Asphalt producers increasingly are turning to reclaimed asphalt pavement (RAP) as an alternative to virgin materials for use in hot mix asphalt (HMA). This article discusses the benefits and challenges that exist in increasing RAP use. RAP is used as a substitute for a portion of the aggregate and asphalt binder in asphalt paving. Historically, state department of transportation (DOT) specifications have set limits on the maximum amount of RAP permitted in HMA and further restrict the material's use in surface layers, certain mixture types, and large or critical projects. The restrictions largely stem from the fact that RAP amounts greater than 15% can require changes in the binder performance grade and additional tests. DOTs also are concerned about the consistency, quality, durability, and performance of high-RAP pavements. The major concerns and obstacles that limit or preclude RAP use concern the blended virgin and RAP binder qualities, and stiffening of the mix with high-RAP quantities. Recent increases in asphalt costs and diminishing supplies of acceptable quality aggregate have prompted the asphalt paving industry to push for using higher percentages of RAP. The Federal Highway Administration (FHWA), along with its partners, is leading the effort to increase responsible RAP use and provide guidance on overcoming barriers to adoption, especially for mix design and performance. The FHWA is working with Purdue University to improve understanding of HMA mixtures through laboratory testing. To promote best practices for increased RAP use, FHWA also has initiated a task group to provide technical input. FHWA and industry partners have initiated several demonstration projects that are using high proportions of RAP. The objectives of the field projects are to document mixture design processes; assess procedures for production, construction, and performance testing; and highlight best practices. The FHWA has also launched its Mobile Asphalt Pavement Mixture Laboratory to provide the mixture design replication and performance testing of RAP and control mixes. The lab has participated in high-RAP field projects in three states. In each case, the State DOT approved higher RAP percentages than its specification previously allowed. FHWA is continuing to document the long-term performance of RAP projects to highlight successful practices and share lessons learned in using higher percentages of the material. (Author/publisher)
Samenvatting