Applications and Innovations
| August 02, 2011 |
Rubberized asphalt paves the way for happy taxpayers and road travelers . . . even four-legged ones
By Mike Anderson
Over the past 20 years, Gary Shaw spent considerable time educating people in his rural Ontario, Canada county and beyond about rubberized asphalt pavement. And for those people not part of the local elementary school classes or international conferences he spoke to, the former County of Grey transportation and public safety director had huge signs posted along portions of rubberized county roads that would ensure they understood clearly what they were traveling on.
Not that horses need to read.
Shaw recalls a sudden drop-in to his Owen Sound office a few years ago from a member of the intensely private, highly devout, completely respectful Mennonite community that farms alongside the most quiet of secondary roads, as about as far away, literally and figuratively, from even the quaint villages and small towns that dot the Ontario county. When Mennonite community members do need to go to town, it’s most often via horse-pulled buggies. “We really like those rubber roads,” Shaw was told by his surprise visitor. “So I asked him, ‘Why do you like them?’ And he said, ‘Well, our horses can tell when they go off conventional asphalt onto rubber, because their gait will increase.’”
If that isn’t the ultimate testament to highway productivity, then what is?
The County of Grey, with a closed-loop tire recycling process, turned its own increasing stockpiles of discarded tires into a new highway pavement program; a problem for one department of local government thus became a solution for another. Other jurisdictions throughout the continent secure the crumb rubber they incorporate into their asphalt from companies specializing in the recycling of tire rubber.
“Our whole purpose is to try to educate the engineer on how to make the road act more like a tire, really,” says Doug Carlson, vice president of asphalt products with Liberty Tire Recycling, which itself reclaims more than one-third of all discarded tires in the United States. Different types of asphalt mixes are used depending on climate, and overall the range for the paving material is about 80 degrees C; comparatively, says Carlson, tires have a range of about 150 degrees C and, most of the time, users don’t change them from condition to condition. “The big challenge with asphalt is that it gets too soft when it’s hot out and too brittle when it’s cold,” he says. “Well, the tire rubber now used in asphalt counteracts that weakness. Rubber in an asphalt binder will make it last longer under a wide range of temperatures and climatic conditions.”
No More Bouncing Checks
The use of crumb rubber in an asphalt mix goes back 40 years, particularly in the U.S. Southwest, but the technology is growing in application throughout the world, says Carlson.
“The biggest factor for that is the realization that tire rubber can be used as a substitute to virgin polymers commonly used in asphalt. The switch from a virgin polymer to a tire rubber component is a driving factor for increased usage, and of course that is related to the cost of crude oil. As crude oil has increased, the cost of polymers has increased,” he says. “Cost savings is the biggest issue in today’s market, with high asphalt prices and high polymer prices. Tire rubber’s been steady in price – very stable over the past 15 years.
“If state agencies are not using it routinely, at least they are developing a specification that they can use if there might be a shortage of polymers – if polymers become scarce or just too expensive.”
States once leery of noise-reducing rubberized asphalt in open graded friction courses, due to negative experiences with failing binders in the ‘80s, are increasingly coming on board with the benefits of the elasticized asphalt in such applications, he’s observed. “Many are taking a second look, maybe even a third look, at these mixes,” says Carlson, whose company is based in Pittsburgh, “particularly in the Northeast, where you have a lot of benefits for the splash and spray reduction.” He notes: New Jersey has started used rubber in its open graded friction courses; Massachusetts is using rubber in a surface wearing course as part of its routine short-line pavement rehab program.
On the whole, says Carlson, “where they’re substituting tire rubber for polymers, the contractors are saving the state’s DOT anywhere from $2 to $5 per ton of mix. It adds up. On big projects, you can save anywhere from $50,000 to $250,000 rather quickly.”
This could result in a fund-strapped agency, local or state, being able to complete one additional project per year than otherwise possible.
Back in rural Ontario, where healthy skepticism and vocal opinions on most issues have never gone out of vogue, today there’s more than just the universal desire for more roadwork, but an actual enthusiasm for what that additional paving job should entail.
“The public believes in this program now so much,” says Shaw, “that they’ll actually phone in and say, ‘We hear you’re going to pave our road this year . . . we just want to make sure it’s going to be a rubberized asphalt road.’
‘Re-Made in America’
a Statement of Liberty
From two locations in 2000, Liberty Tire Recycling now operates 33 facilities across North America capable of producing more than 250 million tons of crumb rubber for uses ranging from welcome mats and weightlifting plates to railroad ties and highway asphalt.
What began 11 years ago as a scrap tire collection service to solve a solid-waste problem remains the starting point in a process, says Doug Carlson, vice president of asphalt products for the Pittsburgh-based company.
Liberty has contracts to collect scrap tires from leading big-box tire retailers. The tires are taken to a Liberty facility, where they are run through shredding machines, removing the steel via magnets and the fiber and fluff via vacuum or air-blown systems. “You end up with a pure scrap tire rubber particle that’s about the size of ground coffee,” says Carlson, “and that is packaged and shipped to the contractors, where they can add it to an asphalt product for a mix in accordance with the state’s specs.”
The crumb rubber is shipped in a bulk bag, or “a super sack” as Liberty calls it: “It will vary in weight depending on the size of the rubber that’s in it, anywhere from 1,800 pounds to 2,200 pounds, but generally it’s about a ton.”
What does that translate to on the road? “It depends on the type of mix,” says Carlson. “The rubber content in an asphalt mix can vary from 10 pounds per ton all the way up to 30 pounds per ton of mix, so one super sack can go a long way in production of hot mix.” At one to three tires per ton of hot mix, “that translates anywhere from 800 to 2,000 tires per lane-mile of roadway.”
Company Makes A Flexible Argument
Calling it “The Road to Sustainability,” Liberty Tire Recycling pitches rubberized asphalt by educating on its benefits:
Cracking and rutting resistance: Superior elasticity reduces the occurrence of cracking caused by vertical or horizontal movements beneath the overlay as a result of traffic loads, temperature fluctuations and shifting earth.
Skid resistance: In wet conditions, decreased splash and spray combine with better traction for a safer traveling environment.
Maintenance cost reduction: While in most cases using the same equipment as traditional asphalt application on roadways, longer-lasting properties reduce long-term maintenance costs.
Noise reduction: By upwards of 5 decibels, a quieter traveling surface meets the increasing requirements of public-complaint-conscious agencies.
Here’s A Clean Spec For You
Among the challenges encountered when Ontario’s rural County of Grey started laying rubberized hot-mix asphalt 20 years ago was the picking up of freshly-laid material by the compactors.
Then county transportation and public safety director, Gary Shaw, made an adjustment that today is written into every tender put out for county rubberized pavement work. It reads: Ivory liquid soap must be used with the water solution of the rollers in order to reduce the pickup of asphalt on the roller tires and drums.
No word whether Shaw, having just ended a 45-year career with the County of Grey, is the next Ivory Guy.