Soil Stabilization using Coffee Husk Ash and Lime

Abstract

Paddy soils pose significant construction challenges due to their unique physical properties. High water content, low bearing capacity, and high compressibility make them prone to settlement and deformation issues. Additionally, paddy soils have low shear strength, high plasticity index, and low permeability, increasing the risk of landslides, foundation instability, and waterlogging. Hence, there exists a need of improving the engineering properties of soil before using for construction by soil stabilization techniques. Here we are going to use coffee husk ash and lime as stabilizer in various proportion. The main objective of this study is to investigate the effect of coffee husk ash and lime on the engineering properties of paddy soil such as strength, Atterberg’s indices and CBR values. Coffee Husk Ash was added in two proportions, 10% and 20% with three proportions of lime, 4%, 5%, 6%.

Introduction

Background

Problematic soils like paddy soil—rich in clay and moisture-sensitive—are unsuitable for construction due to low strength, high plasticity, and instability. Stabilization improves their geotechnical properties. Traditional methods use chemical additives, but there is growing interest in sustainable alternatives. This study explores Coffee Husk Ash (CHA), an agricultural byproduct with pozzolanic properties, in combination with hydrated lime as a green stabilizer for paddy soil.

Objectives

1. Analyze the strength improvement due to CHA-lime stabilization.

2. Assess changes in soil index properties (LL, PL, PI).

3. Determine optimal CHA-lime mix ratios.

4. Evaluate effects on Maximum Dry Density (MDD) and Optimum Moisture Content (OMC).

5. Measure improvement in California Bearing Ratio (CBR).

6. Highlight environmental and economic benefits of CHA reuse.

Materials & Methods

• Paddy Soil: High clay content, moisture-sensitive, obtained locally.

• Coffee Husk Ash (CHA): From Malappuram, Kerala; created by uncontrolled burning of coffee husks.

• Hydrated Lime: Reacts with clay to reduce plasticity and enhance strength.

Six mix trials with varying CHA (10% & 20%) and lime (4%, 5%, 6%) proportions were tested. Laboratory tests included Atterberg limits, UCC, compaction, and CBR.

Key Results

1. Index Properties (Atterberg Limits)

• Plasticity Index (PI) reduced significantly from 10.56% to 2.04% (with 10% CHA + 6% lime).

• Liquid Limit (LL) dropped from 45% to 39% (same mix).

• Indicates lower water sensitivity and better workability of soil.

2. Unconfined Compressive Strength (UCC)

• Increased from 3.2 × 10?³ to 7.2 × 10?³ kg/cm² (at 10% CHA + 6% lime).

• 10% CHA with 6% lime found to be optimal; 20% CHA led to strength drop due to poor mix balance.

3. Compaction Characteristics

• Maximum Dry Density (MDD) improved from 1.74 to 1.82 g/cc.

• OMC decreased from 20.8% to 17.96% (at 20% CHA + 5% lime), indicating denser soil with less water.

4. California Bearing Ratio (CBR)

• CBR surged from 0.89% to 21.75% (at 20% CHA + 5% lime).

• Improved bearing capacity attributed to cementitious compounds formed via pozzolanic reaction (CSH, CAH).

Conclusion

Soil stabilization improves strength, durability, and load-bearing capacity. This study examined the effects of Coffee Husk Ash (CHA) and lime on soil properties. The liquid limit decreased from 45% to 39% with 10% CHA and 6% lime, while the plastic limit increased from 34.44% to 37.89% with 20% CHA and 4% lime. The plasticity index dropped from 10.56% to 2.04% with 10% CHA and 6% lime, making the soil less sticky. UCC strength improved from 3.5 × 10?³ Kg/cm² to 7.2 × 10?³ Kg/cm² with 10% CHA and 6% lime, but excess CHA (20%) reduced strength. MDD increased from 1.74 g/cc to 1.82 g/cc with 20% CHA and 5% lime, while OMC decreased from 20.8% to 17.96%. However, more lime increased OMC and reduced MDD due to excessive flocculation. The CBR value increased significantly from 0.89% to 21.75% with 20% CHA and 5% lime but decreased with higher lime content. CHA-lime treatment improved soil stability, reduced plasticity, and enhanced strength, with 10% CHA and 6% lime as the optimal mix. Future research should optimize mix ratios, explore other stabilizers, and assess long-term durability. CHA-lime stabilization is a sustainable, cost-effective method for improving soil in construction projects.

References

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Copyright

Copyright © 2025 Anees K, Fabi Sulaika P, Jyothisha K S, Fidha A P, Muhammed Ajlal K. 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.