Print this page Open-Graded Friction Courses (OGFC)
Gregory J. Taylor, P.E.
Course Outline
This two-hour course presents an introduction to the subject of open-graded friction courses (OGFC). The contents of this document are intended to serve as guidance and not as an absolute standard or rule.
The primary objectives of this course are to:
- Provide technical information on open-graded friction courses (OGFC)
- Present their advantages and limitations
- Recommend factors to be considered when choosing an OGFC
Some of the topics for consideration include: the advantages of using open-graded courses; safety benefits; noise reducing features; economic issues; service life; limitations or past problems; current OGFC mix design and usage; real world examples; and European designs. The course research data will be used to provide material for generating any conclusions and recommendations for open-graded friction courses (OFGC).
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
By taking this course, the participant will:
- Become familiar with the benefits of OGFC;
- Learn the safety aspects;
- Recognize noise reduction features;
- Understand higher costs and longer life cycles of OGFC;
- Know OGFC limitations;
- Be familiar with past problems;
- Learn current uses of OGFC; and
- Become acquainted with State and European designs.
Intended Audience
This course is intended for civil engineers and contractors.
Benefit for Attendee
Attendees of this course will be given an in-depth look at design principles to be considered for open-graded friction courses.
Course Introduction
An “open-graded friction course” is defined as a thin, permeable layer of asphalt that integrates a skeleton of uniform aggregate size with a minimum of fines. These mixes contain a small percentage of fine aggregate which produces a large number of air voids. The pavement consists primarily of single size coarse aggregate with a high asphalt content. The aggregate skeleton is responsible for the pavement's ability to resist trucks and carry the loads without undergoing permanent deformation. The load is carried by the stone while the asphalt keeps everything in place.
Course Content
The course content is contained in the following PDF file:
Open-Graded Friction Courses (OGFC)
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Course Summary
For over 60 years, open-graded friction courses (OGFC) have been used to improve the frictional resistance of asphalt surfaces throughout the United States. OGFC allows surface water to drain through and away from the roadway. Benefits include: reduced hydroplaning; improved wet pavement friction; less vehicle splash and spray; better surface reflectivity; and quieter roadways.
During the early 1970’s, the Federal Highway Administration developed an OGFC mix design procedure which was used by several state DOTs. Although many states reported good initial experiences, others stopped using these open-graded courses due to unacceptable performance. Recent OGFC modifications have produced significant improvements in mix performance. Many states now use modified open-graded mixes as the final surface on all interstates and state routes with daily traffic volumes over 25,000 vehicles.
Coarse gradation for OGFC mixes provides a better performing roadway pavement. Most open-graded friction courses are 0.75-inch thick with a maximum thickness of 2 inches. Gradations near 15% passing the No. 4 (0.187-inch) sieve performed much better than finer gradations. Polymer and/or fiber modifiers were also shown to enhance the performance of open-graded mixes.
A thin film of asphalt and compaction keep the OGFC mix together. The final density of these mixes reflects its strength and durability. By using a grading of mostly 0.375-inch stone, open-grading mixes build up a thick film of asphalt on the stone without allowing the mixture to drain or flush - increasing the service life of the pavement. The asphalt film viscosity is usually 4 to 6 times that of dense-graded mixes.
Related Links and References
The following reference books were used by the author in the preparation of this course:
Hawaii Asphalt Paving Industry - www.hawaiiasphalt.com
National Center for Asphalt Technology - www.ncat.us
Center for Transportation Research - ctr.utexas.edu
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
