Mississippi Thin Lift Presentation

Report
ThinLAY Asphalt for Pavement
Preservation
Tone Garrett
Executive Director
Mississippi Asphalt Pavement Association
Too Much Month
At The End Of The Money
 Now more than ever we are expected to do more
with less.
 We don’t have the funding to maintain roads we
have, much less build new ones.
 Traffic is still increasing
 No Quick Fix on the Horizon
Objective
• What is ThinLay Asphalt?
• Why ThinLay Asphalt?
• Where ThinLay Asphalt?
Why ThinLay Asphalt?
• Funding Crisis
Escalating Construction Costs
Declining Revenues
Increasing Regulations
More Miles To Maintain
Dollars
–
–
–
–
Revenue
Time
Fewer Road
Miles
Less New
Construction
Current Overlay Practice
= Never Catch UP
 Example - Lane miles in MDOT Dist. 1= 5,399
 26.2 % of these or 1,405 lane miles are shown in
Poor or Very Poor Condition.
 It would cost over $141 million to do a typical overlay
on this 26.2 %
 Current Funding Level is about $18 million per year.
 So it will take 8 years to overlay the pavements
currently in poor condition.
The Opportunity
• Focus nationwide has shifted from
construction to preservation
• Lane miles increased only 8% 1980-2009
• The value of our National highway and road
system estimated at $1.75 trillion
• Preservation of the system will dominate
future expenditures
The Opportunity
• Map 21 moves the nation to performance
management
• Agencies will be required to track and report
pavement condition
• Smoothness will be an important element in
the condition rating
Opportunity/Threat
• Agencies are looking at new ways to extend
their preservation $$
• Have developed a 1R (pave mainly) program
• In Mississippi for the first time the DOT is
increasing chip seals in their Preservation
program at the expense of asphalt overlays
What about thinlay asphalt?
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•
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•
•
We have promoted thin lifts for many years
Have had our successes
Many states have made inroads with thin lifts
Ohio’s Smoothseal for example
In Mississippi with the help of MDOT we have
had a good experience
We have a great message
•
•
•
•
•
•
•
We do everything the seal treatments do +
We improve smoothness
We last longer
We add structure
We’re faster
We’re quieter
The public prefers asphalt to chip and slurry
seals
So why aren’t we dominating the market?
• First cost often
dominates the decision
process
• Pavement managers
have to cover specific
numbers of miles
annually with available $
So why aren’t we dominating the market?
• Common Condition rating
systems do not recognize the
added benefits provided by
smoother treatments or
treatments that add structure
• We have not done a good job
of quantifying the cost and
structural benefits
3 Key Messages
• Performance benefits
• Structural benefits
• Cost benefits
Preventive Maintenance
Pavement Condition
Preventive
Maintenance
Time or Traffic
Condition Rating Systems
• Pavement Condition Index (PCI) is a
measure of visual surface distress “only”
• Most thin treatments therefore only
address surface distress
• Most thin treatments do not improve ride
and some actually reduce ride quality
Present
Serviceability Index
(PSI)
(Very Good) 5.0
(Very Poor)
Treatments that both
repair pavement
distresses and improve
pavement profile can
restore serviceability to
new pavement levels.
Lowest
acceptable
level of
serviceability
(Terminal
Serviceability)
0
Accumulated Traffic Over Life of Pavement
Preventive maintenance treatments differ widely in their ability to
improve serviceability.
Present
Serviceability Index
(PSI)
(Very Good) 5.0
(Very Poor)
Treatments that primarily
repair pavement
distresses without
improvement to pavement
profile have minimal effect
on serviceability.
Lowest
acceptable
level of
serviceability
(Terminal
Serviceability)
0
Accumulated Traffic Over Life of Pavement
Preventive maintenance treatments differ widely in their ability to
improve serviceability.
Present
Serviceability Index
(PSI)
(Very Good) 5.0
(Very Poor)
Performance
more typical of
ThinLay asphalt
applications.
Lowest
acceptable
level of
serviceability
(Terminal
Serviceability)
0
Accumulated Traffic Over Life of Pavement
Preventive maintenance treatments differ widely in their ability to
improve serviceability.
