thin asphalt overlays for pavement preservation overlays for pavement... · thin asphalt overlays...
TRANSCRIPT
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THIN ASPHALT OVERLAYS FOR
PAVEMENT PRESERVATION
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Why Thin Asphalt Overlays?
➢ Shift from new construction to renewal and preservation
➢ Functional improvements for safety and smoothness are needed more than structural improvements — Perpetual Pavements
➢ Material improvements
Binders — Superpave binder spec and polymers
SMA, OGFC, and Dense-Graded
Superpave volumetric mix design
Warm Mix Asphalt (WMA)
Reclaimed Asphalt Pavement (RAP)
Reclaimed Asphalt Shingles (RAS)
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Thin Asphalt Overlays are the Most
Popular Treatment for Pavements
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Benefits of Thin Asphalt Overlays
➢ Long life and low life-
cycle cost!
➢Safety / User
• Minimize traffic delays
• Staged construction
• Smooth surface
• Restore skid resistance
• No loose stones &
minimizes dust
• Lower noise
➢Structural
• Maintain grade & slope
• Withstands heavy traffic
• Easy to maintain
➢Sustainable
• Recycled materials
• Seals surface & no
binder run-off
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Topics
• Project Selection
• Materials Selection and Mix Design
• Construction and Quality Control
• Performance
• Conclusions
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PROJECT SELECTION
Avoid Projects Needing Structural Rehabilitation!!
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Basic Evaluation
➢Visual Survey
➢Structural Assessment
▪No structural improvement required
➢Drainage Evaluation
▪What changes are needed
➢Functional Evaluation
▪Ride quality
▪Skid resistance
➢Discussion with Maintenance Personnel
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Visual Survey
➢ Part of a good Pavement
Management System
➢ Get current project-
specific data
➢ Need to know:
▪ Type of distress
▪Extent
▪Severity
➢ Visit the site and validate
the data
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Types of Distress
➢ Raveling
➢ Longitudinal Cracking (not in wheelpath)
➢ Longitudinal Cracking (in wheelpath)
➢ Transverse Cracking
➢ Alligator Cracking
➢ Rutting
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Raveling
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Longitudinal Cracking
(not in wheelpath)
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Longitudinal Cracking
(wheelpath)
Temporary Fix for Minor Distress
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Transverse Cracking
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Alligator (Fatigue) Cracking
Temporary Fix for Minor Distress
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Rutting or Shoving
Surface Failure –
Milling RequiredSevere Structural Failure
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Ride Quality and Skid Resistance
Rough surfaces
should be milled Skid problems can be
milled, but not required
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Noise Can Be Reduced
92
94
96
98
100
9.5 mm(Rt. 50)
12.5 mm(I-270)
12.5 mm(I-495)
19 mm(I-83)
No
ise
Le
ve
l, d
B(A
)
NCAT Noise Trailer
Smaller Aggregate = Less Noise
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Drainage Evaluation
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How do you
select the mix
type for a thin
overlay?
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01020304050607080
DFG
4.7
5
DFG
9.5
DFG
12.5
DFG
19
SM
A 9
.5
SM
A 1
2.5
SM
A 1
9.0
OGFC
9.5
OGFC
12.
5
DCG 9
.5
DCG 1
2.5
DCG 1
9.O
Mix Type
Min
Lif
t T
hic
k R
an
ge
, m
mRecommended Mix Types
Surface CoursesLow Traffic
Medium Traffic
High Traffic
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If a Thin Overlay is the
answer, you need to decide:
➢Surface Preparation
▪ Distresses
▪ Roughness
▪ Considerations for Curb
Reveal and Drainage
➢Materials
▪ Traffic
▪ Availability
▪ Climate
➢Thickness
▪ NMAS
▪ Geometrics
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Surface Preparation
Mill
Fill Cracks
with Mix
Clean and
Tack
Raveling
Long. Crack –
not in w.p.
Long. Crack – w.p.
