Performance assessment of three alkali-treated fly ashes as a pavement base-course material

Abstract

Alkali-treated fly ash can efficiently serve as a construction material for various purposes. The efficacy of these alkali-treated fly ash must be critically studied for their proper usage in real-life scenarios. In the present study, the effectiveness of an alkali-treated low calcium fly ash (Class F) as a pavement base course material in the pre and post-construction period of the pavement has been investigated. The low calcium fly ash (Class F) was treated with three different alkalis, namely sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2), to study the influence of alkali type, its dose and curing period on the compressive strength and permeability characteristics of alkali-treated fly ash samples as these properties would prominently influence its behavior as a base course. In addition, the microstructural study of different alkali-treated ash samples was done to correlate the microstructural developments with these engineering properties. It was observed that 12% NaOH-treated fly ash samples, 16% KOH, and 16% Ca(OH)2-treated fly ash samples at 28 curing days show an optimum compressive strength value for a stabilized base material in pavements as per various guidelines. Finally, the usability of these optimized alkali-treated fly ash samples as a base material was investigated through a numerical study of a simple two-layered pavement structure. The surface and interface deformations of the pavement under various loading conditions revealed that these optimized alkali-treated fly ashes serve as a better base course than granular material. Also, of the chosen three alkali-treated fly ashes, optimized Ca(OH)2-stabilized fly ash performs comparatively better than others in terms of compressive strength and resisting deformation for these typical pavements.