ENHANCING ROAD CONSTRUCTION WITH COIR AND WASTE PLASTIC IN BLACK COTTON SOIL

Abstract

This study explores the use of coconut fiber and micro-shredded waste plastic powder as stabilizers to enhance the engineering properties of black cotton soil for road construction. Two compositions were tested: 2% coir fiber with 4% plastic powder, and 0.9% coir fiber with 8% plastic powder. Laboratory analyses, including Atterberg’s limits, grain size distribution, compaction, California Bearing Ratio (CBR), and shear strength tests, assessed the impact of these additives on soil characteristics. Results revealed marked improvements in soil stability, compaction density, and shear strength, demonstrating the effectiveness of coir and waste plastic as eco-friendly stabilizing agents. These findings highlight the viability of sustainable materials in civil engineering, offering a promising solution for enhancing road infrastructure on expansive soils while contributing to waste management and environmental sustainability.

Specification

Description:FIELD OF INVENTION
This invention improves road construction on black cotton soil by reinforcing it with coir fibers and waste plastic materials. The addition of coir enhances soil stability and tensile strength, while waste plastic improves durability and reduces environmental waste. Together, these materials increase load-bearing capacity, minimize soil swelling, and create sustainable, cost-effective, and longer-lasting road surfaces.
BACKGROUND OF INVENTION
Road construction on black cotton soil poses challenges due to its high shrink-swell potential, low strength, and poor load-bearing capacity. These soils are expansive, causing roads to crack and deteriorate under varying moisture conditions, leading to costly repairs and maintenance. Traditional stabilization techniques often rely on chemical additives like cement or lime, which, while effective, contribute to environmental pollution and increase construction costs.
To address these issues, this invention utilizes coir fibers and waste plastic as eco-friendly, sustainable reinforcements for black cotton soil. Coir fibers, a natural byproduct of coconut processing, possess excellent tensile strength, flexibility, and biodegradability, making them suitable for soil reinforcement. When mixed with soil, coir fibers help reduce shrink-swell behavior and improve structural stability. Waste plastic, on the other hand, is abundantly available and offers durability and resistance to water absorption, which are critical for long-lasting road surfaces.
Incorporating these materials not only enhances the strength and durability of the road but also promotes environmental sustainability by repurposing waste plastic and agricultural byproducts. This approach provides a cost-effective solution for constructing resilient roads on challenging soils, with reduced environmental impact compared to conventional methods.
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SUMMARY
This invention presents an innovative approach to road construction on black cotton soil by integrating coir fibers and waste plastic to enhance soil stability, durability, and sustainability. Black cotton soil, known for its expansive properties, tends to swell when wet and shrink when dry, leading to cracking and weakening of road structures. Traditional stabilization techniques are often costly and environmentally harmful, necessitating a more sustainable solution.
The proposed method incorporates coir fibers, a natural, biodegradable material, and waste plastic, a durable, water-resistant material, into black cotton soil. Coir fibers significantly improve the tensile strength of the soil, reducing shrink-swell behavior and increasing resilience under varying moisture levels. Waste plastic, being non-biodegradable, enhances soil stability and water resistance, making the road structure more durable and less susceptible to damage from moisture fluctuations.
Together, coir fibers and waste plastic create a composite material that distributes loads more effectively, minimizes soil movement, and enhances the longevity of the road surface. This approach not only provides a practical solution to black cotton soil limitations but also promotes environmental sustainability by recycling waste materials, resulting in an eco-friendly, cost-effective method for building durable roads in challenging soil conditions.
DETAILED DESCRIPTION OF INVENTION
