Abstract

Expansive soils, which are considered as problematic soils, swell when they imbibe water and shrink when water evaporates from them. Because of the alternate swelling & shrinkage the structures founded in these soils get severely cracked resulting in a huge financial loss. Present study was undertaken to evaluate the strength properties of soil after addition of stabilizing agents like industrial by-products such as Copper Slag and a chemical stabilizer named Zycobond. Laboratory tests were conducted to analyze the influence of varying percentages of Copper Slag (6%, 10%, 14%, 18%and 22% by dry weight of soil) along with a fixed dosage of Zycobond. Differential free swell Test, Modified Proctor Test, Atterberg’s Limits, California Bearing Ratio (CBR) and Triaxial tests were performed. The obtained results indicated that the addition of Copper Slag and Zycobond significantly reduced the Liquid limit , plasticity index and increased the maximum dry density. The CBR values also showed remarkable improvement. In this study the 82% ES + 18% CS mix was found to be optimum and with the addition of chemical additive Zycobond in 1.5 % to this mix , the soil attains greater CBR value.

Introduction

Expansive soils are clay-rich materials containing minerals like Montmorillonite, Smectite, and Bentonite, which undergo significant swelling and shrinkage with moisture changes. Due to their high compressibility, low strength, and low bearing capacity, they cause foundation failures, pavement damage, slope instability, and structural distress. Stabilization methods such as lime, cement, copper slag, and chemical additives like Zycobond can improve their engineering behavior.

Stabilizers Used

1. Copper Slag

A by-product of copper smelting with low silica, high strength-to-water ratio, and good environmental compatibility. It improves soil strength, reduces swelling, enhances shear parameters, and promotes waste utilization.

2. Zycobond

A water-soluble acrylic co-polymer that binds soil particles, increases hardness, reduces dust, and improves mechanical properties through chemical bonding.

Objectives of the Study

1. Evaluate expansive soil properties.

2. Study the effect of varying copper slag doses (6–22%) on soil strength.

3. Identify optimum copper slag content.

4. Study the effect of Zycobond (0.5–2%) on strength.

5. Find the best combined copper slag + Zycobond proportion.

6. Compare mechanical and chemical stabilization performance.

Findings from Literature

Previous research shows:

• Copper slag increases maximum dry density (MDD), decreases optimum moisture content (OMC), and reduces free swell index.

• Combinations of copper slag with rice husk ash improve CBR and reduce swelling significantly.

• Using Zycobond or nanomaterials reduces plasticity and enhances strength.

• Optimum copper slag content generally improves CBR but declines beyond certain percentages.

• Combined treatments significantly enhance subgrade suitability.

Methodology Summary

• Expansive soil was collected from East Godavari, Andhra Pradesh.

• Different mix proportions of Copper Slag (6–22%) and Zycobond (0.5–2%) were prepared.

• Tests conducted:

  • Differential Free Swell (DFS)

  • Atterberg Limits

  • Modified Proctor Compaction

  • California Bearing Ratio (CBR)

  • Triaxial Test

• Baseline soil properties:

  • Liquid limit: 67%

  • Plastic index: 38.6%

  • DFS: 95%

  • CBR: 1.34%

  • MDD: 1.51 g/cc

  • Soil type: CH (Highly Plastic Clay)

Key Results

1. Differential Free Swell (DFS)

• Swell index reduced drastically from 75% → 39% when Zycobond increased from 0 to 2% (with 18% CS).

• Combined stabilization provides the highest reduction.

2. Atterberg Limits

• Liquid limit (LL) and plasticity index (PI) decreased.

• Plastic limit (PL) increased.

• PI reduced from 23.2 → 9.5, showing major improvement in workability and reduced expansiveness.

3. Compaction Characteristics

• MDD increased from 1.74 → 1.87 g/cc with up to 1.5% Zycobond.

• OMC decreased, indicating improved densification.

4. CBR Strength

• CBR increased from 4.66% → 8.11% at 1.5% Zycobond (with 18% CS).

• Slight decline at 2% Zycobond.

• Indicates significant improvement in load-bearing capacity.

5. Shear Strength (Triaxial Test)

• Cohesion decreased gradually (78.4 → 62.25 kN/m²) due to reduced clay content.

• Angle of internal friction (φ) increased from 4.7° → 6.5° due to improved granular structure.

• Overall shear strength improved because frictional resistance increased.

Conclusion

The following conclusions were based on the laboratory studies carried out of Copper Slag and Zycobond found through the laboratory on this study. From the laboratory investigations the Optimum percentage research is 18% and 1.5% respectively Table -7: Optimum Percentages of FS and ZB, observed the laboratory investigations S.NO Additives Optimum percentage addition 1 Copper Slag 18% 2 Zycobond 1.5% 1) It was observed from the laboratory investigations that the addition of 18 % Copper Slag reduced the free swell of the expansive soil by 21 %, while the addition of 3 % Zycobond reduced the free swell of the Copper Slag treated expansive soil by 49.47% to untreated expansive soil. 2) It was noticed from the laboratory investigations that the addition of 18 % Copper Slag reduced the liquid limit of the expansive soil by 11.94%, while the addition of 3 % Zycobond reduced the liquid limit of the Copper Slag treated expansive soil by 22.68% to untreated expansive soil. 3) The laboratory investigations revealed that the plastic limit of the expansive soil Was increased by 26.50% with the addition of 18% CS and the plastic limit of CS treated expansive soil was Increased by 27.62% with the addition of 3 % Zycobond as an optimum when compared to untreated expansive soil. 4) It was observed from the laboratory investigations that the addition of 18% Copper Slag reduced the plasticity Index of the expansive soil by 39.89%, while the addition of 3% Zycobond reduced the plasticity index of the Copper Slag treated expansive soil by 67.09% to untreated expansive soil 5) It was found from the laboratory investigations that the optimum moisture content of the expansive soil has been decreased by 37.17% on addition of 18%% Copper Slag and further the optimum moisture content of Copper Slag treated expansive soil has been decreased by 45.90% with the addition of 3% Zycobond as an optimum when compared with untreated expansive soil. 6) It is observed from the laboratory tests that the OMC of the Expansive soil has been decreased from 28.06% to 17.63% on the addition of 18% CS and it has been further decreased from 17.63% to 15.18% with addition of 1.5% Zycobond. 7) It was found from the laboratory investigations that the maximum dry density of the expansive soil has been improved by 13.21% on addition of 18% Copper Slag and the maximum dry density of Copper Slag treated expansive soil has been improved by 19.25% with the addition of 3% Zycobond as an optimum when compared with untreated expansive soil. 8) It was observed from the laboratory investigations that the Soaked CBR value of the expansive soil has been improved by 71.24% on addition of 18% Copper Slag as an optimum and further the CBR value of Copper Slag treated expansive soil has been Improved by 83.47% with the addition of 3% Zycobond as an optimum when compared with untreated expansive soil. 9) It was observed from the laboratory investigations that the cohesion value of the expansive soil has been decreased by 17.82% on addition of 18 %Copper Slag as an optimum and further the value of Copper Slag treated expansive soil has been decreased by 32.78% with the addition of 3 % Zycobond as an optimum when compared with untreated expansive soil. 10) It is observed that the Angle of Internal Friction of the Expansive soil has been increased from 2.4? to 4.7? on addition of 18% CS and it has been further increased from 4.7? to 6.5? with addition of 1.5% Zycobond.

References

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Copyright

Copyright © 2025 MD. Ameena Begum, Dr. K. Ramu. 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.