Date of Award

2026

Document Type

Open 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

Committee Member 1

Quang Tran

Committee Member 2

Abdolmajid Erfani

Committee Member 3

Edward Laitila

Abstract

Over the past 30 years, the use of crumb rubber–modified asphalt (CRMA) has expanded significantly due to its enhanced mechanical performance and the sustainability benefits associated with recycling waste tires. As many of these pavements reach the end of their service life, they present a growing recycling challenge because the aging behavior and recycling mechanisms of CRMA are not yet fully understood. To address this gap, the research develops and evaluates a multiscale framework to characterize, rejuvenate, and design recycled CRMA using performance‑based criteria. Three integrated studies, supported by an extensive literature review, controlled laboratory aging, chemical analysis, and balanced mechanical performance testing were conducted to meet the rising need for sustainable recycling strategies as aged CRMA becomes increasingly common in reclaimed asphalt pavement (RAP) streams.

Study 1, presented in Chapter 2, synthesizes U.S. and international field experiences with CRMA recycling. The review shows that conventional milling and hot‑mix asphalt production equipment can effectively reclaim, process, and reuse aged CRMA pavements. At the same time, it identifies critical gaps in binder extraction procedures, understanding of rubber–binder interactions, and mix design protocols. These findings support the development of a hierarchical framework to guide pavement engineers and transportation agencies in selecting and implementing recycling strategies for aged CRMA. Study 2, documented in Chapter 3, examines the mechanical behavior of long‑term aged CRMA mixtures. Results indicate that soybean‑oil rejuvenation restores cracking resistance to levels comparable to or exceeding those of unaged mixtures, although rutting resistance decreases under moisture and shear‑induced loading. This underscores the importance of balanced performance considerations when designing recycled CRMA mixtures. Study 3, presented in Chapter 4, integrates Fourier Transform Infrared (FTIR) spectroscopy with IDEAL CT and IDEAL RT testing to quantify oxidation severity and rejuvenation efficacy. Soybean‑based rejuvenators reduce carbonyl and sulfoxide indices by 20–55% and significantly improve cracking performance, providing chemical justification for observed mechanical restoration.

Collectively, the findings demonstrate that aged CRMA pavements can be recycled, benefit from rejuvenation, and require balanced performance‑based design. The work establishes the chemical, mechanical, and practical foundation needed to support future recycling standards and optimize rejuvenator use for rubber‑modified asphalt pavements.

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