EVALUATION OF COKE DUST-MODIFIED ASPHALT USING SUPERPAVE

The Atlantic Richfield Products Company located in Blaine, Wash. gener ates about 6,356 Mg (7,000 tons) of coke dust every year. The coke dus t is produced during the process of calcination in the hearths, storag e silos, conveyor systems, and during the loading process into rail ca rs. The main objective of this research study is to investigate the po tential use of calcined and green coke (uncalcined) dusts as modifiers in hot mix asphalt paving mixtures. Six different blends including co ntrol were subjected to binder testing and grading using Superpave tes ting equipment and procedures. Hveem mix designs also were conducted o n the six mixtures. Coke dust was added by total weight of the asphalt cement binder. Research results indicate that both coke dusts will ac t as reinforcing agents for the asphalt cement binders. Both coke dust s seem to improve asphalt cement performance (high stiffness) at high temperatures (58 and 64 degrees C) with minimal adverse effect (increa sed stiffness) at low temperatures (-12 and -18 degrees C). At interme diate temperatures, penetration values at 25 degrees C will decrease a nd dynamic shear values at 19 and 22 degrees C generally will increase as a result of coke dust addition. Viscosity (stiffness), dynamic she ar, Hveem stability, and voids in mineral aggregate tend to increase a s a result of adding coke dust (whether it is calcined or green). Also , there is a slight improvement in retention of asphalt coating when c oke dust is used. All mixtures exceeded the minimum Washington State D epartment of Transportation specification requirements for class B hot mix asphalt concrete. Thus, if proper aggregate is used, permanent de formation (rutting) and stripping will be reduced in coke dust-modifie d asphalt pavements.