Advances in asphalt

Mix designs focus on longevity, drainage and noise reduction

By Angelle Bergeron

Throughout America's history, asphalt has often been ignored, but it has paved the way for motorists and met their increasing demands for noise reduction, durability, skid resistance, reduced splash and spray and a smoother ride.

Failures in asphalt roadways are usually related to design, application or post-construction maintenance, said Kent Hansen, director of engineering for the National Asphalt Pavement Association in Lanham, Md.

Consequently, the emphasis on asphalt in the South Central region is in education, testing and concocting increasingly refined mixes for the desired applications.

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"Many problems we see on the road are related to construction issues like compaction, poor longitudinal joints and segregation, so we are constantly trying to develop better techniques for application," said Dr. Ray Brown, director of the National Center for Asphalt Technology.

Located at Auburn University in Alabama, NCAT was established by NAPA in 1986 to provide a centralized, systematic approach to asphalt research.

The hottest new design concept being studied there now is perpetual pavement, Brown said. As the name implies, perpetual pavement may last indefinitely.

"We do have to come in and take off the top and replace it every 12 to 15 years," Brown added.

Although NCAT has only been officially studying perpetual pave over the past couple of years, it has been used in "a number of places by mistake," Brown said. "All we had to do was go back and check the criteria." In order to meet the criteria, the application must be at least 35 years old and not have been overlaid more than once every 13 years, Brown added. "The new criteria has been used in 10 to 15 states at this point, and it's getting more visibility."

Perpetual pavement is an entire pavement and may consist of Superpave, some integrated hot-mix asphalt and stone-matrix asphalt, Brown said.

"It doesn't cost more when you put it down," he added. "It's just a matter of following the same criteria with that process."

Application processes are the greatest challenge facing contractors using what may be spectacular designs and mixes, NAPA's Hansen said. In May, he presented a series of seminars on porous asphalt pavements, which have been attracting attention because of the role they play in sustainable site design and stormwater management.

Porous asphalts have been primarily used in low-traffic parking areas to reduce peak flow and total volume of storm water, Hansen said.

"With porous asphalt, we're talking about a system that includes a large stone bed beneath an open-graded friction course that is topped with a very thin layer," he said. "We need to keep the bottoms of the beds flat and with undulations on highways that is difficult to do."

Still, Hansen said the technology is interesting and involves the filtration of runoff through the open-grade mix that creates the least impact on the surrounding environment. NAPA is scheduling up to five more seminars in late September and October, he added.

"The real reason we are doing these seminars is that we want people to correctly apply the technology."

Regardless of the advanced level of the technology, maintenance is necessary to ensure adequate, safe roadways, said Tone ("Tony") Garrett, director of the Mississippi Asphalt Pavement Association.

"Road deterioration is not a linear curve," Garrett said. "It goes out for a while and if you catch it at the first of the curve it costs very little to maintain. If you wait, it takes more dollars to get it corrected."

Garrett said that the money needed for Mississippi's legislative mandate for four-lane highways has been drained from maintenance funds.

"The state needs to return to a 10- to 12-year maintenance cycle," he said. "Why would you add a new room to your house if you have a leak in your roof? We need to maintain our existing roads before we build new roads."

The Arkansas Highway and Transportation Department recently received an award for its cost-effective and innovative $966.1 million, five-year interstate rehabilitation program to improve 356 mi. of the state's interstate system. The program involved rubblizing existing concrete pavement and overlaying with asphalt.

While states are awaiting approval from Congress on the most recent Transportation Equity Act (TEA-21), Arkansas asphalt industry representatives are waiting on a state bill to finance non-interstate improvements. They are also hoping the voters pass a bond initiative to finance perpetual maintenance of interstate roadways, said John Suskie, executive director of the Arkansas Asphalt Pavement Association.

"We are sort of catching our breath and looking at stone-matrix asphalt mixes and all of that," Suskie said.

Although stone matrix asphalt has been around for more than 10 years, inappropriate application in initial trials caused it to fail and gave the mix a bad reputation among some highway departments, said NAPA's Hansen.

"It does require a little learning curve and some people don't like to change very fast," he added. "One of the biggest problems was we didn't get enough liquid asphalt in the mix at the time. Now we're adding fibers to the mix, which lets us keep our asphalt high and improves durability. We're also now using polymer-modified asphalts, which weren't as widely used then."

