Sustainable Utilisation of Fly Ash in Asphalt Road Construction

Full description

Road networks continue to expand due to population growth, increasing vehicle ownership, and economic development. This expansion requires large quantities of construction materials, including aggregates, binders, and filler materials. The extensive use of these materials in pavement construction contributes to the depletion of natural resources. At the same time, Australia generates millions of tonnes of fly ash annually, creating environmental and disposal challenges.

This research investigated the feasibility of using fly ash as a replacement for conventional hydrated lime filler in AC14 asphalt mixtures. The study aimed to evaluate whether fly ash could provide a more sustainable alternative while maintaining or improving pavement performance. A quantitative research approach was adopted to assess the chemical and physical characteristics of fly ash and its suitability as a filler material.

Fly ash was incorporated at replacement levels of 2%, 4%, and 6% by weight of the total aggregate mix and compared with a control mix containing 6% hydrated lime. Laboratory testing was conducted at the CQUniversity Mackay Pavement Laboratory to evaluate filler properties and key volumetric parameters, including air voids, densities, voids in mineral aggregate, voids filled with binder, moisture content, and optimum binder content. In addition, mechanistic pavement analysis was undertaken using CIRCLY 7.0 software to assess pavement structural performance through critical stress and strain responses.

The findings demonstrated that fly ash improved filler–binder interaction and enhanced mix densification. Mixtures containing 2% and 4% fly ash exhibited improved volumetric properties and lower critical pavement strains, indicating enhanced resistance to fatigue cracking and rutting. These results suggest that fly ash can serve as a sustainable and effective alternative to hydrated lime in asphalt pavement applications.