Assessment on the applicability of heavy oil advanced refining byproducts for bituminous road pavements

Vacuum tower bottom/vacuum residue (VTB/VR), a byproduct of petroleum refining, is a hard and brittle asphalt material. If directly applied to road pavements, it can lead to early crack damage. Thus, this study developed a softening additive to reduce its brittleness and, in conjunction, laboratory experiments were employed to explore the fundamental characteristics of the VTB, VR, and traditional asphalt binder (PG 64-22). A method for determining the VTB/VR mixing ratio and softening additive ratio, such that the resulting material satisfies the present standards for road pavement asphalts in South Korea. In the mix design procedure, the softening ingredient was adjusted between 0, 2, and 4% by mixture weight while the VR mixing ratios were varied in increments of 10% by weight of VTB. The test results reveal that the penetration value of VTB can reduce linearly with the addition of VR compound. By using proper polypropylene glycol admixture, the findings confirm that VTB/VR mixture was a potential material for paving roads since this mixture meets almost all fundamental properties compared to conventional asphalt mixture. Especially, the dynamic modulus of the VTB/VR mixture was approximately 10% greater than that of the control at low temperatures. Based on varying amounts of softening additive and the maximum input amount of VTB that satisfied the PG 64-22 grade, the ideal VTB/VR mixture consists of 70% VTB, 30% VR, and 2% softening additive. The proposed asphalt alternative was also evaluated through field test construction, where it demonstrated its feasibility as an alternative to conventional road pavement asphalt.