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ThinLAY Asphalt for Pavement Preservation

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Presentation on theme: "ThinLAY Asphalt for Pavement Preservation"— Presentation transcript:

1 ThinLAY Asphalt for Pavement Preservation
Tone Garrett Executive Director Mississippi Asphalt Pavement Association Alabama Quality Asphalt Conference

2 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

3 Objective What is ThinLay Asphalt? Why ThinLay Asphalt?
Where ThinLay Asphalt?

4 Lawyers behind every tree
Why ThinLay Asphalt? Funding Crisis Escalating Construction Costs Declining Revenues Increasing Regulations More Miles To Maintain Lawyers behind every tree Construction Cost Fewer Road Miles Less New Construction Funding Crisis – As construction and material cost continue to rise, revenue from fuel taxes remains flat. This fact creates a situation in which fewer miles of road can be paved per year and less new construction can be expected. Both areas are important. New construction is needed to alleviate congestion and provide opportunity for economic development. Maintenance of our existing roads is important to keep a good level of service and avoid major reconstruction efforts. Dollars Revenue Time

5 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.

6 The Opportunity Focus nationwide has shifted from construction to preservation Lane miles increased only 8% The value of our National highway and road system estimated at $1.75 trillion Preservation of the system will dominate future expenditures

7 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

8 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

9 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

10 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

11 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 $

12 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

13 3 Key Messages Performance benefits Structural benefits Cost benefits

14 Preventive Maintenance
Pavement Condition The difference between the effect of preventive and reactive maintenance is significant. Not only is the timing of application different, but the effect (represented by the slopes of the after-treatment performance curves) is also different. Time or Traffic

15 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

16 Present Serviceability Index (PSI)
Treatments that both repair pavement distresses and improve pavement profile can restore serviceability to new pavement levels. (Very Good) 5.0 Accumulated Traffic Over Life of Pavement Present Serviceability Index (PSI) Lowest acceptable level of serviceability (Terminal Serviceability) (Very Poor) Preventive maintenance treatments differ widely in their ability to improve serviceability.

17 Present Serviceability Index (PSI)
(Very Good) 5.0 Treatments that primarily repair pavement distresses without improvement to pavement profile have minimal effect on serviceability. Accumulated Traffic Over Life of Pavement Present Serviceability Index (PSI) Lowest acceptable level of serviceability (Terminal Serviceability) (Very Poor) Preventive maintenance treatments differ widely in their ability to improve serviceability.

18 Present Serviceability Index (PSI)
(Very Good) 5.0 Performance more typical of ThinLay asphalt applications. Accumulated Traffic Over Life of Pavement Present Serviceability Index (PSI) Lowest acceptable level of serviceability (Terminal Serviceability) (Very Poor) Preventive maintenance treatments differ widely in their ability to improve serviceability.

19 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

20 Structural Benefits Most pavements designed for 20 years with AASHTO design They have finite bottom up fatigue life TENSILE STRAIN

21 Structural Benefits A seal type treatment applied on those pavements will have no impact on the tensile strain TENSILE STRAIN

22 Structural Benefits Preventive seals on pavements will only mask the impending structural distresses and eventually lead to full depth failures

23 Change

24 Timely thin overlays “Thinlays” can save your structure

25 Asphalt Thickness VS. Fatigue Life
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

26 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

27 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

28 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

29 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 would further extend the fatigue life to beyond 50 years

30 Initial Costs

31 Economics of Preventive Maintenance Treatments

32 Cost Comparison. Thin Lift Overlay = $2.53 per square yard
Micro-Surfacing = $1.92 per square yard 32% cost increase

33 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

34 Life 5 4 9 13

35 Structure?

36 Look Familiar?

37 Pavement Preservation?


39 The Idea Whose Time Has Come

40 Jones County ¾”

41 Mix Design Requirements
Sieve Size Percent Passing 1/2 inch 100 3/8 inch 95-100 No. 4 75 min No. 8 22-70 No.16 -- No. 200 4-12 Gradation 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.

42 What Is ThinLay Asphalt?

43 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 Mixture Specifications were developed with help from industry to allow for flexibility in design to optimize the cost.

