Graduation Semester and Year

2022

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Unknown

Abstract

In recent past, the act of waste recycling has been diversified in manifolds across the world leading to evolution of newer recycling technique and fresh recycled product. Albeit plastic is one of those waste materials which is getting extremely difficult to get substantially recycled because of its record-breaking production, consumption, and its wide range of variations in properties ultimately leading to substandard recycling status of plastics globally. This seemingly poor status of waste plastics recycling against the gargantuan amount of fresh plastic products being added to consumer stream gives rise to a menacing one directional problem: Plastic Pollution, which is getting worse day by day. Having said that, designing a viable way for repurposing large scale plastic wastes instead of traditional recycling could divert that one directional problem to a more prosperous circular economy. One such way to repurpose large scale waste plastics is construction of an integrated plastic road incorporating shredded waste plastics in multiple layers of a flexible pavement. Concept of integrated plastic road would not only ensure macroscale use of plastic waste but also refrain the plastics being accumulated in the landfills eventually minimizing the worldwide waste plastics crisis. For this study, different types of plastics (HDPE, LDPE, PP, PET) have been incorporated with other recyclable components like Recycled Crushed Concrete Aggregate (RCCA) and regular pavement material like bitumen for base and surface course of a flexible pavement. However, introduction of plastics as a roadway material gives rise to the potential environmental hazard, and most importantly microplastic risk which itself is an emerging global concern. This study aims at identifying, quantifying, and characterizing microplastic risk associated with a plastic road from an ecotoxicological point of view. Moreover, a number of common environmental leaching tests (COD, TDS, TSS, Specific Conductance) have also been carried out and compared against the USEPA urban stormwater runoff benchmarks. Microplastic risk has been assessed with respect to the toxicity parameter called Predicted No Observed Effect Concentration (PNEC). PNEC is the maximum allowable microplastic concentration that could be tolerated by microorganisms without having any adverse physiological impacts. Microplastic concentration has been quantified using an optical microscope and qualified by using Fourier Transform Infra-Red (FTIR) spectroscopy to corroborate the presence of microplastic in experimented sample. Measured concentration was then divided by PNEC to get the Risk Characterization Ratio (RCR). If RCR value is less than 1, the corresponding microplastic concentration does not pose any threat to the ecological system. RCR values have been measured for two different weathering cases of base course and surface course of a plastic road. For case I, where base course cylindrical representative specimens are kept submerged in contained water for 28 days to collect the leaching sample, average RCR has been observed as 0.103 which is significantly lower than 1. In case I, samples incorporating PP plastic type exhibit relatively more RCR values ranging from 0.063 to 0.253. Case II also represent base course yet a different weathering condition where the cylindrical specimens were subject to cyclic loading before 28 days water submergence. This case resembles the long term microplastic risk characteristics. For this case, average RCR obtained is 0.735 which is higher that of case I, yet lower than the RCR threshold 1. In this case, however one incidence attributes to a RCR more than 1 involving PP type of plastic. The final case is representative of surface course incorporating shredded plastics. Leaching samples for this case are collected from submerged cylindrical specimen exerted by repetitive wheel passing in a Hamburg rutting test setup. For this case, average RCR observed is 0.186 which is the lowest of all three cases. Regardless of the case, weathering condition, plastic type, constituent percentage, this study shows that RCR value remains less than 1 implying that plastic road does not pose any ecological threat in terms of microplastic toxicity. And finally, this study also envisages Multiple linear Regression (MLR) models for both base and surface course to predict the RCR value based on primary constituent parameters and resulting predictor variables.

Keywords

Microplastic, Plastic road

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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