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Characterization of Open-Graded Aggregates

Project Information

Project ID: 
Project Status: 
Start Date: 
Tuesday, March 1, 2011
End Date: 
Monday, August 19, 2013
FHWA Program: 
FHWA Subprogram: 
TRT Terms: 
Transportation; Test Procedures; Design; Materials; Infrastructure; Research; Aggregates
FHWA Discipline: 
Design, Geotechnical, Pavement and Materials
Subject Area: 
Bridges and other structures, Design, Geotechnology, Highways, Materials, Pavements, Research, Transportation (General)

Contact Information

First Name: 
Last Name: 
(202) 493-3075
Email Address: 
Bridge Engineering Team
Office of Infrastructure Research and Development
Office Code: 

Project Details

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.