Rubberized Asphalt

How old tires become part of smooth, durable freeway pavement

How old tires become part of smooth, durable freeway pavement


How old tires become part of smooth, durable freeway pavement

How old tires become part of smooth, durable freeway pavement

May 12, 2017

By Doug Nintzel / ADOT Communications

You’ve heard the saying that you don’t want to know how hot dogs are made.

Well, that’s not true of rubberized asphalt. In fact, some ADOT staffers recently took a tour of a couple of the Valley businesses involved in the process of creating the smooth, durable asphalt that features rubber from recycled tires as a key ingredient.

Since an 11-mile stretch of Interstate 17 in Phoenix is being resurfaced this spring, we wanted to take a look at how they make that pavement.

We started at the Crumb Rubber Manufacturers plant in east Mesa. This facility takes mountains of old tires and turns them into tiny granules of rubber that eventually go into the mix for rubberized asphalt.

First stop: The plant’s large back lot, featuring those big tire piles. It’s here that workers place tire after tire on conveyor belts that feed them through a series of machines that chew them up while spitting out smaller and smaller pieces. The screeching and stretching sound of a tire giving up its original life to become part of a freeway’s pavement is something to behold.

Along the way at this rubberized version of Charlie’s Chocolate Factory, the steel in the tires is removed along with fibers and other similar material. There are magnets that help collect it. What we couldn’t see inside the plant involves a freezing process that’s included in reducing the tire rubber down to the consistency of ground coffee. It’s all placed in large white storage bags.

From there, large containers of the crumb rubber are trucked out, destined for another company that starts the process of blending those tire particles with the liquid asphalt.

The rubberized asphalt being used on the current project to resurface Interstate 17 in Phoenix is manufactured at a Vulcan Materials Co. plant near Broadway Road and 43rd Avenue. The large dirt lot where the plant operates is dotted with various mounds of aggregate – the rock material used in asphalt pavement.

Our ADOT crew was provided with great access to see how the asphalt is made. Safety comes first as you keep an eye out for vehicles that are coming and going, including a front loader hauling aggregate to bins that will feed the small rocks onto a conveyor belt.

Nearby, the liquid asphalt and melted crumb rubber blend flows from special heat tanks. The key ingredients are mixed in rotating drums that also keep the rubberized asphalt hot before it is shipped along one more conveyor system into tall silos for storage.

Those silos are mounted on top of an open steel platform, which large dump trucks are able to pull under. Each driver pulls in beneath the correct silo. Hatch doors then open, allowing the rubberized asphalt to drop into the truck’s bed.

From there the still hot asphalt is delivered to the freeway job site, ready to be paved into a one-inch thick overlay that by the end of any one weekend, thousands of I-17 drivers will be traveling on.

Enjoy the ride. Remember: Thousands of tires went into making it a smooth one.

ADOT’s use of rubberized asphalt gives new life to recycled tires

ADOT’s use of rubberized asphalt gives new life to recycled tires

I-17 101 traffic interchange

ADOT’s use of rubberized asphalt gives new life to recycled tires

ADOT’s use of rubberized asphalt gives new life to recycled tires

May 11, 2017

PHOENIX – The rubberized asphalt used by the Arizona Department of Transportation on many highway paving projects not only creates a smooth ride for drivers, it also provides a second life for the rubber from thousands of old, worn tires that might otherwise be dumped in landfills.

Such is the case with the ongoing project to put a fresh layer of rubberized asphalt on a busy stretch of Interstate 17 in Phoenix. Rubber from about 75,000 tires will be used in the layer of asphalt being added to 11 miles of I-17 between Dunlap and 19th avenues in Phoenix.

For the I-17 project, the process for recycling tires begins at the Crumb Rubber Manufacturers plant in east Mesa, where a complex series of conveyor belts, blades and other equipment removes the internal metal belts from the tires while turning the rubber into granules that look like ground coffee.

The crumb rubber is a key ingredient that is blended with hot asphalt and aggregate to become rubberized asphalt. For the I-17 project, the mixing occurs at a Vulcan Materials Co. plant in Phoenix. The heated rubberized asphalt is then delivered in trucks when weekend paving on the freeway is underway.

ADOT has used rubberized asphalt on many stretches of the state’s highways, including metro Phoenix freeways, for decades. As a result, rubber from millions of tires has been used to help provide a smooth, durable ride for drivers across Arizona.

