Date of Award

2021

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering (PhD)

Administrative Home Department

Department of Civil, Environmental, and Geospatial Engineering

Advisor 1

Zhanping You

Advisor 2

Qingli Dai

Committee Member 1

Jacob Hiller

Committee Member 2

Gregory M. Odegard

Committee Member 3

Markus Oeser

Abstract

Asphalt mixture is the most widely used pavement engineering material. Because the laboratory tests of asphalt mixture are costly, researchers keep searching for a practical numerical simulation approach to facilitate their study on mixture design, compaction process, and service performance. Although the discrete element method (DEM) had been introduced into those research areas for more than three decades and has been proved to be an effective tool, its utilizing is still limited by lacking coarse aggregate morphologies, efficient modeling approaches, and complete mechanical theories. This study aims to extend the application of DEM in asphalt mixture research by 1) establishing a coarse aggregate morphology database. Coarse aggregates were categorized according to shape information and then scanned through a three-dimensional scanner. The essential morphology factors, including grain size, dimensions, surface area, volume, and specific surface area, were collected and analyzed; 2) building the gyratory compaction process. Loose material assembly was precisely generated through the developed algorithm according to the mixture design. The loose material was then compacted through the programed gyration moment. The impacts of contact parameters on compaction were investigated. Speed-up techniques were proposed and verified by analyzing the internal structure of the compacted mixtures; 3) developing a set of modeling procedures with high efficiency, low cost, reliable accuracy, and wide application. The new modeling procedures use coarse aggregate temples from the database to improve simulation accuracy and use geometry information from the gyratory compacted mixtures or random generation method to save laboratory specimens. Hexagonal close-packed (HCP) structure, which has advantages in simulating shear failure and Poisson’s ratio, was employed instead of the simple cubic-centered (SCC) structure. The corresponding mechanical calculation for contact micro-parameters was then derived and verify through simple stiffness/bond tests and complete indirect tensile (IDT) tests; 4) applying DEM models to research practice. Based on those improvements, this study involved DEM in the research of the mechanical performance of asphalt mixtures with high contents of ground tire rubber (GTR). Incorporate with laboratory tests, although asphalt mixtures with high contents of GTR have lower IDT strength of was than a conventional mixture, its cracking resistance and fatigue resistance were proved to be higher. By analyzing the contact force distribution in the DEM models, rubber particles with low moduli were found to be the endogenous reason for better performance. By further investigation, the rubber particles functioned as buffers that disperse the loadings. With the above four parts of research, the application of the DEM in asphalt mixture has significant improvement in modeling techniques, mechanical theories, simulation efficiency, and scope of application.

Available for download on Tuesday, August 09, 2022

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