Evaluation of Coke Dust-Modified Asphalt Using Superpave

Abstract

The Atlantic Richfield Products Company located in Blaine, Wash. generates about 6,356 Mg (7,000 tons) of coke dust every year. The coke dust is produced during the process of calcination in the hearths, storage silos, conveyor systems, and during the loading process into rail cars. The main objective of this research study is to investigate the potential use of calcined and green coke (uncalcined) dusts as modifiers in hot mix asphalt paving mixtures. Six different blends including control were subjected to binder testing and grading using Superpave testing equipment and procedures. Hveem mix designs also were conducted on the six mixtures. Coke dust was added by total weight of the asphalt cement binder. Research results indicate that both coke dusts will act as reinforcing agents for the asphalt cement binders. Both coke dusts seem to improve asphalt cement performance (high stiffness) at high temperatures (58 and 64°C) with minimal adverse effect (increased stiffness) at low temperatures (−12 and −18°C). At intermediate temperatures, penetration values at 25°C will decrease and dynamic shear values at 19 and 22°C generally will increase as a result of coke dust addition. Viscosity (stiffness), dynamic shear, Hveem stability, and voids in mineral aggregate tend to increase as a result of adding coke dust (whether it is calcined or green). Also, there is a slight improvement in retention of asphalt coating when coke dust is used. All mixtures exceeded the minimum Washington State Department of Transportation specification requirements for class B hot mix asphalt concrete. Thus, if proper aggregate is used, permanent deformation (rutting) and stripping will be reduced in coke dust–modified asphalt pavements.