“What we like most about rubberized asphalt is its durability,” said Dallas Hammit, ADOT’s state engineer and deputy director for transportation. “When our riding surface pavement lasts longer – in some areas for well over a decade – it is cost effective and limits traffic disruptions.”

Rubberized asphalt has also been recognized for reducing traffic noise, specifically the sound from vehicle tires, by approximately four decibels in neighborhoods near urban freeways.

The weekend paving of sections of I-17 is scheduled to be completed in June. This weekend, northbound I-17 will be closed between Glendale and Dunlap avenues from 10 p.m. Friday to 5 a.m. Monday, May 15, for the resurfacing work. Drivers should consider alternate routes, including northbound State Route 51, to avoid heavy traffic approaching the I-17 closure.

Timing of paving work is sometimes decided by Mother Nature

Timing of paving work is sometimes decided by Mother Nature


Timing of paving work is sometimes decided by Mother Nature

Timing of paving work is sometimes decided by Mother Nature

April 28, 2016

By Caroline Carpenter / ADOT Communications

We all know weather can affect the roads. Ice makes highways slippery and wind can make it difficult to keep your vehicle in its lane. But did you know weather affects paving operations too? ADOT needs Mother Nature to cooperate when paving our highways.

That was the case this week with our project on approximately 17 miles of Interstate 10 between Tucson and Benson, which includes paving as well as replacing the westbound bridge at Davidson Canyon. Final paving was set to begin earlier this week, but the lower-than-expected temperature forced us to postpone it.

It’s fairly obvious why you can’t pave during the rain, but the temperature of the air and the temperature of the road surface also have to be right to get best results with rubberized asphalt. The air temperature should be in the low 70s, and the road surface should be at least 85 degrees.

While rubberized asphalt may be temperature-sensitive, it offers many benefits:

  • It's environmentally friendly: About 1,500 rubber tires are recycled for every mile of every lane paved with rubberized asphalt.
  • It's quiet: Rubberized asphalt reduces traffic noise by at least four decibels.
  • It's durable: A surface paved with rubberized asphalt will last about 10 years, meaning less money is spent no repairs and replacement. replacing and repairing the rubberized asphalt roads.

Please watch ADOT’s video to learn a few quick facts about turning tires into rubberized asphalt.

Transportation Defined: Asphalt

Transportation Defined: Asphalt


Transportation Defined: Asphalt

Transportation Defined: Asphalt

February 3, 2015

A view of an asphalt sample and a rubberized asphalt sample, right.

When someone hears the word “asphalt,” they might picture the road that they drive on, but asphalt is actually one component of that surface...

We recently dropped by ADOT’s binder lab and learned all about asphalt and the testing that ADOT conducts. We’ll share that information with you soon, but for today, we thought we’d start off by showing you a couple photos of asphalt – the thick, sticky, black substance that acts as a binder when mixed with aggregate.

Asphalt, which is basically the residual hydrocarbons that are left over when oil is distilled, has multiple uses. At ADOT we use it for road paving.

You’ll notice the photo at left looks smooth and the one at right looks a little chunky. That’s because the sample on the right is rubberized asphalt and already has the crumb rubber mixed in (you can watch this video to get a detailed look at how rubberized asphalt is made).

Stay tuned … we’ll have more on asphalt coming up soon. 

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

How it's made: Rubberized asphalt

How it's made: Rubberized asphalt


How it's made: Rubberized asphalt

How it's made: Rubberized asphalt

April 23, 2014

If you’ve been reading this blog for a while, by now you should know plenty about rubberized asphalt. We’ve covered what it is, why it’s used and the many benefits it offers. However, we’ve never before explained how it gets made … until today.

The process is really fascinating and, as you can see in the video above, it all starts with tires – lots and lots of tires.

First they’re taken to a facility where much of the wire is pulled out. Next, they get shredded and sent off to a cryogenic system that freezes the rubber to -300 F. The cold temperature gives the rubber glass-like properties, allowing it to be smashed into millions of pieces. From there, the remaining steel and fiber components of the tires are removed…vacuums and magnets are utilized in this step.

After all that, the crumb rubber is blended into a liquid product to create rubberized asphalt. That mixture, also called a binder, gets dried and blended with oil before being applied to the road.

