Graduation Semester and Year

Fall 2024

Language

English

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering

Department

Civil Engineering

First Advisor

MD Sahadat Hossain

Abstract

Managing solid waste, particularly non-degradable plastics, is a growing environmental concern due to its persistence and limited disposal options. With landfill space dwindling and costs increasing, innovative and sustainable solutions are critical. One promising approach is incorporating plastic waste into construction materials, specifically for subgrade soil stabilization in pavements. This study suggests a method that involves mixing recycled plastic with soil to enhance its properties.

To find out how useful this method is, LDPE, HDPE, PET, and PP plastics were shredded and mixed with soil in different amounts (2%, 3%, 4%, and 5% by weight). Laboratory tests, including compaction, unconfined compressive strength (UCS), and swelling tests, were conducted to evaluate the effects of plastic addition. The results showed that adding plastic reduced the maximum dry density (MDD) and increased optimal moisture content (OMC). The UCS of plastic-treated soils increased significantly, with improvements of up to 60% for LDPE, 105% for LDPE+PP, 27% for LDPE+PP+PET, and 130% for LDPE+PP+PET+HDPE. At 5% plastic content, swelling reduced for all combinations. Overall, the combination of LDPE, PP, PET proved to be the most effective in reducing soil swelling.

In conclusion, the study demonstrates that recycled plastics can effectively improve subgrade soils, providing both environmental and engineering benefits.

Keywords

Pavement, Subgrade, Plastic waste, Soil stabilizer

Disciplines

Geotechnical Engineering

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Available for download on Monday, December 29, 2025

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