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<p>Expansive clay or Black Cotton Soil (BCS) poses notable challenges in pavement and foundation construction due to its behaviour of high swelling, plasticity, and low strength. This study aims to evaluate the geotechnical and microstructural performance of BCS stabilized with Red Mud (RM) under 10&#xa0;M sodium silicate activation and to determine the optimum blend suitable for subgrade applications. BCS was blended with 10–30% RM, and laboratory investigations including Atterberg limits, Free Swell Index (FSI), compaction characteristics, pH, and Unconfined Compressive Strength (UCS) tests were conducted. Microstructural and chemical analyses were performed using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The addition of RM reduced the Plasticity Index from 26.63% to approximately 20% and decreased FSI from 52.17% to 16.67%. Maximum Dry Density increased from 1.82&#xa0;g/cm<sup>3</sup> to 1.89&#xa0;g/cm<sup>3</sup> at 25% RM, while Optimum Moisture Content decreased. Under sodium silicate activation, UCS increased Substantial from 142.71 kN/m² for untreated BCS to 329.80 kN/m² for the 75BCS25RM blend. XRD and SEM analyses confirmed the formation of N-A-S-H and C-A-S-H gels and development of a dense cemented matrix. The improved engineering performance is attributed to the alkaline environment created by RM and sodium silicate, which promotes flocculation, reduces diffuse double-layer thickness, and facilitates geopolymeric gel formation. The resulting microstructural densification explains the reduction in swelling and the substantial enhancement in strength. The 75BCS25RM and 70BCS30RM mixes satisfy IRC:36-2010 requirements for embankment and subgrade layers. The findings demonstrate that chemically activated red mud is an effective and sustainable stabilizer for expansive soils.</p>

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Assessment of Geotechnical and Microstructural Properties of Expansive Clay amended with Bauxite Residue using Sodium Silicate

  • 期刊论文

  • 发表日期：

    2026年8月1日

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  • Lakshman Kumar Gope,
  • Brahmdeo Yadav,
  • Rohit Raj,
  • Sumit Kumar

摘要

Expansive clay or Black Cotton Soil (BCS) poses notable challenges in pavement and foundation construction due to its behaviour of high swelling, plasticity, and low strength. This study aims to evaluate the geotechnical and microstructural performance of BCS stabilized with Red Mud (RM) under 10 M sodium silicate activation and to determine the optimum blend suitable for subgrade applications. BCS was blended with 10–30% RM, and laboratory investigations including Atterberg limits, Free Swell Index (FSI), compaction characteristics, pH, and Unconfined Compressive Strength (UCS) tests were conducted. Microstructural and chemical analyses were performed using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The addition of RM reduced the Plasticity Index from 26.63% to approximately 20% and decreased FSI from 52.17% to 16.67%. Maximum Dry Density increased from 1.82 g/cm3 to 1.89 g/cm3 at 25% RM, while Optimum Moisture Content decreased. Under sodium silicate activation, UCS increased Substantial from 142.71 kN/m² for untreated BCS to 329.80 kN/m² for the 75BCS25RM blend. XRD and SEM analyses confirmed the formation of N-A-S-H and C-A-S-H gels and development of a dense cemented matrix. The improved engineering performance is attributed to the alkaline environment created by RM and sodium silicate, which promotes flocculation, reduces diffuse double-layer thickness, and facilitates geopolymeric gel formation. The resulting microstructural densification explains the reduction in swelling and the substantial enhancement in strength. The 75BCS25RM and 70BCS30RM mixes satisfy IRC:36-2010 requirements for embankment and subgrade layers. The findings demonstrate that chemically activated red mud is an effective and sustainable stabilizer for expansive soils.