Document Type

Thesis - Open Access

Award Date

2023

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Rouzbeh Ghabchi

Abstract

In recent decades, the use of different types of fibers in asphalt has become increasingly popular. Fibers are used in an asphalt mix to improve its durability and resistance against distresses such as rutting and cracking due to repetitive vehicle loading at high temperatures, and low-temperature contraction. Consequently, accurate rheological and performance characterization of asphalt binders and mixes containing fibers is of vital importance. With increased concerns over the environmental disruptions as a result of disposing end-of-life plastics in landfills and the need for improving sustainability of the construction materials, incorporating plastic in construction materials has always been an important topic for researchers. Among different types of plastics, containers made from polyethylene terephthalate (PET) constitute a large portion of the waste plastic problem. While using waste PET particles in asphalt mixes has been found to be a feasible option, mechanical properties of final product may not adequately benefit from the high modulus and tensile strength of PET plastic. In this study the end-of-life PET plastic obtained from bottled water containers was used for production of PET microfibers using a fiber production technique known as electrospinning. A solution-based electrospinning method was employed in the laboratory to produce electrospun PET microfibers (EPM) by using different concentrations of PET in the solution and discharge rates. Then, the effect of using EPM as an additive on asphalt mix properties was investigated. The selection of PET as the feedstock for EPM production was made due to its high thermal stability, ductility, surface area, and strain resistance. EPM was produced from a solution of micronized PET (MPET) in a mix of dichloromethane (DCM) and trifluoroacetic acid (TFA). Two MPET concentrations, namely 15 and 20% and various solution discharge rates, namely 40, 50, 60, 120, and 250 μL/min were utilized to determine the effects of the electrospinning parameters on the mechanical and chemical characteristics of the produced EPM. For this purpose, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and tensile strength tests were conducted on produced EPMs. To evaluate the feasibility of incorporating EPM in the asphalt mixes, a comprehensive testing program was carried out in this study. The performance of asphalt mixes containing different amounts of EPM was assessed by conducting Hamburg wheel tracking (HWT), semi-circular bend (SCB), and tensile strength ratio (TSR) tests. These tests were included in the experimental design to determine the resistance of the asphalt mixes to rutting, cracking, and moisture-induced damage. FTIR spectroscopy analysis revealed that the electrospinning parameters and solution’s proportions did not alter the molecular structure of the PET or generate new molecules. Analyzing the SEM micrographs showed that the diameter distribution in the EPM fibers decreased with a reduction in discharge rates at a constant MPET concentrations. In addition, morphological examination of SEM micrographs suggested that the most uniform and smooth fibers were consistently produced at the lowest discharge rate. Increasing the discharge rates resulted in the formation of fibers with rough textures, non-uniform in shape and size, and fractured. The mechanical properties of the produced EPM also exhibited a correlation with the fibers’ diameters. More specifically, fibers having smaller diameter resulted in enhanced mechanical properties. In view of the findings pertinent to the EPM’s chemical composition, morphological characteristics, mechanical properties, and yield consideration electrospinning using a solution of 20% MPET concentration and a discharge rate of 60 μL/min was found to result in EPMs of optimal mechanical and morphological properties. Performance tests conducted on asphalt mixes revealed that the addition of EPM to asphalt mixes improved their resistance to rutting, based on the HWT test. Asphalt mixes containing 0.5 and 1.0% EPM by binder weight tested in a HWT device exhibited a resistance to rutting and moisture-induced damage which were greater than those of the mixes which did not contain any EPM. However, increasing the EPM content to 1.5% by the weight of binder was not found to benefit its resistance to rutting. Conducting TSR tests on asphalt mixes revealed that incorporating EPM in the mixes enhanced their resistance to moisture-induced damage, confirming the findings of the HWT tests. Finally, conducting SCB tests revealed that incorporating EPM in asphalt mixes resulted in an improved resistance to cracking when compared to mixes which did not contain any EPM. Overall, it was concluded that incorporating EPM in asphalt mixes can potentially be a feasible approach to reduce plastic landfills and improve the performance and sustainability of the ground transportation system.

Publisher

South Dakota State University

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Rights Statement

In Copyright