Thin Lift Overlays. Pavement Preservation 2/13/2013. Definition. A Maintenance Alternative

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1 Thin Lift Overlays A Maintenance Alternative David R. Johnson, P.E. Regional Engineer Asphalt Institute Billings, Montana Definition A thin overlay, typically 3/4 to 1-1/2 inches thick, of a gap graded (SMA), open graded, or dense graded asphalt concrete bonded to existing materials intended to correct minor defects while reducing noise and improving ride. Pavement Preservation Road failures are rarely catastrophic; they occur over long periods of time, so the trouble often goes unnoticed until it s advanced Traditionally, agencies have waited until distresses become very noticeable. By then, they require major rehabilitation to return them to good quality 1

2 Pavement Preservation Agencies have often applied maintenance reactively to roads in poor condition rather than proactively to roads still in good structural condition The Pavement Preservation concept applies several minor treatments while the road is minimally distressed at a far lower cost than one major rehabilitation or reconstruction Reasons for Thin Overlays Works Well in All Climates Can Improve Structural Capacity (minor) A Reasonable Catch All Treatment Ub Urban Environments Maintain clearances Curb relief Utility clearances Good Service Life (about 10 years) Reasons for Thin Overlays Smooth Surface Quiet Surface Handles Heavy Traffic Conditions No Loose Stones Easily Recycled Seals Surface Can Improve Skid Resistance Typically Quick Construction 2

3 From NAPA Water- Proofing Dense-graded mixes used for thin overlays have smaller void sizes, low-to-no permeability 3

4 Polishing Raveling Longitudinal Cracking Not in Wheelpath 4

5 Low-severity thermal cracking Low-severity rutting If larger cracks are to be overlaid, they should be routed, cleaned, and sealed Plastic movement in top lift only - great candidate for a mill & fill 5

6 Soft subgrade - if localized, can patch & then overlay (cut in nice, straight lines at least 1 on each side into sound pavement, clean & tack all faces) When not to use a thin asphalt overlay Roads with unrepaired structural damage and/or insufficient structural capacity When not to use a thin asphalt overlay Bottom-up cracking Stripped layers 6

7 When not to use a thin asphalt overlay Alligator cracking Reflective cracking When not to use a thin asphalt overlay Excessive rutting Excessive thermal cracking Material Selection Binders Polymer Modified? Aggregates Top Quality (CDOT Spec. 703) LA Abrasion: 45 maximum Sodium Sulfate: 12 maximum Sodium Sulfate: 12 maximum FA Angularity (Uncompacted Voids): 45 Fractured Face: Table 3.14, 2013 Pavement Design Manual (60-90%) 7

8 Material Selection Aggregates Continued Plastic Index: 0 Clay Lumps and Friable Particles: None Natural Fines: Controlled by Fractured Face requirement Lift Thickness 3-5 times NMAS Material Selection Gradation SMA OGFC Dense-Graded Innovative Materials Sustainability Warm Mix Reclaimed Asphalt Pavement (RAP) Roofing Shingles (RAS) Crumb Rubber Mix Design Superpave CO Gyrations Table 3.9, 2013 Pavement Design Manual Nationally about average Nationally about average Typically 4-6% air voids VMA typically 15-16% minimum. NMAS? 8

9 Constructing Thin Lift Overlays On the project: For thin lifts, the bond between the old surface and the new overlay is especially important Because the overlay is thin, the interface between the old and new pavement is in close proximity to the shear forces created by vehicles during turning an braking movements. Constructing Thin Lift Overlays On the project: Realize that when paving thin lifts, each ton goes a long way and the paver can get down the road very quickly Don t allow the paver to leave the rollers behind Thin lifts cool very rapidly and need to be compacted more quickly than thicker lifts Hello-o-o-o-o back there! Constructing Thin Lift Overlays 3 Inch Lift 50 F Air, Surface Temp Mix Delivery temp F 44 minutes to complete compaction operations 1 Inch Lift 50 F Air, Surface Temp Mix Delivery temp F 7 minutes to complete compaction operations 9

10 Construction Highlights Moisture Stockpile management Plant speed Milling Adds cost Improves performance Profile Interlayer bond Use a fine-toothed drum Construction Highlights Tack Coat About 0.12 gal/yd 2 undiluted emulsion Paving Mixture cooling Compaction No vibration generally Pneumatic breakdown caution Steel finish OGFC? 10

11 Checklist Items of Note Surface Preparation Cracks sealed or otherwise corrected Rutting corrected typically with milling Proper grade and cross-slopeslope Leveling of manholes, catch basins, and utilities Clean dry surface Properly applied and cured tack coat Checklist Items of Note Trouble Shooting Low discharge temperatures Uncoated aggregate Mix segregation Poor density Dull or lean appearing mix Slumped mix Tearing of mix while rolling Poor pavement smoothness Resources 11

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13 Wrap Up Thin Lift Overlay Benefits Distress corrector Ride improver Noise reducer Noise reducer Geometrics preserver Life Expectancy 10 years plus over a sound asphalt surface 8-10 years over PCC 13

14 Questions? 14