The rapid growth of infrastructure projects calls for innovative and sustainable materials for soil stabilization, particularly in areas where traditional methods are less effective. Black cotton soil, known for its expansive and shrink-swell characteristics, presents notable challenges in road construction, often resulting in structural failures, high maintenance costs, and shorter roadway lifespans. Thus, there is a pressing need for approaches that improve the durability and stability of black cotton soil in construction.
Recent advancements in material science suggest that agricultural and industrial by-products offer promising, sustainable alternatives for soil stabilization. Coconut fiber, a natural and biodegradable material, has garnered attention for its beneficial properties, including high tensile strength, elasticity, and low density. When incorporated into soil, coconut fiber enhances its physical and mechanical properties, increasing load-bearing capacity and reducing plasticity.
In parallel, the rise in global plastic waste creates an urgent demand for effective recycling solutions. Micro-shredded waste plastic powder provides a dual benefit: it repurposes plastic waste while contributing to soil stabilization. Adding this material to black cotton soil mitigates moisture-induced expansion and shrinkage, enhancing road layer performance.
This study examines the combined effects of coconut fiber and micro-shredded waste plastic powder in varying proportions to improve black cotton soil's engineering properties. Through laboratory tests-including Atterberg limits, grain size analysis, compaction, California Bearing Ratio (CBR), and shear strength tests-the research aims to identify optimal material ratios for soil stabilization. The findings promise to advance geotechnical engineering and foster sustainable practices in road construction by utilizing eco-friendly materials.
The methodology outlined here describes a structured approach to enhancing the engineering properties of black cotton soil (a type of expansive soil known for its high swelling and shrinkage potential) by incorporating coconut fiber and micro-shredded waste plastic powder. Below is a more detailed breakdown of the materials, preparation, tests conducted, and analytical approach.
Materials
1. Black Cotton Soil: Black cotton soil, known for its high swelling and shrinkage properties, was sourced locally. It was air-dried to eliminate excess moisture, then sieved to remove larger particles, ensuring a homogenous mixture and consistent test results. This soil type is prone to structural challenges like cracking due to its high expansiveness.
2. Coconut Fiber (Coir): Sourced from local suppliers, coconut fiber was chosen due to its availability, eco-friendliness, and biodegradability. Coir fibers add tensile strength and reduce soil cracking. The fibers were processed into short lengths (1-2 cm) to facilitate uniform mixing with the soil matrix, enhancing soil stability without disrupting soil structure.
3. Micro-Shredded Waste Plastic Powder: Recycled waste plastic was mechanically shredded into fine powder to aid in uniform mixing with the soil. The small particle size promotes even distribution, improving the soil's resilience and reducing swelling potential while contributing to waste reduction.
Methodology
Preparation of Soil Samples
Two mixtures of black cotton soil, coconut fiber, and waste plastic powder were created with predetermined ratios:
• Mixture 1: 2% coconut fiber + 4% micro-shredded waste plastic powder.
• Mixture 2: 0.9% coconut fiber + 8% micro-shredded waste plastic powder.
These additives were thoroughly mixed with the black cotton soil in the lab. The preparation ensured uniform distribution of fibers and plastic particles within the soil, essential for consistent test results and reliable comparisons between mixtures.
Laboratory Testing
To evaluate the treated soil's engineering properties, various standardized laboratory tests were performed, focusing on parameters critical to soil stabilization.
1. Atterberg's Limits:
o Liquid Limit: Using the Casagrande method, this test determines the water content at which soil changes from plastic to liquid state. The treated mixtures were evaluated to assess improvements in water resistance.
o Plastic Limit: The soil samples were rolled into threads until they broke, establishing the water content at which the soil transitions from plastic to semi-solid state. This is critical for assessing shrinkage control.
2. Grain Size Analysis: Using a sieve analysis, this test categorizes the soil's granular composition into gravel, sand, silt, and clay fractions, important for understanding soil texture and potential improvements in structural stability due to the additives.

