Warm-Mix and Recycled asphalt a cost-saving combo that should be used whenever possible

The benefits of warm-mix asphalt (WMA) with recycled asphalt pavement (RAP) are well documented in paving research, with high percentages of RAP mixes holding their own against controls.

These mixes have tested so well National Center for Asphalt Technology (NCAT) Director Randy West has said the combination should be used whenever possible. “They go together, like peanut butter and jelly or macaroni and cheese,” he said after a 2009 study that showed “excellent” rut resistance and no cracking in high-RAP pavement.

Quality and endurance is one factor, but the economics of a process seal the deal for contractors. With WMA, less time is needed for production, compaction is easier and faster and the mix can be hauled longer distances.

WMA is heated to a lower temperature, so less fuel is needed—on the order of 20 percent or more—and it is heated faster as a result. It’s more dense and can be worked and compacted easier than hot-mix asphalt (HMA) and hauling time and distance is extended because WMA cools slower than HMA.

Eastern North Dakota’s Cass County, with the largest population in the state and one of the largest in terms of highway miles, provides a good case study in using WMA and RAP in combination. In 2012, contractors for the county completed an 8-mile stretch of County Road 26 using the mix. By doing so, they were able to come in under the original bid by nearly 14 percent.

Andrew Wrucke, currently an associate research fellow at the North Dakota State University’s Upper Great Plains Transportation Institute, was working as a design and construction engineer for the Cass County Highway Department at the time of the project. The contractor, Knife River Materials, told him if the county allowed them to use warm mix, they would match the project’s original bid price.

“The contractor also suggested we use RAP within that, because they found warm mix and RAP tend to work well together,” he said. “And it would give us an additional costs savings. We crunched the numbers and found it would save about $200,000.”