Extending Pavement Life

By Bob Berkley | September 28, 2010

For those of us in the business of building roads, today's market is rough. Escalating global prices for fuel and other raw materials are driving up construction costs, leaving many state highway transportation officials searching for ways to fill the gaps in their annual budgets. In these volatile times, however, research is showing that modified asphalt is a practical solution to the budget concerns currently facing the road construction industry.

In 2005, the Asphalt Institute and the Association of Modified Asphalt Producers (AMAP) commissioned a study designed to quantify the effects of using polymer-modified asphalts as compared to conventional mixtures in terms of increasing pavement life and reducing the occurrence of surface distress. The study determined that using modified asphalt could extend the life of pavement by as much as two to five years more than by using non-modified asphalt for existing pavements in good condition — a time frame that can add up to long-term financial benefits for state highway departments and ultimately for the taxpayer.

"Modified asphalt costs a bit more at the onset of a project, but the long-term cost savings are clear," says Bob Kluttz, staff research chemist for Kraton Polymers and chair of the AMAP Education Committee. "Since it performs better, modified asphalt lasts longer and requires less interim maintenance, so there's a lot of added value associated with its use."

In addition to a reduction in overall cost, Kluttz notes that less frequent rehabilitation and maintenance also yields reduced negative impact on drivers and improved safety.

Further cost reductions may soon be possible thanks to emerging warm-mix technologies for modified asphalt. Such technologies allow the producers of hot-mix asphalt paving material to lower the temperatures at which the material is mixed and placed on the road, helping to significantly cut fuel consumption as well as hydrocarbon emissions.

"With warm-mix technologies, modified asphalt can be produced at temperatures 50 to 70 degrees Fahrenheit lower than those typically required for modified asphalt mixes," says Gerald Reinke, technical director for Onalaska, WI-based Mathy Construction and president of Mathy Technology & Engineering. "This reduction in temperature, which helps to save energy and reduces mixing costs to contractors, also results in reduced aging to the polymer-modified binders. Warm-mix technologies also allow for shorter pavement rolling times, which can result in further cost reductions."

At Kraton Polymers, research is under way to prove that thinner pavements containing polymer modifiers can provide the same level of performance as thicker unmodified pavements. If the research is found to be conclusive, contractors could benefit from additional budget relief.

"If given the choice between pavement which is 8 inches thick versus pavement that's 10 inches thick, we're working to demonstrate that owners will be able to modify the thinner pavement and still enjoy the same performance benefits which are provided by the thicker material," says Kluttz. "The ability to do so can save contractors approximately 20 percent on materials costs during the initial construction phase."

Kluttz adds that thinner pavements also use fewer raw materials per highway mile, which can help to ease industry concerns over raw materials supply.

Using Modified Asphalt

Currently the use of modified asphalt is determined on a state-by-state basis. As such, AMAP continues to work with state DOTs on the research, technology and training that demonstrate the benefits of specifying modified asphalt.

In recent months, the Federal Highway Administration has begun hosting training courses for DOTs on its new Mechanistic Empirical Pavement Design Guide, which serves as a model for predicting pavement performance based on road design and geographic location. The guide features specific calibration factors for polymer-modified asphalts, which owners and contractors can use to help determine how modified asphalt will perform in their individual states compared with unmodified asphalt.

The calibration factors featured in the guide are the result of a study commissioned by the Asphalt Institute and AMAP in 2008 to build on the findings of its 2005 study, which provides that modified asphalt reduced pavement distress and extended pavement service life, but did not determine specific calibration factors for predicting the distresses of polymer-modified asphalt mixtures.

"As more and more DOTs are educated on how to use the new calibration factors, the hope is that there will be increased interest in modified asphalts from states that aren't currently utilizing them," Kluttz notes.

As road construction costs continue to skyrocket, the value of modified asphalt is becoming much clearer. An investment in modified asphalt today is an investment in roads that last longer, perform better and cost significantly less in the long term. Looking to the future, emerging technologies in modified asphalt hold the promise of even greater cost savings down the line, even when economic times are tough.

Editor's note: Bob Berkley is executive director of the Association of Modified Asphalt Producers.