Semester of Graduation

Fall 2020

Degree

Master of Civil Engineering (MCE)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

Infiltrated moisture combined with repeated action of traffic and environmental loading generates distresses which adversely affect the durability of asphalt pavements. Almost 94% of states' highway agencies use either the Loaded Wheel Tracking (LWT) test or the Modified Lottman test to capture asphalt mixtures' moisture susceptibility. However, the current LWT and the modified Lottman test practice lack accuracy in relating laboratory performance to observed field performance.

The study's primary objective was to evaluate the capability of different laboratory mechanical test methods to predict moisture susceptibility of asphalt mixtures. Asphalt binder and mixture experiments were conducted to achieve the objective of the study. The study utilized two asphalt binder types (PG 67-22 and PG 70-22) along with three aggregates (limestone, crushed gravel, and semi-crushed gravel). Both the asphalt binder and asphalt mixture experiments included five levels of moisture conditioning; 1) short-term aging (control); 2) single freeze-thaw (FT-1); 3) triple freeze-thaw (FT-3); 4) MiST 3500; and 5) MiST 7000. The asphalt binder experiment included rheological characterization of conditioned asphalt binder using Frequency Sweep test and MSCR test. Seven 12.5mm NMAS asphalt mixtures were employed in the asphalt mixture experiment. A suite of mechanical test methods, including the LWT, the modified Lottman, and the SCB test, was conducted on moisture conditioned asphalt mixtures.

Freeze-thaw and MiST conditioning resulted in a stiffer asphalt binder when compared to the control. The LWT and the SCB test exhibited an increase in moisture damage associated with progressive freeze-thaw and MiST conditioning of asphalt mixtures. In contrast, the modified Lottman test showed consistent test results only with freeze-thaw conditioning. Observing moisture damage caused by conditioning levels made it possible to predict moisture susceptibility of the asphalt mixture. Employed mechanical test methods reported an increase in moisture resistance of asphalt mixtures with either SBS modified asphalt binder or with anti-strip asphalt binder when compared to conventional asphalt binder. Furthermore, the SCB test and the LWT test results showed a similar trend in predicting the aggregate type's effect on the asphalt mixture's moisture susceptibility. The SCB test exhibited the potential to capture moisture damage in asphalt mixtures. To standardize the SCB test as a moisture damage test, a thorough investigation to relate laboratory performance to observed field performance should be done

Committee Chair

Mohammad N. Louay

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