Minnesota Department of Transportation

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Road Research

NRRA Geotechnical Team

Large-Aggregate Granular Materials (3-6+ inch) Used as Bases or Sub-bases

Status: Complete


Several states currently allow the use of large-aggregate (3-6”, and up to 12”) granular material layers below unbound base course materials in a pavement structure. This larger material can be part of the unbound base course layer and located under a thin layer of standard-sized base (Illinois and Missouri DOT), or used as a sub-base/subgrade enhancer under a typical-thickness dense-graded base course (Wisconsin DOT). There are differing historical experiences with this material, and differing credit given to this material in the structural pavement design process. The project involves sharing existing uses/applications, research information, and structural pavement design philosophies concerning the use of these larger granular materials below standard unbound dense-graded base course granular materials that are located below a final pavement surface. In addition, the following are expected to be provided: design guidance for the use of this material, recommendations on how to incorporate this material into pavement designs, and typical construction Special Provisions for this material.

Project tasks/status:

Original Need Statement: Larger Subbase Materials (doc)

Task 1

Perform a literature search of existing information in this area. This includes collecting and summarizing Midwest States’ (and other states/national/international) information on use, past/current research studies, potential degradation and/or deterioration, contamination, drainage properties, pavement design material properties and methods for use of this material, future research needs, and other relevant issues/topics as they apply to base/sub-base usage of this material.

Task 2

Develop recommended guidelines on the use of this material, methods to incorporate it into the ME pavement design process, and special issues related to construction placement and quality control inspection.

Tech Transfer “State of Practice”

Task 3

Develop recommended contract Special provisions for this material. This includes material testing procedures and values for design and construction.

Task 4

Develop and conduct a webinar to present all synthesis findings and recommendations.

Task 5

Summarize all work/findings into a final report.

Project team

Project Technical Advisory Panel (TAP) – Email the TAP

  • Tim Andersen, MN DOT
  • Terry Beaudry, MN DOT
  • James Bittmann, MN DOT
  • Ed Johnson, MN DOT
  • Dan Wegman, Braun Intertec