Wetting and Drying Characteristics of Recycled Asphalt Pavement-Fly Ash Blend as a Sustainable Pavement Material

Abstract

The usage of Recycled Asphalt Pavement (RAP) and Fly Ash (FA) blend in pavement applications contributes to the sustainable usage of such waste by-products. Although RAP-FA blend has been proven as a pavement material based on strength and leachate requirement, the durability of this blend when exposed to an aggressive environment has not been investigated to date. This research presents the effect of wetting-drying (w-d) cycles on the strength and microstructural changes of RAP-FA blend. The strength characteristic of this material was determined by Unconfined Compression Strength (UCS) test. The mineralogical and microstructural changes of the compound pavement material were also analyzed using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Test results show that the UCS of RAP-FA blend increases with increasing the number of w-d cycles (C), reaching its peak at 6 w-d cycles. The XRD and SEM analyses indicate that the increased UCS of RAP-FA blend is due to stimulation of the chemical reaction between the high amount of Calcium in RAP and the high amount of Silica and Alumina in FA during w-d cycles leading to production of more Calcium Silicate Hydrate (C-S-H) and Calcium Aluminate Hydrate (C-A-H). For C > 6, the significant macro-cracks due to the loss of moisture content during drying stage cause strength reduction. However, its reduced UCS is still greater than the minimum strength requirement even at C = 20. The outcome from this research confirms the viability of using RAP-FA blends as an alternative sustainable pavement material.