44 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 Construction Specifications were developed to maximize the Tons per Mile. Depending on the road condition, Thin Lift Mixtures can be designed to be placed as thin as ½”. In reality, ¾” is likely a good thickness for most candidate roadways. If there are deficient areas along the roadway, spot leveling, bump grinding, or structural pavement repair may be necessary prior to the placement of Thin Lift Asphalt. Density – Because of the thin nature of this mixture, density determination by core or nuclear gauge is very difficult. DENSITY IS STILL IMPORTANT. Density is the most important indicator of a long lasting pavement. The specification allows for a monitored roll to refusal. Smoothness – It is expected that even with a ¾” lift there will be some improvement to the smoothness/ride.

45 Square Yards of Pavement Placed
MDOT Test Locations Route/ County Approx. Length AADT Design Thickness Theo. 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

46 SR 370 Lee/Prentiss ¾ Inch Before 36 Months

47 SR 370 Lee/Prentiss ¾ Inch Before 36 Months

48 SR 370 Lee/Prentiss ¾ Inch Before 6 Months 36 Months

49 SR 371 Prentiss 1 Inch Before 6 Month 24 Month

50 SR 371 Prentiss 1 Inch Before 6 Month 36 Months

51 SR 371 Prentiss 1 Inch Before After 36 Months

52 SR 370 Itawamba 1/2 Inch Before 6 Month 36 Months

53 SR 370 Itawamba 1/2 Inch Before 6 Months 36 Months

54 SR 370 Itawamba 1/2 Inch Before 6 Month 36 Months

55 SR 370 Itawamba 1/2 Inch Before 6 Months 36 Months

56 SR 370 Itawamba 1/2 Inch Before 6 Month 36 Months

57 Preservation Comparisons
ThinLay 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

58 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 ” 1” ¾” ½” $40, $27, $20, $13, Lane Mile $ $ $ $ Square Yard 0% % % % Savings Cost Comparison – Illustration suggests/demonstrates how Thin Lift Asphalt can be used to save the cost per lane mile in MDOT’s resurfacing program. Main point – The idea that Cost/square yard/year Life Cycle Cost analysis is important when considering types of resurfacing treatments

59 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 Life Cycle Cost of Thin Lift Maintenance Treatments Higher Initial Cost – Later when discussing the mixture specifications, point out the cost saving measures that have been included in the specification. Thinner Lifts helps optimize the cost per mile of resurfacing. Cost/Square Foot/Year – On pavement structures that are structurally sound and have low traffic volumes, a new asphalt overlay CAN realistically last 10 years or more. If a 10 year design is assumed, the Cost/Square Foot/Year goes down dramatically.

60 Benefits to the Traveling Public
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 Benefits to the Traveling Public Improved Ride – Even at ¾” good paving practices indicate that there WILL be an improvement in the ride. We have excellent producers and lay down crews in Mississippi that will maximize the ride. Public Perception – The public expects and wants fresh, newly paved asphalt pavements. The public perception of a single lift overlay is that it is a NEW ROAD.

61 Why ThinLay Asphalt? Concept of Pavement Preservation
Pavement Preservation Concept – Describe Level of Service Curve vs. Time Motto of Pavement Preservation – “The right treatment at the right time” This mindset AVOIDS/Postpones major reconstruction cost.

62 Where ThinLay Asphalt?

63 NCAT Mississippi Test Sections

64 Where ThinLay Asphalt? Low Volume ST Routes (3 Digit Roads) - City Streets – County Roads Low Volume Roads – The Thin Lift Maintenance Mix is intended for ST type routes with low traffic volumes and low truck traffic. A High Performance 4.75 mm Mixture can be used for MT or HT routes. The 4.75 mm mixture is not covered by this presentation.

65 Special Thanks I could not have made this presentation without help from: James Williams – Deputy Chief Engineer, MDOT Mark Holly – 1st District Engineer, MDOT

66 Safe, Smooth, Sustainable
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!!

67 Questions Remember that the only stupid question is the one that goes unasked.

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