This document summarizes research on using thin whitetopping to extend the life of asphalt pavements. Finite element models were used to analyze the behavior of thin whitetopping under different conditions. Key findings include: 1) the interface bonding condition between the thin whitetopping layer and existing asphalt is the most important factor affecting performance, with unbonded interfaces experiencing much higher stresses; 2) having a tied and paved shoulder is effective at reducing stresses, especially for unbonded interfaces; and 3) thicker thin whitetopping layers and stiffer existing asphalt layers can further reduce stresses. The research provides guidance on thin whitetopping design to optimize performance and extend service life.

1. Extending Asphalt Pavement Life
Using Thin Whitetopping
Mustaque Hossain, Ph.D., P.E.
Department of Civil Engineering
Kansas State University

2. Disclaimer
The contents of this report reflect the views of
the authors, who are responsible for the facts
and the accuracy of the information presented
herein. This document is disseminated under the
sponsorship of the Department of Transportation
University Transportation Centers Program, in
the interest of information exchange. The U.S.
Government assumes no liability for the contents
or use thereof.

3. Slide design © 2009, Mid-America Transportation Center. All rights reserved.
Sharmin Sultana
University of Texas, Austin
Acknowledgements

4. Outline
 Background
 Objective
 Modeling of Thin Whitetopping Pavement
 Results
 Conclusions
 Recommendations

5. Background
 Whitetopping is the process of rehabilitating
asphalt concrete (AC) pavements using a
concrete overlay
 There are three types of whitetopping:
 Conventional: thickness > 8 in.
 Thin: thickness = 4-8 in.
 Ultra-thin: thickness < 4 in.

6. Thin Whitetopping Pavement
(US 287, Lamar, Colorado)

7. Thin Whitetopping Construction
(I-70, Salina, Kansas)

8. Thin Whitetopping Pavement
(I-70, Salina, Kansas)

9. Background
 Whitetopping Interface Bonding Condition:
 Bonded
 Unbonded
(After Rasmussen and Rozycki 2004)

10. Background
 Cases where whitetopping is feasible:
 Existing AC pavements highly deteriorated
(rutted and cracked)
 Adequate vertical clearance
 No AC layer settlement issues

11. Background
 Existing design procedures for whitetopping:
 AASHTO*
 Colorado*
 New Jersey
 PCA/ACPA
 Modified ACPA
 Illinois
 Texas*
* Thin whitetopping only

12. Objectives
 To assess the behavior of thin whitetopping
(TWT) with respect to:
 Thin whitetopping thickness (5 in., 6 in., and 7.5 in.)
 Existing AC thickness (5 in., 7 in., and 9 in.)
 Interface bonding conditions (Bonded and Unbonded)
 Existing AC modulus (250 ksi and 350 ksi)
 Shoulder (Unpaved or Paved)
 Temperature gradient
 To estimate the service life

13. Finite Element Modeling
 Structure: Thin whitetopping (TWT) on
existing AC pavement
 FE software: SolidWorks
 Pavement model: A three-layer pavement
system:
 TWT
 Existing HMA/AC layer
 Subgrade layer
(After McGhee 1994)

14. Finite Element Modeling
 Layer materials: Isotropic and linear elastic
 Mesh: High quality
 Symmetry: Both geometry and loading
 Pavement segment : 3-ft. wide & 30-in. in depth
 Joint spacing: 6 ft.

15. Finite Element Models
With Tied and Paved Shoulder No Tied or Paved Shoulder

16. Model Loading
• Loading: 20,000 lbs on a single axle with
dual tires (legal load in Kansas)
• Loaded area: Rectangular, normal,
uniform, and equal to the tire inflation
pressure
• Self weight: Considered for all layers

17. Model Loading
No Paved Shoulder
Paved Shoulder (After Dumitru 2006)

18. Analysis Results
• The critical response, maximum transverse
tensile stress, was found at the bottom of the
thin whitetopping (TWT) layer
• It varied from 75 psi for bonded 7.5-in. TWT
to as much as 442 psi for unbonded 5-in. TWT

19. Effect of Interface Condition
0
50
100
150
200
250
300
350
400
450
500
Bonded Unbonded
Interface Condition
PCCStress(psi)
5 in.TWT
6 in. TWT
7.5 in.TWT

