Improving the Engineering Properties of Expansive Soil Using Bagasse Ash and Magnesium Chloride

Abstract

Expansive soils present significant challenges in geotechnical engineering due to their high shrink–swell potential and poor strength characteristics, making them unsuitable for pavement and foundation applications without treatment. This study examines the stabilization of Black Cotton Soil, using bagasse ash (BA) and magnesium chloride (MgCl?) as sustainable additives. Bagasse ash was incorporated at 5%, 10%, 15%, and 20%, while MgCl? was added at 2%, 4%, 6% and 8% Laboratory investigations, including index properties, modified compaction, California Bearing Ratio (CBR), and triaxial strength tests, were performed on untreated and treated soil to assess changes in engineering behavior. The results indicated that BA and MgCl? effectively reduced soil plasticity and enhanced density and shear strength within moderate dosage ranges. Higher contents, such as 20% BA and 8% MgCl?, produced inferior results, suggesting that excessive additive levels disturb the soil structure. Overall, the study confirms that the combined use of BA and MgCl? offers a practical and sustainable approach for improving the geotechnical performance of expansive soils.

Introduction

Expansive soils, particularly Black Cotton Soils rich in clay minerals such as montmorillonite, pose serious engineering challenges due to their high swelling–shrinkage behavior, low shear strength, and resulting structural damage. These soils are widespread in India and several other countries, making their stabilization an important global concern. Traditional stabilizers like lime and cement are effective but raise issues related to cost, carbon emissions, and environmental sustainability.

This study investigates a sustainable stabilization approach using Bagasse Ash (BA), an agro-industrial by-product rich in silica and alumina, and Magnesium Chloride (MgCl?), a hygroscopic salt that improves soil particle bonding. The combined use of BA and MgCl? aims to modify soil structure, reduce plasticity and swelling, and enhance strength and bearing capacity.

Black Cotton Soil collected from Chintalapudi Mandal, Eluru District, Andhra Pradesh, was classified as highly plastic clay (CH). BA was added in proportions of 5–20%, and MgCl? in proportions of 2–8% by dry weight, with higher dosages (20% BA and 8% MgCl?) found to be ineffective. Laboratory investigations were carried out on untreated and treated soil samples following Indian Standard codes.

Tests included differential free swell, Atterberg limits, compaction, California Bearing Ratio (CBR), and unconsolidated undrained triaxial shear tests. The methodology demonstrated that optimal combinations of BA and MgCl? significantly reduced swelling and plasticity while improving compaction characteristics, bearing capacity, and shear strength. Overall, the study highlights the potential of Bagasse Ash and Magnesium Chloride as environmentally friendly and effective stabilizers for expansive soils.

Conclusion

This study evaluated the effectiveness of Bagasse Ash (BA) and Magnesium Chloride (MgCl?) in improving the engineering properties of expansive Black Cotton Soil collected from Chintalapudi Mandal, Eluru District. Based on the laboratory investigations carried out on both untreated and treated soil samples, the following conclusions are drawn: 1) The untreated soil exhibited a high Differential Free Swell (DFS) value of 100%, confirming its highly expansive nature. The addition of BA and MgCl? significantly reduced the swell potential, with the minimum DFS of 32.5% obtained for the mix containing 79% soil + 15% BA + 6% MgCl?. 2) Specific gravity increased from 2.36 for untreated soil to 2.57 for the optimum treated mix, indicating an improvement in soil particle density due to chemical reactions and formation of stable compounds. 3) Atterberg limit results showed a considerable reduction in Liquid Limit and Plasticity Index with the addition of stabilizers. The Plasticity Index decreased from 49.51% to 7.32%, reflecting a substantial reduction in workability problems and swelling tendency. 4) Maximum Dry Density (MDD) improved from 1.42 g/cc (untreated soil) to 1.57 g/cc for the optimum mix, while the Optimum Moisture Content decreased from 44.4% to 34.22%. This demonstrates better soil packing and reduced moisture demand after stabilization. 5) The CBR value of the natural soil was very low (1.48%), making it unsuitable for pavement subgrades. Treated samples showed a significant increase, with the highest CBR of 8.74% achieved for the mix containing 15% BA and 6% MgCl?, indicating improved suitability for pavement layers. Laboratory results clearly show that moderate dosages of Bagasse Ash and Magnesium Chloride effectively enhance the strength, stability, and load-carrying capacity of expansive soil. Higher dosages such as 20% BA and 8% MgCl? produced inferior results, confirming that optimum stabilizer content is essential for achieving desirable performance. The combination of 15% Bagasse Ash and 6% Magnesium Chloride is identified as the optimum mix for improving the engineering behavior of the expansive soil used in this study. The use of BA and MgCl? provides a sustainable, cost-effective, and environmentally beneficial method for stabilizing expansive soils in geotechnical applications.

References

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Copyright

Copyright © 2025 Sajida Sulthana Mohammed, Songa Madhuri, Dr. D. Koteswara Rao. 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.