Asphalt spotlight

Price fluctuations, diminishing funds create challenges for industry

By Angelle Bergeron

Since the introduction of Superpave in the 1970s, contractors have been using pretty much the same mixes, varying somewhat from state to state according to highway department specifications. But the rising cost of petroleum and environmental concerns provide the impetus for scientists to develop new asphalt products.

In the South Central region, where everyone continues to feel the effects of the 2005 hurricane season, all construction materials are at a premium. While highway departments have diverted much-needed funds from new construction to hurricane recovery, contractors and engineers are faced with the perpetual challenge of looking for new ways to deliver more at reduced cost.

"The price of mix is going up very quickly and the way the tax system is set up, the money to maintain and build roads is not increasing at the same rate," said Dr. Ray Brown, director of the National Center for Asphalt Technology (NCAT) at Auburn University.

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"As fuel and asphalt prices go up, if people reduce their amount of travel, we'll see a reduction in the money going into this fund. That means we've got less money to do work with, but at the same time the price of asphalt is going up. This can be a very significant problem."

In the near future, contractors will likely be using warm mix asphalt, mixes with higher percentages of Recycled Asphalt Product (RAP) and increasingly specialized polymer additives.

Warm Mix Asphalt (WMA), pioneered in Europe several yeas ago, previously sparked interest here in the states, but the flames have really been fanned by increased fuel costs, last hurricane season, the war in the Middle East and instability in Iran, said Margaret Cervarich, vice president of marketing and public affairs for the National Asphalt Paving Association.

"Before the price of fuel went up, people were interested," Cervarich said. "Now they're really interested."

Missouri, Texas, Wisconsin and Ohio all have test sites using WMA, but the South Central region is pulling up the rear in experimenting.

"In some areas, they think they can extend the paving season if they can use warm mix because it's easier to get density," Cervarich said, explaining why colder climes became interested sooner.

The biggest advantage to WMA is the reduction in emissions, NCAT's Brown said. "It's become more difficult to meet requirements where mixes don't meet emission standards, especially in metropolitan areas."

WMA wasn't produced and applied in Europe until the last three or four years, and the first sections were done in the U.S. less than two years ago, Brown said.

"The real question is can we put this down and still get good performance from this product?," he added. "Up to this point, it has performed very well under heavy loads and high volumes of traffic. We have placed some on our test track and we're starting to collect data."

Since WMA is produced at lower temperatures, it will also greatly reduce fuel heating costs. The cost of hot mix asphalt still hasn't surpassed concrete, but the margin is narrowing, said Skip Paul, director of the Louisiana Transportation Research Center in Baton Rouge.

"We have premium prices on hot mix product because of the high cost of petroleum, but also because all materials are getting premium prices because of the cost of the hurricanes, either due to a perceived shortage or because they are being hauled extra distance," Paul said.

Another cost-reduction attempt spawned by increased cost is the trend toward using higher percentages of Recycled Asphalt Material in highway mixes.

"Right now we use recycled asphalt to the tune of maybe 20% in our mixes, but I would like to show that if it's engineered right we can use much higher percentages," said Chris Abadie, materials research administrator at LTRC.

In Louisiana, as in other states, RAP was typically used for the aggregate material and not considered valuable to contractors performing new asphalt construction, Paul said. "Now, because of the cost of asphalt cement and hot mix product in total, there is more value in RAP material than just the aggregate."

Whereas contractors were previously restricted to obtaining 40% of RAP removed from a job, LTRC is proposing they be allowed to bid on the cost of the RAP. If testing indicates higher percentages of RAP are safe for new applications, contractors may opt to use what they remove from a site, reducing fuel and material costs.

NCAT expects to develop a standard practice for using a higher percentage of RAP by the end of the summer, Brown said.

"There is some concern about the quality of the mix as we go to higher percentages of this material, whether additional testing and additives are necessary," he added. "Another issue is concern for the quality of the overall mix if the RAP comes from a lot of different places, but we believe we can test for that."

NCAT currently has a study underway to determine an accurate mixing and >> compaction temperature for asphalt. Although general guidelines are available for contractors, mix-specific temperatures that take into consideration polymer modifiers have been sorely lacking, Brown said.

"The bottom line is that the contractor doesn't feel comfortable with the temperature they are mixing with, and we want to give them a better way to determine what the temperature should be."

When contractors don't have a specific temperature, they generally heat mixes to the highest allowable temperature, which gives them more time for application, but isn't necessarily good for the quality of the asphalt, Brown said.

"Now that we are using modified asphalts the old procedure doesn't work," he added. "What contractors really need is something that tells them the temperature they should be working at." NCAT will complete that study by the end of 2007.

LTRC is also currently engaged in several studies that should result in more durable, environmentally-friendly products, with clearly defined application specifications for contractors. LTRC's Louay Mohammad is the principal investigator for a National Cooperative Highway Research Program study that is testing designs for asphalt treated permeable mixes that can be used as a drainage layer and withstand traffic.

