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Thin Hot Mix Asphalt Overlays PennDOT Research Findings

Thin Hot Mix Asphalt Overlays PennDOT Research Findings. Pennsylvania Asphalt Pavement Association. 53 rd Annual Asphalt Paving Conference Hershey, PA December 12, 2012. Thin Overlay Development. Back Ground- NEPPP: Smooth Seal in Ohio, THMAO in NY PAPA Technical Sub Committee

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Thin Hot Mix Asphalt Overlays PennDOT Research Findings

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  1. Thin Hot Mix Asphalt Overlays PennDOT Research Findings Pennsylvania Asphalt Pavement Association 53rd Annual Asphalt Paving Conference Hershey, PA December 12, 2012

  2. Thin Overlay Development Back Ground- • NEPPP: Smooth Seal in Ohio, THMAO in NY • PAPA Technical Sub Committee • Created draft specification • 6.3mm PG 76-22, Polymer Modified, 75 Gyration mix • Research Project approved

  3. Special Provision 6.3 mm – 100% passing 3/8 in. Dense –graded ( 6 sieve sizes) - SRL PG 76-22 polymer modified N design = 75 gyrations Design voids = 4.0% Min. VMA = 16.5 No RAP or RAS Greater than 50 F Optimum Rolling Pattern

  4. Use Guidelines Only on structurally sound pavement Same as micro-surfacing For correcting surface distresses only Consider grinding PCC first

  5. Tack Coat Specification SS – 1h or CSS – 1h RS – 1h or CRS – 1h 60% min residue Low pen (40-90) asphalt residue 0.05-0.06 gal/sy rate.

  6. Mix Design – Hempt Bros. 6 trial blends to get minimum VMA Component materials -baghouse fines ( 1.9%) -TolandConc sand Type A, SRL-E (39.4%) -Toland ¼ in. SRL-E - 4.0% passing #200 - 43% passing #8 - NuStar PG 76-22 binder (6.7%)

  7. Mix Design (cont’d) Volumetrics - N design : 75 gyrations - design voids: 4.0% - VMA: 17.1% - VFA: 77% - TSR: 83% (without antistrip)

  8. 6.3 mm NMAS Mix Placed at 1 inch thickness Aggregate: Sandstone, Skid Resistance Level (SRL): E Polymer Modified Binder: PG 76-22 Gyration Level: 75 Design Air Void: 4%, Design VMA: 17.1 Design Binder Content: 6.7% NO RAP

  9. Construction All night work 1/3 mile of four lanes (612 tons) Including intersection and turn lane 1 in thick overlay on diamond ground PCC CSS-1h tack coat 0.06 gal/sy tack application rate

  10. Performance Evaluation - HWTD Good Performance

  11. Performance Evaluation – Overlay Tester Test Temperature: 25ºC # of load cycles: 1200 Or until load reduced to 93% of original Repeated loading (triangular form) under constant deformation Deformation magnitude per load cycle: 0.025 inches (0.6 mm) Duration of each load cycle: 10 seconds

  12. Performance Evaluation – Overlay Tester Good Performance Cycles to failure > 500 High variability in data

  13. Tack Coat Evaluation Notice Displacement of the Asphalt Layer

  14. Tack Coat Evaluation Shear Strength = 44.5 psi (307 KPa) - Good Performance

  15. Emulsion Tack Coat Application

  16. Smooth Mat Right Behind The Paver

  17. Mat Temperature Data is courtesy of Mr. Garry Hoffman

  18. Core Densities

  19. Friction Improvement Data: Courtesy of PennDOT BOMO

  20. Ride Quality (Smoothness) Improvement Data: Courtesy of PennDOT BOMO

  21. Summary/Findings • Good Mix Lab Performance • Permanent Deformation (SST) • Rutting and Moisture Resistance (HWTD) • Crack Resistance (Overly Test) • Good Tack Shear Resistance • Improved Ride and Friction • In-Place Average Density: 92.2% (based on 9 cores) • (Cores from Test Strip Only) • Could be better if compaction finished at higher temperature? • Mat Temperature After Placement: 280-315ºF • Rapid Mat Cooling • No Apparent Segregation • Coring Not A Problem

  22. Conclusions • Thin Overlays for Pavement Preservation • Improved Ride Quality • Improved Friction • Maintained Road Geometrics • Reduced Noise • Reduce Life Cycle Costs • Provide Long Lasting Service • Place before extensive rehab required according to use guidelines • Expected performance • 10 years on asphalt • 6 or more on PCC

  23. Thin HMA Overlays Thin HMA overlays are an added solution to pavement preservation. They are economical, long-lasting, and effective in treating a wide variety of surface distresses to restore ride quality, skid resistance, and overall performance.

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