State and local transportation agencies frequently use open-graded aggregates for wall, roadway, and bridge construction. The primary advantages of using this type of material in wall and abutment applications are ease of constructability, lighter in-place density than well-graded materials, very low fine content, free-draining characteristics, and simpler quality assurance testing using a method specification for field density.

The American Association of State Highway and Transportation Officials (AASHTO) classifies open-graded aggregates according to the M43 gradation based on standard sizes for processed aggregates. Despite common use of these aggregates, their strength characteristics have not been systematically measured or used in design. Instead, engineers frequently use a default friction angle of 34^o, leading to potential conservatism in retaining wall and foundation design. The primary purpose of this course  is to present research results on the strength properties of standard open aggregates tested in a large-scale direct shear (LSDS) device to improve the state of practice for the design of structures using these materials. This course material is based on FHWA Publication Number FHWA-HRT-13-068: Friction Angles of Open Graded Aggregates from Large Scale Direct Shear Testing.

At the conclusion of this course, the learner will have a better understanding of the Influence of Friction Angles of Open Graded Aggregates on Performance of the Structure as well as an understanding of the following topics:

• Various friction angles of open graded aggregates
• Different testing procedures for the performance of aggregates
• Comparative analysis of testing results
• Performance monitoring based on friction angle of aggregates