Niloy Gupta

Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Civil Engineering


Civil Engineering

First Advisor

Sahadat MD Hossain

Second Advisor

Warda Ashraf


Plastic waste generation has become a global concern, with a large portion of plastics ending up in landfills. China's recent decision to stop importing waste from various countries, including the USA, has exacerbated the issue of plastic pollution. These plastics, as coming from the household and commercial trash, contain impurity and contamination. This makes the recycling process of plastics more hectic and causes issues in reusing them for other purposes. Impurity and contamination, in fact, is a major issue in material science. Researchers have been studying ways to improve the performance of bituminous pavement, as highways are experiencing increased demand and various distresses such as rutting, fatigue cracking, and moisture-induced stripping. One potential solution being explored is the use of recycled plastic waste as an asphalt modifier. Studies in different countries have shown that waste plastic can effectively enhance pavement performance. However, most studies have used clean plastics, while plastics directly collected from landfills may contain impurities that can affect the performance of the aggregate-bitumen-plastic mix. This is particularly relevant in developing countries where plastics may not undergo thorough cleaning procedures. Therefore, the objective of this study is to find out the effect of impurity present in waste plastics in evaluating the performance of plastic road asphalt mix design. The experimental program for this study was divided into two parts. Preliminary, plastic wastes have been collected and the amount of impurity that the waste plastics can contain was determined. It was found that Low Density Polyethylene (LDPE) contains a higher amount of impurity than the other grades. Concurrently, the effect of impurity was determined on the performance and volumetric tests of the asphalt mix design. Since the effect was certain, further experiments have been carried out introducing specific percentage (10%, 20% and 30%) of impurity that replaces the plastic. 4% and 8% plastics have been mixed in the asphalt as a replacement of bitumen. High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE), and Polypropylene (PP) type plastics were utilized in this study to mix with Superpave SP-C mix with virgin and recycled aggregates such as Type C rock, Type D rock, man sand and Recycled Asphalt Pavement (RAP). According to this study, impurities in plastic waste can make the asphalt mix perform reciprocally in rutting depending on the type of plastic and the impurity contained by it. LDPE at 4% with impurity decreased the rut depth by 20%, however, PP at 4% with 30% impurity can increase the rut depth more than 30% compared to clean plastic use. Nevertheless, in all combinations of plastic and impurity, the rut depth is less than 4mm. In tensile strength, 4% HDPE with the increasing impurity showed a decline in the strength, however, using 8% HDPE with impurity resulted in the increased tensile strength. Allowing impurity in the asphalt mix with plastic made the mix more moisture susceptible compared to the clean plastic mix, however, PP with impurity up to 20% proved to be moisture resilient. Overall, the volumetric tests and the performance tests proved that plastics with up to 20% impurity can be allowed in the asphalt mix. Lastly, a Multiple Linear Regression (MLR) model was developed to determine the value of indirect tensile strength (IDT) for different combinations of plastic type, plastic content, and the impurity content present in the plastic. IDT was taken as the response variable because IDT values altered mostly due to the intrusion of impurity in the asphalt mix with waste plastic. This research work aimed to study the potential impurities present in the waste plastic that can affect the enhancing performance of plastic road. This study can help in the method of collecting and reusing waste plastics and reduce the cost of different variables in the process of managing the waste plastic before using them in the asphalt mix.


Rutting, Cracking, Moisture susceptibility, Skid resistance, Asphalt, Bitumen, Impurity, Contaminant, Waste Plastic, Plastic road


Civil and Environmental Engineering | Civil Engineering | Engineering


Degree granted by The University of Texas at Arlington

Available for download on Friday, August 01, 2025