Structural Benefits
• Preventive Maintenance treatments are
supposed to be non-structural
• Slurry seals, Chips Seals, micro sufacing add
no structure
• A 1/2 to 1 inch asphalt overlay does and
should be recognized and credited
Structural Benefits
• Most pavements designed for 20 years with
AASHTO design
• They have finite bottom up fatigue life
TENSILE
STRAIN
Structural Benefits
• A seal type treatment applied on those pavements
will have no impact on the tensile strain
TENSILE
STRAIN
Structural Benefits
• Preventive seals on pavements will only mask
the impending structural distresses and
eventually lead to full depth failures
Timely thin overlays “Thinlays” can save your
structure
What’s in an inch?
Asphalt Thickness VS. Fatigue Life
Thickness
Micro strain
Reps to failure
2”
-652
30,234
3”
-495
71,537
4”
-383
160,693
5”
-302
340,507
6”
-242
682,133
Structural contribution of 1”
• A 1 inch overlay of an existing 4 inch
pavement will double the fatigue life
• Once you achieve a perpetual design
thickness you can focus on managing at
the surface for functional attributes as
your structural worries are over
Perpetual 1” at a time
• Thin overlays add up and can get you
there
• Here is a simple example
• You have an existing pavement 4 inches
thick designed for 20 years so at year 10
you have consumed 50% of its fatigue life
Perpetual 1” at a time
• If you apply a chip seal at year 10 the
strain at the bottom is unchanged and
fatigue consumption will continue at the
same rate
• The pavement will develop full depth
cracking over the next 10 years,
roughness will increase and full depth
repairs will be required
Perpetual 1” at a time
• Alternatively if you apply a 1 inch overlay at
year 10 you reduce the strain and extend the
fatigue life to near 40 years (5 inch pavement
has double the fatigue life of a 4 inch
pavement)
• You now have only used up 25% of the life
instead of 50%
• A second 1 inch overlay at year 20-25 would
further extend the fatigue life to beyond 50
years
Initial Costs
Economics of Preventive
Maintenance Treatments
Cost Comparison.
• Thin Lift Overlay = $2.53 per square yard
• Micro-Surfacing = $1.92 per square yard
• 32% cost increase
Life Cycle Costs
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20 Years, I=4%, assume thinlay =10 year life
Average micro surfacing life = 5 years
Thinlay = $5.82
Micro Surface = $8.20
Thinlay Saves $2.38/yd2 in 20 Years, adds structure,
and provides high serviceability
Annualized Cost per SY (OHIO data)
- no discount (Based on Ave. Years Between Treatment)
(Sep 16 '10 to Sep 20 '12 data)
Life
5
$0.37
Microsurfacing (surface crse.)
4
$0.40
Single Chip Seal w/polymer
9
$0.52
AC Surface, Type 1 (1.25" thick)
Smoothseal Type B (3/4" thick)
Smoothseal Type A (3/4" thick)
$-
$0.28
13
$0.29
13
$0.20
$0.40
$0.60
Structure?
Look Familiar?
Pavement Preservation?
WE CAN’T GO BACK
EVEN IF WE WANTED TO!
The Idea Whose Time Has Come
Jones County ¾”
Mix Design Requirements
Gradation
Sieve Size
1/2 inch
3/8 inch
No. 4
No. 8
No.16
No. 200
Percent Passing
100
95-100
75 min
22-70
-4-12
ASTM C1252 Fine aggregate angularity of 40 or greater. Up to 30%
rap may be used which must be separated on a ½ inch screen.
What Is ThinLay Asphalt?
