Subgrade Stabilization of Roads by Plastic Waste

Abstract

The dual global challenges of managing escalating plastic waste and constructing resilient, cost-effective infrastructure demand innovative geotechnical solutions. This research investigates the feasibility of stabilizing problematic lateritic silty soil—a common subgrade material—using an eco-friendly composite binder. The study evaluates a proposed method blending 6% Cement, 4% plastic waste (comprising a mix of 2-4mm HDPE bottle strips and shredded waste cement bags), and 2% Rice husk Ash. The primary objective was to create a sustainable stabilization alternative that mitigtates the drawbacks of traditional methods, such as the high cost and carbon footprint of cement-only stabilization, and the poor durability of plastic-only applications. An experimental program was conducted to compare the geotechnical performance of the proposed blend against untreated (control) soil, soil treated with 4% plastic only, and soil treated with 6% cement only. The results demonstrated a significant enhancement in soil properties. The untreated soil exhibited very low bearing capacity (CBR: 2-6%; UCS: 0.05-0.15 MPa). The proposed composite blend achieved a superior California Bearing Ratio (CBR) ranging from 20-45% and an Unconfined Compressive Strength (UCS) of 0.8-3.0 MPa. This performance surpassed the cement-only stabilization (CBR: 15-35%; UCS: 0.6-2.0 MPa) by providing not only higher strength but also improved toughness and reduced brittleness. This study concludes that the proposed 6% Cement + 4% Plastic + 2% Rice husk Ash blend is a highly effective, economical, and sustainable solution. It successfully converts problematic waste materials into valuable engineering resources, reduces the overall carbon footprint by lowering cement consumption, and produces a balanced subgrade material with high strength and durability. This method presents a promising and eco-friendly alternative for road subgrade and foundation works.

Introduction

This research addresses two major global challenges: the environmental impact of construction materials, particularly cement, and the growing problem of plastic waste pollution. The study explores a sustainable solution by using waste plastic and agricultural waste to improve weak soils used in road construction and foundations.

The research focuses on lateritic silty soil, a problematic subgrade material with low bearing capacity and high moisture sensitivity. Traditional stabilization methods such as cement, lime, fly ash, and geotextiles have drawbacks including high cost, environmental impact, brittleness, long curing times, and installation complexity. Therefore, the study proposes a balanced stabilization method that is strong, durable, economical, and environmentally friendly.

Environmental Impact of Plastic Waste

The paper highlights the harmful effects of unmanaged plastic waste:

• Environment: Plastics block drainage systems, reduce soil fertility, contribute to flooding, release greenhouse gases, and pollute oceans and ecosystems.
• Humans: Exposure to plastic waste and microplastics can cause respiratory illnesses, hormonal disruptions, reproductive problems, and increased disease risks.
• Animals: Plastic ingestion and entanglement harm wildlife, causing injury, starvation, suffocation, and death. Plastic contamination also enters the human food chain through seafood consumption.

Materials Used

The study investigates the stabilization of lateritic silty soil using:

1. Ordinary Portland Cement (6%)
   • Provides strength through chemical binding.
   • Improves bearing capacity and compressive strength.
   • Drawbacks include high cost, CO? emissions, and brittleness.
2. Waste Plastic Strips (4%)
   • Made from HDPE bottles and shredded cement bags.
   • Improve flexibility, toughness, and crack resistance.
   • Provide mechanical reinforcement but limited bonding strength.
3. Rice Husk Ash (2–10%)
   • An agricultural waste product with pozzolanic properties.
   • Enhances durability, moisture resistance, and long-term strength.
   • Reduces cement consumption and environmental impact.

Proposed Composite Blend

The study proposes a combination of:

• 6% Cement
• 4% Waste Plastic
• 2% Rice Husk Ash

This composite blend combines:

• Cement's binding strength,
• Plastic's flexibility and crack resistance,
• Rice husk ash's durability and sustainability.

Key Results

Compared to untreated soil:

The results demonstrate:

• Significant improvement in strength and durability.
• Better resistance to moisture and cracking.
• Reduced construction cost.
• Lower environmental impact through waste utilization and reduced cement use.

Methodology

The experimental study compared four soil conditions:

1. Untreated soil (control)
2. Soil with 4% plastic only
3. Soil with 6% cement only
4. Soil with the proposed composite blend (6% cement + 4% plastic + 2% rice husk ash)

The stabilized soils were tested for geotechnical performance using standard laboratory methods.

Conclusion

In this case, the research shows that there are improvements in terms of increasing soil strength and sustainability through the integration of these materials. It is clear that the improvement can be noticed from the increase of CBR values from 6% to 43%, while UCS was enhanced to 3.10 MPa from 0.052 MPa. Moreover, deflection and swelling were also decreased significantly.

References

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Copyright

Copyright © 2026 Dr. Ajit Patil, Jay Shailesh Chotaliya, Shaikh Zaid Mohd Younus, Falaksh Pandurang Walke, Pravin Pandit Togare. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.