What Is and Is Not High Friction Surfacing

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Elinor Lydia Cain
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1 What Is and Is Not High Friction Surfacing ATSSA 2015 Tampa, Florida Frank Julian FHWA Resource Center Safety & Design Team

2 HFST as a Safety Treatment HFST is not a pavement treatment that happens to have safety benefits! HFST is a safety treatment that happens to be a pavement! To be applicable, HFST must still provide the functions of a pavement for durability, but it must greatly reduce crashes for a significant duration to distinguish its unique value.

3 Pennsylvania Success Story

4 The Marquette Interchange

6 What is a High Friction Surface Treatment? High Friction Surface Treatments (HFST) are pavement surfacing overlay systems with: exceptional skid-resistant properties that are not typically acquired by conventional materials retains the higher friction property for a much longer time. Commercially available resin-based products and processes Generally applied in short sections to improve spot locations where friction demand is critical.

7 HFST Binder Materials Polymer system (proprietary blends) Epoxy-resin Polyester-resin Polyurethane-resin Acrylic-resin Thin layer that allows for 50% aggregate embedment depth

8 HFST Aggregates Recommended aggregate is calcined bauxite which provides the highest resistance to polishing. Typically referred to as a 3 mm aggregate Calcined Bauxite

11 Some Common Methods to Restore or Add Friction Chip Seal (pavement preservation) Micro Milling Shot Blasting Grooving (concrete) Resurface with a friction course Nova Chip HFST (critical spot Improvement) Any of these methods may be an appropriate solution depending on the definition of the problem

12 Why High Friction Surface Treatment? In-place friction characteristics must meet a minimum requirement of 65 FN40R when tested in accordance to AASHTO T 242 upon completion of the installation

13 Texas Transportation Institute Friction Test Results The 3 run average, SN40 wet value on the concrete pavement was 52 The 3 run average, SN40 wet value on the HFST was 85 The stopping difference was 25% - 30%, regardless of the speed.

14 Comparison Skid Testing Conducted at TTI

15 How long will HFST last? National Center for Asphalt Technologies, Auburn University

16 The National Center for Asphalt Technologies, Auburn University. NCAT TESTING OF HFST AGGREGATES

17 NCAT Aggregate Durability Study 15 Taconite Emery Steel Slag Silica Basalt Flint 100 Bauxite Granite

18 NCAT Aggregate Durability Study Laboratory Testing Three Wheel Polishing Device Friction and Texture tested at 70k and 140k cycles 2 replicates for each aggregate type NCAT

19 Strategies for Reducing Crashes (Where Can HFST Benefit Safety?) 1. Horizontal curves 2. Approach to intersections 3. Grades When the pavement has: Marginal friction effected from weather Low friction Friction values not compatible with approach speeds and geometrics (friction demand)

20 AASHTO Horizontal Curve Design Model e + f = V 2 /15 R R = V 2 /15(e + f) e = superelevation f = side friction factor V = design speed (mph) R = radius of curve (ft)

21 Friction Demand, Speed, and Friction Availability Source NCHRP 108

22 Side Friction Demand, g Side Friction Demand for Different Radii Speed, mph Source TRR 2075

23 Side Friction Demand, g Side Friction Demand for Different Radii Speed, mph Source TRR 2075

24 Combined Braking and Cornering

25 2011 AASHTO Greenbook Where practical, the maximum side friction factors used in design should be conservative for dry pavements and should provide an ample margin of safety against skidding on pavements that are wet as well as ice or snow covered. The need to provide skid-resistant pavement surfacing for these conditions cannot be overemphasized because superimposed on the frictional demands resulting from roadway geometry are those that result from driving maneuvers such as braking, sudden lane changes, and minor changes in direction within a lane. In these shortterm maneuvers, high friction demand can exist but the discomfort threshold may not be perceived in time for the driver to take corrective action.

Truck Operations on Curves Trucks with high centers of gravity may overturn before losing control due to skidding Trucks on downgrade curves generate

26 Truck Operations on Curves Trucks with high centers of gravity may overturn before losing control due to skidding Trucks on downgrade curves generate greater lateral friction (Superelevation Is Not As Effective) Margin of safety for f is lower for trucks Friction demand varies for curves Reference NCHRP 505

27 Summary of Friction Demand Issues Friction Demand is what accelerates aggregate polishing Increasing superelevation can help reduce FD but can have other negative effects Transition cross slope may run past PC and as much as 1/3 is common practice Geometric design that excessively relies on pavement friction leads to excessive pavement polishing and may need HFST to provide a durable friction

28 Common Questions What is Calcined Bauxite and where does it come from and is it in short supply?

29 Numbers for 2010's total proven bauxite reserves x 1,000 tonne Country Mine production (est.) Reserves Reserve base Guinea 17,400 18,000 7,400,000 8,600,000 Australia 68,400 67,000 6,200,000 7,900,000 Vietnam ,100,000 5,400,000 Jamaica 8,540 10,200 2,000,000 2,500,000 Brazil 28,100 31,000 3,600,000 2,500,000 Guyana 1,760 2, , ,000 India 18,000 20, ,000 1,400,000 China 44,000 46, ,000 2,300,000 Greece 2,100 2, , ,000 Iran 500 Suriname 4,000 5, , ,000 Sierra Leone 1,090 1, ,000? Kazakhstan 5,310 5, , ,000 Venezuela 2,500 4, , ,000 Russia 5,480 5, , ,000 United States 30 NA 20,000 40,000

30 Hamilton County Ohio Thank you!

2018 NACE Conference Wisconsin Dells, WI. Joseph Cheung P.E. FHWA Office of Safety

2018 NACE Conference Wisconsin Dells, WI Joseph Cheung P.E. FHWA Office of Safety Skid related crashes are determined by many factors: Tire issues Weather Conditions Friction Demand Road Geometry Vehicle