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Pavement Thickness Design

Pavement Thickness Design. CTC 440. Objectives. Know how to determine the thickness of flexible/rigid pavements. Comprehensive Pavement Design Manual (PDM). NYS PDM can be found at https://www.dot.ny.gov/divisions/engineering/design/dqab/cpdm

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Pavement Thickness Design

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  1. Pavement Thickness Design CTC 440

  2. Objectives • Know how to determine the thickness of flexible/rigid pavements

  3. Comprehensive Pavement Design Manual (PDM) • NYS PDM can be found at https://www.dot.ny.gov/divisions/engineering/design/dqab/cpdm • Chapter 4 (New Construction/Reconstruction) is what we’ll cover https://www.dot.ny.gov/divisions/engineering/design/dqab/cpdm/repository/chapter4.pdf

  4. CPDM-Other Areas • Ch 2 Evaluation of Existing Pavements • Ch 3 Project Development Process • Ch 5 Rehabilitation • Ch 6 Materials • Ch 7 Shoulders • Ch 8 Pavement Joints • Ch 9 Subsurface Pavement Drainage • Ch 10 Preventative Maintenance

  5. Introduction: • NYSDOT uses a modified version of the AASHTO’s 1993 Guide for the Design of Pavement Structure • Features include • Thickness design procedure for pavements • 50-year design life • Permeable base layer for drainage • Edge drains or daylight • Full-depth shoulders

  6. Rigid Pavt. (PCC) Used for • High volume traffic lanes • Freeway-to-freeway connections • Exit ramps Advantages • Durability • Long service life • Withstands repeated flooding and subsurface water w/o deterioration DisAdvantages • May lose original nonskid surface • Must have even subgrade/uniform settling • Joints Reinforced • Contraction joints (50-100ft) • Epoxy-coated steel to prevent corrosion Unreinforced • Contraction joints (15-30x pavt thickness)

  7. Flexible Pavt. (HMA) Used for • Traffic and auxiliary lanes • Ramps, parking areas, frontage roads and shoulders Advantages • Adjusts to limited amounts of differential settlement • Easily repaired and overlaid • Non-skid properties do not deteriorate Disadvantages • Loses flexibility/cohesion over time • Must be resurface sooner than concrete • Not usually chosen where water is expected Minimum layer is usually 1-1/2” • 1-1/2” top course • 1-1/2” binder course • Remaining thickness is base course

  8. Material Design-Asphalt • Superpave http://www.youtube.com/watch?v=GPwWNKYrQw8 • Marshal Mix (old)

  9. Perpetual Pavement • Introduced in 2003 by the National Center for Asphalt Technology and the Asphalt Pavement Alliance • HMA pavement designed to last 50 years or more without major structural rehabilitation or reconstruction Ref: http://asphaltroads.org/images/documents/ghg-carbon_footprint_of_various_pavement_types.pdf

  10. Carbon Footprint of HMA and PCC Pavements http://asphaltroads.org/images/documents/carbon_footprint_web.pdf

  11. Why the Difference • Carbon is sequestered in the HMA pavement • CO2 is released when producing portland cement via kiln; limestone disassociation produces CO2 Ref: http://asphaltroads.org/images/documents/ghg-carbon_footprint_of_various_pavement_types.pdf

  12. Other “Greener” Pavements • Warm-Mix Asphalt (WMA) • 86.7 million tons in 2012 • Reclaimed Asphalt Pavement (RAP) • 68.3 million tons in 2012 • Reclaimed Asphalt Shingles (RAS) Other: Ground tire rubber, steel and blast furnace slag, other waste materials (repurposed into pavement) Reference Report: http://www.asphaltpavement.org/index.php?option=com_content&view=article&id=872&Itemid=61

  13. Basis for Thickness Design • Axle loading from truck traffic • An 80kN axle load (18-kip axle load in English units) is standard loading. All traffic is converted into the number of 80-kN passes that would cause the same structural damage • The converted # is referred to as the 80kN ESAL (Equivalent Single Axle Loads) • The effect of passenger cars, pickups, 2-axle trucks w/ single rear tires and buses (FHWA vehicle classes 1-4) are not even considered

  14. Rigid Pavements-ESAL • Modified AASHTO equation is used • Modified because NYSDOT experience is that pavements in NYS last longer than would be predicted from the original equation • Other method • Fatigue Strength

  15. Flexible Pavement-ESAL • AASHTO equation is used • Other methods • CALTRANS • Asphalt Institute

  16. Determining ESAL-Simple Method (worksheet on 4-9) • Design life • Initial 2-way AADT • % HV (class 4 or greater) • % of all trucks in the design direction • % of all trucks in the design lane • Truck equivalency factor • Annual truck volume growth rate • Annual truck weight growth rate

  17. ESAL Method-Steps • Determine ESAL • Determine HMA thickness by using table 4-5 • Mr-subgrade resilient modulus (load carrying capabilities of the materials below the pavt.) • Mr=28 (clay); Mr=62 (gravel) • Determine PCC thickness by using Table 4-4

  18. ESAL-example-both PCC and HMA (assume Mr=48 MPa)

  19. Example: Steps • Determine whether the traffic growth rate is simple or compound • Determine the growth rate and % traffic in the design direction • Determine the ESAL • Determine the pavement thickness

  20. Example-Answers • Determine whether the traffic growth rate is simple or compound (compound) • Determine the growth rate (2%) and % traffic in design direction (60%) • Determine the ESAL (see next slide) • HMA – 6.42E6 • PCC – 8.80E6 • Determine pavt. thickness • HMA 165 mm (7”) • PCC 225 mm (9”)

  21. ESAL-Based Method • Projects over 1.5 km in length

  22. Conventional Method • Projects < 1.5 km in length • Use Table 4-1 • For Interstate Highway Conventional Pavement Requirements see page 4-2 • For our previous example: • HMA 160mm (6.5”) • PCC not applicable

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