Synthesis of Information Related to Highway Problems. Topic 43-03. Practices for Unbound Aggregate Pavement Layers

Granular aggregate base layers are very important in pavement construction and performance. Properly designed and constructed bases have the potential to improve pavement performance and longevity, while also addressing today's issues concerning the costs of other pavement materials and the need to save energy and reduce greenhouse gas emissions associated with the construction and reconstruction of pavements. A synthesis is needed concerning the full range of granular aggregate base and subbase issues for both flexible and rigid pavement systems. These issues include: (1) Materials characterization and quality of natural aggregate and common recycled materials that relate to performance; (2) Properties of unbound aggregate layers that are used in the design of pavements and how they are determined (need to first determine the method of design); (3) Influence of gradation on permeability; (4) Current practices and innovations in construction, compaction, and quality assurance (QA) procedures (such as compaction in thicker layers, use of intelligent compaction systems, and the use of tests other than just density in evaluating in-place modulus, stiffness and quality); (5) Performance of different base types in research pavement sections such as LTPP and MnRoad; (6) Potential to save energy and hauling costs by better utilizing local aggregates and recycled materials; (7) How states manage storage, transport and placement of materials to minimize degradation of material properties and performance: lessons learned; (8) How states address climatic, subgrade and drainage considerations in design of aggregate base layers. States have diverse specifications and construction practices for base layers; sharing this information among the states may lead to better design and construction practices. Research (e.g. from ICAR, the International Center for Aggregates Research) is now available that provides proposed improvements in the design models and in the compaction of granular aggregate lifts in thicker layers. Interest has also developed in the inverted base concept of a granular layer over a stiff layer at depth, with several tests sections having been built in Georgia, Louisiana, and Virginia.


  • English


  • Status: Active
  • Contract Numbers:

    Project 20-05, Topic

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program (NCHRP) Synthesis

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC    20001
  • Project Managers:

    Williams, Jon

  • Start Date: 20110701
  • Expected Completion Date: 0
  • Actual Completion Date: 0
  • Source Data: RiP Project 29020

Subject/Index Terms

Filing Info

  • Accession Number: 01463278
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 20-05, Topic
  • Files: TRB, RiP, USDOT
  • Created Date: Jan 3 2013 2:20PM