Transcript Pavement Preservation II:

Pavement Maintenance II
Part 2: Rehabilitation Alternatives
Idaho
Roads Scholar
Program
Objectives
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Review use of paving fabrics with thick
AC overlays,
Explore thin hot mix overlays,
Investigate cold in-place recycling, and
Discuss full depth reclamation.
When to Rehabilitate?
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Rough road,
Excessive pavement distress,
Loss of skid resistance,
Excessive maintenance needs,
Inadequate structure for planned
use.
Rehabilitation Alternatives
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Thick overlay with paving fabric,
Thin overlay,
Cold in place recycle (CIR),
Full depth reclamation.
Paving Fabrics
Paving Fabric Basics
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Keeps water out of the base and
subgrade
Provides support to retard reflection of
existing cracks and distresses
Controls evaporation over the longterm, keeping uniform moisture content
in the subgrade.
How does it work?
AC Overlay
Fabric
Existing AC
Pavement
Base or
Subgrade
Selection Considerations
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Can provide strength up to
equivalent of 1.0 inch of AC (if
pavement is stable and fabric is
properly installed)
Cost of fabric (based on DOT
studies) is about the same as 0.5
inches of AC
Application Considerations
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Not suitable for severely
distressed pavements.
Generally not suitable
where there is inadequate
base/subgrade support.
Do not use where free
water problems exist.
Construction Considerations
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Minimum overlay
thickness when using
a fabric is 1.5 inches.
Major contributor to
failure is lack of tack
and/or uniformity of
tack coat application.
Read manufacturer’s
literature for detailed
instructions.
Sample Products
1/4 inch
What is a “Thin”
HMA Overlay?
3/8 inch
Overlay  1.5”
1/2 inch
Why Thin Hot Mix
Overlays?
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Restores Serviceability
Low Initial Cost & Life Cycle Cost
Minimal Road User
Delays/Impacts
Adds Structure
Reduces Noise
Cost Comparison of
Pavement Treatments
Treatment
Life, years
Fog seal
1-2
Slurry seal
3-5
Chip seal
4-7
Thin HMA O’lay 10 - 15
Cost ($/yd2)
0.25 - 0.35
0.85 - 1.00
0.90 - 1.20
2.50 - 3.50
Construction Issues
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Structurally Sound Pavement Section
Surface Preparation
Correct Localized Weak Areas
Clean Surface/Adequate Tack
Laydown
Time Available for Compaction is
Reduced
Breakdown Must Stay Close to
Paver
Need a structurally sound pavement
for compaction...
Correct localized areas...
Surface Preparation
Tack Coats
 Applied to bound surface
 Light application of asphalt emulsion
 (0.03-0.07 gal/sy residual asphalt)
 Example materials
 SS-1,1h
 CSS-1,1h
Tack Coat Application
Uniform application?
Time avail. for Compaction, min
Mix Temp. = 275F
90F 60F 30F
30
30
20
20
10
10
0
0
1
2
3
Compacted Thickness, in
4
Temperature is Critical
> 185ºF
Compaction-Lift/Layer Thickness
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1/2 inch Dense Mixes
 1 to 1 1/2 inch Thick Lift
3/8 inch Mixes
 3/4 to 1 inch Thick Lift
½ inch Open Mixes
 1 inch Thick Lift
Thinner lift loses heat fast!
Compaction Equipment
For all types of rollers, the primary compaction
variables that can be controlled during the rolling
process are:
 Roller
speed
 Number of roller passes
 Rolling zone
 Rolling pattern
Easy does it!
Thin Overlays: Rules of Thumb
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Pre-level rutted areas
Minimum lift thickness is 1 1/2”
Roll while mix is hot (>185ºF)
Minimum of 3 passes
Introduction to Cold In-Place
Recycling
Milling
Machine
Crusher
Mixer-Paver
Advantages
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Reduced cost of construction
Conservation of aggregate and binders
Preservation of existing pavement
geometrics
Hauling Costs Minimized
Minimal Air Quality Problems
Conservation of energy
Less user delay
Advantages for
the Road
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Significant Structural
Improvements
Most Pavement Distress
Treated
Ride Quality Improved
Primary
Distresses
Equipment Train
Pulverize, Crush, Add
and Mix Recycling
Agent, and Place on
Roadway
Prepare
Construction
Area
Compact
Single Machine
Pulverize, Add and Mix
Recycling Agent, and
Place on Roadway
Depth of treatment typically 3 to 4”.
Tack and
Place
Surface
Course
Cold Milling
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Mill below depth of
distress (rutting,
surface-initiated
cracking)
Don’t leave “scabs” of
HMA
Avoid milling to within
½ inch of layer
interface
Cold In-Place Recycling Train
Emulsion
Milling Machine
Paver
Roller
Tanker
Recycler
Single Machine
Emulsion Tanker
Recycler
Curing and Compaction
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Curing or Aeration Needed to Reduce
Water and Volatiles
Delay Rolling or Blade the Mix
Use Steel-Wheel, Pneumatic-Tired or
Vibratory Rollers; Use Heavy PneumaticTired Roller for Breakdown
Achieve Optimum Compaction
Application of Wearing Surface
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Additional Curing Needed to Avoid
Moisture Retention
Apply Fog Seal, if Necessary,
Before Allowing Traffic
Wearing Course: HMA Overlay or
Double Surface Treatment
View before Recycling
View after Recycling
View before
Recycling
View after Recycling (Good Condition)
View after Recycling (Poor Condition)
Single Seal Coat
Final Considerations
CIR?
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Availability of Equipment
Availability of Experienced Contractor
First cost
Life cycle cost
Full Depth Reclamation
Construction Methods
and Case Study
Definition
Recycling method where all of
asphalt pavement section and a
predetermined amount of underlying
materials are treated to produce a
stabilized base course.
Advantages
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Pavement structure (especially poor base)
improved without significantly affecting
pavement geometry,
Eliminates ruts, rough areas, and potholes
and restores desired profile,
Eliminates alligator, transverse, longitudinal
and reflection cracking,
Provides a uniform pavement structure.
Advantages (continued)
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Frost susceptibility may be improved,
Low production cost,
Conservation of materials and energy,
No air quality problems.
Common Recycling Additives
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Emulsified Asphalts (MS and
SS)
Portland Cement
Lime
Fly Ash
Calcium Chloride
Foamed Asphalt
Main Steps
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Pulverize existing pavement,
Introduce additive and mix,
Shape the mixed material,
Compact,
Apply a wearing course.
Summary
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FDR can improve pavement
structure, restore profile and
eliminate cracks.
Steps consist of pulverization,
introduction of additive, shaping of
mixed material and compaction.
Proper aeration of mix required.
Objectives
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Review uses of paving fabrics,
Explore thin hot mix overlays,
Investigate cold in-place recycling, and
Full depth reclamation.
Questions?