Moderated by Rick Badie
Here’s a way to reuse old tires: grind them into asphalt pavement mix. The GDOT is experimenting with the technology, which was pioneered in Arizona, where it’s been routinely used since the 1990s. Two GDOT officials write about this environmentally-friendly, cost-saving measure in our state while an Arizona official gives a historical perspective.
By Thomas Howell and Eric Pitts
Ten million vehicle tires are discarded in Georgia every year. That’s more than 27,000 tires scrapped every single day of every single week. What to do with them, how to pay for it, and how to prevent more than a million of them from being illegally dumped are questions that have frustrated the tire industry, environmentalists, and state and local governments for years.
Now, researchers and engineers for the Georgia Department of Transportation have developed two programs that will put tens – perhaps hundreds of thousands of these scrap tires, as well as those ubiquitous truck tire “gators” that haunt our highways, to good use.
What’s more, we’ll save state taxpayers money at the same time.
One of the efforts already underway converts scrap tires into an actual component of pavement. Ten percent of the asphalt the department uses to construct and resurface portions of Georgia’s 19,000 miles of federal and state roads requires the addition of polymers to enhance component bonding and add strength and elasticity to the pavement mix.
The more traffic a road carries, the higher Georgia DOT’s requirements for the durability of its asphalt. Until now, polymers for that high-grade asphalt have only come via direct chemical injection. But department and industry researchers like those at Lehigh Technologies, LLC in Tucker, GA, have determined that shredded tire carcasses – crumb rubber – can satisfactorily provide the same polymer qualities, and do so about $3 per ton cheaper. So beginning this past April, we began allowing contractors who bid on our asphalt paving jobs to utilize either the chemical-polymer modified or crumb-rubber modified mixture.
And when you use some seven million tons of asphalt a year like Georgia DOT, the potential savings are significant.
So is the possible reduction in those unsightly mountains of vermin-infested, disease-promoting scrap tires. Some 2,000 tires are required to produce the necessary polymer content for one mile’s worth of asphalt. The Ddepartment potentially could use 7 million pounds of the material each year, a staggering 280,000 tires.
And that’s just one of our tire recycling programs.
The other focuses on illegally dumped tires and those ugly and dangerous “gators” – carcasses of tractor trailer retreads – that seem to line our major freight corridors.
The program already is underway on a demonstration basis in Mmetro Atlanta and has the potential to save the Ddepartment – and Georgia taxpayers – more than $40,000 a year. As DOT maintenance forces routinely clean roadways of trash and debris, instead of paying for its disposal, they’re setting aside as many as five tons a week of illegally dumped tires and tread carcasses they collect. Liberty Tire Recycling, LLC, periodically picks up this refuse rubber, grinds it into crumbs; and sells it to companies like Georgia’s Mohawk Industries where it is converted into commercial products and applications.
In short, we’re using a Georgia waste product to create jobs for Georgians at Georgia companies and, in the process, saving Georgia taxpayers money.
Innovative recycling programs like these perhaps aren’t the first thought that comes to mind when one thinks of the Georgia DOT. But they play an integral part in fulfilling our mission to provide a safe, seamless and sustainable transportation system that supports Georgia’s economy and is sensitive to both its citizens and its environment.
Thomas Howell is director of construction for the Georgia Department of Transportation. Eric Pitts is the agency’s maintenance director.
By Mark Belshe
When most people visit their local tire shop to replace their worn tires, they give very little thought to what happens to their scrap tires. As it turns out, scrap tires are an particularly onerous solid waste problem. The tire companies produce a very durable and resilient product that can typically last 40,000 to 60,000 miles. This is very admirable, but when it comes time to dispose of the tire, these same long-lasting properties make them almost indestructible.
You can’t just throw them in a landfill. Whole tires, due to their shape, will trap landfill methane gas and actually work their way back to the surface. Most agencies require that scrap tires be processed to some kind of size reduction before disposal, but this adds costs that are hard to recover in simple landfill dumping. Fortunately, there are several value-added uses for scrap tires that are available.
One of the most advantageous outlets for crumb rubber derived from scrap tires is the asphalt paving market. Since the 1960’s, the engineers in Arizona enigneers have been perfecting methods to modify asphalt cement, the great workhorse of America’s paving industry, to create longer lasting and quieter roads. They have been adding up to 20 percent % percent crumb rubber to theliquid asphalt cement in what is known as the “wet” method to achieve a modified binder that resists aging, retards crack reflection and provides roads that are skid-resistant and reduce splash and spray.
The process, known as asphalt rubber, was originally developed by a Ccity of Phoenix engineer. It is not patented or proprietary and the open technology is available to anyone wishing to implement it. By the mid-1990s, the Arizona Department of Transportation was routinely using asphalt rubber mixes throughout the state. , and mMany of the state’s cities and counties include it their paving programs. Today it is not possible to drive on Arizona’s roads without driving on asphalt rubber.
Are they doing it because they want to get rid of scrap tires? No.
There are no legislative or fee incentives for any agency to use asphalt rubber. They are using it because they have found the asphalt rubber mixes provide lower life-cycle costs, and in the long run, these roads are more economical than conventional mixes. But back to the disposal problem, Is this an effective way to avoid massive scrap tire piles?
It is estimated every man, woman and child in America generates one scrap tire every year. In a state like Arizona, whose population is over 6-million plus, this means annually 6 million tires must be disposed. Unlike almost every other state in the Union, Arizona has no scrap tire piles. And all of this is due to a market-driven, innovative industry that came up with an engineering solution which also had great environmental benefits. This is true economic environmentalism.
The great untold Arizona success story is finally starting to get out. States such as California, Texas, Nevada, Louisiana, Florida, New Jersey, Delaware and Massachusetts are all using asphalt rubber. And as the industry has developed and matured, highway engineers are discovering new ways to economically use crumb rubber to modify asphalt cement.
In the past, the production of modified asphalt binders was largely accomplished using polymers, such as styrene-butadiene-styrene. Within the last few years, processes have advanced where crumb rubber is substituted for polymers, the so-called “polymer switch” process. This has been shown to reduce the costs of asphalt concrete mix by as much as $2 to $5 per ton.
The Georgia DOT, along with many others DOTs, are looking at these cost savings as well as the stable supply chain that recycled tire rubber can provide. And iIf we can put some of those Georgia scrap tires back to use, so much the better.
Mark Belshe is executive director of the Rubber Pavements Association in Tempe, Ariz.