Transverse Crack
Alligator Crack
Rutting
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Materials & Mix Design
➢ Materials Selection
➢ Mix Design for Dense-Graded Mixes
➢ Other Mix Types
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Materials Selection — Aggregate
➢ Thin overlays need small NMAS
▪ Thin overlays < 1.5 inches thick
▪ Aggregate size between 4.75 and 12.5 mm NMAS
▪ Ratio of lift thickness to NMAS range 3:1 to 5:1
➢ Quality
▪ LA Abrasion: 35–48 maximum
▪ Sodium Sulfate: 10–16 maximum
▪ CA Fractured Faces (does not apply to 4.75 mm)
• 2 or More: 80–90
• 1: 10–100
▪ Sand Equivalent: 28–60
▪ FA Angularity (Uncompacted Voids): 40–45
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Example Gradations
0
10
20
30
40
50
60
70
80
90
100
0.075 0.3 1 .18 4.75 9.5 12.5 19
North Carolina
Utah
Maryland
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Materials Selection — Binder
➢Most specifications use PG system to select
binder grade based on climate and traffic
▪ Minnesota — Unmodified binder
▪ Ohio — Polymer modified PG 64−22 or PG 76−22
▪ New York — PMA for 6.3 mm & special situations for
other mixes
▪ New Jersey — PG 76−22 for high performance mix
▪ North Carolina — depends upon traffic level
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Materials Selection — RAP
➢ Small NMAS mixes should
utilized fine RAP
➢ RAP or RAS will help
▪ Stabilize cost by reducing
added asphalt and added
aggregate
▪ Prevent rutting
▪ Prevent scuffing
➢ Use maximum allowable while
maintaining gradation and
volumetrics
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Mix Design
➢ Laboratory Compaction
▪ Low Volume — 50 gyrations in MD and GA
▪ Medium Volume — 60 to 75 in MD, NY, AL
▪ High Volume — 60 (AL) to 125 (UT)
▪ Needs to be enough compaction for interlock without
fracturing aggregate
➢Volumetrics
▪ Void Requirements — Mixes are relatively
impermeable
▪ VMA — Should increase as NMAS decreases
▪ Asphalt Content — Should depend on voids and VMA
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Mix Design RequirementsNMAS 12.5 mm 9.5 mm 6.3 mm 4.75 mm
State AL NC NV UT NY MD GA OH
Comp.
Level60 50–125 75 50/65 50 50/75
Design
Voids3–6 3.5 4.0 4.0 4.0–7.0 3.5
% VMA 15.5 min 12–22 16 min 15 min
% VFA 70-80 70-78 50-80
% AC 5.5 min 4.6–5.6 6.0 min 5.0–8.0 6.0–7.5 6.4 min
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Permeability
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CONSTRUCTION &
QUALITY CONTROL
❖ Construction
❖Production
❖Paving
❖ Quality Control
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Construction — Production
➢Aggregate
▪ Proper stockpiles
• Slope and Pave
• Cover, if needed
▪ Moisture content
➢Plant operations
▪ Slower because
• More time to coat
• Higher moisture content
• Thicker aggregate veil
▪ Aggregate moisture management
▪ WMA can help coat aggregates — lubricity
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Construction — Production
➢RAP – Process for size and consistency
▪ Max size < NMAS
➢Storage and Loading
▪ Follow normal best practices
➢Warm Mix
▪ Increase haul distance
▪ Pave at cooler temperatures
▪ Achieve density at lower temperatures
▪ Extend paving season
▪ Pave over crack sealer
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Construction —
Paving Surface Preparation
➢Milling▪ Remove defects
▪ Roughen surface
▪ Improve smoothness
▪ Provide RAP
▪ May eliminate need for tack
▪ Size machinery properly
➢ Tack
▪ Emulsion or hot asphalt
▪ Polymer emulsion or unmodified
▪ Rate: 0.10 to 0.15 gal/sy (undiluted emulsion)
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Construction —Paving Placement and Compaction
➢Paving
▪ Best to move continuously
▪ MTV or windrow can help
▪ Cooling can be an issue
▪ 1” cools 2× faster than 1.5”
▪ Warm mix
➢Compaction
▪ Seal voids & increase stability
▪ Low permeability
▪ No vibratory on < 1”
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Quality Control — Plant
➢Aggregate
▪Gradation
▪Moisture Content
➢Mix Volumetrics
▪Air Voids
▪VMA
▪Asphalt Content
▪Gradation
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Quality Control — Field
➢Field Density
▪ Thin-lift NDT gauges OK for > 1” mat
▪ Cores may not be representative
▪ Permeability not as big an issue
➢Ride Quality
▪ Depends on
• Condition of existing pavement
• Surface preparation
• Overlay thickness
▪ Specification should be based on existing condition
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Performance
➢ Immediate Benefits
➢ Pavement Life
➢ Economics
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Immediate Benefits
➢Pavement Condition (Labi et al., 2005)
▪ 18 to 36% decrease in roughness
▪ 5 to 55% decrease in rut depth
▪ 1 to 10% improvement in condition rating
➢Noise
▪ Corley-Lay and Mastin (2007): 6.7 dB reduction on
overlaid PCC
▪ FHWA (2005): 5 dB reduction on overlaid PCC in
Phoenix
➢ 3 dB reduction = ½ traffic volume
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Pavement Life
Location Traffic Underlying
Pavement
Performance,
yrs.