3. Compaction Tests:
o Heavy Compaction (Standard Proctor Test): This test measures the soil's maximum dry density and optimum moisture content under high compactive effort. It's essential for evaluating the bearing capacity of the treated soil.
o Light Compaction: Similar to the heavy compaction test but with a reduced compactive force, this evaluates the soil's compaction characteristics under lighter loads, useful for different field applications.
4. California Bearing Ratio (CBR) Test: Performed on unsaturated samples, this test assesses the subgrade strength of the soil mixtures, indicating their load-bearing capacity and suitability for road base applications.
5. Free Swell Index: Measures the swelling potential of soil, which is crucial for expansive soils. Lower values in treated samples would indicate a reduction in swelling tendency, thus enhancing structural stability.
6. Specific Gravity: Determined using a pycnometer, specific gravity aids in understanding the density of soil particles, which helps in identifying the overall stability improvements imparted by the additives.
7. Moisture Content: Using the oven-drying method, moisture content is calculated, providing a basis for understanding water retention in the soil, which is essential for maintaining consistency in expansive soils.
8. Consolidation Test: This test evaluates the soil's compressibility under incremental loads, assessing its potential for settlement. This is important for long-term stability under load.
9. Direct Shear Test: Measures shear resistance, assessing the soil's angle of shearing resistance and cohesion, indicating the degree of stabilization achieved with additives.

10. Permeability Tests:
o Constant Head Method: Measures permeability in coarse-grained soils.
o Falling Head Method: Used for fine-grained soils like black cotton soil to assess how the additives affect water flow through the soil, relevant for drainage and soil stability.
11. Shrinkage Limit: Determines the moisture level at which soil volume remains constant upon drying, important for understanding shrinkage characteristics and reducing the cracking potential of expansive soils.
12. Swelling Pressure: Measures the pressure exerted by the soil when it swells, which is critical for expansive soils. Lower pressures in treated samples would indicate effective stabilization.
13. Tri-Axial Shear Test: A more comprehensive shear strength test under controlled conditions, it evaluates shear angle and cohesion, providing deeper insights into the soil's structural stability with additives.
14. Unconfined Compressive Strength (UCS): This test assesses the soil's load-bearing capacity without lateral confinement, indicating improvements in structural stability from the additives.
Data Analysis
The test results were compiled for statistical analysis to compare the engineering properties of the treated mixtures. The analysis aimed to identify the optimal ratios of coconut fiber and waste plastic powder that most effectively improve soil stability and reduce expansion. Key parameters evaluated include:
• Swelling Reduction: Changes in the free swell index and swelling pressure values to assess the impact on soil expansiveness.
• Shear Strength: Direct and tri-axial shear test results to evaluate soil's resistance to shearing forces.
• Load-Bearing Capacity: Improvements in CBR and UCS values indicating enhanced strength.
• Water Retention and Compaction: Comparison of moisture content, compaction, and Atterberg's limits results to determine the treated soil's suitability for different environmental conditions and load scenarios.
This methodology provides a comprehensive evaluation of the structural properties of black cotton soil treated with coconut fiber and waste plastic powder. Through rigorous testing and analysis, the study aims to develop a stabilized soil mixture that is both environmentally sustainable and structurally sound for civil engineering applications.
The data in Table I provide a comparative analysis of the geotechnical properties of black cotton soil under different treatment conditions, specifically examining the effects of adding coconut fiber and micro-shredded waste plastic powder (MSWPP). Initially, the liquid limit of untreated soil was 40%, which dropped significantly to 25% after treatment with 1.2% coir fiber and 4% MSWPP, demonstrating improved workability and reduced plasticity-qualities that enhance the soil's potential for road construction. Likewise, the plastic limit decreased from 26% in the untreated soil to 12% in the treated mixture, indicating that the coir fiber and MSWPP additives bolstered the soil's structural integrity and lowered its tendency to deform under varying moisture conditions.





TABLE I. Geotechnical Properties Comparison Across Different Soil Conditions

Based on Graph I, grain size analysis shows that the gravel content rose with the addition of coir fiber and MSWPP, peaking at 13% in the sample treated with 1.2% coir fiber and 4% MSWPP, which is within the ASTM D422 permissible limits. However, the sand content also increased in the treated samples, surpassing the allowable limit in the 0.9% coir fiber treatment, indicating a possible imbalance in soil gradation that warrants further investigation.

