Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/597582
EquipmentWorld.com | November 2015 53 highway contractor | by Chris Hill | ChrisHill@randallreilly.com Compaction of warm-mix asphalt on an I-70 project in St. Louis, Missouri. One of the benefi ts of warm-mix is that it can be compacted quicker and more densely than hot-mix. (Missouri DOT) WARM - MIX AND RAP: Cost-eff ective and sustainable paving T he benefi ts of warm- mix asphalt (WMA) with recycled asphalt pavement (RAP) are well documented in paving research, with high percent- ages of RAP mixes holding their own against controls. These mixes have tested so well National Center for Asphalt Tech- nology (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 resis- tance and no cracking in high-RAP pavement. Quality and endurance is one factor, but the economics of a pro- cess 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 tem- perature, 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, pro- vides 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 as- sociate research fellow at the North Dakota State University's Upper Great Plains Transportation Insti- tute, was working as a design and construction engineer for the Cass