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Research and Development (R&D) Project Sites

Project Information
Project ID:   FHWA-PROJ-11-0014
Project Name:   Characterization of Open-Graded Aggregates
Project Status:   Completed
Start Date:  March 1, 2011
End Date:  August 19, 2013
Contact Information
Last Name:  Nicks
First Name:  Jennifer E
Telephone:  202-493-3075
E-mail:  jennifer.nicks@dot.gov
Office:   Office of Infrastructure Research and Development
Team:   Bridge and Foundation Engineering Team [HRDI-40]
Program:   Turner-Fairbank Highway Research Center
Laboratory:   Geotechnical Laboratory
Project detail
Project Description:   This project characterized crushed, manufactured open-graded aggregates, designated based on the American Association of State Highway and Transportation Officials (AASHTO) Designation: M43-05 (and the American Society for Testing and Materials (ASTM) Designation: D 448-03a). State departments of transportation (DOT) and counties use this designation (or an equivalent) to specify the aggregates used in the construction and maintenance of highways and bridges (e.g. reinforced soil, engineered fills, etc.). To obtain the strength properties of these materials accurately, a large-scale test device, such as a large shear box or a large diameter triaxial cell, must be used; however, this type of testing had not been systematically performed for the AASHTO open-graded aggregates. Since many transportation agencies do not have access to these large-scale devices, a default value for the friction angle, which often leads to a conservative design. This project involved a series of large-scale (12") direct shear tests to test the strength properties and provide engineers with more accurate friction angles for these commonly used materials. In the absence of testing, a new default friction angle is also recommended based on the results. Since the friction angle is based on other factors besides gradation and size, the influence of saturation, source, and angularity was also investigated. Continued research in this area (see FHWA-PROJ-12-0039) includes testing with a large diameter (6") triaxial device and investigating the influence of in-place density. The results of this applied research have immediate benefits for transportation agencies and designers.
The objectives of this research are:
(1) Provide engineers with the strength properties of the common American Association of State Highway and Transportation Officials (AASHTO) open-graded aggregates used in construction.
(2) Describe the influence of saturation, angularity, and source on the strength.
More Information URL(s):  
  1. http://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/13068/index.cfm
Product Type:   Techbrief
Test Methodology:   Laboratory Testing (e.g. Large-Scale Direct Shear Testing)
Expected Benefits:   More cost-effective foundation and retaining wall design by using higher friction angles for projects with AASHTO open-graded aggregates.
Deliverables: Name: TechBrief: Friction Angles of Open-Graded Aggregates From Large-Scale Direct Shear Testing
Product Type(s): Techbrief
Description: The deliverable is a TechBrief outlining the strength properties of the American Association of State Highway and Transportation Officials (AASHTO) aggregates. Recommendations are also provided on a new default friction angle for design, in the absence of testing.
Publication URL(s):
FHWA Topics:   Research/Technologies--Turner-Fairbank Highway Research Center (TFHRC)
TRT Terms:   Transportation
Test Procedures
FHWA Disciplines:   Design
Pavement and Materials
Subject Areas:   Bridges and other structures
Transportation (General)


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