Graph I. Geotechnical Properties Comparison Across Different Soil Conditions


The treatment of black cotton soil with coir fiber and micro-shredded waste plastic powder (MSWPP) showed a noticeable reduction in silt and clay content, especially in the coir and MSWPP mixture, which is beneficial for enhancing drainage and reducing the soil's swelling potential. A key measure of soil expansiveness, the Free Swell Index (FSI), was significantly high in the untreated soil at 57.89%, indicating a strong tendency to swell. With the addition of 1.2% coir fiber and 4% MSWPP, however, the FSI decreased to 38%, marking a significant improvement in the soil's behavior in response to moisture. Nonetheless, FSI values remained above the permissible limit of 30%, suggesting that while these stabilization techniques positively affect soil properties, further adjustments to material ratios might be necessary to fully meet performance criteria. Overall, the results highlight that incorporating coconut fiber and MSWPP can substantially improve the geotechnical properties of black cotton soil, rendering it more suitable for road construction applications, although some fine-tuning of material proportions may be needed for optimal outcomes.
The Proctor test results, as summarized in Table II, provide useful data on the compaction characteristics of black cotton soil across different treatment setups. Maximum dry density (MDD) and optimum moisture content (OMC) were evaluated under both heavy and light compaction methods. For the untreated soil, heavy compaction produced an MDD of 1.98 gm/cc, while light compaction resulted in a slightly lower MDD of 1.94 gm/cc, with corresponding OMC values of 14% and 16%. These figures serve as reference points for assessing the impact of various additives on soil performance.





Table II: Proctor Test Results


GRAPH II. Proctor Test Results
Graph II shows that introducing 0.9% coir fiber led to a noticeable reduction in maximum dry density, with values dropping to 1.67 gm/cc under heavy compaction and 1.75 gm/cc under light compaction. This decrease suggests that the fibrous nature of coir fiber may be hindering compactibility, likely due to the formation of voids that prevent optimal particle packing. In contrast, adding 8% micro-shredded waste plastic powder (MSWPP) improved the maximum dry density to 1.82 gm/cc for heavy compaction and 1.92 gm/cc for light compaction, implying that MSWPP enhances compaction by filling voids and increasing overall soil density. When both materials were combined-1.2% coir fiber with 4% MSWPP-the maximum dry density was 1.78 gm/cc for heavy compaction and 1.87 gm/cc for light compaction, demonstrating an improvement in compaction with a stable optimum moisture content of 12%. This stability indicates that the coir and MSWPP mixture balances moisture effectively, enhancing soil compactibility. Overall, these results suggest that while coconut fiber alone reduces maximum dry density, MSWPP compensates for this effect, and a balanced combination of the two materials can improve compaction characteristics, potentially making black cotton soil more suitable for road construction. Further optimization of coir and MSWPP proportions may be beneficial to maximize density and minimize moisture content for practical use.
The California Bearing Ratio (CBR) test results in Table III offer important insights into the unsoaked load-bearing capacity of black cotton soil under various treatment conditions, which is essential for assessing subgrade strength in road construction. The CBR value is a crucial metric for determining the ability of subgrade materials to support traffic loads.
Table III: Unsoaked CBR Test Results

These CBR values reflect the enhanced load-bearing potential of the treated soil, highlighting the potential of coir fiber and MSWPP in improving the engineering properties of black cotton soil for road construction applications.

Graph III. Unsoaked CBR Test Results

These parameters are essential in evaluating the soil's stability under various loading conditions, offering valuable guidance for its application in road construction.

