New construction is being cut back; recycling and preservation are the orders of the day
By Daniel C. Brown
Across the nation, prices of paving materials have increased significantly. Meanwhile, gasoline tax revenues have dropped as people drive fewer miles in more fuel-efficient vehicles. Simply put, state transportation budgets have been hit with the double whammy of higher costs and declining revenues.
To cope, state transportation departments are postponing projects, reducing the scope of others, doing more in-place asphalt recycling and using more reclaimed asphalt pavement (RAP) in hot mix asphalt. Generally speaking, however, states are not sacrificing quality to achieve a quick repair for a lower price.
“We have 1,200 miles programmed (for surface treatments) in the 2009 construction season, but we’ll only be able to do about 800 miles,” says Roy Rissky, Chief of Construction and Maintenance for the Kansas Department of Transportation (DOT). “Preservation is really important, but if a road has deteriorated beyond a certain point, to chip seal it would be a waste of money. In the long term, though, we’ll have to go to lighter action to cover the same miles.”
The Maryland State Highway Administration is running two mega-projects that have been seriously impacted by reduced funds and higher prices. “It’s brutal,” says Brian Dolan, President of the Maryland Asphalt Association Inc.
One Maryland project, the $2.5-billion Intercounty Connector, calls for 18.8 miles of new six-lane highway. Three of four contracts have been let, but the fourth has been delayed indefinitely because of funding issues, Dolan says. Another project, a $900-million reconstruction on Interstate 95, called for 1.7 million tons of hot mix asphalt. Most of the project has been let. But recently the state “went through it carte blanche and cut out one inch of hot mix to help reduce the cost,” says Dolan.
In Colorado, the DOT had planned to complete about 70 asphalt projects in 2008. But because Colorado contractors had some problems obtaining SBS polymer, 25 of those projects were delayed until next year, said Tim Aschenbrener, Project Development Branch Manager for the Colorado DOT.
“We usually do $150 million per year of asphalt surface treatment projects,” says Aschenbrener. “And several years ago, we could get two million tons of hot mix for the $150 million. But last year, with asphalt ranging up to $300 per ton of liquid binder, we were only able to purchase 1.3 million tons. For next year, we may be looking at $650 to $800 per ton, and some of our estimators say it may go to $900 a ton. So we won’t be able to buy nearly as many tons with our money.”
In January 2007, the Colorado DOT identified several strategies to help the state cope with funding difficulties. “You can’t do preventive maintenance everywhere, but one of our strategies is to look at more preventive maintenance,” says Aschenbrener. “We want to use more preventive maintenance treatments that have worked in the past. In this new economy, it’s possible that the extra lane-mile-years that you get from a chip seal may be even more for the money than an overlay will give you.”
The second strategy is to examine new preventive maintenance treatments. For example, Aschenbrener says Colorado has experimented with Brazier mix, which is a cold mix made by mixing milled asphalt with emulsion in a pugmill. Another relatively new technique – one that Colorado borrowed from Nebraska – is the use of Armor Cote, a mixture of rounded river rock and emulsion. The end product resembles a chip seal.
Yet another strategy is to use more hot in-place and cold in-place recycling. “We’ve done a lot of those projects in certain regions of the state,” says Aschenbrener, “and we’d like to spread those techniques to other parts of the state.”
The use of cost effective wearing surfaces, such as stone matrix asphalt (SMA), is also one of Colorado’s strategies. “SMA may be more expensive than regular hot mix, but you can get more lane-mile-years out of it,” says Aschenbrener. “We want people to realize that some of these high-end strategies are still cost effective to use. We don’t just want to cheapen everything.”
For a 36-lane-mile stretch of Interstate 5 in Oregon, the state found early signs of stripping in the asphalt pavement. On projects with similar issues, the state had previously designed deep asphalt inlays to replace the stripped asphalt and reduce the potential for wider failures.
“With the increased costs of paving materials, we considered a reduced section,” says Liz Hunt, P.E., Pavement Services Engineer for the Oregon DOT. Using the AASHTO Mechanistic Empirical Pavement Design Guide software, the state determined that a two-inch inlay, (versus a five-inch inlay) would provide about a 10-year life in terms of structural adequacy. “Based on a life cycle cost analysis we determined that it was more cost-effective to use up the remaining life of the section rather than step in now and do the deep inlay,” says Hunt.
Oregon recently placed a chip seal on a rural section of Interstate 84 in the truck lane. “We don’t usually place chip seals on our interstates, but this section includes an open-graded wearing course that is raveling,” says Hunt. “We are hoping to forestall the raveling and delay the need for a full inlay. Two types of binders were placed, each over a two-mile section. We used a high float emulsion and a hot oil (asphalt) that includes 5 percent tire rubber. We will be monitoring the chip seals over the winter to determine their effectiveness. If they prove effective, we plan to place additional chip seals in this location next year on a much larger scale.”
