International Journal of Advanced Engineering Application

Geotechnical Stabilisation of Expansive Black Cotton Soil Using Fly Ash and Lime Sludge: Swell-Shrink Behaviour, Strength Development and Microstructural Evaluation

Author(s):Priya Deshmukh

Affiliation: Department of Civil Engineering, Visvesvaraya National Institute of Technology (VNIT) Nagpur, Maharashtra, India

Page No: 94-97

Volume issue & Publishing Year: Volume 3, Issue 6, 2026/06/13

Journal: International Journal of Advanced Engineering Application (IJAEA)

ISSN NO: 3048-6807

DOI:

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Abstract:
Expansive black cotton soils, covering approximately 20% of India's land area and predominant across Maharashtra, Madhya Pradesh, Karnataka, and parts of Telangana, present a persistent geotechnical challenge for highway embankments, foundations, and canal linings due to their high swell-shrink potential under seasonal moisture variation. Chemical stabilisation using lime is an established remediation technique, but the carbon footprint and cost of conventional hydrated lime have motivated investigation of industrial by-products — fly ash from thermal power generation and lime sludge from paper and sugar industry effluent treatment — as partial or complete substitutes that simultaneously address industrial waste disposal challenges and soil stabilisation requirements at reduced cost. This study evaluates the geotechnical behaviour of black cotton soil (sourced from Nagpur district, Maharashtra) stabilised with fly ash (10%, 20% by dry weight), lime sludge from a calcium-carbide based acetylene plant (8%, 12% by dry weight), and a combined fly ash-lime sludge blend (8% lime sludge + 10% fly ash). Properties evaluated include Atterberg limits (liquid limit, plastic limit, plasticity index), free swell index, compaction characteristics (OMC, MDD), unconfined compressive strength (UCS) at 7, 14, and 28 days curing, California Bearing Ratio (CBR) under soaked conditions, and SEM/XRD microstructural analysis at 28 days to identify cementitious reaction products. The combined fly ash-lime sludge blend achieves a 28-day UCS of 562 kPa (205% above untreated soil) and a soaked CBR of 11.8% (321% above untreated soil), outperforming all individually stabilised mixes. The plasticity index reduces from 38.6% in untreated soil to 17.6% in the blended mix, and the free swell index reduces from 112% to 36% — a 68% reduction indicating substantial mitigation of swell-shrink potential. SEM and XRD analyses confirm the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) cementation products bridging soil particles, with the blended mix showing the most extensive cementitious matrix development at 28 days.

Keywords: expansive soil, black cotton soil, fly ash, lime sludge, soil stabilisation, free swell index, unconfined compressive strength, California Bearing Ratio, SEM, XRD, pavement subgrade

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