landfills," says Dr. David Richardson, a UMR associate professor of civil engineering, who supervised the installation and evaluation of the glasphalt being used in the airport demonstration project. "Glasphalt is also a means of disposing of very large quantities of waste glass and even for small projects like a parking lot or street repair, which can use several hundred tons of waste glass."
In addition to demonstrating the usefulness and practicality of using glasphalt for airport uses, the reflective properties of glasphalt will also be evaluated. Glasphalt has been used extensively in Baltimore, Md., for many years because the glass particles tend to reflect the street lights and give the road surface a "sparkle."
"The higher reflectivity of a glasphalt runway could be an advantage at night since the runway should reflect the aircraft's landing lights and be more visible than an ordinary asphalt runway," Day says.
In addition, the tendency of glasphalt to dry faster after a rain than ordinary asphalt is an advantage for aviation use, and that will also be evaluated during the demonstration. The glass particles in glasphalt do not absorb water like the rock in regular asphalt, Day says. "And in tests made by the Missouri Highway Department, skid resistance of glasphalt was proven to be 50 percent higher than typical asphalt, which is important to aviation when planes land and take off at high speeds," he says.
The paint used to mark the glasphalt runway also used waste glass ground to a fine powder. Dr. Harvest L. Collier, a UMR professor of chemistry, has formulated and produced a "glass paint" that uses the finely ground glass as part of the pigments. The properties of the glass paint meet the specifications for use on highways, but it has never been used for marking airport runways and taxiways. Because of the glass it contains, this paint may also be reflective. The long term durability of this paint to weather conditions will also be evaluated during the demonstration.
The information to be gained from this project and the technology being demonstrated could benefit many small Missouri communities that have difficulty in disposing of waste glass and that want to avoid the cost of putting the glass in a landfill.
"There are more than 180 small airports in Missouri, and thousands throughout the U.S., which could benefit from the results of this project," Day says. "Glasphalt offers the opportunity to dispose of large amounts of waste glass in a way that could improve the general aviation airports in small communities.
"These small airports often play an important role in industrial development," Day says.
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