Geotechnical Enhancement of Subgrade Soils Using Recycled Polymeric Waste - A Review

Abstract

Subgrade soils form the foundation of pavement structures, and their mechanical properties play a crucial role in ensuring pavement durability and performance. Weak soils often result in deformation, low load-carrying capacity, and premature failure of pavements. Traditional stabilization methods, such as lime, cement, and fly ash, have limitations related to cost, carbon footprint, and sustainability. With the increasing accumulation of polymeric waste, researchers are exploring the use of recycled plastic materials (PET, PE, PP) as a sustainable soil stabilizer. This review critically examines 20 previous research studies on geotechnical enhancement of subgrade soils using polymeric waste. The analysis highlights improvements in strength, CBR, compaction, permeability, and resilient modulus, while identifying key limitations in current research. The study emphasizes the research gaps and proposes directions for future investigations to optimize polymer use for sustainable and durable subgrade soil improvement.

Introduction

Soil stabilization is a critical aspect of civil engineering, particularly for weak and expansive soils like clayey and black cotton soils, which are prone to low bearing capacity, high compressibility, and volume instability. To address these issues, researchers are turning toward sustainable and eco-friendly materials for improving soil performance.

Key Focus Areas:

1. Use of Plastic Waste in Soil Stabilization

• Plastic waste (e.g., PE, PP, PET) has been widely studied due to its non-biodegradability, availability, and reinforcement potential.

• Adding plastic in the form of shredded pieces, strips, or polymer-cement mixes has shown improvements in:

  • California Bearing Ratio (CBR)

  • Unconfined Compressive Strength (UCS)

  • Resilient modulus

  • Swelling reduction

2. Hybrid Stabilization Methods

• Researchers have combined plastic waste with other materials like natural fibers (e.g., coir), lime, recycled aggregates, and nanomaterials to further enhance strength, durability, and slope stability.

3. Emerging Technologies

• Innovative techniques such as:

  • Polymeric emulsions

  • Bio-mediated soil improvement

  • Microbial-Induced Calcite Precipitation (MICP)
    are being explored for more sustainable and efficient soil stabilization.

Notable Research Findings from Literature:

? Plastic & Gypsum Stabilization (Aly Ahmed et al., 2011):

• Combining recycled gypsum and plastic trays improved compressive and tensile strength.

• Reduced frost heave potential and capillary rise.

• Addressed recycling challenges for difficult-to-recycle materials like polystyrene.

? Plastic Bottle Chips (Sivakumar Babu et al., 2011):

• Adding 1% plastic improved UCS by up to 93.7%.

• Reduced pavement thickness and cost.

• Showed good stress–strain behavior and interlocking benefits.

? Waste Plastics in Subgrades (Hamid et al., 2017):

• Plastic strips enhanced bearing capacity and embankment stability.

• Provided a dual environmental and engineering benefit.

? Geopolymer vs. Cement (Ghadir et al., 2018):

• Volcanic ash-based geopolymer outperformed OPC in dry conditions (12 MPa vs. 4 MPa).

• Provided a lower-emission, high-strength alternative to traditional cement.

? Plastic in Earth Bricks (Akinwumi et al., 2019):

• Adding 1% plastic raised compressive strength by 244.4% in compressed earth bricks.

• Suitable for low-cost, sustainable housing.

? Nano CaCO? & Carpet Fibers (Choobbasti et al., 2019):

• Significant strength and ductility improvements in clayey soil.

• Showed effective nanotech + waste fiber synergy.

? HDPE Additives (Gupta et al., 2019):

• Improved soil’s shear strength, bearing capacity, and reduced swelling.

• Cost-effective and sustainable alternative to lime or cement.

? E-Waste in Soil (Kiran Kumar et al., 2019):

• E-waste remains underexplored in soil stabilization.

• Offers potential for improving soil and managing hazardous waste.

? Ceramic Waste + Coir Fiber (Shihab et al., 2020):

• Improved CBR, cohesion, and load-bearing capacity of clayey soils.

• Promoted eco-friendly subgrade stabilization using local waste materials.

? PET Bottle Strips (Peddaiah et al., 2020):

• Optimal improvement with 0.4% PET in silty sand.

• Strip size and placement orientation significantly affected performance.

• Called for broader testing and advanced geotechnical analysis.

? Comparative Waste-Based Stabilization (Amit Kumar Rai et al., 2020):

• Evaluated glass powder, plastic, and e-waste for stabilization.

• All showed potential for increasing UCS and CBR, with environmental benefits.

• Emphasized the need for integrated approaches and comparative studies.

Current Challenges & Research Gaps:

• Optimization of plastic type, size, and dosage for specific soils.

• Limited field testing under realistic environmental conditions.

• Lack of standard guidelines for practical implementation.

• Insufficient lifecycle assessments, cost-benefit analysis, and long-term durability studies.

Conclusion

In conclusion, the incorporation of plastic waste, natural fibers, recycled aggregates, and bio-mediated additives offers a sustainable and eco-friendly approach for improving the geotechnical performance of weak and expansive soils. Numerous studies have demonstrated that such materials can significantly enhance soil strength, bearing capacity, deformation resistance, and reduce swelling-shrinkage behavior, making them suitable for subgrade stabilization, embankments, and pavement applications. Hybrid stabilization techniques, combining plastics with fibers, lime, cement, or biological agents, have shown synergistic improvements in both mechanical and hydraulic properties, highlighting their potential for sustainable road construction. Despite these advancements, challenges remain in optimizing material type, size, content, and combinations for specific soil types. Limited field-scale validation, long-term performance assessment under environmental and cyclic loading, and lack of standardized guidelines continue to constrain practical implementation. Therefore, further experimental and field-based studies are required to establish optimal usage parameters, evaluate durability, and ensure environmental and economic feasibility. Overall, the sustainable utilization of plastic and other waste materials in soil stabilization not only addresses critical waste management issues but also contributes to resilient, cost-effective, and environmentally responsible infrastructure development.

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Copyright

Copyright © 2025 Krish Durge, Sujal Bhalerao, Pranav Kode, Isha Chilkewar, Prof. Atul D Gautam. 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.