Date of Award

January 2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

First Advisor

Daba Gedafa

Abstract

Pavements are essential for economic development and mobility, with asphalt dominating the US road network due to its cost-effectiveness, ease of maintenance, and recyclability. However, the environmental impacts of asphalt production and the depletion of virgin materials have driven the integration of waste products into asphalt mixtures to improve sustainability. This study evaluated the engineering properties of waste-modified asphalt binders and mixtures as performance-based inputs for the Mechanistic-Empirical Pavement Design Guide (MEPDG). The rutting performance of ten asphalt mixtures commonly used in North Dakota was assessed using mechanistic and empirical tests. Mechanistic tests included the dynamic modulus (|E*|), Flow Number (FN), and incremental Repeated Load Permanent Deformation (iRLPD). Empirical results from the Hamburg Wheel Tracking Test (HWTT) performed by the North Dakota Department of Transportation (NDDOT) served as a comparative benchmark for rutting performance. Comparing FN and iRLPD parameters with HWTT rut depths yielded R2 values of 0.7498 and 0.6023, respectively, indicating their suitability as surrogate rutting performance tests. However, comparing |E*| values at 54.4°C and 5 Hz and at 37.8°C and 0.1 Hz with HWTT rut depths yielded R2 values of 0.5006 and 0.477, respectively, suggesting that additional research is needed to validate |E*| as a predictor for rutting under varying field conditions. Fatigue cracking performance was assessed on eight North Dakota mixtures using the Simplified Viscoelastic Continuum Damage (S-VECD) model. The values of damage characteristics, DR failure criteria, and apparent damage capacity index (Sapp-index) were derived from |E*| and cyclic fatigue test data using FlexMAT™ software. Comparison with the Cracking Tolerance index (CT-index) provided by the NDDOT yielded an R2 value of 0.3859, which was attributed to the different mechanisms between the two tests. Among the evaluated mixtures, HWY 52, which did not contain any RAP, exhibited the highest fatigue resistance. Conversely, the HWY 6 mixture, with 25% RAP, showed the lowest resistance, confirming the stiffening effect of high RAP content. The HWY 1 mixture, which incorporated 15% RAP and a softer PG 58S-34 binder, showed high fatigue resistance, highlighting the critical role of binder grade in counteracting RAP-induced stiffness. To improve the performance of high-RAP mixtures, this study also investigated the use of two waste-derived rejuvenators: waste engine oil (WEO) and wastewater bio-oil (WWB). A 50% RAP binder was blended with 10% and 40% WWB and 3% and 6% WEO, and evaluated using rheological (viscosity, Superpave grading, Multiple Stress Creep Recovery [MSCR], Linear Amplitude Sweep [LAS], Glover-Rowe Parameter [GRP]) and chemical (Fourier Transform Infrared Spectroscopy [FT-IR]) tests. WEO-modified blends demonstrated a significant restoration of rheological properties, and an optimal dosage of 4.3% was determined, whereas WWB showed limited rejuvenating capability. FT-IR spectra confirmed the presence of functional groups similar to conventional asphalt, supporting the compatibility of WEO and WWB as modifiers. Three asphalt mixtures were prepared: a control mixture containing virgin aggregates and PG 58S-28 binder, a 50% RAP mixture, and a 50% RAP mixture modified with 4.3% WEO. |E*| and uniaxial fatigue tests on these mixtures revealed that the WEO-modified RAP mixture displayed enhanced fatigue life and ductility compared to the 50% RAP mixture, while maintaining rutting resistance. Overall, the findings of this research support the use of FN and iRLPD tests as complementary to the HWTT, reinforcing their applicability within MEPDG frameworks. Although the CT and Sapp indices exhibited an R2 of 0.3859, their ability to characterize fatigue cracking resistance was validated, reflecting the differing mechanisms they capture. The study also confirmed the potential of WEO as an effective rejuvenator for high-RAP asphalt mixtures, restoring binder performance and improving fatigue resistance without compromising rutting resistance. These outcomes support the use of waste-derived materials in high-RAP mixtures and highlight the importance of integrating binder and mixture mechanistic tests for performance evaluation. The study also reinforces the need for localized calibration and test harmonization to implement these findings within the MEPDG framework, thus promoting sustainability.

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