Transcript Chip Seal Design Chapter 2

Chip Seal Design
Chapter 2
North America
(ranked by prevalence)
• Empirical / Past Experience
• No Design Method
• Own Method
• McLeod (1960’s) - Asphalt Institute
• Kearby (1953) - Modified Kearby
• Hanson (1934 / 1935) - Obsolete
Source: NCHRP Synthesis 342, 2005
• Earliest formal method
• Developed for liquid asphalt (cutback)
• Based on Average Least Dimension (ALD)
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Binder rate based on average thickness, aggregate
embedment and voids
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Recommended uniformly graded aggregates
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Embedment based on aggregate hardness
(increase for hard, decrease for soft)
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Larger aggregates -less embedment (high ADT)
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Medium aggregates -more embedment (low ADT)
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Officially adopted by Asphalt Institute in 1969
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Based partially on Hanson (1953)
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Aggregate rate based on gradation, shape, specific
gravity, waste correction factors
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Binder rate based on aggregate gradation, pavement
condition, traffic volume, asphalt type
(absorption)
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For years marked end of chip seal design research
• Kearby and McLeod (1953)
• UK TRL Road Note 39 (1996)
• AustRoads (2001)
• New Zealand P/17 (Mod of Australia)
• South Africa TRH 3 (Hybrid of UK & Australia)
• Binders selected based on viscosity
• Polymer modified binders encouraged
• Binder grade based on traffic, season
• Aggregate size based on traffic, pavement hardness,
desired friction
• Binder rate based on aggregate, surface texture,
embedment by traffic
• Aggregate rate based on size, shape, relative density
• Performance-based method
• Binder and aggregate rates based on:
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Aggregate angularity
Traffic volume
Road geometry
Aggregate ALD
Aggregate absorption
Pavement absorption
Texture depth
• Aggregate one layer thick
• Aggregate:
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Angularity
Size ALD
Absorption
Embedment
Traffic volume
Road geometry
Pavement Absorption
Texture Depth
Application immediacy (2nd seal)
• Surface texture
• Traffic conditions (ADTs, speed,% commercial)
• Chip seal type
• Aggregate selection
• Binder application rate
• Surface Properties of Asphalt Pavement
• Not Quantitatively Used in N. America
• Overseas, (75% quantify)
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Sand Patch Method (ASTM E 965)
• Surface Hardness (expected embedment depth)
• Non-uniform Textures makes binder
application rate problematic
• Also known as the “Sand Circle Method”
• Method for determining pavement macro-texture
• Spread known volume of sand or glass beads
• Calculate volume of material that fills surface voids
to determine surface texture
• The greater the texture depth, the greater the
quantity of sand or glass beads that will be lost
in the surface voids
• Know local traffic conditions and volumes
• Heavy vehicles must be considered in
addition to total volume
• Calculate ADT and use adjustment for
heavy vehicles
• Intersections – starting, stopping, turning
• Weather conditions
• Ambient and road surface temperatures
• Aggregate moisture content
• Apply chip seals in the earliest part of
the construction season as possible!
CHIP SEAL DESIGN
Chip
Seal
DESIGN
PROGRAM
Developed by:
Minnesota
DOT
Metro FA-3Chip
chip seal 05
Metro FA-3
Seal 05
0.46
0.45
0.44
Badly pocked, porous, and oxidized
0.43
BINDER APPLICATION RATE (gal/yd2 )
0.42
0.41
0.40
0.39
0.38
0.37
0.36
Slightly pocked, porous, and oxidized
0.35
Slightly porous, and oxidized
0.34
0.33
0.32
0.31
0.30
0.29
0.28
Over 2,000
1,000 to 2,000
500 to 1,000
TRAFFIC VOLUME (ADT)
100 to 500
Under 100
Design for FA-3 (3/8 inch) chip
• Aggregate
– Without design: Avg. 30 lbs/yd²
– With design: Avg. 17 lbs/yd²
• Emulsified Asphalt
– Without design: Avg. Binder 0.30 gal/yd²
– With design: Avg. Binder 0.42 gal/yd²
• Chip Seal Designs and Proper Construction:
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Allows more miles
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Uses less money
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Achieves better results
Download at:
http://www.dot.state.mn.us/materials/researchsealcoat.html
Different seals require different designs
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Construction sequence
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Number of courses
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Variations in aggregate nominal size
Chopped Fiberglass
Strands
• Protects binder from traffic wear
• Establishes seal thickness
• Influences surface texture and impacts
ride and noise
• Potential for windshield damage
• Cost issues - Life Cycle Analysis
• Compatibility with Asphalt
• Maximum size: 3/8 inch
• Single size aggregate
• Cubical or pyramidal and
angular
• < 1% passing No. 200 sieve
̶ No Clay if possible
• Abrasion < 30%
Single Chip Seals
• ⅜ inch (10 mm)
Double Chip Seals
The bottom layer should be twice as big as the top layer!
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½ inch (12.5 mm) (1st App)
¼ inch (6.25 mm) (2nd App)
Design for each Aggregate Layer
• Combine binder requirements for both seals
̶ Normally recommend to apply 40 % of binder
total first and large stone.
̶ Sweep then apply remaining binder and smaller
stone.
• Other methods
Metric: V  1 
W
1000(G )
 W 
V

1

English:
 62.4G 


where:
V = voids as fraction of aggregate vol.
W = loose unit weight of aggregate
G = bulk specific gravity of aggregate
Achieve an even, single layer
The Goal:
Achieve 70+% Aggregate Final Embedment
Considerations
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Initial embedment will vary by
environmental region
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Avoid bleeding
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Avoid loose aggregate
Percentage of residual asphalt (RA) is critical
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Emulsion 65% RA average
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Cutbacks 85% RA average
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Hot applied AC 100%
Fills existing pavement voids
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What seals and protects the HMA
Holds aggregate in-place
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Binder selection is critical
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Single size aggregate
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Uniform aggregate distribution
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70+% final embedment of aggregate
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Apply to roads with low surface distress
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Characterize texture and surface hardness
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Racked-in seals for bleeding
Roadway needs to be structurally sound
Two options
• Option #1: Prime and Chip Seal
A. Prime with
— Cutback like MC 70 (0.30 to 0.40 gal/yd²)
— Penetrating Prime Emulsion (Formulate for
aggregate type)
B. Chip Seal - Use large chip
• Option #2: Otta Seal
A. Use emulsion like HFMS-2 (0.50 gal/yd²)
B. Use surfacing gravel
— 5/8” – 1” (50 lbs/yd²)
— Two applications
— 2 to 3 weeks apart
Questions?