In the past 2 years, State highway agencies have built more than 400 Superpave pavements. For most of these pavements, construction went smoothly, with no more problems than would be experienced with conventional asphalt pavements. However, highway agencies and contractors have learned through the school of hard knocks that Superpave mixes don't always behave like conventional asphalt mixes.

The Superpave system uses the same basic materials as conventional hot-mix asphalt, but Superpave mixes often have coarser aggregate gradations and call for a greater percentage of angular aggregates. In addition, Superpave mixes for pavements with high traffic volumes and loads may use modified binders. These and other factors can affect the production of asphalt mixes and the construction of asphalt pavements. For example, coarse graded Superpave mixes often cool faster than conventional mixes and thus require closer attention to temperature during compaction.

Now, a new report, Superpave Construction Guidelines, published by the National Asphalt Pavement Association (NAPA) under a cooperative agreement with the Federal Highway Administration (FHWA), can make the learning process easier for highway agency and contractor staff.

Superpave Construction Guidelines points out the differences between Superpave mixes and conventional mixes and provides tips on how to prevent these differences from creating problems in mix production and pavement construction. The guidelines include:

• A brief description of the materials used in Superpave mixes.
• Information on how to store and mix materials at the asphalt plant.
• Tips on hauling the mix to the project site.
• Recommendations on placing and compacting the mix, including rolling methods and lift thickness.
• Suggested changes to contractors' quality control procedures.

According to NAPA, the guidelines are a supplement to—not a replacement for—the best practices in asphalt mix production and construction.

The guidelines were developed by a group of 21 representatives from State highway agencies, contractors, materials suppliers, equipment manufacturers, universities, and FHWA. "FHWA and NAPA hand-picked the participants, based on their experience with Superpave," says NAPA's Dale Decker. "In October, we held a 1-day meeting so they could flesh out ideas on where we're going with the Superpave system and how we could help people understand what they need to do to build Superpave pavements."

FHWA's Byron Lord, who led the meeting, says the guidelines will be "very valuable to the many people who this construction season will be using Superpave for the first time." Lord says the guidelines will be particularly useful to local governments and their contractors, who are increasingly building Superpave pavements.

Superpave Construction Guidelines (Special Report 180) can be purchased from NAPA. To order, contact NAPA (phone: 301-731-4748; toll free: 888-468-6499; fax: 301-731-4621; Web: www.hotmix.org).