A paving project in Maryland involved the removal and replacement of a failed concrete pavement at an intersection, at left shows a roller at work and, at right, a paving operation. The new pavement is a Superpave mixture. Photos: NAPA
In the end, it should become common practice to optimize our use of recycled asphalt materials in pavements. Improved processing and characterization of the materials will help achieve this goal. Mixture performance tests are needed to ensure that the materials will resist the distresses that can result in premature failure. Encouraging innovation and economical use of resources are keys to sustaining the U.S. infrastructure, and increasing the RAP content of HMA mixtures is an approach that can be used today.
The following new publications are especially helpful in the area of reclaimed asphalt in hot-mix asphalt. The first two mentioned can be used by agencies, consultants, and contractors interested in increasing the amount of recycling done in hot-mix asphalt pavements (HMA). They may be ordered through http://www.store.hotmix.org, or you can click on the name of the publication's below to go straight to the shopping section.
Designing HMA Mixtures with High RAP Content: A Practical Guide(order number QIP-124). Increasing the proportion of RAP in hot-mix asphalt is the focus of this new publication from the National Asphalt Pavement Association (NAPA) and the Federal Highway Administration. The guide discusses materials characterization, mix design, plant verification, and quality control/quality assurance procedures associated with the production of high-RAP-content HMA.
Recycling Hot-Mix Asphalt Pavements(order number IS-123). NAPA's companion document on RAP processing is another valuable resource. Recently updated by NAPA, this technical document has been significantly expanded and enhanced with new photographs and illustrations. It explains the how-tos of RAP: how to reclaim, size, store, and process the material. The various types of HMA plants are covered. Calculations for determining the value of using RAP are also provided.
Conventional wisdom from National Cooperative Highway Research Program (NCHRP) Report 452, Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Technicians Manual, provides procedures for the widely accepted standard practice for selecting virgin binder grades. It recommends:
- For RAP contents up to 15%, no change in virgin binder grade
- For PG binders from 15% to 25% RAP, a one temperature grade decrease
- For RAP contents of more than 25%, it recommends that blending charts be constructed to show the relationship between the amount of aged binder and the critical temperature at the low- and high-temperature ends of the grading spectrum.
— Dave Newcomb, PE, PhD, is vice president, research and technology, with the National Asphalt Pavement Association, Lanham, Md.