Enhancing the Properties of Expansive Soil Using Copper Slag and Ferric Chloride

Abstract

Expansive soils present a significant geotechnical challenge to pavement infrastructure due to their susceptibility to large volume changes with fluctuating moisture content, a behaviour manifests as differential settlement, cracking, and premature structural failure. While conventional soil stabilization techniques exist, they are often hindered by high costs, complex applications, or environmental concerns. This research, therefore, explores a sustainable and cost-effective alternative by utilizing industrial by-products to enhance the engineering properties of expansive soils. The primary objective is to systematically evaluate the efficacy of incorporating copper slag, in conjunction with ferric chloride, as a stabilization agent. This study assesses the impact of these admixtures on key geotechnical parameters, including Optimum Moisture Content (OMC), Maximum Dry Density (MDD), and California Bearing Ratio (CBR), to determine their suitability for pavement subgrade applications

Introduction

1. Introduction

Expansive soils, commonly known as black cotton soils, occupy around 20% of India’s land area and pose serious threats to infrastructure durability due to their high shrink–swell behavior.
This instability is caused by the presence of montmorillonite, a clay mineral that expands when wet and contracts when dry, resulting in deep cracks and structural damage to pavements, foundations, and canals.

Traditional stabilization methods using lime or cement improve strength but are energy-intensive and carbon-emitting. Hence, research has shifted toward eco-friendly, low-cost industrial by-products such as copper slag and chemical activators like ferric chloride.

2. Objectives of the Study

The study aimed to:

1. Determine the basic properties of expansive soil.

2. Examine the effect of varying copper slag content (13–17%) on soil strength.

3. Identify the optimum copper slag dosage for maximum improvement.

4. Evaluate the impact of ferric chloride content (0.5–2%) on stabilized soil.

5. Determine the best combination of copper slag and ferric chloride for peak strength enhancement.

3. Literature Review (Key Findings)

• Copper Slag: Studies by Amit Kumar Jangid (2023) and Rajendra Kumar (2017) showed that copper slag reduces the free swell index by up to 70% and increases CBR significantly (up to 495% unsoaked).

• Ferric Chloride: Sakr (2021) and Venkateswarlu (2019) found that FeCl? effectively reduces swelling and increases shear strength.

• Combined Use: Few studies have explored the synergistic effects of copper slag and ferric chloride together, creating a research gap that this study aims to fill.

4. Methodology

The experiment followed a systematic process including:

• Soil Collection: Expansive soil was collected from Yanamadala, Andhra Pradesh.

• Material Preparation:

  • Copper Slag (CS): Sourced from a smelting plant and used as a soil replacement (13–17%).

  • Ferric Chloride (FeCl?): Used as a chemical activator (0.5–2%) in solution form.

• Testing Phases:

  1. Atterberg Limits Test – to study plasticity and consistency.

  2. Differential Free Swell (DFS) Test – to assess swelling reduction.

  3. Modified Proctor Compaction Test – to find MDD and OMC.

  4. California Bearing Ratio (CBR) Test – to determine load-bearing strength.

5. Results and Discussion

(a) Untreated Soil Properties

• Liquid Limit: 81.7%

• Plasticity Index: 42.85%

• MDD: 1.54 g/cc

• OMC: 28.47%

• DFS: 100%

• CBR: 1.74%

• Classified as CH (Highly Plastic Clay)

(b) Effect of Copper Slag and Ferric Chloride

Observations:

• DFS decreased drastically from 100% to 10%, indicating a major reduction in swelling.

• Plasticity Index reduced from 42.85% to 16.24% with 15% CS + 1% FeCl?.

• MDD improved from 1.54 to 1.825 g/cc, and OMC reduced to 18.95%, showing better compaction.

• CBR increased from 1.74% to 9.05%, reflecting enhanced load-bearing capacity.

• The soil’s classification improved from CH to CI, signifying a shift to a less plastic, more stable material.

Optimum Combination:
?? 15% Copper Slag + 1% Ferric Chloride produced the best overall performance.

