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Thin and Ultra-Thin Overlays

Thin and Ultra-Thin Overlays. Learning Outcomes. List benefits of thin and ultra-thin HMA overlays Describe recommended materials Describe recommended construction procedures List key quality control activities. Learning Outcomes (continued).

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Thin and Ultra-Thin Overlays

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  1. Thin and Ultra-Thin Overlays

  2. Learning Outcomes • List benefits of thin and ultra-thin HMA overlays • Describe recommended materials • Describe recommended construction procedures • List key quality control activities

  3. Learning Outcomes (continued) • Describe potential construction and performance problems • Identify troubleshooting solutions

  4. Thin vs. Ultra-Thin Overlays • Description: • “Thin” overlays—thickness between 19 and 38 mm (0.75 and 1.50 in) • “Ultra-Thin” overlays—thickness between 10 and 20 mm (0.4 and 0.8 in)

  5. Benefits • Improved ride quality • Improved surface friction • Corrected surface defects • Enhanced appearance • Sealed surface • Reduced splash and spray • Balancing the industry

  6. Thin HMA OverlaysDefinition THIN • Plant-mixed • Three types (based on gradation) • Dense-graded • Open-graded friction course (OGFC) • Stone matrix asphalt (SMA)

  7. Thin HMA OverlaysAdvantages THIN • Long service life • Smooth riding surface • Low noise emissions • No stone loss • No curing time • No binder run-off • Placed as part of staged construction

  8. Ultra-Thin HMA OverlaysDefinition ULTRA-THIN • Single pass placement • Polymer-modified asphalt emulsion tack coat • Dense-graded or gap-graded HMA

  9. Ultra-Thin HMA OverlaysAdvantages ULTRA-THIN • Rapid application • Excellent adhesion • Short, concise construction zone • Quick opening to traffic • Minimal effects on curb reveal, utilities, and guardrails

  10. Introduction to HMA Materials

  11. Thin HMA OverlaysMaterials THIN • Tack coat • Aggregates • Asphalt binder • Additives

  12. Thin HMA OverlaysAggregate Gradations THIN Dense-Graded Open-Graded Gap-Graded

  13. Thin HMA OverlaysAggregate Requirements THIN • Clean, high quality materials • Polish resistant • Conventional specifications for dense-graded overlays • OGFC and SMA overlays have more stringent requirements • Thickness = 2 times maximum aggregate size

  14. Thin HMA OverlaysMix Design—Dense-Graded Overlays THIN • Conventional mix design procedures • Binder choice influenced by traffic and climate • Typically same asphalt grade used in conventional HMA mixtures

  15. Thin HMA OverlaysMix Design—Open-Graded Friction Courses THIN • Methods vary considerably between states • FHWA draindown test • Other draindown tests • Viscosity-temperature charts • Optimum asphalt binder content

  16. Thin HMA OverlaysMix Design—Stone Matrix Asphalt THIN • High percentage of mineral filler • Stabilizing additives • Design procedure available from NAPA • Asphalt content >6% • Air void content >4% • Voids in mineral aggregate >17%

  17. Ultra-Thin HMA OverlaysMaterials ULTRA-THIN • Polymer-modified asphalt tack coat • Aggregates • Gap- or dense-graded • Thickness = 1.5 times maximum aggregate size • Asphalt binder

  18. Ultra-Thin HMA OverlaysMix Design ULTRA-THIN • Binder selection based on: • Climate • Traffic speed • Loading conditions • Elastic recovery requirement • Compatibility with asphalt emulsion tack coat

  19. Thin HMA Overlay Construction THIN

  20. Thin HMA Overlay Construction Process THIN • Pre-overlay repair • Surface preparation • Tack coat application • Overlay placement • Compaction

  21. Preoverlay Repair and Surface Preparation THIN • Repair weak areas • Deteriorated cracks • Localized distresses • Potholes • Pavements with extensive distress may not be good candidates • Clean surface (airblasting)

  22. Tack Coat Application THIN • Promotes bonding • Usually same as for conventional HMA overlays • Applied immediately prior to the placement of the overlay • Apply uniformly

  23. Overlay Placement THIN • Conventional HMA paving equipment • Continuous paving operation • Minimize starts and stops • Use material transfer device • Effective longitudinal and transverse paving joint construction necessary

  24. Placement Considerations: OGFC and SMA THIN • OGFC and SMA mixtures should not be placed in cold weather • Use short haul times • SMA mixtures may be harsh and sticky immediately behind paver

  25. Compaction THIN • Minimal time available for compaction • Roll as close to laydown machine as possible • Uniform rolling • Avoid turning wheels on mat • Turn off vibratory system at stop or change in direction