In Missouri, the DOT recently delayed letting $72.85 million in asphalt overlay treatments from August, September, and October to November or later. “We will let most of these projects within fiscal 2009, but a few will probably be pushed back into later years,” said John Donahue, P.E., Pavement Engineer for the Missouri DOT. “We’re delaying projects to see if asphalt prices will settle a little more or stabilize.”
Missouri’s fiscal 2010 budget for all road construction projects drops to less than $600 million – less than half of the $1.3 billion slated for fiscal 2009. The budget cut greatly reduces the number of new construction projects and capacity expansions.
“We’ll be mostly in a maintenance mode of work activity,” says Donahue. “Sometimes you need to take care of the roads that need immediate attention and delay treatment of other roads that can go awhile longer,” he adds.
“We won’t compromise structure or safety,” says Donahue. “We’ll make sure there are no added features that wouldn’t be noticed; we constantly go through that scrutiny.” Economizing, he said, might mean narrowing shoulders from 10 feet wide to four or six feet wide if the situation permits.
Recycled Roofing Shingles
In Wisconsin, a contractor has set up hot mix operations to include the recycling of roofing shingles. What is more, that contractor has won the contract to build a project on State Trunk 120 in Walworth County. Originally the contract did not call for the use of recycled shingles, but the change was proposed and the DOT accepted, says Scott Schwandt, Executive Director of the Wisconsin Asphalt Pavement Association.
“We’re changing the way that people look at RAP,” says Schwandt. “Historically we have talked about using 20 percent RAP by weight. Now we have recycled asphalt shingles (RAS). We’re trying to hold the amount of binder replaced by RAP and shingles to 20 percent of the binder.”
Five percent of recycled shingles, by weight of the total mixture, is about the same as 20 percent binder replacement, Schwandt says. Still, state officials and contractors do not want to change the engineering properties of the mix. The ultimate blend of liquid binder should have the same resistance to thermal stresses – at both the high and low temperature extremes – as the original design with all-virgin binder.
“We’re replacing a certified product, PG-graded binder, with a blended asphalt cement that incorporates binder from shingles or from RAP,” says Schwandt. “So we’re looking to establish a similar quality control procedure for the recycled shingles as we have for liquid binder.”
Binder contained in shingles is considerably stiffer than conventional PG-graded binders, Schwandt says. But if needed, you can lower the stiffness of the blended binder by lowering the low-temperature spec on your virgin binder. “Typically we’re not concerned about the higher number, but we want the low-temperature number to be lower to prevent thermal cracking,” says Schwandt.
For the Wisconsin shingles project, however, the numbers indicate that the contractor need not change the PG grade of the virgin binder to soften the ultimate blend. The contractor submitted test results to the state DOT showing that by replacing up to 20 percent of the virgin binder with liquid from shingles, the engineering properties of the blend were not changed enough to affect the specified binder’s PG grade.
Mill and Inlay
In Kansas, Rissky says the state is milling out the travel lanes on some roads and inlaying them with two inches of hot mix. That precludes the need to overlay the shoulders. Plus, the state is applying thin treatments like chip seals, which mean the shoulders can be left untreated or simply sealed.
And Kansas contractors are using more RAP. In general, contractors can use up to 15 percent RAP and not change their PG grade of asphalt. If they use between 15 and 25 percent RAP, they have to lower the grade of the virgin binder by one grade, to compensate for the stiffer RAP. And if contractors go to more than 25 percent RAP, they must submit a blending curve to prove that the PG grade of the blend is the one originally specified. “Sometimes they don’t want to do that,” says Rissky. “They don’t want to spend the money to lower the PG grade.”
The Georgia DOT allows high percentages of RAP – up to 40 percent for surface courses on state routes. “Our spec allows for up to 40 percent RAP in drum plants and 25 percent for a batch plant,” says Peter Wu, Technical Assistance Bureau Chief, Office of Materials and Research. “We encourage contractors to use a high percentage of RAP, as a way to stretch the dollar.”
In structural mixes, Georgia allows 20 percent RAP. However, RAP is not permitted in open-graded wearing courses. Georgia does not require contractors to add softer virgin binder to meet the low temperature PG specification.
“You do an Abson Recovery Test on the blend,” says Wu. “Your viscosity has to be between 6,000 and 16,000 poises. If it exceeds 16,000 poises, that is considered too stiff. We find that the performance is satisfactory with mixes specified that way.”
In fiscal 2008, Georgia will purchase only about 25 percent of the asphalt tonnage that it bought in 2007. Last year the state let contracts for 8.2 million tons of hot mix. This year, Wu estimates that the number will be between 2 and 3 million tons. The reasons: lower tax revenues, internal budgeting factors, and higher costs.
For the near term, it looks like lowered budgets, reduced new construction, and an increased emphasis on pavement preservation are the orders of the day.
|Dan Brown is the principal of TechniComm.