20. Effect of Interface Condition
Unpaved Shoulder Paved Shoulder
0
50
100
150
200
250
300
350
400
450
Bonded 0.75 0.5 0.25 0
Frictional Coefficiant
PCCStress(psi)
AC Modulus
250 ksi
AC Modulus
350 ksi
0
50
100
150
200
250
300
350
400
Bonded 0.75 0.5 0.25 0
Frictional Coefficiant
PCCStress(psi)
AC Modulus
250 ksi
AC Modulus
350 ksi

21. Effect of TWT Thickness
Bonded TWT with Paved Shoulder Unbonded TWT with No Shoulder
PCC Stress vs. Bonded Unpaved TWT Thickness
(AC Modulus 250 ksi)
0
50
100
150
200
250
300
350
400
450
500
5 6 7.5
TWT Thickness (in.)
PCCStress(psi)
5 in.AC
7 in. AC
9 in.AC
PCC Stress vs. Unbonded Unpaved TWT Thickness
(AC Modulus 250 ksi)
0
50
100
150
200
250
300
350
400
450
500
5 6 7.5
TWT Thickness (in.)
PCCStress(psi)
5 in.AC
7 in. AC
9 in.AC

22. Effect of AC Thickness
0
20
40
60
80
100
120
140
160
180
5 7 9
AC Thickness (in.)
PCCStress(psi)
5 in.TWT
6 in. TWT
7.5 in.TWT

23. Effect of Existing AC Modulus
0
20
40
60
80
100
120
140
160
180
250 350
AC Modulus (ksi)
PCCStress(psi)
5 in.AC
7 in. AC
9 in.AC

24. Effect of Paved Shoulder
0
20
40
60
80
100
120
140
160
180
Unpaved Paved
Shoulder Condition
PCCStress(psi)
5 in.AC
7 in. AC
9 in.AC

25. Effect of Temperature Gradient
0
50
100
150
200
250
5 6 7.5
TWT Thickness (in)
CurlingStress(psi)
Bonded
Unbonded

26. Computation of Service Life
• In PCA method, allowable load
repetitions are calculated based on the
stress ratio (= calculated tensile
stress/modulus of rupture)
• If the stress ratio is less than 0.45, the
pavement can take unlimited load
repetitions

27. PCA model
• For S.R. > 0.55
• For 0.45 ≤ S.R. ≤ 0.55
• For SR < 0.45 N=Unlimited
S.R. = ration of flexural stress to modulus of rapture
N = number of allowable load repetitions
0828.0
97187.0
)(log10
SR
N


268.3
43248.0
2577.4








SR
N

28. Service Life (full bonding)
(for various ADTT level)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500

29. Service Life
(unbonded TWT & 5” AC)
(250 ksi AC Modulus and Unpaved Shoulder)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500
(350 ksi AC Modulus and Unpaved Shoulder)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500
(AC, 250 ksi AC Modulus and Paved Shoulder)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500
(AC, 350 ksi AC Modulus and Paved Shoulder)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500

30. Service Life
(unbonded TWT & 7” AC)
(250 ksi AC Modulus and Unpaved Shoulder)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500
(350 ksi AC Modulus and Unpaved Shoulder)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500
(250 ksi AC Modulus and Paved Shoulder)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500
(350 ksi AC Modulus and Paved Shoulder)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500

31. Service Life
(unbonded TWT and 9” AC)
0
2
4
6
8
10
12
5 6 7.5
TWT Thickness (in.)
ServiceLife(yrs)
≤200
300
400
500

32. Conclusions
• Interface bonding is the most important
factor that affects the longevity of thin
whitetopping
• Bonding has a more pronounced effect on
transverse tensile stress for the unpaved
shoulder condition than that of the tied
and paved shoulder condition
• Thin whitetopping thickness has a more
pronounced effect for the unbonded
interface condition than the bonded
condition

33. Conclusions (cont.)
• Tied, paved PCC shoulder decreases
stresses in thin whitetopping
• Tied, paved PCC shoulder is
particularly useful for unbonded thin
whitetopping with low truck traffic

34. Recommendations
• Field experimentation to investigate
actual behavior of thin whitetopping
• The effect of environment, subgrade
soil types, and different joint spacing
can be investigated

35. Recommendations (cont.)
• Pavement response under moving
loads would give a better
approximation of the actual scenario
• Partial bonding at the interface should
be investigated as it is very difficult to
achieve full bonding in the field

36. Thank You!