Investigating the effect of preheating conditions and size effect on asphalt blending in recycled asphalt mixture: New approach based on artificial aggregate and laser scanning confocal microscopy

The blending phenomena between virgin and reclaimed asphalt is a significant concern in asphalt paving, which play a crucial role in the final performance of the recycled asphalt mixture. Although past studies broadly discussed the asphalt blending by various test methods, the blending process holds 3D features due to the different aging degrees of reclaimed asphalt and different dispersity of virgin asphalt. The three-dimensional observation in the asphalt blending is still limited. Simultaneously, many factors (e.g., preheating temperature and time, transportation temperature, storage time, and aggregate gradation) will affect the blending process. The relationships between those factors and the blending phenomena are still unknown. To overcome this problem, this paper proposed a 3D fluorescence image method by laser scanning confocal microscopy and artificial aggregate. The artificial aggregate in the wooden cube form was used to analyze the blending process of virgin and RAP aggregate in three-dimension, respectively. Meanwhile, preheating conditions and size effect on the blending phenomena were also evaluated. The results indicate that temperature presents a more significant influence on the blending than the curing time. A longer curing time does not mean better blending, which exists a limited value and an optimal storage time. Compared to RAP aggregate, more homogeneous blending occurred on virgin aggregate after 2 h curing time at 180 °C, so the blending process on virgin aggregate should also be considered by researchers. This study may help to explain the production of recycled asphalt mixture and understand the blending phenomena in asphalt paving.