pavement thickness design

PAVEMENT THICKNESS DESIGNCTC 440

OBJECTIVESKnow 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 well cover https://www.dot.ny.gov/divisions/engineering/design/dqab/cpdm/repository/chapter4.pdf

CPDM-OTHER AREASCh 2 Evaluation of Existing PavementsCh 3 Project Development ProcessCh 5 RehabilitationCh 6 MaterialsCh 7 ShouldersCh 8 Pavement JointsCh 9 Subsurface Pavement DrainageCh 10 Preventative Maintenance

INTRODUCTION:NYSDOT uses a modified version of the AASHTOs 1993 Guide for the Design of Pavement Structure Features includeThickness design procedure for pavements50-year design lifePermeable base layer for drainageEdge drains or daylightFull-depth shoulders

RIGID PAVT. (PCC) Used forHigh volume traffic lanesFreeway-to-freeway connectionsExit rampsAdvantagesDurabilityLong service lifeWithstands repeated flooding and subsurface water w/o deterioration DisAdvantagesMay lose original nonskid surfaceMust have even subgrade/uniform settlingJoints

ReinforcedContraction joints (50-100ft)Epoxy-coated steel to prevent corrosionUnreinforcedContraction joints (15-30x pavt thickness)

FLEXIBLE PAVT. (HMA) Used forTraffic and auxiliary lanesRamps, parking areas, frontage roads and shouldersAdvantagesAdjusts to limited amounts of differential settlementEasily repaired and overlaidNon-skid properties do not deteriorate

DisadvantagesLoses flexibility/cohesion over timeMust be resurface sooner than concreteNot usually chosen where water is expected

Minimum layer is usually 1-1/21-1/2 top course1-1/2 binder courseRemaining thickness is base course

MATERIAL DESIGN-ASPHALTSuperpave http://www.youtube.com/watch?v=GPwWNKYrQw8

Marshal Mix (old)

PERPETUAL PAVEMENTIntroduced 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 DIFFERENCECarbon 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 PAVEMENTSWarm-Mix Asphalt (WMA)86.7 million tons in 2012Reclaimed Asphalt Pavement (RAP)68.3 million tons in 2012Reclaimed 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 DESIGNAxle loading from truck trafficAn 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 damageThe 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-ESALModified AASHTO equation is usedModified because NYSDOT experience is that pavements in NYS last longer than would be predicted from the original equationOther methodFatigue Strength

FLEXIBLE PAVEMENT-ESALAASHTO equation is usedOther methodsCALTRANSAsphalt 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 laneTruck equivalency factorAnnual truck volume growth rateAnnual truck weight growth rate

ESAL METHOD-STEPSDetermine ESALDetermine 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% HVDHVDDHV2006316563251952011-ETC34946359215202142606437262203151926533329204163306650390

EXAMPLE: STEPSDetermine whether the traffic growth rate is simple or compoundDetermine the growth rate and % traffic in the design directionDetermine the ESALDetermine the pavement thickness

EXAMPLE-ANSWERSDetermine 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 8.80E6Determine pavt. thicknessHMA 165 mm (7)PCC 225 mm (9)

ESAL-BASED METHODProjects over 1.5 km in length

CONVENTIONAL METHODProjects < 1.5 km in lengthUse Table 4-1For Interstate Highway Conventional Pavement Requirements see page 4-2For our previous example:HMA 160mm (6.5)PCC not applicable

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