Effect of Fly Ash in Soil Subgrade: Study On Design Implications and Cost-effectiveness

Abstract

The objective of this study was to evaluate the effect of fly ash in soil sub-grade modification on pavement design and quantify the cost-effectiveness of the construction. The scope of the research encompassed the investigation of soil with fly ash modification, conducting pavement design for three design traffic, and computing the initial cost of construction based on the unit rate of materials. With three levels of design traffic: low, medium, and high, three fly ash contents: 5, 10, and 15%, along with control soil, totaling 12 pavement sections were considered in the design. Laboratory investigation revealed that when fly ash content increased, the CBR of soil also increased consistently. Next, the improvement of soil properties quantified through CBR was used as an input for pavement design. In the design, it was found that there existed a scope for thickness reduction in the WMM and GSB layers. The highest reduction in thickness, around 14.5%, was practicable in the WMM layer at medium traffic conditions. Furthermore, the cost-effectiveness analysis during the initial construction phase revealed that the addition of fly ash did not have any negative impact on the costeffectiveness of pavement. A marginal saving was noticed when fly ash content was 10% at medium traffic conditions. Overall, it was envisaged that the research methodology adopted as part of this study would help road agencies, practitioners, and other stakeholders evaluate various alternative strategies for improving the quality of subgrade layers.