The development of a novel, microwave assisted, half-warm mixed asphalt

Abstract

Global warming is an imminent threat that the world and its inhabitants have to confront. As such, it is the duty of the pavement industry as a contributor of greenhouse gas emissions, to pave the way by lowering its carbon footprint. It is vital that new measures are adopted in order to do so such as employing the use of emulsion-based mixtures (EBM). The problem with this is that the performance properties of such mixtures are inferior to that of traditional hot mix asphalts (HMAs). The air void content of EBM is very high and considered unacceptable by road engineers for application as a surface layer. That said, these mixtures are not only environmentally friendly but also boast ecological and economic advantages. An innovate approach was applied in this research by using a pre-compaction microwave processing technique to develop a novel, half-warm mix asphalt mixture (H-WM). This new mix was shown to have improved mechanical properties and lower air void content. EBM mixtures comprised of cementitious binary blended filler, were prepared using microwave heating applied over different lengths of time. Stiffness modulus, air voids content and temperature were used to establish the optimum microwave radiation time. The results indicated that 1.5 min of microwave processing decreased air void content from 8.92% to 7.12%. A 7% improvement in stiffness modulus was also found and the temperature was within lower limits (43°C). Hydration was accelerated by the microwave radiation, and the demulsification of bitumen emulsion was promoted. Microwave processing was found to have a positive impact on permanent deformation at elevated temperatures in comparison to the two reference HMAs used. It also proved to be an adequate technique to produce a fast-curing H-WM with lower air voids content. Water damage resistance for the microwaved H-WM (99%) is better than the reference HMA mixes. The findings of this study show that the novel half-warm asphalt mixture has superior properties in comparison to EBM.