pavement design tips

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/engineeri
ng/design/dqab/cpdm
 Chapter 4 (New
Construction/Reconstruction) is what we’ll
cover
https://www.dot.ny.gov/divisions/engineeri
ng/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)

8. 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

10. MATERIAL DESIGN-ASPHALT
 Superpave http://www.youtube.com/watch?v=GPwWNKYrQw8
 Marshal Mix (old)

11. 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

12. CARBON FOOTPRINT OF HMA AND PCC
PAVEMENTS
http://asphaltroads.org/images/documents/carbon_footprint_web.pdf

13. 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

14. 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

15. 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

16. 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

18. FLEXIBLE PAVEMENT-ESAL
 AASHTO equation is used
 Other methods
 CALTRANS
 Asphalt Institute

20. 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

22. 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

23. 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

24. 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

25. 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”)

27. ESAL-BASED METHOD
 Projects over 1.5 km in length

28. 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