Presentation on theme: "ThinLAY Asphalt for Pavement Preservation"— Presentation transcript:
1ThinLAY Asphalt for Pavement Preservation Tone GarrettExecutive DirectorMississippi Asphalt Pavement AssociationAlabama Quality Asphalt Conference
2Too 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 increasingNo Quick Fix on the Horizon
3Objective What is ThinLay Asphalt? Why ThinLay Asphalt? Where ThinLay Asphalt?
4Lawyers behind every tree Why ThinLay Asphalt?Funding CrisisEscalating Construction CostsDeclining RevenuesIncreasing RegulationsMore Miles To MaintainLawyers behind every treeConstruction CostFewer Road MilesLess New ConstructionFunding 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.DollarsRevenueTime
5Current Overlay Practice = Never Catch UP Example - Lane miles in MDOT Dist. 1= 5,39926.2 % 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.
6The OpportunityFocus nationwide has shifted from construction to preservationLane miles increased only 8%The value of our National highway and road system estimated at $1.75 trillionPreservation of the system will dominate future expenditures
7The Opportunity Map 21 moves the nation to performance management Agencies will be required to track and report pavement conditionSmoothness will be an important element in the condition rating
8Opportunity/ThreatAgencies are looking at new ways to extend their preservation $$Have developed a 1R (pave mainly) programIn Mississippi for the first time the DOT is increasing chip seals in their Preservation program at the expense of asphalt overlays
9What about thinlay asphalt? We have promoted thin lifts for many yearsHave had our successesMany states have made inroads with thin liftsOhio’s Smoothseal for exampleIn Mississippi with the help of MDOT we have had a good experience
10We have a great message We do everything the seal treatments do + We improve smoothnessWe last longerWe add structureWe’re fasterWe’re quieterThe public prefers asphalt to chip and slurry seals
11So why aren’t we dominating the market? First cost often dominates the decision processPavement managers have to cover specific numbers of miles annually with available $
12So 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 structureWe have not done a good job of quantifying the cost and structural benefits
14Preventive Maintenance Pavement ConditionThe 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
15Condition Rating Systems Pavement Condition Index (PCI) is a measure of visual surface distress “only”Most thin treatments therefore only address surface distressMost thin treatments do not improve ride and some actually reduce ride quality
16Present Serviceability Index (PSI) Treatments that both repair pavement distresses and improve pavement profile can restore serviceability to new pavement levels.(Very Good)5.0Accumulated Traffic Over Life of PavementPresent Serviceability Index (PSI)Lowest acceptable level of serviceability (Terminal Serviceability)(Very Poor)Preventive maintenance treatments differ widely in their ability to improve serviceability.
17Present Serviceability Index (PSI) (Very Good)5.0Treatments that primarily repair pavement distresses without improvement to pavement profile have minimal effect on serviceability.Accumulated Traffic Over Life of PavementPresent Serviceability Index (PSI)Lowest acceptable level of serviceability (Terminal Serviceability)(Very Poor)Preventive maintenance treatments differ widely in their ability to improve serviceability.
18Present Serviceability Index (PSI) (Very Good)5.0Performance more typical of ThinLay asphalt applications.Accumulated Traffic Over Life of PavementPresent Serviceability Index (PSI)Lowest acceptable level of serviceability (Terminal Serviceability)(Very Poor)Preventive maintenance treatments differ widely in their ability to improve serviceability.
