Experimental study on the microwave processing of waste tyre rubber aggregates to enhance their surface properties for their use in rubberized bituminous mixtures

This experimental study uses the microwave technology to process the waste tyre rubber aggregates to enhance the interaction properties of waste rubber and bitumen by smoothing its surface. This was to make the waste rubber less reactive to the bitumen sample at the elevated temperatures of around 140–170°C. Parameters such as the microwave power, the height of the sample inside the processing chamber, and the processing time have been considered and optimized. The results show that the microwave processing technique designed in this study has significantly smoothened the surface of waste rubber. Scanning electron microscope surface analysis has been carried out to confirm the changes and smoothness of the rubber surface in comparison with the untreated waste rubber aggregates. In addition, microwave spectroscopy analysis has been carried out to confirm the reduction in the absorption properties of waste rubber. The microwave curves of the bitumen samples extracted from the treated rubber–bitumen blend are comparable with the pure bitumen sample with minute shifts in the resonant peaks. The results show the potential of the technique and recommends designing a dedicated processing unit to further improve it through parameters such as volumetric and uniform surface treatment, penetration depth of the microwaves.