  26. Influencing Factors on Compaction Timing THIN • Wind • Solar flux • Mix temperature • Air temperature • Pavement temperature

  27. Compaction Timing: MultiCool 3.0 Software THIN www.hotmix.org

  28. Compaction Timing: MultiCool 3.0 Software THIN

  29. Compaction of OGFC and SMA Layers THIN • OGFC • No density specifications for OGFC • Two to three passes with steel wheeled roller required • SMA • Rolling immediately behind paver • Two or three passes with steel wheeled roller commonly used

  30. Steel-Wheeled Roller THIN

  31. Ultra-Thin HMA Overlay Construction ULTRA-THIN

  32. Ultra-Thin HMA Overlay Construction Process ULTRA-THIN • Pre-overlay repair • Surface preparation • Tack coat application and HMA placement • Compaction

  33. Preoverlay Repair and Surface Preparation ULTRA-THIN • Repair weak areas • Deteriorated cracks • Localized distresses • Potholes • Pavements with extensive distress may not be good candidates • Clean surface

  34. Tack Coat Application and HMA Placement ULTRA-THIN • Special paving equipment • Tack coat and HMA overlay placed at same time • Minimized starts and stops • Application temperature range: 143 to 165 °C (290 to 330 °F)

  35. Ultra-Thin HMA Overlay Paver ULTRA-THIN Mix Hopper Distributor Screed

  36. Ultra-Thin HMA Overlay Paver Augers ULTRA-THIN

  37. Ultra-Thin HMA Overlay PaverTack Coat and HMA Application ULTRA-THIN HMA Tack Coat

  38. Compaction ULTRA-THIN • Vibratory screed acts as breakdown roller • Two passes of a 9-ton (10-T) steel double drum roller • Roll immediately after application (static mode)

  39. Compaction ULTRA-THIN

  40. Quality Control • Aggregate gradation • Asphalt content • In-place density • Thickness and spread rate of overlay • Tack coat application rate (ultra-thin HMA overlay)

  41. NJ’s Thin-Lift Requirements New Jersey requirements Thin-lift ≤ 25mm thick (Ideally) – Minimal change to existing infrastructure (bridge clearances, drainage, etc.) Minimal Impact to Users (Coverage vs Unit Time) Re-new and upgrade road surface – Ride Quality (Smoothness) No “Cure-time” dependent materials (i.e. – cold applications) – Typical high ESAL’s limit use

  42. High Performance Thin-Overlay Focused Applications Preventative Maintenance – NJDOT – Placed after signs of initial surface distress – Also potential use of “Shim” course on PCC prior to Wearing Course Pavement Overlay – Locals/Municipalities – Place immediately on surface of pavements showing signs of surface distress with or without milling – Low severity wheelpath alligator cracking (base issues) – Surface cracking with minimal rutting

  43. Cracking Potential Areas of Application Low Severity Wheelpath Low to Mod. Transverse Cracking

  44. Direct Overlay – No Milling Existing Surface Existing Base HPTO

  45. High Performance Thin-Overlay FAA > 45% (AASHTO T304) Fine aggregate of stone sand (no natural sands) Sand Equivalency > 45% (AASHTO T176)

  46. Asphalt Binder Polymer-modified binder – PG76-22 (NJDOT Spec) RTFO Elastic Recovery > 65% @ 25oC (AASHTO T301) Separation Test < 4.5oC after 4 hrs (ASTM D5976) Performance Specification Utilize the Asphalt Pavement Analyzer (AASHTO TP 63) for stability check High Performance Thin-Overlay

  47. Asphalt Pavement Analyzer - AASHTO TP 63 - 100 lb wheel load; 100 psi hose pressure - Tested at 64oC for 8,000 loading cycles - Samples at 5 +/- 0.5% air voids - APA Rutting < 4 mm to PASS

  48. Mixture properties relative to field performance Permanent Deformation Stability – Asphalt Pavement Analyzer (AASHTO TP63) – Repeated Load Simple Performance (NCHRP Report 465) Fatigue resistance – Flexural Beam Fatigue (AASHTO T321) Resistance to PCC Slab Horizontal Movement – Overlay Tester Dynamic Modulus (AASHTO TP62) – HMA stiffness at various temperature and loading speeds Permeability – Flexible Wall Permeability (ASTM D5084) HPTO Lab Performance Evaluation

  49. 3. Rutting Stability – APA

  50. Repeated Load Test – NCHRP Report 465 I4 HD from AC Expressway 54.4oC 130oF)

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