Thin pavements expected to last longer, save money
If thin is in, then the new pavements being developed by researchers at the Texas A&M Transportation Institute (TTI) and the Texas Department of Transportation (TxDOT) are all that, and then some.
Instead of the traditional two-inch overlays that are typical for road rehabilitation, TTI researchers have dared to go much thinner — developing pavements that are one inch in height and, in one case, a mere half inch high. Because these new pavements are made with high-quality stones and polymer-modified asphalt, they are expected to last longer and require less maintenance. As a result, state, county and city officials are jumping on the thin overlay bandwagon in order to save taxpayers money and inconvenience and, at the same time, provide smoother rides.
In Brazos County, County Engineer Alan Munger is sold on TTI’s new mixes (called fine-graded stone-matrix asphalt). In July, he supervised the paving of five roadways with a one-inch overlay covering a total of five miles. This was Brazos County’s first use of the thin mix.
“I am confident that thin lift asphalt will work. I visited test sites [State Highway 6 access roads] where the Bryan TxDOT District placed TTI’s thin lifts, and I was impressed that the pavements are performing so well,” Munger says.
From now on, Munger says he plans to incorporate the use of the thin mixes on higher volume County Roads that are good candidates for thin-lift hot-mix asphalt overlays. He expects them to require fewer repairs over a longer period of time.
“We have been developing and conducting rigorous testing procedures on these thinner pavements for several years now,” Tom Scullion, manager of TTI’s Flexible Pavements Program, explains. “We found out that by using smaller, higher quality aggregate, we were able to go much thinner and increase longevity.” Scullion says the lab tests show the pavements are rut and crack resistant. He expects agencies to see a 30 percent savings per square yard in their road maintenance budgets.
In College Station, a section of two roads, which have much different traffic types, have now been overlaid with a ¾-inch pavement. Crews recently put down the thin pavements on 1,500 foot sections of Brentwood Drive East and Rock Prairie Road West. More than 500 tons of the thin overlays were used on both locations.
“What made me interested in these new overlays is the quality of materials used in the mixes,” says College Station Street Supervisor Marshall Wallace. “It’s a lot better quality than what we and everybody else typically use. Based on my meetings with TxDOT and TTI, all indications are that these pavements will last longer than the two-inch overlays we are accustomed to.”
Wallace says the sections of new pavement are considered test sites, and the city will monitor the locations through the spring. If they perform well in the rainy season and hold up to the traffic, the city could start using the pavements on a much larger scale. He says longer-lasting pavements and less maintenance could represent an entire city street being overlaid each year as a result of the cost savings.
Other areas that are beginning to use the new pavements include Houston, Austin, Beaumont, San Antonio and Brownwood.
“These thin mixes are really starting to take off,” Scullion says. “When we go this thin, the mixes have to pass stricter laboratory performance tests. I’ve been extremely pleased with these results and I think they’re the pavements of the future.”
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