Graph IV. Direct Shear Test Results
The virgin soil exhibited an angle of shearing resistance of 27°, suggesting moderate shear strength. This value provides a baseline for evaluating soil behavior improvements when stabilization materials are incorporated. The cohesion value for the virgin soil was zero, typical of unconfined soil conditions, indicating a lack of inherent bonding forces.
When 0.9% coir fiber was added, the angle of shearing resistance slightly decreased to 26.88°. This marginal reduction suggests that, under these conditions, coir fiber alone may not significantly enhance the soil's shear resistance. As seen in Graph IV, the cohesion value remained at zero, indicating that coir fiber did not contribute to bonding within the soil mixture. In contrast, adding 8% micro-shredded waste plastic powder (MSWPP) increased the angle of shearing resistance to 30°, demonstrating that MSWPP positively impacts the soil's frictional resistance, likely due to mechanical interlocking within the soil matrix. However, the cohesion value stayed at zero, indicating no improvement in cohesive strength.
A combination of 1.2% coir fiber and 4% MSWPP led to a noticeable decrease in the angle of shearing resistance to 23°, while cohesion increased to 0.21 kg/cm². This result suggests that although shear resistance may be reduced, the mixture's cohesion improved, indicating that both materials together foster bonding within the soil structure, albeit with a trade-off in shear resistance. Overall, Direct Shear Test results indicate that while MSWPP enhances the soil's frictional properties, coir fiber alone does not significantly boost shear strength. The combination of both materials offers a balance between cohesion and friction, though further optimization is needed to improve overall shear strength for road construction applications. These findings highlight the complex response of soil to stabilization methods, underscoring the need for comprehensive testing in future studies.
The results from the Triaxial Test, shown in Table V, provide essential insights into the shear strength parameters of black cotton soil under various treatment conditions, focusing on cohesion and friction angle. These parameters are critical for understanding soil behavior under different loads, especially in road construction and foundation design contexts.
TABLE V. Triaxial Test Results


Graph V. Triaxial Tests Results
In the virgin soil, as shown in Graph V, the cohesion value was zero, which is typical for unconfined soil conditions, and the friction angle was 22.80°. These baseline values indicate that the soil has limited internal bonding and moderate shear strength, providing a reference point to assess the effects of various stabilization techniques.
With the introduction of 0.9% coir fiber, the friction angle increased to 24.10°. This suggests that coir fiber may enhance the soil's frictional resistance, likely due to the improved interlocking of particles facilitated by the fibrous structure. However, the cohesion value remained at zero, indicating that while frictional resistance improved, no significant cohesive strength developed from the fiber alone.
Adding 8% micro-shredded waste plastic powder (MSWPP) resulted in a slight cohesion increase to 0.25 kPa and a notable rise in the friction angle to 26.66°. This improvement suggests that the plastic powder positively impacts shear strength, potentially through mechanical interlocking and an increase in particle surface area, which enhances frictional resistance. The slight cohesion development implies that the plastic powder may introduce some bonding within the soil matrix.
The combination of 1.2% coir fiber and 4% MSWPP produced a cohesion value of 0.11 kPa and a friction angle of 25°. While this combination still enhances frictional properties relative to the virgin soil, it is less effective than using MSWPP alone. The reduced cohesion compared to the MSWPP-only sample suggests that the combination may not create as strong a bond as when the plastic is used independently.
In summary, the Triaxial Test results demonstrate that adding micro-shredded waste plastic significantly enhances both the friction angle and cohesion of the treated soil. In contrast, coir fiber's impact on cohesion is limited, though it may still improve frictional resistance when combined with other materials. These findings highlight the need to optimize the ratios of coconut fiber and MSWPP to achieve balanced improvements in cohesion and friction for enhanced soil stability in engineering applications. Further research is warranted to explore additional combinations and treatment strategies for maximizing these materials' benefits in soil stabilization.
The Swelling Pressure Test results in Table VI provide valuable insights into the expansive behavior of black cotton soil under various treatment conditions. Swelling pressure is a critical factor in assessing potential volume changes in clayey soils, like black cotton, which can undergo significant expansion and contraction with moisture changes.
TABLE VI. Swelling Pressure Test Results


