More performance-based specifications and more design-build projects will permit greater freedom in hot mix design and construction methods.
Contractors will complete large milling and resurfacing projects in record times.
There will be more knowledge-based systems for delivering mix to projects. Pavers will become more automated and operator friendly. Global Positioning Systems (GPS) and intelligent compaction systems will enable asphalt compactors to measure density on the go, then send the information to an analysis center, which will return information telling the roller where more compaction is needed.
Warm mix asphalt will extend the paving season on both ends. The use of material transfer vehicles to remix and move asphalt from trucks to the paver will grow. As a result, smoothness and quality control will improve.
These are some of the changes expected in the future of asphalt construction.
“Historically we have restricted ourselves in highway construction because we have been too content not to privatize the process,” said Charlie Potts, CEO of Heritage Construction and Materials. “And we’ve been too much tied to public agencies’ specifications. Once we unleash ourselves from those specifications, you’ll see a lot of innovation.”
For projects with enough asphalt tonnage, Potts said, contractors will set rights of way. That will speed hot mix delivery and permit earlier completions. Temporary permits will allow on-site plants and nighttime construction. More and more, winning contractors will be the ones that produce the least traffic disruption, Potts said.
The traveling public objects to road closures, and needs to be better informed about highway construction projects.
“We have to go even further in reaching out to the public,” Potts said. “Our communication process has not been what it should be.”
Tracking and Communicating
By the year 2014, Dean Potts, engineering manager of Caterpillar Global Paving, believes a contractor should be able to remove and repave the top 3 to 4 in. of asphalt pavement on a three-lane section of interstate highway that is 6 mi. long and place traffic back on it in less than six hours. Special equipment will rapidly redirect traffic to create safe work zones. Equipment will be staged to enter the work area and move massive amounts of old and new asphalt quickly, Dean Potts said.
Paving will occur at night to avoid heavy traffic, Dean Potts said. Sophisticated equipment will measure asphalt volume, smoothness and compaction values on-the-go, using GPS mapping. Each section of road will be finished and ready for traffic the next morning. Automated traffic control devices will redirect traffic to the newly paved road. Changeable lanes will accommodate peak directional flows of traffic.
In the future, GPS systems will enable paving superintendents to know how far away their trucks are, predicted Richard Schreck, executive vice president of the Virginia Asphalt Association.
“Maybe a cell phone-type device on the superintendent’s belt tells him that the next truck is 30 minutes out. That tells him he’s got to build a joint in the pavement,” Schreck said. “I think you’ll see cameras mounted on pavers, similar to the way they’re mounted on some sport-utility vehicles. For example, cameras could tell how close rollers are running to the back of the paver. If you’re doing a ride job, a lot could be learned from reviewing game-type films of a project. We could refine the process and manage it better.”
Caterpillar’s Potts predicts the birth of intelligent paving. Smarter and more automated machines will allow operators to achieve mat smoothness, correct lift thicknesses and timeliness of completion. There will be wireless data communication between machines and control centers. And we’ll have, Potts said, inexpensive, high-speed digital signal processors; inexpensive, powerful machine controllers; and inexpensive, smart sensors for vehicle controls and warnings.
Future pavers, according to Schreck, may be equipped with sensors and alarm systems that sound when the hopper is nearly empty. Such an alarm would tell the paving superintendent, and the paver operator, to fill the hopper soon. To prevent segregation, paver operators know not to run the hopper empty but, considering the human element, it happens. If the superintendent also knows when the paver runs near empty, it would happen much more rarely, he contended.
Charlie Potts and Schreck agree that more operator-friendly equipment will help the industry attract workers and deal with a changing work force.
“In the future you’ll see more simplistic, more automated pavers,” Schreck said. “You’ll still have an operator, but he’ll do fewer and fewer adjustments.”
Both Charlie Potts and Don Brock, CEO of Astec Industries, see more movement toward aggregates that are fractionated into single sizes.
“Forty years ago we made mixes with three cold-feed bins,” Potts said. “Now it’s not unusual to see seven or eight cold-feed bins. They give you more control over your mix and more flexibility in your production process.”
More Uniform Mix
“If you could say three words that would make our product better, they would be uniformity, uniformity and uniformity,” said Brock.