More about rubberized asphalt

Roughly 1,500 tires are used for every lane-mile of rubberized paving. To give you an idea of what that means, on just one 10-mile, six-lane highway ADOT covers 60 “lane miles.” Multiply that by 1,500 old tires and that equals 90,000 old tires that have been recycled and re-used.

While the environmental benefit is significant, there are several reasons why ADOT uses rubberized asphalt, including its noise-reducing properties and its ability to resist cracking.

“When we started using asphalt rubber and started using the crumb rubber from the tires, we didn’t do it so much to recycle tires,” says Assistant State Engineer for Construction Julie Kliewer in the video above. “The material is a better material because of it because it helps resist not only cold-weather cracking, but the normal cracking that happens from the fatigue or the aging of the roadway. The bonus is that we’re taking those tires out of the waste stream.”

For more information on rubberized, visit ADOT’s Quiet Pavement Web page or check out our previous blog posts and videos.

Building a Freeway: Rubberized Asphalt

Building a Freeway: Rubberized Asphalt


Building a Freeway: Rubberized Asphalt

Building a Freeway: Rubberized Asphalt

July 26, 2013

Rubberized asphalt is durable, smooth and uses recycled materials that otherwise would be headed to a landfill ... what’s not to like?

ADOT is fond of the stuff for those reasons and more, which is why rubberized asphalt continues to be used on projects around the state, including the Loop 303.

What is rubberized asphalt?

Rubberized asphalt consists of regular asphalt paving mixed with “crumb rubber” (a.k.a. ground up, used tires).

The used tires are processed by separating the casings, fabric and steel. The extracted rubber then is ground to the consistency of ground coffee. Approximately 1,500 tires are used for every lane-mile of rubberized paving.

You should also know that rubberized asphalt is temperature sensitive and cannot be applied during very cold weather or very hot weather. That means rubberized asphalt can only be applied during the spring and fall in the Phoenix area.

Quiet pavement

Did we mention that rubberized asphalt pavement can reduce traffic noise levels by at least four decibels? If you’ve driven on a roadway paved with rubberized asphalt, you should be able to notice the difference.

OK ... we could go on and on about rubberized asphalt pavement, but we won’t. We’ll just direct you to the above video that gives a new look at rubberized asphalt. If you want more, head over to ADOT’s Quiet Pavement webpage.

Surveys give valuable feedback on quiet pavement

Surveys give valuable feedback on quiet pavement


Surveys give valuable feedback on quiet pavement

Surveys give valuable feedback on quiet pavement

February 7, 2012

Rubberized asphalt is placed on an off-ramp in the west Valley last March.

We asked and you answered!

Back in December when we told you about the Quiet Pavement Pilot Program, we launched a survey asking for your thoughts on freeway surface conditions in Maricopa County.

We had no idea what sort of response to expect, but you can bet we were pretty pleased when more than 3,600 people completed the online questionnaire!

That translates into a lot of quality feedback that will be utilized in the pilot program study. Public comment is vital and will serve as one of the factors that helps determine whether or not the noise mitigating effects of rubberized asphalt last the test of time.

So … are you curious to find out what the survey says?

Well, we’re happy to report that the results were strikingly positive!

As for general surface condition, 93.4 percent of survey respondents describe Phoenix Metro area freeways as either “excellent” or “good.”

When it comes to smoothness, 79.3 percent say Valley freeways are “above average” compared to freeways outside the area and less than 2 percent say road smoothness is “below average.”

And as for noise…86.6 percent say Phoenix metro-area freeways are quieter than freeways outside the area with only 2.8 percent saying they’re louder than average.

A whopping 99 percent indicate they have heard about rubberized asphalt and 96.5 percent of respondents think ADOT should continue to use it on Phoenix metro freeways!  

Since ADOT has been applying rubberized asphalt to Phoenix metro freeways for about six years, we wanted to know if anyone has noticed a difference in smoothness and noise…

95.6 percent say they’ve noticed an improvement and only 2.2 percent have not noticed any change (2.1 percent weren’t sure or hadn’t driven Phoenix freeways prior to six years ago).

And our personal favorite…95.4 percent of survey-takers rate ADOT as either “excellent” or “good” at maintaining freeway surfaces (with only 0.8 percent giving ADOT a “poor” grade)!

One more interesting tidbit …

We asked people to tell us approximately how many miles they travel ONE WAY on their daily commute. Interested to see how your commute stacks up?