The Tennessee Department of Transportation is "very conservative" and only placed its first test site of stone-matrix asphalt about a year ago in the Memphis area, said Kent Starwalt, executive vice president of the Tennessee Road Builders Association.

"We went to make sure that we've got the right mix designs for the materials available and we really want to let the other states make mistakes and learn from them," Starwalt said.

Likewise, the Mississippi Department of Transportation completed its first SMA test project in November on a section of U.S. Highway 72 between Burnsville and Carnes.

"We haven't used any stone matrix in Mississippi before, but we were looking for less rutting and longer life," said Paul Swindoll, first district engineer. The increased stone-on-stone contact with the mix prevents the rutting, Swindoll said.

Swindoll said the mix was only used in one location because it is in the northeast part of the state and close to limestone suppliers, but "we are extremely happy with the mix."

Because it is an open-graded friction course with coarser texture, SMA also offers the added benefit of reducing sound levels, said MAPA's Garrett. He added that concrete projects throughout the country have brought complaints about noise and open-graded friction was the final solution in many cases.

"MDOT just spent millions of dollars coming out of Memphis into Mississippi to put sound walls up," Garrett said. "In Baton Rouge, they let a concrete job through the city on Interstate-10 and received so many complaints about road sound that they've had to go back and spend $7 million or $8 million on sound walls."

Significant South Central asphalt projects

U.S. Highway 43, Lawrence County, Tenn. The Rogers Group of Nashville won a $12.6 million contract for the Tennessee Department of Transportation for the four-laning of a 5-mi. stretch of U.S. Highway 43 in Lawrence County, Tenn.

The project represents the final section of a massive fourlaning that has been underway for more than 10 years and began in Murray County in Columbia and will end at the Alabama State line, said Ed McClain, project engineer for TDOT.

"We're in the early, very first phase of the project," McClain said. The contract was awarded in July 2004 and is scheduled for completion on or before November 2007, he said.

"We've been moving utilities for about a year and have just started on the actual road-building construction," McClain said. "We're not paving at this time, but doing excavation, laying storm drains and building bridges and box culverts."

Interstate 20, Pell City to Riverside, Ala. Goodhope Contracting Co. of Cullman, Ala., began a $25.6 million, 24-month contract in July 2004 to widen a 4.3-mi. section of Interstate 20 between Pell City and Riverside, Ala.

The contractor is placing 1 ft. of a Superpave asphalt mix over the roadway's existing concrete, which is being rubblized.

"Most of the highway work in Alabama has been Superpave for several years," said John Brown, project manager.

Goodhope is hauling 260,000 tons of asphalt from its nearby Asheville plant for the project. The contractor will be topping off the section of I-20 with stone-matrix asphalt because of the 40,000 to 45,000 average daily traffic count, Brown said.

"The SMA is a lot more durable paving and it's becoming the rule of thumb for high traffic count," he said. "We've used the SMA on the last three interstate jobs we've done."

U.S. Highway 231, Montgomery, Ala. In September, McInnis LLC/APAC-Southeast Inc. began work on an $18 million joint venture project for the Alabama Department of Transportation for improvements and widening of U.S. Highway 231 from North Boulevard to Brooks Road in Montgomery, Ala.

In spite of an excessive amount of rain, the project is still on track for completion by August 2006, said Bill Langham, project manager.

Work on North and Northeast boulevards include construction of a new railroad bridge, widening the roadway from four to seven lanes with a turn lane in the middle, the extension of several culverts and installation of a mile of 42-in. water main, Langham said.

U.S. Highway 79, Stewart County, Tenn. Mountain States Contractors of Mt. Juliet, Tenn., began work in November on the $13.3 million contract for TDOT to fourlane a 3.5-mi. stretch of US Highway 79 (SR 76) in Stewart County.

"We're still in phase one, getting one side of the new roadway ready to pave," said Shay Deason, project engineer with TDOT. "We'll be utilizing part of the old road as two lanes and constructing two new ones."

Deason said a standard mix would be used.

"HMA out of Clarksville will be doing the pavement," he said.

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For more information about new mix designs being developed or tested, go to: http://www.hotmix.org/