"The design concept is similar to an OGFC but with lower aggregate quality," Paul said. "This is not on the surface like OGFC but at bottom to send water down sides." Within the NCHRP study, Mohammad is also testing applications of tac coats - thicknesses of application, binding principals and wearing.

LTRC is also looking at ways to increase density in construction of longitudinal joints. "Density is nationally recognized as problematic and Louisiana doesn't even have any specifications to define density at that spot," Abadie said. "One thought is that a polymer modified tac coat might improve density."

Nationwide, porous asphalt for parking lots is getting a lot of attention, said NAPA's Cervarich. "It's a way of building a parking lot so when you develop a site you don't have to build a retention base the way you used to," she said.

The porous topping, asphalt pavement surface and uniformly sized large stones beneath make parking lots part of the storm water management system. "There is also some evidence that a porous parking lot can help reduce the urban heat island effect," Cervarich said.

In spite of climbing costs, contractors are performing numerous asphalt jobs throughout the region. This fall, James Construction Group of Baton Rouge, La., will begin laying asphalt on a $21.9 million project for the Louisiana Department of Transportation and Development (DOTD).

Awarded to JCG last August, the project requires the widening of U.S. Hwy. 165 from a two- to four-lane highway beginning at LA 847 and extending to the Ouachita Parish line, a total of 6.67 mi. The work is part of a larger DOTD project designed to four-lane 173 mi. of U.S. 165 from Alexandria to the Arkansas state line.

The project requires construction of two 2,200-lin.-ft. Type IV concrete girder bridges with pile and drilled shaft footings; one 100-lin.-ft. concrete slab bridge, and roadwork consisting of 65,700 cu. yds. of excavation; 254,000 cu. yds. of embankment; 6,660 linear ft. of RCP; soil lime treatment; Class II base; and 52,124 tons of Superpave asphalt.

"As of mid-April, the job was already 38 percent complete," said Charles Poole, JCG vice president of north Louisiana operations.

The tiny town of State Line, Miss., is situated between DeSoto National Forest and the Alabama state line, an unlikely site for millions of dollars of highway work. But Tanner Construction Co. of Ellisville, Miss., is currently busy on three contracts totaling nearly $50 million for the Mississippi Department of Transportation to create a bypass of State Line on U.S. Hwy. 45 and State Route 57.

"I think they are just providing another evacuation route off the coast there," said Byron Burge, project manager for Tanner. "There is no traffic road demand for this unless people need to leave quickly, like during a hurricane."

Under a $25.7 million contract, Tanner is four-laning a 5.3-mi. section of U.S. Hwy. 45 and SR 57 in Greene and Wayne counties. Under another, $13.4 million contract, Tanner is four-laning 8.3 mi. of SR 57 from Turkey Creek to Stateline in Greene County. The third, $10.8 million contract is for grading, drainage and bridge work, but no asphalt.

"We are rehabilitating the old roads and building other lanes beside them," Burge said.

"We have to clear and grub, do dirt work and bridges and then come up with soft cement base and asphalt. We're mixing 6 in. of sub grade, 6 in. of topping and then 4 in. of asphalt drainage layer on top of that."

Tanner has set up a portable plant on site and is using about 50 percent native crushed gravel and 35 percent limestone for the mix. The two asphalt projects are scheduled for completion by the end of this month. Eight of the nine bridges are complete under the third contract, which will be finished this fall.

"Between these two projects, we are using about 200,000 tons of asphalt," Burge said. The contractor was originally scheduled for completion earlier this year, but experienced delays because of Hurricane Katrina. "We couldn't get fuel for about four weeks and all our help was still trying to dig out and live," Burge said. "We were handicapped for about a month."

Gilbert Central of Little Rock, Ark., recently wrapped up a $4.7 million contract for the City of Rogers, Ark., to construct a new runway at Rogers Municipal Airport. Under the fast-paced, 150-day contract, Gilbert Central excavated 222,000 cu. yds., installed 19,500 tons of hot mix asphalt (HMA) base, 9,600 tons of HMA Surface, 18,000 tons of sub base and 3,500 sq. yds. of ditch paving to create the (4,338 ft. by 50 ft.) taxiway parallel to the exiting runway.

"The asphalt portion of the job consisted of paving a new taxiway 4100 ft. long by 50 ft. wide, with three connectors," said Dave Fintel, project manager for Gilbert Central. "The HMA base was 8 in. thick and placed in three lifts. The HMA surface was 4 in. thick and placed in two lifts."

Since the paving had to be performed with only one cold joint in the crown of the taxiway, the contractor had to work with two pavers simultaneously for a total width of 26 ft., Fintel said.

To meet FAA requirements, the contractor laid an asphalt test strip (300 by 50 ft.) using the same type and weight equipment that would be used on the taxiway.