What Is and Is Not HFS
What Is and Is Not High Friction Surfacing
ATSSA 2015 Tampa, Florida Frank Julian FHWA Resource Center Safety & Design Team
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.
Pennsylvania Success Story
The Marquette Interchange
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.
HFST Binder Materials Polymer system (proprietary blends) • Epoxy-resin • Polyester-resin • Polyurethane-resin • Acrylic-resin • Thin layer that allows for 50% aggregate embedment depth
HFST Aggregates Recommended aggregate is calcined bauxite which provides the highest resistance to polishing. Typically referred to as a 3 mm aggregate
Calcined Bauxite
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
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
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.
Comparison Skid Testing Conducted at TTI
How long will HFST last? National Center for Asphalt Technologies, Auburn University
The National Center for Asphalt Technologies, Auburn University.
NCAT TESTING OF HFST AGGREGATES
NCAT Aggregate Durability Study
15’
Taconite Emery Steel Slag Silica Basalt Flint
100’ Bauxite Granite
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
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)
AASHTO Horizontal Curve Design Model
e + f = V2/15 R 𝑹 = 𝑽2/15(e + f) e = superelevation f = side friction factor
V = design speed (mph) R = radius of curve (ft)
Friction Demand, Speed, and Friction Availability
Source NCHRP 108
Side Friction Demand, g
Side Friction Demand for Different Radii
Speed, mph
Source TRR 2075
Side Friction Demand, g
Side Friction Demand for Different Radii
Speed, mph
Source TRR 2075
Combined Braking and Cornering
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 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
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
Common Questions What is Calcined Bauxite and where does it come from and is it in short supply?
Numbers for 2010's total proven bauxite reserves x 1,000 tonne Country Guinea Australia Vietnam Jamaica Brazil Guyana India China Greece Iran Suriname Sierra Leone Kazakhstan Venezuela Russia United States
Mine production 2010
2011 (est.)
17,400 68,400 80 8,540 28,100 1,760 18,000 44,000 2,100 — 4,000 1,090 5,310 2,500 5,480 30
18,000 67,000 80 10,200 31,000 2,000 20,000 46,000 2,100 500 5,000 1,700 5,400 4,500 5,800 NA
Reserves
Reserve base
7,400,000 6,200,000 2,100,000 2,000,000 3,600,000 850,000 900,000 830,000 600,000 — 580,000 180,000 160,000 320,000 200,000 20,000
8,600,000 7,900,000 5,400,000 2,500,000 2,500,000 900,000 1,400,000 2,300,000 650,000 — 600,000 ? 450,000 350,000 250,000 40,000
Hamilton County Ohio
Thank you! [email protected]
ATSSA 2015 Tampa, Florida Frank Julian FHWA Resource Center Safety & Design Team
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.
Pennsylvania Success Story
The Marquette Interchange
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.
HFST Binder Materials Polymer system (proprietary blends) • Epoxy-resin • Polyester-resin • Polyurethane-resin • Acrylic-resin • Thin layer that allows for 50% aggregate embedment depth
HFST Aggregates Recommended aggregate is calcined bauxite which provides the highest resistance to polishing. Typically referred to as a 3 mm aggregate
Calcined Bauxite
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
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
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.
Comparison Skid Testing Conducted at TTI
How long will HFST last? National Center for Asphalt Technologies, Auburn University
The National Center for Asphalt Technologies, Auburn University.
NCAT TESTING OF HFST AGGREGATES
NCAT Aggregate Durability Study
15’
Taconite Emery Steel Slag Silica Basalt Flint
100’ Bauxite Granite
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
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)
AASHTO Horizontal Curve Design Model
e + f = V2/15 R 𝑹 = 𝑽2/15(e + f) e = superelevation f = side friction factor
V = design speed (mph) R = radius of curve (ft)
Friction Demand, Speed, and Friction Availability
Source NCHRP 108
Side Friction Demand, g
Side Friction Demand for Different Radii
Speed, mph
Source TRR 2075
Side Friction Demand, g
Side Friction Demand for Different Radii
Speed, mph
Source TRR 2075
Combined Braking and Cornering
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 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
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
Common Questions What is Calcined Bauxite and where does it come from and is it in short supply?
Numbers for 2010's total proven bauxite reserves x 1,000 tonne Country Guinea Australia Vietnam Jamaica Brazil Guyana India China Greece Iran Suriname Sierra Leone Kazakhstan Venezuela Russia United States
Mine production 2010
2011 (est.)
17,400 68,400 80 8,540 28,100 1,760 18,000 44,000 2,100 — 4,000 1,090 5,310 2,500 5,480 30
18,000 67,000 80 10,200 31,000 2,000 20,000 46,000 2,100 500 5,000 1,700 5,400 4,500 5,800 NA
Reserves
Reserve base
7,400,000 6,200,000 2,100,000 2,000,000 3,600,000 850,000 900,000 830,000 600,000 — 580,000 180,000 160,000 320,000 200,000 20,000
8,600,000 7,900,000 5,400,000 2,500,000 2,500,000 900,000 1,400,000 2,300,000 650,000 — 600,000 ? 450,000 350,000 250,000 40,000
Hamilton County Ohio
Thank you! [email protected]
