Producers and state agencies worked together to design mixes that could accept 10 to 25 percent RAP in an effort to lower the amount of required liquid asphalt and virgin aggregate. At the time, recycling asphalt became common place, since this percentage of RAP generated significant savings for the producer. However as the price of AC dropped, producers became content with the status quo on savings and remained at this level of recycling.
"It's time to consider means for increasing RAP content even further," says NAPA's Newcomb. The reenergized thinking is not to simply "dump" RAP into the mix to lower costs. Rather, recycled product should be designed into the mix like any other material in HMA. "Understanding the asphalt content and gradation will help the mix designers integrate the recycled material in the right proportion and adjust the virgin materials," he adds.
NAPA is currently conducting a study of its members to determine the current and potential levels of RAP usage. The study includes usage of recycled material for the base, surface and binder courses. Preliminary results indicate that the average use of RAP among NAPA members falls approximately 10 percent below the potential usage. Therefore, there is room for more RAP in mix designs to further increase savings and reduce natural resource demand.
While recycling asphalt has been an established practice for nearly 30 years, there are emerging mix designs and technologies that may help to reduce asphalt costs today and in the future. For example, mixes that include a larger nominal maximum aggregate size (NMAS) require less asphalt binder for the same film thickness than mixes using a smaller aggregate size.
A 1998 NAPA publication mentions that a large-stone, 1.75 inch NMAS requires 1.7 percent less asphalt than conventional 5/8 inch NMAS mixtures. A project requiring 10,000 tons of HMA would use 170 tons less liquid asphalt with the large-stone mix, representing a $59,500 savings at a $350 per-ton AC cost.
While its initial thrust was to lower emissions, warm mix asphalt may also help to reduce the overall asphalt production cost by significantly lowering mix temperatures. Many of the warm mix asphalt additives are reducing mixing temperatures at the plant to between 200 and 250 degrees Fahrenheit. One additive manufacturer reports a 30 percent fuel savings by lowering asphalt mixing temperatures by 50 degrees F. An advantage of warm mix asphalt is it can be used on every lift — base, binder and surface — so the savings can be realized on a wider variety of mixes.
Selecting the perpetual pavement approach for a new road or reconstruction project may or may not save money on asphalt now, but it will result in future savings. By using this mechanistic approach to constructing the pavement, the base is designed to last indefinitely without requiring major rehabilitation. Only the surface level will require periodic milling and overlays. This can significantly reduce the amount of asphalt required for future pavement repairs.
The right stuff
It may sound fundamental, but make sure the right asphalt is being used for the application. Agency officials sometimes specify a road with more expensive grades of asphalt and polymer-modified asphalt, even when they are not necessary.
"Layers that are deeper in the pavement structure, low volume pavements and overlays of existing cracked pavement are all circumstances where specifications requiring premium asphalts should be reviewed and changed if necessary," suggests Newcomb. Using standard-grade versus premium-grade liquid asphalt in Ohio can result in a $50 to $70 per-ton savings, based on historical pricing.
Overlays are another potential cost savings area. Often an overlay is placed more to improve a road's smoothness rather than to strengthen the pavement. Where appropriate, the use of a thinner overlay can save the contractor money. "The use of a 9.5 mm mix that is 1.5 inches thick will use 25 percent less material than a 12.5 mm mix that must be placed at 2 inches thick," says Newcomb. Although the thinner overlay will require higher asphalt content, there will be a net cost savings for the project.
Increasing the amount of RAP, exploring new technology and using the right asphalt for the application are but a few ways asphalt producers and contractors can save money during this time of volatile liquid asphalt prices. Although few want to see high asphalt prices, the optimist can see a silver lining to this dark cloud.