Ohio
High/Low Asphalt 16
Low Composite 11
High Composite 7
North Carolina ― Concrete 6–10
Ontario High Asphalt 8
Illinois Low Asphalt 7–10
New York ― Asphalt 5–8
Indiana Low Asphalt 9–11
AustriaHigh/Low Asphalt >10
High Concrete >8
Georgia Low Asphalt 10
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Location Traffic Underlying
Pavement
Performance,
yrs.
Ohio
High/Low Asphalt 16
Low Composite 11
High Composite 7
North Carolina ― Concrete 6–10
Ontario High Asphalt 8
Illinois Low Asphalt 7–10
New York ― Asphalt 5–8
Indiana Low Asphalt 9–11
AustriaHigh/Low Asphalt >10
High Concrete >8
Georgia Low Asphalt 10
Pavement Life
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Location Traffic Underlying
Pavement
Performance,
yrs.
Ohio
High/Low Asphalt 16
Low Composite 11
High Composite 7
North Carolina ― Concrete 6–10
Ontario High Asphalt 8
Illinois Low Asphalt 7–10
New York ― Asphalt 5–8
Indiana Low Asphalt 9–11
AustriaHigh/Low Asphalt >10
High Concrete >8
Georgia Low Asphalt 10
Pavement Life
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Economics
➢Chou et al. (2008):
▪ Thin overlays on asphalt — almost always most cost
effective
▪ Thin overlays on PCC — not as cost effective, but
greater deterioration prior to overlay
➢ 2008 NAPA Survey of State Asphalt Associations
Treatment Expected
Life, yrs
Range Cost, $/SY Range Annual
Cost,
$/lane-mile
Chip Seal 4.08 2.5–5 2.06 0.50–4.25 3,554.51
Slurry Seal 3.25 2–4 1.78 1.00–2.20 3,855.75
Micro-surfacing 4.67 4–6 3.31 2.30–6.75 4,989.81
Thin Surfacing 10.69 7–14 4.52 2.40–6.75 2,976.69
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Economics
0.00
1,000.00
2,000.00
3,000.00
4,000.00
5,000.00
6,000.00
Chip Seal Slurry Seal Microsurfacing Thin Overlay
An
nu
al C
ost,
$/l
an
e-m
ile
Annual Cost of Preservation Treatment
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Conclusions — Benefits
➢Thin Overlays for Pavement Preservation
▪ Improve Ride Quality
▪ Reduce Distresses
▪ Maintain Road Geometrics
▪ Reduce Noise
▪ Low Life Cycle Costs
▪ Provide Long Lasting Service
➢Place before extensive rehab required
➢Expected performance
▪ 10 years or more on asphalt
▪ 6 to 10 years on PCC
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Conclusions — Check-list
✓Evaluate
✓ Candidate for thin asphalt overlay?
✓ Distresses
✓Determine Mix Type
✓Proper Surface Preparation
✓Materials
✓Thickness
✓Production, Construction, and Quality Control
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Thin Asphalt Overlays
Thin asphalt overlays are a popular solution to pavement
preservation. They are economical, long-lasting, and
effective in treating a wide variety of surface distresses
to restore ride quality, skid resistance, and overall
performance.
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Resources
• NCAT website: www.ncat.us
• NAPA Publication: www.thinlayasphalt.com
–IS-135: Thin Asphalt Overlays for Pavement
Preservation
• Transportation Research Record:
–Labi et al., 2005.
• Ohio DOT:
–Chou et al., April 2008.