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PPTG Thin Overlays Task Group

PPTG Thin Overlays Task Group. (TOADS) Team Overlay Asphalt Debaters Presented by Basem Muallem (CT) - Tony Limas (Industry) April 19, 2005. Toads Initial Meetings. Caltrans co chair Bill Moses Elected industry co chairs Skip Brown (no relation to Lance) Tony Limas (Back Up).

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PPTG Thin Overlays Task Group

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  1. PPTG Thin Overlays Task Group (TOADS) Team Overlay Asphalt Debaters Presented by Basem Muallem (CT) - Tony Limas (Industry) April 19, 2005

  2. Toads Initial Meetings • Caltrans co chair • Bill Moses • Elected industry co chairs • Skip Brown (no relation to Lance) • Tony Limas (Back Up)

  3. Toads Initial Meetings • Requested input from TG members • Outlined issues and priorities • Proposed changes to specifications • Discuss current state of pavements in CA

  4. TOADS Initial Work Plan • Prioritize the Issues • Set time tables to address issues • TG to provide recommendations to Caltrans • Caltrans shall consider and approve several recommendations to be successful with thin lift pavements • Safety for the public and employees will be enhanced

  5. Issues Received from Task Group • Issue: Specifications require maximum aggregate size in HMA mixture too large for specified lift thickness resulting in mat segregation and excessive in-place air voids • Recommendation: Select maximum aggregate size in accordance with industry standards to: • Attain target air voids to slow oxidation and reduce stripping potential • Reduce permeability in mat and at joints • Minimize segregation • Provide longer life pavements

  6. Industry Standard “if the nominal maximum aggregate size exceeds one third of the compacted lift thickness of the pavement layer, the surface texture of the mix can be affected, and the degree of density of the mix obtained by compaction may be reduced.”

  7. Industry Standard “the layer thickness should be should be equal to or greater than three times the nominal maximum aggregate size.”

  8. Recommended Lift Thickness for Quality Pavements • 19-mm Maximum Medium requires a 57-mm to 76-mm lift thickness • 12.5-mm Maximum Medium requires a 38-mm to 50-mm lift thickness • 9.5-mm Maximum requires a 29-mm to 38-mm lift thickness

  9. Issues Continued • Issue: Newer non-nuclear (electrical impedance) density gauges are replacing nuclear density gauges in the industry. Caltrans does not allow the use of the newer non-nuclear gauges. • Recommendation Caltrans should seriously consider adopting existing test procedures and modify specifications to accept the use of non-nuclear density gauges.

  10. Issues Continued • Issue: Contractors are not using pneumatic tire rollers on thin lift overlays when paving over rutted and/or uneven substrates. • Recommendation: Encourage the utilization of pneumatic tire rollers on thin lift overlays (Except for ARHM) when paving over a rutted and/or uneven substrates.

  11. Issues Continued • Issue: HMA bid quantities are based on the specified lift thickest resulting in significant underuns and insufficient layer thickness when the pavement substrate is rutted or uneven. • Recommendation: Base bid quantities on the thinnest or median lift thickness anticipated to eliminate significant underuns.

  12. Issues Continued • Issue: The single ambient temperature spec (50°F min.) is not (by itself) adequate to determine if there will be adequate time to compact the pavement to the desired density (in-place air voids). • Recommendation: Include other factors to determine if the compaction window is reasonable.

  13. MultiCool Software Program computes the time available for compaction. Example: • 300 ° F. mix temperature • 50°F substrate temperature • 50°F ambient temperature • 5 MPH wind

  14. 2-inch Lift (Time VS. Temp) 9 225.09 10 220.58 11 216.36 12 212.39 13 208.64 14 205.1 15 201.76 16 198.58 17 195.56 18 192.69 19 189.96 20 187.35 21 184.86 22 182.48 23 180.21 24 178.02 25 175.93 0 300 1 281.4 2 269.85 3 260.97 4 253.43 5 246.74 6 240.66 7 235.07 8 229.9

  15. 1-inch Lift (Time VS. Temp) 0 300 1 265.48 2 244.42 3 228.77 4 216.28 5 205.96 6 197.23 7 189.72 8 183.17 9 177.39

  16. Under Similar Conditions: A 2-inch lift takes approximately 25 minute to reach cessation temperature A 1-inch lift takes approximately 10 minutes to reach cessation temperature

  17. Other Considerations for Thin Lift AC Paving: • Coordinate trucking • Consider changing initial compaction temperatures • Include CQS1H in specs for a tack coat • Review all thin lift specs for needed improvements • Remove automatic screed control requirements for thin lift overlays with the exception of the joint matcher

  18. Gather Existing Best Practices for Thin Lift Paving • Utilize Existing Experiences from: • FHWA • Other DOT • Super Pave • PG Binders • NCPP • NCAT • TRB

  19. TOADS MISSION Bring Added Value to our State by: • Constructing longer lasting Pavements • Reducing cone zone days • Making California pavements safer • Makes the movement of goods and services more efficient. (Vital to California's Economy) Thank you, and be safe!

  20. Questions?

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