Extending Asphalt Pavement Life Using Thin Whitetopping

Mustaque Hossain, Ph.D., P.E. Department of Civil Engineering

Kansas State University

DisclaimerThe 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.

Slide design © 2009, Mid-America Transportation Center. All rights reserved.

Sharmin SultanaUniversity of Texas, Austin

Acknowledgements

OutlineBackgroundObjectiveModeling of Thin Whitetopping PavementResultsConclusions Recommendations

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.

Thin Whitetopping Pavement(US 287, Lamar, Colorado)

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

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

Background

Whitetopping Interface Bonding Condition:BondedUnbonded

(After Rasmussen and Rozycki 2004)COE1

Slide 9

COE1 I removed the comma. o/k. default, 2/10/2012

Background

Cases where whitetopping is feasible:

Existing AC pavements highly deteriorated (rutted and cracked)Adequate vertical clearanceNo AC layer settlement issues

Background

Existing design procedures for whitetopping:

AASHTO*Colorado*New JerseyPCA/ACPAModified ACPAIllinoisTexas*

* Thin whitetopping only

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

Finite Element Modeling

Structure: Thin whitetopping (TWT) on existing AC pavement FE software: SolidWorksPavement model: A three-layer pavement system:

TWTExisting HMA/AC layerSubgrade layer

(After McGhee 1994)

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.

Finite Element Models

With Tied and Paved Shoulder No Tied or Paved Shoulder

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

Model Loading

No Paved Shoulder

Paved Shoulder (After Dumitru 2006)

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

Effect of Interface Condition

0

50

100

150

200

250

300

350

400

450

500

Bonded Unbonded

Interface Condition

PCC

Stre

ss (p

si)

5 in.TWT6 in. TWT7.5 in.TWT

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

PCC

Str

ess

(psi

)

AC Modulus250 ksiAC Modulus350 ksi

0

50

100

150

200

250

300

350

400

Bonded 0.75 0.5 0.25 0

Frictional CoefficiantPC

C S

tres

s (p

si)

AC Modulus250 ksiAC Modulus350 ksi

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.)

PCC

Stre

ss (p

si)

5 in.AC7 in. AC9 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.)PC

C St

ress

(psi

)

5 in.AC7 in. AC9 in.AC

Effect of AC Thickness

0

20

40

60

80

100

120

140

160

180

5 7 9

AC Thickness (in.)

PCC

Stre

ss (p

si)

5 in.TWT6 in. TWT7.5 in.TWT

Effect of Existing AC Modulus

0

20

40

60

80

100

120

140

160

180

250 350

AC Modulus (ksi)

PCC

Stre

ss (p

si)

5 in.AC7 in. AC9 in.AC

Effect of Paved Shoulder

0

20

40

60

80

100

120

140

160

180

Unpaved Paved

Shoulder Condition

PCC

Stre

ss (p

si)

5 in.AC7 in. AC9 in.AC

Effect of Temperature Gradient

0

50

100

150

200

250

5 6 7.5

TWT Thickness (in)

Curli

ng S

tress

(psi

)

BondedUnbonded

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

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 raptureN = number of allowable load repetitions

0828.097187.0)(log10

SRN −=

268.3

43248.02577.4

⎟⎠⎞

⎜⎝⎛

−=

SRN

Service Life (full bonding)(for various ADTT level)

0

2

4

6

8

10

12

5 6 7.5

TWT Thickness (in.)

Serv

ice

Life

(yrs

)

≤200300400500

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.)

Serv

ice

Life

(yrs

)

≤200300400500

(350 ksi AC Modulus and Unpaved Shoulder)

0

2

4

6

8

10

12

5 6 7.5

TWT Thickness (in.)

Serv

ice

Life

(yrs

)

≤200300400500

(AC, 250 ksi AC Modulus and Paved Shoulder)

0

2

4

6

8

10

12

5 6 7.5

TWT Thickness (in.)

Serv

ice

Life

(yrs

)

≤200300400500

(AC, 350 ksi AC Modulus and Paved Shoulder)

0

2

4

6

8

10

12

5 6 7.5

TWT Thickness (in.)

Serv

ice

Life

(yrs

)

≤200300400500

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.)

Serv

ice

Life

(yrs

)

≤200300400500

(350 ksi AC Modulus and Unpaved Shoulder)

0

2

4

6

8

10

12

5 6 7.5

TWT Thickness (in.)

Serv

ice

Life

(yrs

)

≤200300400500

(250 ksi AC Modulus and Paved Shoulder)

0

2

4

6

8

10

12

5 6 7.5

TWT Thickness (in.)

Serv

ice

Life

(yrs

)

≤200300400500

(350 ksi AC Modulus and Paved Shoulder)

0

2

4

6

8

10

12

5 6 7.5

TWT Thickness (in.)

Serv

ice

Life

(yrs

)

≤200300400500

Service Life(unbonded TWT and 9” AC)

0

2

4

6

8

10

12

5 6 7.5

TWT Thickness (in.)

Serv

ice

Life

(yrs

)

≤200300400500

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 unbondedinterface condition than the bonded condition

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

Recommendations

• Field experimentation to investigate actual behavior of thin whitetopping

• The effect of environment, subgrade soil types, and different joint spacing can be investigated

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

Thank You!