Graph VI. Swelling Pressure Test Results
For the virgin soil, the swelling pressure was recorded at 0.32 kg/cm², reflecting the natural tendency of black cotton soil to expand upon exposure to moisture. This tendency underscores the soil's susceptibility to volumetric changes, which could affect its structural integrity and performance in construction settings. With the addition of 0.9% coir fiber, the swelling pressure slightly increased to 0.39 kg/cm². This modest rise indicates that while coir fiber may influence the soil's swelling capacity, it does not substantially reduce its expansive behavior. The coir fiber may improve soil structure by enhancing interparticle friction, but its effect on reducing swelling potential is limited.
The inclusion of 8% micro-shredded waste plastic powder (MSWPP) led to a more notable increase in swelling pressure, reaching 0.45 kg/cm². This suggests that MSWPP may actually elevate the soil's swelling potential, likely due to its hydrophobic properties, which could cause increased moisture retention within the soil matrix. The plastic particles may impede natural drainage and moisture control, contributing to a heightened swelling response.
The combination of 1.2% coir fiber and 4% MSWPP resulted in a swelling pressure of 0.42 kg/cm², lower than the 8% MSWPP treatment alone but still higher than the virgin soil. This outcome, as illustrated in Graph VI, indicates that while this mixture somewhat moderates the swelling pressure, it does not sufficiently reduce the expansive tendencies of the soil.
In summary, the Swelling Pressure Test results reveal that while adding coir fiber and micro-shredded plastic powder affects the swelling characteristics of black cotton soil, the overall swelling potential remains a challenge. The MSWPP addition appears to increase swelling pressure, while coir fiber alone does not significantly mitigate it. Therefore, further research into alternative combinations and additional additives is recommended to create an optimal mixture that minimizes swelling and improves black cotton soil's performance in engineering applications. Effective moisture management is crucial in ensuring stability and longevity for structures built on expansive soils.





DETAILED DESCRIPTION OF DIAGRAM
Graph I. Geotechnical Properties Comparison Across Different Soil Conditions
GRAPH II. Proctor Test Results
Graph III. Unsoaked CBR Test Results
Graph IV. Direct Shear Test Results
Graph V. Triaxial Tests Results
Graph VI. Swelling Pressure Test Results , Claims:1. Enhancing Road Construction with Coir and Waste Plastic in Black Cotton Soil claims that the Atterberg Limits and grain size analysis revealed that adding coir fiber and MSWPP positively affected the soil's plasticity and particle distribution, enhancing its suitability for construction.
2. Incorporating 0.9% coir fiber lowered both the liquid and plastic limits, indicating improved workability and stability in treated soil.
3. The addition of 8% MSWPP had a mixed impact on soil gradation, showing some benefits in particle distribution but with varied results depending on soil properties.
4. Proctor compaction tests showed that coir fiber reduced soil density while MSWPP enhanced it, suggesting that combining the two materials can create a balanced effect, although further ratio adjustments are recommended.
5. The California Bearing Ratio (CBR) values increased significantly with 0.9% coir fiber, achieving a CBR of 9.60%, highlighting coir fiber's strong contribution to load-bearing capacity. MSWPP alone had a limited effect on CBR.
6. Direct shear tests showed that coir fiber alone did not improve soil cohesion, but MSWPP enhanced frictional resistance. Combining both materials slightly reduced shear strength, underscoring the importance of optimizing their proportions.
7. Triaxial tests confirmed that MSWPP increased the soil's friction angle, while coir fiber and MSWPP combined slightly reduced cohesion. This balance suggests that precise ratios are critical to maximizing the advantages of both materials.
8. Swelling pressure tests indicated that coir fiber had minimal impact on reducing swelling, while MSWPP slightly exacerbated it, highlighting the need to manage swelling in expansive soils.
9. Overall, coir fiber demonstrated a more significant improvement in the mechanical properties of black cotton soil, while MSWPP contributed additional frictional resistance.
10. These findings support the potential for coconut fiber and MSWPP as soil stabilization agents, but optimal proportions are essential to achieve the best balance of strength and swelling control, paving the way for effective future applications.

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