Effective use of Waste Materials: A Case Study of Utilization of Fly Ash in Flexible Pavement Structures

Abstract

Generation of energy through thermal processes is still dominant in many parts of the world. One of the by-products of this process is fly ash, whose safe disposal incurs monetary and environmental costs. To mitigate this issue, utilization of fly ash, as a construction material, has been increasing remarkably; however, evaluation and summarization of its use in pavement construction are not very common. This study reviews its utilization in construction from different aspects and attempts to fill the gap within the literature with a critical review of fly ash usage in pavement construction engineering for the last few decades. Further recommendations have also been suggested in this context. Class ‘C’ fly ash is used for soil stabilization and class ‘F’ is used in concrete. Review of the literature found the following results. Application of fly ash, in both flexible (asphalt) and rigid (concrete) pavement, is common in the form of a filler material. However, this paper only focuses on its use in flexible pavement layers. In the case of flexible pavement, fly ash is used can be used in surface, base, and sub-grade layers. The surface layer is made up of concrete, wherein it can be used as mineral filler or partial replacement of asphalt. The most common types of test performed on asphalt concrete are Marshall stability and tensile strength. However, there is a lack of field testing studies on asphalt concrete modified with fly ash. As for the other layers of flexible pavement, fly ash has been used with activators for their stabilization as these layers are made up of natural compact materials. Fly ash has shown promising results when used with cement, with both used within a proportion of 10%. The future research areas, identified through this review, are modeling of pavement layers modified with fly ash, and standardization of fly ash properties for use in pavement layers.