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

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

Outline Background Objective Modeling of Thin Whitetopping Pavement Results Conclusions 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:  Bonded  Unbonded (After Rasmussen and Rozycki 2004)

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

Background Existing design procedures for whitetopping:  AASHTO*  Colorado*  New Jersey  PCA/ACPA  Modified ACPA  Illinois  Texas* * 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: SolidWorks Pavement model: A three-layer pavement system: TWT Existing HMA/AC layer Subgrade 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

Unpaved ShoulderPaved Shoulder

Effect of TWT Thickness Bonded TWT with Paved ShoulderUnbonded TWT with No Shoulder

Effect of AC Thickness

Effect of Existing AC Modulus

Effect of Paved Shoulder

Effect of Temperature Gradient

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 rapture N = number of allowable load repetitions

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

Service Life (unbonded TWT & 5” AC)

Service Life (unbonded TWT & 7” AC)

Service Life (unbonded TWT and 9” AC)

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

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!