thin lay asphalt for pavement preservation tone garrett executive director mississippi asphalt...

ThinLAY Asphalt for Pavement Preservation

Alabama Quality Asphalt Conference

Tone GarrettExecutive Director

Mississippi Asphalt Pavement Association

Too Much MonthAt 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

Construction Cost

Revenue

Time

Dol

lars

Fewer Road Miles

Less New Construction

Lawyers behind

every tree

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?

• 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

Time or Traffic

Pa

vem

ent

Co

nd

itio

n

PreventiveMaintenance

Preventive Maintenance

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

Accumulated Traffic Over Life of Pavement

Pres

ent

Serv

icea

bilit

y In

dex

(PSI

)

0

Preventive maintenance treatments differ widely in their ability to improve serviceability.

(Very Good)

(Very Poor)

5.0

Lowest acceptable level of serviceability (Terminal Serviceability)

Treatments that both repair pavement distresses and improve pavement profile can restore serviceability to new pavement levels.


Pres

ent

Serv

icea

bilit

y In

dex

(PSI

)

0


(Very Good)

(Very Poor)

5.0


Treatments that primarily repair pavement distresses without improvement to pavement profile have minimal effect on serviceability.


Pres

ent

Serv

icea

bilit

y In

dex

(PSI

)

0


(Very Good)

(Very Poor)

5.0


Performance more typical of ThinLay asphalt applications.

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

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

What’s in an inch?Asphalt Thickness VS. Fatigue Life

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

• 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

Smoothseal Type A (3/4" thick)

Smoothseal Type B (3/4" thick)

AC Surface, Type 1 (1.25" thick)

Single Chip Seal w/polymer

Microsurfacing (surface crse.)

$- $0.10 $0.20 $0.30 $0.40 $0.50 $0.60

$0.29

$0.28

$0.52

$0.40

$0.37

Annualized Cost per SY (OHIO data)- no discount -

(Based on Ave. Years Between Treatment)(Sep 16 '10 to Sep 20 '12 data) Life

5

4

9

13

13

Structure?

Look Familiar?

Pavement Preservation?

WE CAN’T GO BACKEVEN IF WE WANTED TO!

The Idea Whose Time Has Come

Jones County ¾”

Mix Design RequirementsSieve Size Percent Passing1/2 inch 1003/8 inch 95-100

No. 4 75 minNo. 8 22-70No.16 --

No. 200 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.

Gradation

What Is ThinLay Asphalt?

• 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 Mixture 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

General Construction Specifications

MDOT Test Locations

Route/ County

Approx. Length AADT Design

ThicknessTheo. Tons HMA

Actual Tons HMA

Square Yards of Pavement Placed

SR 370 Lee/Prentiss

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

SR 370 Lee/Prentiss¾ Inch

36 Months

Before

SR 370 Lee/Prentiss¾ Inch

6 Months 36 Months

Before

SR 371 Prentiss1 Inch

6 Month 24 Month

Before


6 Month 36 Months

Before


After 36 Months

Before

SR 370 Itawamba1/2 Inch

6 Month 36 Months

Before


6 Months 36 Months

Before


6 Month

Before

36 Months


6 Months 36 Months

Before


6 Month

Before

36 Months

Preservation ComparisonsThinLay Microsurface Slurry Seal Chip Seal

Corrects Surface Distress √ √ √ √

Increase Skid Resistance √ √ √ √

Minimizes Curb Loss √ √ √ √

Can Be Applied In One Pass √ √ √ √

Eliminates Loose Aggregate √ √

Corrects Minor Rutting √

Minimizes Delamination √

Improves Ride Quality √

Increases Structural Strength √

Improves Pavement Drainage √

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


• 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


• Improved Ride– Improved Smoothness– Less Road Noise

• Public Perception– Freshly Paved Road – New Road– No Broken Windshields

Benefits to the Traveling Public


• Concept of Pavement Preservation

Where ThinLay Asphalt?

S2 S3 S6NCAT Mississippi Test Sections

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 AsphaltSafe, 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.

thin lay asphalt for pavement preservation tone garrett executive director mississippi asphalt...

Documents