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 ng/design/dqab/cpdm
Chapter 4 (New Construction/Reconstruction) is what we’ll cover 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
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:

12. Carbon Footprint of HMA and PCC Pavements

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:

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: ew=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
359
215
2021
4260
437
262
2031
5192
533
329
2041
6330
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

30. Other Pavement Software
Simplified pavement design. Version 2.0 has anew module for asphalt overlay designs.
Developed to analyze roughness data from the FHWA’s 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.