Volume change behavior of clayey soil–fly ash mixtures

At present, more than 150 million tonnes of fly ash is generated annually in India, posing serious health and environmental problems. To control these problems, the most commonly used method is addition of fly ash as a stabilizing agent in combination with soils. For the bulk utilization of fly ashes in geotechnical applications such as embankments/dykes, as back fill material, as base material and in water retaining structures either alone or with soil, the volume change behavior of soil–fly ash mixture forms an important consideration. Only few data are available concerning the volume change behavior of clayey soil–fly ash mixtures and require further investigations. In the present study, high-calcium (ASTM Class C-Neyveli fly ash (NFA)) and low-calcium (ASTM Class F-Badarpur fly ash (BFA)) fly ashes in different proportions by weight (10, 20, 40, 60, and 80%) were added to a highly expansive soil [known as Black Cotton (BC) soil from India] to evaluate the effect of fly ashes on the volume change behavior of clayey soils–fly ash mixtures. Compacted clay-fly ash samples were cured for 7 and 28 days and subjected to consolidation test under different pressures ranging from 50 kPa to 800 kPa. In this study, the void ratio, the compression index, swelling potential, coefficient of consolidation, permeability, and preconsolidation pressure of clayey soil–fly ash specimens were investigated. The test results indicate a significant decrease in compressibility characteristics and swell potential of the treated soils. It was seen that 20% high-calcium fly ash content is the optimum quantity to improve the compressibility characteristics of clayey (BC) soil cured for 7 days against 60% for immediate tests. It is also observed that 10% of NFA is the optimum amount required to minimize the swell potential compared to 40% of BFA. Thus, the main objective of the study was to study the effect of fly ashes on the volume change behavior of fly ash treated clayey soil and bulk utilization of industrial waste by-product without adversely affecting the environment.