Civil Engineering ETDs

Md Islam

Publication Date

9-1-2015

Abstract

Fatigue damage can be defined by a decrease in stiffness of Asphalt Concrete (AC) under repeated traffic loading. For each cycle of traffic loading, tensile strain develops at the bottom of AC layer of an asphalt pavement. Some localized damages occur in the material at minute-scale due to this developed tensile strain. These damages cause decrease in stiffness (E) of AC. Damage caused by a single vehicle is small. However the accumulated damage is not small if a large number of vehicles are considered over the design life of an asphalt pavement. After certain level of damage accumulation, bottom-up fatigue cracking initiates and forms alligator cracking at the surface. Like traffic loading, repeated day-night temperature cycle causes damages in AC. Damage due to a single day-night temperature fluctuation may be small. However the accumulated damage due to a large number of day-night temperature cycles may not be small. In this study, fatigue damage due to traffic loading is termed as traffic-induced fatigue damage, and fatigue damage due to temperature is termed as temperature-induced fatigue damage. The recently developed AASHTOWare Pavement Mechanistic-Empirical (ME) Design Guide predicts the fatigue performance of AC based on repeated traffic-induced tensile strain at the bottom of AC layer. Cyclic thermal strain due to day-night temperature fluctuation is not considered due to the fact that there is no closed-form solution or model available for calculating thermal fatigue damage. This study, for the first time, develops a closed-form equation for calculating the temperature-induced fatigue damage of AC. To develop the model, beam fatigue testing was conducted using different AC mixtures in the laboratory. The mechanical beam fatigue test data was correlated with the actual cyclic temperature loading test data. The model was then validated using an unknown test data. To that end, the developed model was calibrated for field conditions using the Falling Weight Deflectometer (FWD) test data. The developed model is used to evaluate fatigue damages of 34 Long-Term Pavement Performance (LTPP) test sections. Fatigue damage predicted by the traditional AASHTOWare Pavement ME Design approach, which considers only traffic-induced fatigue damage, is compared to the fatigue damage by the developed model which considers both traffic- and temperature-induced fatigue. Results show that the error may decrease by up to 29% through the incorporation of temperature-induced fatigue damage in the AASHTOWare Pavement ME Design approach. This means the reliability of alligator cracking prediction can be improved through the use of the developed thermal fatigue model. It is therefore suggested to include the temperature-induced fatigue damage model, which is developed in this study, in the AASHTOWare Pavement ME Design Software.

Keywords

Asphalt Concrete, Fatigue Damage, Temperature, Traffic, Alligator Cracking

Document Type

Dissertation

Language

English

Degree Name

Civil Engineering

Level of Degree

Doctoral

Department Name

Civil Engineering

First Committee Member (Chair)

Maji, Arup

Second Committee Member

Ng, Tang-Tat

Third Committee Member

Shen, Yu-Lin

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