The thin white topping (TWT) can be a cost-effective measure that extends the life of existing asphalt pavements. This project is aimed at calibrating the TWT design method developed by the Colorado Department of Transportation using data from an experiment conducted under the accelerated pavement testing (APT) program at Kansas State University.

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

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

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

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

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

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

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

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

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 0.97187 − SR
log 10 ( N ) =
0.0828
3.268
• For 0.45 ≤ S.R. ≤ 0.55 N =


4.2577 

SR − .43248 
0
• For SR < 0.45 N=Unlimited
S.R. = ration of flexural stress to modulus of rapture
N = number of allowable load repetitions

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

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

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

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

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!