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Dynamic Friction Testing

Dynamic Friction Testing

What is Dynamic Friction Testing?

A new portable device to measure the frictional properties of bound and unbound materials for asphalt pavements.  

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IV creates a virtual world in which to model projects accurately in 3D, then render videos and images as well as immersive visualizations to create interactive simulation products. IV models are built from existing and proposed data, including agency design files (i.e., a Microstation roadway surface), while a game engine powers real-time presentation. When optimized with adjacent infrastructure to produce performance simulation, touch screen kiosks and virtual reality (VR) applications can provide a virtual helicopter tour over a proposed project, for instance.

Project NEON, Nevada's largest and most expensive public works project ever, was the catalyst for the initiative. IV helped convey complex planning and design scenarios to the public while helping project development personnel identify and resolve design and construction challenges, such as site impacts and right of way, geometric, and line-of-sight issues. IV products allowed the traveling public, homeowners, and businesses to see the potential impact of the project on their interests, while addressing their concerns and those of regulatory agencies about safety and environmental impact. As a result, IV vastly enhanced interagency coordination, regulatory review, and approval.

IV supplies much more freedom of camera movement than typical state-of-the-practice project visualizations, which provide views from specific angles. That enables non-outreach products like technical clarity visuals, graphics for related legal cases, landscaping details, and more. While conventional visualizations render various images for delivery via video files from which models are constructed for a given purpose, rapid, real time rendering through IV’s game engine technology eliminates the need to remodel, bringing its overall cost in line with traditional 3D visualization.

Dynamic Friction Testing

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

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