A pavement surface that does not provide enough friction between the vehicle tire and roadway surface is a safety hazard. Pavement friction is critical to mitigating roadway crashes influenced by horizontal curves, wet weather, roadway departure, and other causes. With public safety as the number one priority, highway agencies have a mission of managing the surface frictional characteristics of pavements through their life cycles. Effectively testing the frictional characteristics of materials to be used in pavement surfaces during mix design is critical to that mission.
Highway agencies conduct testing of aggregates used in asphalt and concrete mixtures through a series of laboratory tests to measure properties, such as mineralogy, hardness, soundness, angularity, and shape etc., that are of significance to friction. Testing of aggregates provides a basis for specifications to guide the selection of the appropriate type of aggregate for surface mixtures. In addition, highway agencies have traditionally used the British Pendulum Tester to test the friction characteristics of aggregates in the laboratory. The British Pendulum Tester requires manual adjustment of the pendulum height to obtain the correct span of testing surface often producing inconsistent results. Testing via the British Pendulum Tester also limits agencies to test only one source and size of aggregate and at one speed. Similarly, field devices, such as locked wheel devices, have limited applications in material selection.
The Dynamic Friction Tester (DFT) and a Three Wheel Polishing Device provide a new accelerated method for polishing and friction testing bound and unbound materials for asphalt pavements. With the DFT process, a sample of unbound aggregate is polished by the Three Wheel Polishing Device which simulates the polishing action of vehicular traffic on the coarse aggregate used on asphalt pavements. After polishing the sample, the terminal friction value of the aggregate sample is evaluated by the Dynamic Friction Tester and the result is used to rate or classify different types of aggregates for their friction characteristics and resistance to polishing under traffic.
This new practice uses a more advanced testing device, the DFT, to provide a more consistent and accurate measurement. The DFT does not require manual adjustment of the device and can evaluate friction characteristics over a range of speeds and with mixed designs. Overall, the dynamic friction testing process shortens the evaluation time to within a week, improves roadway safety for the traveling public, and predicts long-term performance reducing future maintenance costs.
Resources
Virgin Aggregate Sample preparation / Testing with DFT/CTM (video)
Webinar - Dynamic Friction Testing with the Three-Wheel Polishing Device (video)
Lead States Team Documents
References/Supporting Information
Contacts
Intikhab Haider, Ph.D., Chair
Division Chief, Soils and Aggregate Technology Division
Maryland State Highway Administration
Phone: 443-572-5162
Email:
Ihaider2@mdot.maryland.gov
Thomas Festa, P.G.
Professional Geologist 2, Materials Bureau
New York State Department of Transportation
Phone: 518-457-5957
Email:
Thomas.Festa@dot.ny.gov
Patricia I. Baer
Unit Manager
Pennsylvania Department of Transportation
Phone: 717-787-2489
Email:
patrbaer@pa.gov
Amanuel Welderufael
Aggregate Lab Team Leader, Soils and Aggregate Technology Division
Maryland State Highway Administration
Phone: 443-572-5275
Email:
awelderufael@mdot.maryland.gov
Darren Swift
Assistant Division Chief Lab Operations, Soils and Aggregate Technology Division
Maryland State Highway Administration
Phone: 443-572-5276
Email:
DSwift@mdot.maryland.gov