19Structural BenefitsPreventive Maintenance treatments are supposed to be non-structuralSlurry seals, Chips Seals, micro sufacing add no structureA 1/2 to 1 inch asphalt overlay does and should be recognized and credited
20Structural BenefitsMost pavements designed for 20 years with AASHTO designThey have finite bottom up fatigue lifeTENSILE STRAIN
21Structural BenefitsA seal type treatment applied on those pavements will have no impact on the tensile strainTENSILE STRAIN
22Structural BenefitsPreventive seals on pavements will only mask the impending structural distresses and eventually lead to full depth failures
24Timely thin overlays “Thinlays” can save your structure
25Asphalt Thickness VS. Fatigue Life What’s in an inch?Asphalt Thickness VS. Fatigue LifeThicknessMicro strainReps to failure2”-65230,2343”-49571,5374”-383160,6935”-302340,5076”-242682,133
26Structural contribution of 1” A 1 inch overlay of an existing 4 inch pavement will double the fatigue lifeOnce you achieve a perpetual design thickness you can focus on managing at the surface for functional attributes as your structural worries are over
27Perpetual 1” at a time Thin overlays add up and can get you there Here is a simple exampleYou have an existing pavement 4 inches thick designed for 20 years so at year 10 you have consumed 50% of its fatigue life
28Perpetual 1” at a timeIf you apply a chip seal at year 10 the strain at the bottom is unchanged and fatigue consumption will continue at the same rateThe pavement will develop full depth cracking over the next 10 years, roughness will increase and full depth repairs will be required
29Perpetual 1” at a timeAlternatively 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
32Cost Comparison. Thin Lift Overlay = $2.53 per square yard Micro-Surfacing = $1.92 per square yard32% cost increase
33Life Cycle Costs 20 Years, I=4%, assume thinlay =10 year life Average micro surfacing life = 5 yearsThinlay = $5.82Micro Surface = $8.20Thinlay Saves $2.38/yd2 in 20 Years, adds structure, and provides high serviceability
41Mix Design Requirements Sieve SizePercent Passing1/2 inch1003/8 inch95-100No. 475 minNo. 822-70No.16--No. 2004-12GradationASTM C1252 Fine aggregate angularity of 40 or greater. Up to 30% rap may be used which must be separated on a ½ inch screen.
43General Mixture Specifications Mixture Gradation between 9.5 mm and 4.75 mmAllows Producer to adjust Nominal Maximum Size to allow use of available/economical materialsAir Voids – Between 4% and 6%Allows Designer to adjust/lower asphalt content while maintaining a “tight” impermeable mixtureRAP – Allowed up to 25%Allows Designer to reduce the virgin binder added to the mixtureSand – Allowed up to 30%Allows additional sand – most economical aggregateGeneral Mixture Specifications were developed with help from industry to allow for flexibility in design to optimize the cost.
44General Construction Specifications Lift Thickness – Specified between ½” to 1”Allows for economy – Less Mixture Tons per MileSingle Lift OverlayUsed as a Preventative Maintenance Technique – Spot Pre-Leveling and Repair of Structurally Deficient Areas RequiredDensity Requirement – Monitored Roll to RefusalRolling Pattern Established by Nuclear GaugeSmoothness – Slight Improvement ExpectedAs good or better than previous pavement surfaceConstruction 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.
57Preservation Comparisons ThinLayMicrosurfaceSlurry SealChip SealCorrects Surface Distress√Increase Skid ResistanceMinimizes Curb LossCan Be Applied In One PassEliminates Loose AggregateCorrects Minor RuttingMinimizes DelaminationImproves Ride QualityIncreases Structural StrengthImproves Pavement Drainage
58Why ThinLay Asphalt?Cost Comparison – Typical Overlay to ThinLay OverlayAssume $70 / mixture TonAssume 110 lbs./yd2/in. Cost Per yd2 Per Year Assuming 10 Life” 1” ¾” ½”$40, $27, $20, $13, Lane Mile$ $ $ $ Square Yard0% % % % SavingsCost 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
59Why ThinLay Asphalt? Life Cycle Cost of ThinLay Maintenance Treatments Higher Initial Cost?? –Can be offset by Thinner LiftsCost/Square Yard/YearAsphalt Mixture with 10 year Design LifeLife Cycle Cost of Thin Lift Maintenance TreatmentsHigher 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.
60Benefits to the Traveling Public Why ThinLay Asphalt?Benefits to the Traveling PublicImproved RideImproved SmoothnessLess Road NoisePublic PerceptionFreshly Paved Road – New RoadNo Broken WindshieldsBenefits to the Traveling PublicImproved 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.
61Why ThinLay Asphalt? Concept of Pavement Preservation Pavement Preservation Concept –Describe Level of Service Curve vs. TimeMotto of Pavement Preservation – “The right treatment at the right time”This mindset AVOIDS/Postpones major reconstruction cost.
64Where ThinLay Asphalt?Low Volume ST Routes (3 Digit Roads) - City Streets – County RoadsLow 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.
65Special ThanksI could not have made this presentation without help from:James Williams – Deputy Chief Engineer, MDOTMark Holly – 1st District Engineer, MDOT
66Safe, Smooth, Sustainable Thinlay AsphaltSafe, Smooth, SustainableLongest Life of all treatmentsLowest life cycle costSuperior SmoothnessPreferred by road usersMaintains Structural integrityThank You!!
67QuestionsRemember that the only stupid question is the one that goes unasked.