“Even in Phoenix, with as much rubber done here, none of the suppliers of hot mix actually own their own rubber plant,” says Belshe. “The market is not quite big enough to spend every day of the week doing rubber. So the market is a mobile market where a contractor like us that is used to moving stuff around can come in for, say, two weeks, then come back to the hot plant two months later and do another project.”
You cannot have the mindset of fixed plants. “Everything that we own is on wheels,” Belshe states. The classic FNF paving job is probably working on an Interstate away from a metropolitan area. “Because of the length of these types of projects, our crews spend a lot of time away from home. It takes a special type of person. It is constant travel.”
Not just for the Southwest
While asphalt rubber primarily got its start in the Southwest, it can be applied almost anywhere. “A lot of people confuse the constructability issues with the performance issues. Nebraska has an ongoing program, but they pick their season very carefully,” says Belshe. “There is some work being done up around Calgary.” FNF is currently doing a project in British Columbia, and has also provided asphalt rubber in Tennessee, New Mexico, Nevada and the many ranging climates of California.
“But you are not going to go out and do it at 45° F,” cautions Belshe. The binder in asphalt rubber is much thicker and more viscous. “It is more difficult to work with as it cools; it gets stiff. So in the construction phase, you need fairly warm weather. But once it is in place and properly compacted, the performance is outstanding.
“The only thing different for laydown is you do not use a pneumatic roller,” says Belshe. “As far as paving, it is like almost any other modified binder-type product. I have personally worked with polymer modified mixes and I would take rubber any day.”
Belshe admits rubber is more difficult to work with than conventional materials. But it really comes down to heat management. “It is critical that the breakdown roller compact the mix at 290° or 300° F. This is usually right behind the paver,” he notes. “There is less margin for error. If you get behind the curve, you are going to get into trouble. With a conventional mix you can kind of push your way through.”
Asphalt rubber mixes are more expensive than conventional mixes. “For one thing, it has more binder in it,” says Belshe. “That’s the most expensive component. On a unit cost per-ton basis, it is probably 40% to 50% more expensive. But when you look at life-cycle costs, you are talking about something that lasts one and a half to two times longer.”
Reducing Noise at the source
Road noise is attracting more attention these days. For example, Phoenix is beginning to address this issue with its Quiet Pavements program. One attractive solution is asphalt rubber. “ADOT’s mode right now is to put a 1-in. open-graded mix on top of the PCCP,” says Mark Belshe, vice president, asphalt rubber general manager, FNF Construction.
As part of the program, ADOT is taking pre-paving and post-paving noise measurements. “There is a sound consultant that attends all of our weekly meetings so ADOT can stay on top of the schedule,” says Belshe. “They have spent a lot of time on this issue.”
The federal government has been slower to react. “Their sound mitigation program is to put up sound barriers. Instead of dealing with the problem after it is created, we are mitigating it right at the source,” says Belshe. But the Feds are now paying closer attention to asphalt rubber.
A side benefit has been the public’s reaction. Normally, people are upset when you block off lanes of a busy freeway. But the asphalt rubber program in Phoenix has drawn a different response.
“You look at the full closures that are going on around here every weekend and the people are very patient considering how disruptive it is,” says Belshe. “On the SR51, we were paving the Southbound just south of Indian School. There is a pedestrian overpass. It was a Sunday afternoon and there were actually people standing up there applauding.”