1. Transportation Engineering II
ECGD4228
Transportation Engineering II
Summer 2008
Saturdays 15:30-18:30 PM
K204
Dr. Wa'el M. Albawwab

2. Dr. Wa'el M. Albawwab albawwab@gmail.com
Lecture 6
Pavement Design Methods
Design Parameters
Flexible Pavement
Rigid Pavement
Dr. Wa'el M. Albawwab

3. Pavement Design Methods
A pavement consists of a number of layers of different materials
Pavement Design Methods:
AASHTO Method
The Asphalt Institute Method for Flexible Pavements
Portland Cement Association (PCA) Method for Concrete Pavements
Texas DOT Method
Other methods
Dr. Wa'el M. Albawwab

4. Dr. Wa'el M. Albawwab albawwab@gmail.com
AASHTO Road Test
AASHTO: American Association of State Highway and Transportation Officials
Objective: To relate axle load repetitions, pavement design configurations & distresses
Dr. Wa'el M. Albawwab

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ASSHTO Design Method
Pavement Performance
Traffic
Roadbed soils (subgrade materials)
Materials of construction
Environment
Drainage
Reliability
Shoulder Design
Life-Cycle Costs
Dr. Wa'el M. Albawwab

6. AASHTO’s Formula Considers: (1) Pavement Performance
Based on Pavement Serviceability concept
Serviceability was defined as the ability of a pavement to serve its intended function under existing conditions
During the test, road users rated pavements
Pavement Serviceability Rating (PSR)
Based on the pavement roughness
0-1: Very Poor; 1-2: Poor; 2-3: Fair; 3-4: Good; and
4-5: Very Good
Dr. Wa'el M. Albawwab

7. AASHTO’s Formula Considers: (1) Pavement Performance
PSR’s used to develop design equations to predict
Present Serviceability Index (PSI)
Initial Serviceability Index = p0 (the servceability immediately after the construction of the pavement, recommended
Terminal Serviceability = pt (2.5-major, 2.0-other), the minimum acceptable serviceability before resurfacing or reconstruction is needed.
In the formula: Serviceability loss
(PSI) = p0 – pt
Dr. Wa'el M. Albawwab

8. Pavement Condition Defined by users (drivers)
Develop methods to relate physical attributes to driver ratings
Result is usually a numerical scale
From the AASHO Road Test
(1956 – 1961)
Dr. Wa'el M. Albawwab

9. Dr. Wa'el M. Albawwab albawwab@gmail.com
Typical PSI vs. Time p0
Serviceability (PSI)
p0 - pt
Terminal Serviceability Level pt
Time
Dr. Wa'el M. Albawwab

10. AASHTO’s Formula Considers:
(2) Traffic
The concept of ESAL – Equivalent Single-Axel Load
The traffic characteristics are determined in terms of the number of repetitions of an 18,000 single-axle load applied to the pavement on two sets of dual tires.
Expressed in Equivalent 18-kip Single Axle Loads (W18)
Axle load equivalency factor was introduced to convert different axle loads to Equivalent 18,000 lb (18-kip) Single Axle Loads.
Dr. Wa'el M. Albawwab

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Vehicle Types
Dr. Wa'el M. Albawwab

12. Vehicle Weight & Size Limits
Weight limits for whole vehicle, single axles & tandem axles
Size limits for length, width & height
Dr. Wa'el M. Albawwab

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ESAL Determination
By Load Equivalency Factors (FE), i.e., number of repetition of 18 kip single-axle load.
Axels (lb)
Single
Tandem
Tridem
10000
0.0877
0.007
0.002
18000
1.0
0.077
0.017
40000
21.08
2.08
0.487
Dr. Wa'el M. Albawwab

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Load Quantification
Load Equivalency
Generalized fourth power approximation
Dr. Wa'el M. Albawwab

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ESAL Determination
For each axle category i; (single, tandem, tridem)
For all categories:
Dr. Wa'el M. Albawwab

16. Dr. Wa'el M. Albawwab albawwab@gmail.com
ESAL Determination
fd – design lane factor, which is the portion of total ESAL acting on the design lane (any lane of two lane highway and outside lane of multilane highway), from field data.
G – traffic growth factor for a specific design period
AADT – first year AADT
N – number of axles (each axle will repeat one load when vehicle is moving)
FE – Load equivalency factor
Dr. Wa'el M. Albawwab

17. AASHTO’s formula considers:
(3) Subgrade materials
Resilient Modulus (Mr) of the soil is considered in design, the value of Mr is normally known/given for design
Another parameter needs to know but not directly used in the AASHTO’s formula is CBR – California Bearing Ratio, which is a parameter indicative of soil’s strength. Relationship between Mr and CBR (or R value) is given by:
Mr = 1500 CBR (for soils with CBR ≤ 10)
Mr = CBR ( for 10 < CBR ≤ 20)
Dr. Wa'el M. Albawwab

18. AASHTO’s formula considers: (4) Materials of construction
SN – The Structural Number
Dr. Wa'el M. Albawwab

19. AASHTO’s formula considers: (4) Materials of construction
SN – The Structural Number for the road profile
Di – depth of layer i
mi – drainage coefficient for layer i
Dr. Wa'el M. Albawwab

20. AASHTO’s formula considers: (4) Materials of construction
Subbase construction materials: layer coefficient a3 is used to represent the quality of the material AND convert the actual thickness of the subbase to Structural Number (SN, is an engineering term indicative of the total pavement thickness).
Base construction materials: a2, and
Surface Course Construction materials: a1.
Dr. Wa'el M. Albawwab

21. AASHTO’s formula considers:
(5) Drainage
Purpose: consider the effect of drainage on the performance of flexible pavement
Represented by: mi, i =2,3 (represents the base and subbase layer.
Dr. Wa'el M. Albawwab

22. AASHTO’s formula considers:
(6) Reliability
Reliability level: the reliability that the pavement designed will survive for its design period.
E.g., a 50 percent reliability design level implies a 50% chance for successful pavement performance.
Presented by FR.
Dr. Wa'el M. Albawwab

23. AASHTO’s formula considers:
(6) Reliability
ZR : Standard normal variation for a given reliability
S0 : Estimated overall standard deviation
Dr. Wa'el M. Albawwab

24. Dr. Wa'el M. Albawwab albawwab@gmail.com
Other Issues
Drainage
Joints
Grooving (noise vs. hydroplaning)
Rumble strips
Climate
Level and type of usage
Failure examples are primarily related to design or life-cycle, not construction
Dr. Wa'el M. Albawwab

25. Dr. Wa'el M. Albawwab albawwab@gmail.com
Primary References
Mannering, F.L.; Kilareski, W.P. and Washburn, S.S. (2005). Principles of Highway Engineering and Traffic Analysis, Third Edition. Chapter 4
Muench, S.T.; Mahoney, J.P. and Pierce, L.M. (2003) The WSDOT Pavement Guide Interactive. WSDOT, Olympia, WA.
Muench, S.T. (2002) WAPA Asphalt Pavement Guide. WAPA, Seattle, WA.
Dr. Wa'el M. Albawwab