General Mixture Specifications
• Mixture Gradation between 9.5 mm and 4.75 mm
– Allows Producer to adjust Nominal Maximum Size to allow use of
available/economical materials
• Air Voids – Between 4% and 6%
– Allows Designer to adjust/lower asphalt content while maintaining a “tight”
impermeable mixture
• RAP – Allowed up to 25%
– Allows Designer to reduce the virgin binder added to the mixture
• Sand – Allowed up to 30%
– Allows additional sand – most economical aggregate
General Construction Specifications
• Lift Thickness – Specified between ½” to 1”
– Allows for economy – Less Mixture Tons per Mile
• Single Lift Overlay
– Used as a Preventative Maintenance Technique – Spot Pre-Leveling and Repair
of Structurally Deficient Areas Required
• Density Requirement – Monitored Roll to Refusal
– Rolling Pattern Established by Nuclear Gauge
• Smoothness – Slight Improvement Expected
– As good or better than previous pavement surface
MDOT Test Locations
AADT
Design
Thickness
Theo.
Tons
HMA
Actual
Tons
HMA
Square Yards of
Pavement Placed
1.5
Miles
1200
¾ inch
938
1144
22745
SR 370 /
Itawamba
2.9
Miles
1000
½ inch
1128
1718
40624
SR 371 /
Prentiss
1.1
Miles
1500
1 inch
997
930
17449
Route/
County
Approx.
Length
SR 370
Lee/Prentiss
SR 370 Lee/Prentiss
¾ Inch
Before
36 Months
SR 370 Lee/Prentiss
¾ Inch
Before
36 Months
SR 370 Lee/Prentiss
¾ Inch
Before
6 Months
36 Months
SR 371 Prentiss
1 Inch
Before
6 Month
24 Month
SR 371 Prentiss
1 Inch
Before
6 Month
36 Months
SR 371 Prentiss
1 Inch
Before
After
36 Months
SR 370 Itawamba
1/2 Inch
Before
6 Month
36 Months
SR 370 Itawamba
1/2 Inch
Before
6 Months
36 Months
SR 370 Itawamba
1/2 Inch
Before
6 Month
36 Months
SR 370
Itawamba
1/2 Inch
Before
6 Months
36 Months
SR 370 Itawamba
1/2 Inch
Before
6 Month
36 Months
Preservation Comparisons
ThinLay
Microsurface
Slurry Seal
Chip Seal
Corrects Surface Distress
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Increase Skid Resistance
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√
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Minimizes Curb Loss
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Can Be Applied In One Pass
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Eliminates Loose Aggregate
√
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Corrects Minor Rutting
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Minimizes Delamination
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Improves Ride Quality
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Increases Structural Strength
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Improves Pavement Drainage
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Why ThinLay Asphalt?
• Cost Comparison – Typical Overlay to ThinLay Overlay
– Assume $70 / mixture Ton
– Assume 110 lbs./yd2/in. Cost Per yd2 Per Year Assuming 10 Life
9.5 mm @ 1.5”
ThinLay @ 1”
ThinLay @ ¾”
ThinLay @ ½”
$40,656
$27,104
$20,328
$13,552
Lane Mile
$0.64
$0.42
$0.32
$0.21
Square Yard
0%
33%
50%
67%
Savings
Why ThinLay Asphalt?
• Life Cycle Cost of ThinLay Maintenance Treatments
– Higher Initial Cost?? –
• Can be offset by Thinner Lifts
– Cost/Square Yard/Year
• Asphalt Mixture with 10 year Design Life
Why ThinLay Asphalt?
Benefits to the Traveling Public
• Improved Ride
– Improved Smoothness
– Less Road Noise
• Public Perception
– Freshly Paved Road – New Road
– No Broken Windshields
Why
ThinLay Asphalt?
• Concept of Pavement Preservation
Where ThinLay Asphalt?
NCAT Mississippi Test Sections
S2
S3
S6
Where ThinLay Asphalt?
• Low Volume ST Routes (3 Digit Roads) - City Streets –
County Roads
Special Thanks
• I could not have made this presentation
without help from:
– James Williams – Deputy Chief Engineer, MDOT
– Mark Holly – 1st District Engineer, MDOT
Thinlay Asphalt
Safe, Smooth, Sustainable
• Longest Life of all
treatments
• Lowest life cycle cost
• Superior Smoothness
• Preferred by road users
• Maintains Structural
integrity
Thank You!!
Questions
• Remember that the only
stupid question is the one
that goes unasked.

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