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