Pavement Thickness Design

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Pavement Thickness Design

• CTC 440

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Objectives

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

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Comprehensive Pavement Design Manual (PDM)

• NYS PDM can be found at https//www.dot.ny.gov/div
  isions/engineering/design/dqab/cpdm
• Chapter 4 (New Construction/Reconstruction) is
  what well cover https//www.dot.ny.gov/divisions/
  engineering/design/dqab/cpdm/repository/chapter4.p
  df

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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

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Introduction

• NYSDOT uses a modified version of the AASHTOs
  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

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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
•  

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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
•  

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Material Design-Asphalt

• Superpave http//www.youtube.com/watch?vGPwWNKYr
  Qw8
• Marshal Mix (old)

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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

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Carbon Footprint of HMA and PCC Pavements
http//asphaltroads.org/images/documents/carbon_f
ootprint_web.pdf
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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

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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/i
  ndex.php?optioncom_contentviewarticleid872It
  emid61

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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

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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

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Flexible Pavement-ESAL

• AASHTO equation is used
• Other methods
• CALTRANS
• Asphalt Institute

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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

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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.)
• Mr28 (clay) Mr62 (gravel)
• Determine PCC thickness by using Table 4-4

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ESAL-example-both PCC and HMA (assume Mr48 MPa)
AADT HV DHV DDHV
2006 3165 6 325 195
2011-ETC 3494 6 359 215
2021 4260 6 437 262
2031 5192 6 533 329
2041 6330 6 650 390
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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

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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)

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ESAL-Based Method

• Projects over 1.5 km in length

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Conventional Method

• Projects lt 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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Other Pavement Software

• http//www.pavexpressdesign.com/
• Simplified pavement design. Version 2.0 has anew
  module for asphalt overlay designs.
• http//iriexplorer.com/home/
• Developed to analyze roughness data from the
  FHWAs Long Term Pavement performance program,
  the tool allows for data to be analyzed by
  climatic region, traffic conditions, or network
  segment. IRI Explorer can also estimate the
  maintenance and use-phase greenhouse gas
  emissions for different pavement options.