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PAVEMENT THICKNESS DESIGNCTC 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
Chapter 4 (New Construction/Reconstruction) is what we’ll cover https://www.dot.ny.gov/divisions/engineering/design/dqab/cpdm/repository/chapter4.pdf
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
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
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)
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
MATERIAL DESIGN-ASPHALT
Superpave http://www.youtube.com/watch?v=GPwWNKYrQw8
Marshal Mix (old)
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
CARBON FOOTPRINT OF HMA AND PCC PAVEMENTS
http://asphaltroads.org/images/documents/carbon_footprint_web.pdf
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
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
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
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
FLEXIBLE PAVEMENT-ESAL
AASHTO equation is used Other methods
CALTRANS Asphalt Institute
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
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
ESAL-EXAMPLE-BOTH PCC AND HMA (ASSUME MR=48 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
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
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 – 6.42E6PCC – 8.80E6
Determine pavt. thicknessHMA 165 mm (7”)PCC 225 mm (9”)
ESAL-BASED METHOD
Projects over 1.5 km in length
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
Recommended