Thin LAY Asphalt for Pavement Preservation. Alabama Quality Asphalt Conference. 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.
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ThinLAYAsphalt for Pavement Preservation Alabama Quality Asphalt Conference Tone Garrett Executive 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 ThinLayAsphalt? WhyThinLayAsphalt? WhereThinLayAsphalt?
WhyThinLayAsphalt? • Lawyers behind every tree Construction Cost Fewer Road Miles Less New Construction Dollars Revenue Time • Funding Crisis • Escalating Construction Costs • Declining Revenues • Increasing Regulations • More Miles To Maintain
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
Preventive Maintenance Preventive Maintenance Pavement Condition Time or Traffic
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 Condition Rating Systems
Treatments that both repair pavement distresses and improve pavement profile can restore serviceability to new pavement levels. (Very Good) 5.0 Present Serviceability Index (PSI) Lowest acceptable level of serviceability (Terminal Serviceability) 0 Accumulated Traffic Over Life of Pavement (Very Poor) Preventive maintenance treatments differ widely in their ability to improve serviceability.
(Very Good) 5.0 Treatments that primarily repair pavement distresses without improvement to pavement profile have minimal effect on serviceability. Present Serviceability Index (PSI) Lowest acceptable level of serviceability (Terminal Serviceability) 0 Accumulated Traffic Over Life of Pavement (Very Poor) Preventive maintenance treatments differ widely in their ability to improve serviceability.
(Very Good) 5.0 Performance more typical of ThinLay asphalt applications. Present Serviceability Index (PSI) Lowest acceptable level of serviceability (Terminal Serviceability) 0 Accumulated Traffic Over Life of Pavement (Very Poor) 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
TENSILE STRAIN 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
Preventive seals on pavements will only mask the impending structural distresses and eventually lead to full depth failures Structural Benefits
What’s in an inch? Asphalt Thickness VS. Fatigue Life
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 Structural contribution of 1”
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
Thin Lift Overlay = $2.53 per square yard Micro-Surfacing = $1.92 per square yard 32% cost increase Cost Comparison.
20 Years, I=4%, assume thinlay =10 year life Average micro surfacing life = 5 years Thinlay= $5.82 Micro Surface = $8.20 ThinlaySaves $2.38/yd2 in 20 Years, adds structure, and provides high serviceability Life Cycle Costs
MixDesignRequirements 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.
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
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