by Daniel Brown, Contributing Editor

With workability, environmental benefits and solid performance reports,Reclaimed Asphalt Pavement — RAP — is becoming a bigger part of the mix.

It’s a trend that’s sweeping the nation: using more reclaimed asphalt pavement (RAP) in hot-mix asphalt. RAP is also making inroads into warm-mix asphalt.

Astec’s foamed asphalt attachment makes warm mix, which will enhance the workability of high RAP mixes.

Since 2007, about half the states, 24 to be exact,* have increased the allowable percentages of RAP in their asphalt pavements. And using RAP can save states a lot of money.

To mill, haul and process RAP costs only a fraction of the cost of virgin mixtures. So RAP allows contractors to produce a lower cost hot mix and pass along savings to owner agencies.

“States are allowing more RAP to guard against future high fluctuations in the price of asphalt binder,” says David Newcomb, vice president of research and technology for the National Asphalt Pavement Association (NAPA). “Plus, RAP is more environmentally friendly. And states have looked at the performance of mixes with higher RAP contents and concluded that RAP doesn’t detract from the quality of the asphalt.”

RAP primarily comes from rehabilitation of existing roadways or parking lots. Typically it is trucked from a milling machine to a stockpile at an asphalt plant. RAP helps reduce the cost of hot mix because the aggregates in the recycled material have already been coated with asphalt.

RAP can be added directly to hot-mix asphalt at the mixing plant in amounts ranging from 10 percent to 50 percent or more by weight of the mix. Properly designed and constructed, pavements with RAP will last as long or longer than roadways built with virgin materials, says Kent Hansen, director of engineering for NAPA

More RAP = lower bid prices

Contractors using more RAP can cut their bid prices for hot-mix asphalt.

The total cost of milling RAP from a project, hauling it to an asphalt plant, and crushing and screening is typically between $6 and $10 per ton, says Randy West, director of the National Center for Asphalt Technology (NCAT) at Auburn University in Alabama. Virgin aggregate costs range from $10 to $25 per ton, depending on the region of the country. In 2008, virgin asphalt prices in 2008 jumped from about $350 to $800 per ton. In 2009, liquid binder stabilized at around $410 per ton.

For example, a virgin mix (5-percent binder but no RAP) with $15-per-ton aggregate and $410-per-ton asphalt binder costs about $34.75 per ton for hot mix materials. (The materials cost is 0.95 x $15 + 0.05 x $410 = $34.75)

By contrast, with a mixture of 5 percent asphalt binder and 20 percent RAP that costs $8 per ton to process, the materials for the RAP mix cost about $29 per ton — more than a 16-percent savings over the $34.75-per-ton virgin mixture. As RAP content and virgin binder costs increase, so do the savings.