Date of Graduation

12-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Andrew F. Braham

Committee Member

Kevin D. Hall

Second Committee Member

Zahid Hossain

Third Committee Member

Gary Prinz

Keywords

Asphalt, Flexibility Index, Fracture Energy, Fracture Test, Master Curve, Ruggedness Test, SC(B)

Abstract

Since cracking is one of the principal distresses to be considered in asphalt concrete, multiple fracture tests and geometries have been used to quantify cracking resistance. One of the most popular geometries that have been used in fracture tests is the Semi-Circular bend (SC(B)). However, for this geometry, most of the fracture test methods use different parameters such as thickness, testing temperatures, and loading rates. Thus, the purpose of this research was first to evaluate fracture energy by performing a ruggedness test based on ASTM E1169. Then, to apply fracture mechanics concepts to evaluate three specimen thicknesses (25, 50, and 100 mm) and three notch configurations (rectangular, semi-circular and fatigue pre-cracked). Also, with the selected thickness and notch configuration, the concept of time-temperature superposition was applied to characterize cracking in asphalt concrete by using four testing temperatures (-12, 0, 12, and 25 ˚C) and five loading rates (0.03, 0.5, 1.0, 30.0, 50.0 mm/min). The results showed that from the ruggedness test, the fracture energy is significantly influenced by the testing temperatures but not the loading rate. When applying fracture mechanics theories, the selected thickness and notch configuration selected were 50 mm and semi-circular, respectively. Finally, when using time-temperature superposition to plot fracture energy versus the loading rate to mimic the steps followed in the Dynamic Modulus |E*|, a typical sigmoidal was not obtained. However, a parabolic curve was found to better describe the cracking behavior. Utilizing this analysis, the concept of local fracture energy was defined as the peak fracture energy from each set of testing temperatures and loading rates. Using the local fracture energy, the global fracture energy was built and defined as the peak fracture energy from all the testing temperatures plotted. In conclusion, when properly applying fracture mechanics properties and the new concepts of local and global fracture energy, these give a new perspective of how the cracking behavior can be quantified at different testing temperatures independently of the loading rate.

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