Conclusion

The following conclusions were drawn based on the laboratory studies of Copper Slag and Ferric Chloride obtained for this study. From the laboratory investigations, the Optimum percentages identified were 15% for Copper Slag (CS) and 1% for Ferric chloride (FeCl3) respectively. 1) The Differential Free Swell (DFS) was reduced by 60% with 15% CS and showed a total reduction of 85% upon the inclusion of 1% FeCl3. 2) The Liquid limit (LL) of the untreated Expansive soil (ES) showed a significant improvement of 25.34% following the incorporation of CS. A further increase of 48.76% was observed when 1% FeCl3 was subsequently added to the CS-treated soil. 3) The plasticity index (PI) demonstrated a substantial increase of 24.47% with the addition of 15% CS, which was further enhanced by 62.10% upon the inclusion of 1% FeCl3. 4) The Optimum Moisture Content (OMC) improved by 19.29% with 15% CS treatment, with an additional33.43% improvement following the inclusion of 1% FeCl3. 5) The Maximum Dry Density (MDD) improved by 14.61% with 15% CS treatment,18.50% with an additional improvement following the inclusion of 1% FeCl3. 6) The California Bearing Ratio (CBR) value improved by 136.78% with 15% CS and was significantly boosted by an additional 420.11% when 1% FeCl3 was introduced 7) The Specific Gravity of the soil improved by 4.58% with the 15% CS and showed a cumulative increase of 9.2% with the final addition of 1% FeCl3. The synergic combination of 15% Copper Slag and 1% Ferric Chloride significantly optimized the geotechnical properties of the air-dried Expansive soil. This stabilization treatment renders the soil suitable for use as a pavement subgrade material, conforming to the requirements outlined in the relevant IRC Codes of Practice

References

[1] Amit Kumar Jangid, Kamaldeep Singh Grover (2023) “Experimental investigation of mechanical properties of problematic expansive soil using copper slag and its statistical validation”. [2] Mohamed A. Sakr et al. (2021) “Enhancing the Swelling Characteristics and Shear Strength of Expansive Soil Using Ferric Chloride Solution”. [3] H. Venkateswarlu et al. (2019) “Strength Behaviour of Expansive Soil Treated with Quarry Dust and Ferric Chloride”. Ground Improvement Techniques and Geosynthetics, Lecture Notes in Civil Engineering 14. [4] C. Lavanya et al. (2017) “Study of Swelling Potential of Copper Slag Cushion Laid Over Expansive Soil Bed”. [5] Mohan chand et al. (2017) “Behavior of black cotton soil with addition of copper slag and steel slag”. International Research Journal of Engineering and Technology (IRJET), e-ISSN:2395-0056, p-ISSN: 2395-0072, Volume:04 Issue: 01 Jan-2017 [6] Mohammed A. Qureshi et al. (2015) “Improvement in soil properties of Expansive Soil by using Copper Slag”. International Journal of advance Research in Engineering, Science & Technology (IJAREST), ISSN(O):2393-9877, ISSN(P): 2394-2444, Volume 2, Issue 7, July- 2015 [7] D. Koteswara Rao, S. Vineela (2017): “A laboratory study oh the performance of expansive soil subgrade treated with Seashell powder and Ferric Chloride”. [8] P. Venkata Muthyalu et al. (2012) “Performance of chemically stabilized expansive soil”. [9] IS: 2720 part- 4 (1975): Grain size analysis. [10] IS: 2720 part-40 (1977): Determination of Free Swell Index. [11] IS: 2720 part-3 (1980): Determination of Specific gravity. [12] IS: 2720 part- 5 (1985): Determination of Liquid limit and Plastic limit. [13] IS: 2720 part- 8 (1983): Determination of Dry density and Optimum moisture content. [14] IS: 2720 Part-16 (1979): Determination of California bearing ratio.

Copyright

Copyright © 2025 Dr. D. Koteswara Rao, K. Jahnavi. 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.