And the machine that permits mixes to be paved at a uniform temperature is a material transfer vehicle that can remix the asphalt. One such device is the Roadtec Shuttle Buggy which has a remixing system to reblend the cooled asphalt from around the truck edges with the hotter asphalt in the interior of the truck load. When the buggy moves the mix to the paver, it has a uniform temperature.
Uniform temperatures permit the paver to create a smooth mat that can be compacted evenly. By contrast, when cooled mix comes out of the truck in one batch, that asphalt causes the birth of a pothole, said Brock.
“The screed raises up to pass over it, a roller can’t compact it, and water gets into it,” he said. “I predict that in a couple of years, material transfer vehicles will be required in every job.”
Recently, a new technology called Intelligent Compaction has been imported by the European-based compactor manufacturers.
“Intelligent Compaction is a system for measuring the stiffness of hot mix asphalt as you compact it, and for documenting the resulting stiffness and temperature of the asphalt mat,” said Chuck Deahl, national accounts manager for Bomag Americas Inc.
These systems measure both stiffness and temperature on the go. Stiffness can be correlated to mat density in terms familiar to quality control people.
“All of this technology is European technology and has been used in Europe for the past four years,” said Deahl. “Most of the manufacturers that have intelligent compaction systems are European or Japanese.”
The documentation of stiffness and temperature can be processed on-board the roller, and can be fed back to allow the roller to make automated decisions. Bomag makes one such operational system, called Variocontrol.
During its initial passes over the mat, a roller equipped with an automated Variocontrol will vibrate the drum vertically and make a direct 90-degree impact on the uncompacted asphalt. As the roller continues to work and the mat approaches final density, the Variocontrol system “tells” the roller to gradually move the vertical force to an angle. At final density, the roller drum will vibrate horizontally.
At least three other manufacturers, said Deahl, have Intelligent Compaction systems: Hamm, a German firm; Amman, a Swiss company; and Sakai, a Japanese company. Typically, an Intelligent Compaction system applies to only one drum on a dual-drum roller.
What’s coming next to the United States, said Deahl, is a roller equipped with an Intelligent Compaction system combined with GPS. Mat stiffness and location information are transmitted to an analysis center, which bounces back information to the roller about on-site densities by location.
“We have used this on single-drum vibratory rollers for compacting embankments,” said Deahl. “We can develop a disk to show specific high- and low-density areas in the embankment.
“That technology has been put on double-drum rollers in Europe, but I don’t know of any manufacturer in the United States that is doing it with double-drum rollers. That’s the next step here in the United States.”
With warm mix asphalt, the producer employs additives or a chemically modified asphalt binder to produce asphalt mixtures at temperatures 50 to 75 degrees below conventional temperatures. Several demonstration projects have been performed in the United States over the past two years. Meanwhile, the Europeans have launched warm mix technologies and are seeing positive performances.
The advantages of warm mix include a reduction in burner fuel needed, lowered stack gas emissions and less odor. Perhaps more significant is the fact that warm mix could allow paving in cooler temperatures — both earlier and later in the construction season.
One warm mix technology involves an organic additive called Sasobit, from the Sasol company in Germany. Sasobit is a long-chain wax that lowers the viscosity of the mix at construction temperatures, but the mix maintains stiffness at service temperatures. After five years, the field performance of Sasobit-modified mixes remains good, Dave Newcomb, vice president of research and technology of the National Asphalt Pavement Association, said. The technology was recently used to pave the main runway at the Frankfurt Airport in Germany, permitting the facility to be opened more quickly after construction.
How quickly might warm mix catch on?
“That depends on forces that influence the market. If energy prices would take another jump, we probably would see more rapid implementation of warm mix,” predicted Newcomb. “We have to figure out how warm mix will fit into the technologies we have. Some changes will be needed in mix design procedures in order to implement warm mix. For example, what implications does this have for performance-grade or PG binders? Would we have to go to a stiffer binder to compensate for the reduced aging of the material during construction?”
The future of asphalt construction, in summary, is a bright one. Plenty of ideas are being floated, both to solve problems and to pioneer into new territory. The trick will be to choose the right ideas and make them happen.
(This article was reprinted with permission from the Spring 2006 edition of “Asphalt” and www.asphaltmagazine.com.)