Phoenix, Arizona is using rubberized asphalt as one way to help control rising material costs and budget cutbacks. 

Arizona recently completed a mid-decade census. Part of the reason for the census was to determine how to divide funds for road construction and rehabilitation. 

A gas tax, the Arizona Highway Users Revenue, is divided based on a city’s population. “Since Phoenix is pretty much built out, the population is moving to the suburbs, [and] so our budget is being cut for the first time,” says Jeff Van Skike, engineering supervisor for the Street Maintenance Division, a sector of the Street Transportation Department of the City of Phoenix. Because the suburbs in the Phoenix area have grown in population, they are entitled to a larger portion of the state’s roadway funds. 

“In 2006, we lost $300,000, and next fiscal year we’ll lose $2 million,” says Van Skike. 

In addition to decreased funds from the gas tax, budgets for Phoenix road projects are being strained further by rising asphalt costs. “The cost of hot-mix asphalt went up 80% from 2005 to 2006,” says Van Skike. 

The loss of funds and increase in cost of materials impacted the amount of work the Phoenix Street Transportation Department is able to do in a given year. Van Skike states that the budget for the annual residential street overlay program has remained fixed between $6.5 and $7 million. “In 1999, we did 120 miles of residential streets, and in 2006, we were down to almost 69 miles.” 

Cutting costs 

While rubberized asphalt has increased in cost like every other asphalt product, Phoenix officials are relying on this durable pavement to keep maintenance costs low and to last many years. In this way, the city saves money while maintaining an acceptable level of street conditions to the public.


Equipment lays down rubberized asphalt on a residential street.

 The intense sun of the Sonoran Desert causes problems with conventional asphalt pavements. “The sun oxidizes conventional asphalt and it starts losing fine material, the fine sands start raveling out,” says Van Skike. “Since rubberized asphalt doesn’t have a lot of fine material, there is no raveling to worry about.” Normally, when fine sands are lost from an asphalt pavement, a slurry seal is applied. Rubberized asphalt protects the city from having to apply a slurry seal, keeping maintenance costs low. 

With conventional asphalt in Phoenix, reflective cracking could begin occurring as early as a year after an overlay project is completed. With rubberized asphalt, it can take five to six times as long before cracks reflect through the pavement from the base.

Binder, aggregates, and rubber are mixed together.

In 2004, the city surveyed the first streets that had been paved with rubberized asphalt in 1989 to check their condition “The cracks are finally getting large enough to require crack sealing,” says Van Skike. “That was the only maintenance they needed. You don’t get any of the alligator cracking reflected through the base with rubberized asphalt. My guess is, every 15 to 20 years, all we’ll have to do is crack seal the road.” 

The material 

Phoenix and the state of Arizona pioneered the use of rubberized asphalt. Rubber is an asphalt modifier, but is unique in that it modifies the asphalt in two ways. Like regular asphalt modifiers, the rubber becomes part of the binder. “Regular asphalt pavement is 5 to 6% binder content. Rubberized asphalt is 7 to 9% binder,” says England. “The reason why we put more binder in rubberized asphalt is to create greater coating on the aggregate. We do that because rubberized asphalt has a much higher viscosity than conventional asphalt.” This makes the rubberized asphalt so much thicker, that a special pump is required on the production plant. In addition, the rubber particles release certain chemicals during the production process that modify asphalt.

Rubber particles are used as a filler in the pavement.

The second way rubber modifies asphalt is that it acts as a filler component. This is why rubberized asphalt does not lose fine materials in the sun like conventional asphalt. Some of the fine material is removed and replaced by rubber. “The rubber particle performs the function of being a filler component in the pavement. For this reason, the rubberized particles are not completely melted during the reaction time,” says England. 

Rubberized asphalt can be produced in a traditional hot-mix asphalt plant, but a rubberized asphalt blending plant is also required. “It’s two operations, blending the rubber and the asphalt and creating the final product,” says England. “We have two crews, one for the rubber plant and one for the asphalt plant.” 

