Soil Stabilization by Using Fly Ash

Abstract

Soil is the basic foundation for any civil engineering structures. It is required to bear the loads without failure. In some places, soil may be weak which cannot resist the upcoming loads. In such cases, soil stabilization is needed. Numerous methods are available in the literature for soil stabilization, but sometimes, some of the methods like chemical stabilization; fly ash stabilization, lime stabilization, cement stabilization etc. adversely affects the chemical composition of the soil. In this study, fly ash mixes with black clay soil to investigate the relative strength gain in terms of unconfined compression, bearing capacity and compaction. The effect of fly ash on the geotechnical characteristics of clay-fly ash was investigated by conducting standard Proctor compaction tests, Atterberg limit, Specific Gravity Test, CBR tests and. The tests were performed as per Indian Standard specifications.

Introduction

Soil stabilization improves soil properties like strength, durability, and compaction, making it suitable for construction. Fly ash, a by-product of coal combustion, is commonly used as an additive to stabilize soils, especially those with poor qualities such as high plasticity or low strength. Mixing fly ash with soil enhances soil performance through chemical and physical interactions while also recycling industrial waste, benefiting the environment. This method is particularly effective for clayey, silty, or weak soils used in road construction, pavements, embankments, and foundations.

The compaction of soil-fly ash mixtures affects strength, compressibility, and permeability. Fly ash has higher air voids and is less sensitive to moisture variation during compaction compared to soil, allowing compaction over a wider moisture range.

The studied soil, sourced from a road construction site in Maharashtra, India, is black, clay-rich (montmorillonite), moisture-retentive, and prone to cracking. Physical tests like sieve analysis and Atterberg limits were performed. The soil showed a maximum dry density of 1.44 g/cc and optimum moisture content of 18.7%.

Fly ash used, collected from a thermal power plant, contains minerals like silica and alumina and enhances soil properties by increasing dry density and reducing water demand. It also alters the soil’s Atterberg limits, reducing flexibility.

Compaction tests on soil-fly ash mixtures at different curing periods revealed that increasing fly ash content generally lowers liquid and plastic limits while increasing optimum moisture content and dry density up to a certain proportion. The Proctor compaction test determined the optimum moisture content for maximum soil density, which varied with fly ash percentage, with maximum dry density reaching about 1.72 g/cc for an 85% soil and 15% fly ash mix.

Conclusion

Fly ash as a stabilizer is being widely used in the geotechnical field of engineering. In this study, different aspects concerning fly ash, Lime and cement stabilization have been reviewed concerning the literature available. The basic mechanism of fly ash stabilization involves action exchange and flocculation in the initial stage and then pozzolanic reactions occur which continue for a longer period of time. Significant changes occur in soil properties but these changes are dependent on soil mineralogy, fly ash type, time, temperature, etc. In the initial stage, we see a marked decrease in the soil plasticity owing to the reduction in diffuse double layer thickness and increase in the viscosity of pore water due to flocculation and action exchange. However, these changes in consistency limits witness a decrease and sometimes a reversal beyond particular fly ash content. The moisture density relation also shows marked variations with a decrease in optimum moisture content and an increase in dry density. we have conducted Standard proctor test and CBR to check for the influence of fly ash treatment on the overall soil strength and they reported a net increase in shear strength, tensile strength and bearing capacity up to an optimum value of fly ash addition owing to the cementation process due to continuous pozzolanic reactions. Studies show differences among researchers about the permeability changes with some reporting an increase while others observed a decrease and a few more reported variabilities in values with increasing fly ash content. Soils treated with fly ash have also shown a remarkable decrease in compressibility and have an increased resistance against strength loss due to alternate wetting-drying or freezing-thawing cycles. fly ash stabilization have been and is being used in a great number of areas like, we have fly ash Columns which help in stabilizing soils underneath buildings, embankments and roads, these columns reduce settlements, dewater soils, increase strength, etc. besides other benefits. Similarly, lime treatment. Adding fly ash (especially 10–20%, 20% being optimum percentage of fly ash mixed) improves the strength, compaction, and stability of black clay soil. It reduces plasticity and Liquid limit, making the soil more suitable for construction applications like subgrade improvement, embankments, and low-cost road bases.

References

[1] Erdal Cokca (2001) “Use of Class C Fly Ashes for the Stabilization – of an Expansive Soil” Journal of Geotechnical and Geo environmental Engineering Vol. 127, July, pp. 568-573. [2] Eldon J. Yoder (1957), “Principles of Soil Stabilization”,JHRPPublicationIndiana USA. [3] Pradip D. Jadhao and Nagarnaik, P.B (2008), Influence of Polypropylene Fibers on Engineering Behavior of Soil – Fly Ash Mixtures for Road Construction, Electronic Journal of Geotechnical Engineering, Vol. 13, Bund.C, pp. 1-11. [4] Compaction and Strength Properties of Expansive Soil”, Journal of Materials in Civil Engineering, Vol. 19, Issue 3, pp. 242-248. [5] Gray D. Hand Lin Y. K. (1972). “Engineering properties of compacted fly ash.” J. Soil Mech. Foundation Engng, ASCE, 98, 361–380. [6] Bureau of Indian Standards. (1973). ‘‘IS 2720, Part 2: Methods of test for soils: Determination of moisture content.’’ [7] https://www.wikipedia.org/ [8] Indian standard “IS 2720, Method for Test of Soil”.

Copyright

Copyright © 2025 Prof. Prajyot Gandhak, Prof. Nikhil Gadge, Mr. Mohammad Hayat Akhtar, Mr. Syed Sufiyan Miyan, Mr. Abdul Saquib, Mr. Mohd Sameer, Mr. Mohd Danish , Mr. Swaroop Deshmukh. 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.