Of the 3,532 people who answered this question …

  • 35.7 percent travel 0-10 miles
  • 28.9 percent travel 10-20 miles
  • 18.4 percent travel 20-30 miles
  • 7.2 percent travel 30-40 miles
  • 4.9 percent travel more than 40 miles
  • 5 percent weren’t sure

The survey is now closed, but you can still leave your comments and questions on our Facebook page or here on the blog (our initial post has 36 comments and counting!). 

Quiet Pavement Pilot Program

Quiet Pavement Pilot Program


Quiet Pavement Pilot Program

Quiet Pavement Pilot Program

December 15, 2011
Blog Default

Back in the early 2000s ADOT started to hear from drivers who said certain stretches of Valley freeways seemed quieter than others.

ADOT and the Maricopa Association of Governments (MAG) noticed a difference, too.

It seemed that areas paved with an asphalt rubber friction course (rubberized asphalt), which MAG funded through the Regional Transportation Plan, were less noisy than freeway surfaces with cement concrete pavement.

ADOT set out to determine whether the rubberized asphalt really did make any difference when it comes to noise abatement. ADOT officials also wanted to know whether the perceived noise-reducing properties of the rubberized asphalt would last as the pavement aged.

Quiet Pavement Pilot Program

After some initial studies showed promise, ADOT, in connection with the Federal Highway Administration, developed the Quiet Pavement Pilot Program in 2003.

The program allows ADOT to use rubberized asphalt on selected freeway sections in the Valley in order to test out and study its noise mitigation properties.

According to the FHWA description, the program is intended to “demonstrate the effectiveness of quiet pavement strategies and to evaluate any changes in their noise mitigation properties over time. Current knowledge on changes over time is extremely limited. Thus, the programs will collect data and information for at least a 5-10 year period, after which the FHWA will determine if policy changes to a state DOT’s noise program are warranted.”

In other words, this study is going to show whether or not the noise mitigating effects of rubberized asphalt last the test of time.

That’s important to know because right now state DOTs cannot consider rubberized asphalt as a method to lessen highway noise. Noise walls and other tools are used primarily to meet noise abatement requirements.

If this study proves rubberized asphalt helps alleviate some road noise over years of use, states could potentially start using rubberized asphalt as an additional tool to help build quieter roads.

Findings to date

The study has shown so far …

Rubberized asphalt works best at high speeds and for average-sized passenger vehicles. It doesn’t have as much of a quieting impact at slow speeds or for larger trucks or motorcycles It’s not a solution for all climates Rubberized asphalt produces an average noise reduction of about 4 to 5 decibels over time.

Where we are today …

We have about three years remaining in the pilot study and we want to hear from you … the people who drive on Maricopa County freeways.

Public comment is an important part of the pilot program. ADOT has committed to collect and document public reactions on the rubberized asphalt for the study.

Research Center guides ADOT toward transportation innovation

Research Center guides ADOT toward transportation innovation


Research Center guides ADOT toward transportation innovation

Research Center guides ADOT toward transportation innovation

August 8, 2011

The ADOT Research Center studies ways to improve transportation in Arizona.

Much has changed since ADOT got its start in 1927.

Back then, the agency was known as the Arizona State Highway Department and roads certainly were built a little differently. Methods, materials and technology have changed so much since then.

Amazingly, they’re still evolving today …

ADOT keeps up with transportation advancements through research. The ADOT Research Center oversees that research, which is aimed at improving all aspects of transportation in the state and beyond.

But, don’t think the studies and research produced by this team just sit on a shelf once completed.

The information generated by ADOT’s Research Center focuses on evaluating new materials and methods. ADOT’s researchers look at developing design and analysis techniques and study the underlying causes of transportation problems.

In other words, this research leads to better methods, innovative practices and new ways of doing things, giving Arizonans a better value when it comes to transportation!

