Performance Analysis of Fly Ash Stabilized, Highly Saline Expansive Clays: A Case Study-Paper

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The study evaluates fly ash stabilization of highly saline expansive clay from Bhavnagar, Gujarat, for potential use as pavement subgrade. The soil is highly expansive (free swell index, FSI, 73%) and has high electrical conductivity. Class F fly ash from Wanakbori Thermal Power Plant was added at 10–25% by soil weight. Researchers compared compaction and index properties across the mixes, then tested the selected 20% mix for electrical conductivity, unconfined compressive strength (UCS), and California Bearing Ratio (CBR) after different curing periods.<br /><br />Fly ash reduced the soil’s plasticity and swelling. At 20% fly ash, FSI fell from 73% to 25%; at 25%, it fell to 17%. The 20% dosage was selected as the overall optimum for further testing. It also reduced electrical conductivity from 10,900 to 2,943 × 10⁻⁴ S/m, indicating lower salinity or fewer free ions in the mix.<br /><br />Strength improved with curing, but only moderately for pavement applications: CBR rose from 2.7% in untreated soil to 4.2%, 6.8%, and 8.1% after 1, 14, and 28 days, respectively. UCS increased from 177.5 kPa in untreated soil to 717.84 kPa after 28 days. The authors conclude that fly ash can mitigate swelling and improve strength, but the resulting CBR may be inadequate for heavy-traffic pavements or uses requiring high structural capacity. They recommend further investigation of alkali activation, unsaturated-soil suction and swell pressure, and long-term performance and durability.

Keywords

fly ash stabilization

saline expansive clay

Bhavnagar Gujarat

pavement subgrade

free swell index

electrical conductivity

unconfined compressive strength

California Bearing Ratio

compaction properties

Class F fly ash