Producing rubberized asphalt is different than conventional asphalts. The rubber and the asphalt must cook during what is called a reaction time. Specifications in Arizona require that virgin asphalt be heated between 375 and 400 degrees F before rubber is added. The asphalt mixed with rubber during the reaction time is heated to 325 to 375 degrees F. “That’s quite a bit higher than just a regular asphalt plant for hot-mix asphalt,” says England. 

Generally, blending plants producing rubberized asphalt have tanks with two compartments. The first compartment heats and agitates the rubber and asphalt. The second tank has completed this reaction time and provides the rubberized asphalt to the aggregate in the hot-mix plant. The hot-mix plant switches between compartments for more efficient production. 

Rubberized blending equipment is expensive, about $1.2 to $1.5 million. With higher heating of the asphalt than conventional asphalt over a longer period of time — the reaction time — and the need for a second crew to run the rubber blending equipment in addition to the asphalt plant, production of rubberized asphalt is more costly. The increased lifecycle of rubberized asphalt outweighs the higher cost of

production. “Engineers in Arizona base everything on a lifecycle cost analysis. I bet they would give rubberized asphalt at least a lifecycle double that of other asphalts. Rubberized asphalt might be three or four times as good as other asphalts,” says England. 

Another benefit of rubberized asphalt is recycling. Most rubber comes from recycled tires. 

On site 

This year, M.R. Tanner Construction completed the overlay of 4 miles of residential streets in north Phoenix with rubberized asphalt produced by Fisher Industries. The roads were paved with 80,000 tons of rubberized asphalt, with 2,500 to 3,200 tons of asphalt being laid each day.

The process began by milling an inch off the streets and then placing a tack coat with a binder and preservative. M.R. Tanner placed rubberized asphalt in lifts of 1 to 1.5 inches. 

There is a limited temperature range to compact the asphalt once it has been laid. The asphalt was 300 degrees F when laid. “The asphalt sets between 240 and 250 degrees F,” says Ralph Conklin, paving foreman for M.R. Tanner. “That means that we have to work faster.” 

The contractor used an Ingersoll Rand PF-3200, moving at 180 feet per minute to place asphalt. The paver was chosen because it has wheels, a benefit when working in residential areas, where space is sometimes tight. 

With a paver moving quickly, M.R. Tanner needed a breakdown compactor able to keep up. They used an Ingersoll Rand DD-118HFA.

Rubberized asphalt was placed in lifts of 1 to 1.5 inches.

The breakdown compactor made three passes on the asphalt and worked in static mode. “We were restricted to operating the compactor in static mode because there are water mains and other utilities under the street,” says Conklin. 

England recommends that contractors keep the finish compactor off rubberized asphalt longer than other asphalts, and that is what M.R. Tanner did with the Ingersoll Rand DD-90HF used to finish the pavement. 

When the rubberized asphalt was compacted, lime water was applied to the surface of the pavement. “The water evaporates and the lime removes the tackiness from the asphalt,” says Conklin. This allows the pavement to be used within 15 minutes after compaction is completed. 

The asphalt production plant was 16 miles away from the jobsite. To make sure that asphalt would be provided at the rate the paving crew needed to work, 18 trucks transported the asphalt. Paving was completed between 6:00 a.m. and 6:00 p.m. During both rush hours, more trucks were added. The trucks avoided the busy freeways and instead used city streets. 

England believes that rubberized asphalt is sometimes dismissed by other agencies because there is no way to apply a PG grade to rubberized asphalt. “You can’t use a dynamic shear ray meter to evaluate rubberized asphalt. It only works on completely homogeneous asphalts, where everything in the asphalt is completely soluble. 

Rubberized asphalt has proven its effectiveness in Phoenix, especially in a time of funding cuts and rising materials costs. Phoenix has 4,700 miles of roads, and has overlaid 1,760 with rubber, polymer, or some type of modified asphalt binder.

Phoenix officials decided the wisest way to spend money available is rubberized asphalt. “We prefer to put the money up front, because we haven’t added a lot of maintenance crews in the last 12 to 15 years,” says Van Skike. “One of the things that helps keep our head above water is rubberized asphalt.”