To get an idea of how this research ends up influencing the way ADOT operates, take a look at the seven emphasis areas within the ADOT Research Center :

  • The Environment emphasis explores the interaction between transportation and the environment. Studies from this discipline look at air quality policy, emissions reduction, transportation-generated noise, wildlife and other environmental topics.
  • The Maintenance emphasis researches how to enhance the maintenance and operation of roadways. A recent study is evaluating the effects of snowplow and deicing chemicals on rubberized asphalt pavements.
  • Materials and Construction studies scrutinize the products and methods used in constructing roads. One study from this emphasis provided research into the noise reduction properties of rubberized asphalt.
  • Research within the Structures emphasis area aims to apply effective modern technology and resources to enhance the implementation of bridge management systems, including the repair of over-stressed bridge decks.
  • Traffic and Safety research not only investigates engineering principles to help solve traffic problems, but it often takes into account the psychology and habits of drivers. Research projects have included a study on seat belt usage in Arizona.
  • Intelligent Transportation Systems analyzes ways to integrate advanced communication technologies into transportation infrastructure. Study topics have included freeway ramp metering, electronic message signs and emerging technology.
  • The Planning and Administration discipline looks to our transportation future – how ADOT can best meet travelers’ needs as the population grows, our society evolves and technology offers more options. This emphasis also addresses organizational issues within ADOT. One ongoing study within this emphasis will report on how new media can bolster ADOT’s community outreach.

There’s much more to learn about this team. Visit the Research Center’s webpage for additional information and stay tuned. In the future we’ll blog about the ADOT Research Center ’s library and product evaluation program.

Listen Up: ADOT works to minimize noise impacts

Listen Up: ADOT works to minimize noise impacts


Listen Up: ADOT works to minimize noise impacts

Listen Up: ADOT works to minimize noise impacts

June 6, 2011

Concrete noise walls reduce traffic noise by blocking the path that sound waves travel from the traffic to the residential area.

Most people don’t find the sound of traffic especially soothing …

ADOT certainly recognizes this and is constantly working to minimize the impacts to surrounding neighborhoods from the noise of new freeways.

You would think figuring out the impact of noise could get tricky because everyone perceives it differently – a sound that’s irritating to you might be tolerable to someone else.

But, federal law requires that ADOT estimate the future noise levels from new freeway projects, and if traffic noise approaches or exceeds 67 decibels, noise abatement must be considered. ADOT has taken it a step further, though, and considers 64 decibels to be the acceptable threshold to consider noise abatement for new projects.

The amount by which noise levels will change in a residential area also is a factor. A road project that will cause noise levels to increase by 15 decibels or more is considered an impact and noise abatement measures must be considered.

Just to give you an idea of what a decibel measurement means … a whisper could register at about 20 decibels, normal conversation comes in around 60 decibels and if you were standing about 15 feet from a loud rock band, you’d be hearing sounds measuring roughly 130 decibels.

Now you might be asking – how do you figure how noisy a new road will be before it’s even built?

Well, experts from ADOT’s Environmental Planning Group use sound pressure level meters to take readings of current noise levels in several areas near a proposed project site.

Measurements aren’t taken during rush hour because traffic is typically a little slower and quieter. Measurements are instead taken at the peak traffic noise hour, when traffic is free-flowing and cars are able to drive the speed limit, but the road is at maximum capacity.

Those measurements and the area’s topographic and weather information are plugged in to a very sophisticated computer program. It creates a model of the area and can tell ADOT what noise levels to expect if a new freeway is built, or an existing freeway is widened.

If it is determined a project will cause a noise impact to the area, ADOT has a few options, including:

  • Install noise walls or berms
  • Implement traffic control measures (speed limits, etc.)
  • Modify the proposed freeway alignment

On top of everything, the abatement method chosen has to meet multiple criteria showing that it is reasonable and feasible … a noise wall isn’t reasonable if the residents of the neighborhood don’t want it or it is cost prohibitive and it isn’t feasible if it won’t effectively reduce noise levels.

A little more on noise walls …

Barriers, such as concrete noise walls, reduce traffic noise by blocking the path that sound waves travel from the traffic to the residential area.

When sound waves hit the noise wall, they must bend over and around it. This is known as diffraction, which absorbs the sound energy, thereby reducing noise. For every decibel of reduction, it is necessary to increase the height of the wall by two feet. Noise walls are most effective when the distance between the source and the receiver is no more than 400-500 feet.

ADOT and the Federal Highway Administration (FHWA) are currently studying the use of rubberized asphalt or “quiet pavement,” which can noticeably reduce traffic noise levels. When ADOT/FHWA completes the study, the results will determine whether quiet pavement can be used for noise abatement.

While no analysis, wall or special pavement can completely eliminate traffic noise, ADOT does have one of the most progressive noise abatement policies in the nation and that is something the citizens of Arizona may find soothing.