The use of sulfer modified bottom ash (SMBA) as an aggregate in asphaltic mixtures

Abstract

Of the 20 million tons of bottom ash and boiler slag generated annually in the United States less than 40 percent is used. The eastern half of Texas is served by 18 coal burning electric power generating plants which produce approximately 3.8 million tons of bottom ash each year. This is also the section of the state in which the sources of quality aggregates are either few. dwindling or nonexistent. While a small fraction of the bottom ash is utilized, the rest is delegated to landfills or on-site disposal areas. Increasing attention is being given to development of new, high-volume uses for this safe and readily available by-product. One such use is as an aggregate in road construction. The use of bottom ash as an aggregate for both roadway surfaces and base courses has been limited due to its absorbency and friability. The former tends to increase asphalt binder demand while the latter adversely affects its ability to withstand the crushing effects of traffic loads. On the other hand, bottom ash is lighter in weight and generally much cheaper than conventional quality aggregates such as limestone, sand and gavel. This research was designed to up-firade the load-bearing characteristics of bottom ash and maximize its use 'in asphaltic concrete roadway mixtures through the use of sulfur. The process essentially coats the ash with liquid sulfur which upon cooling fills the voids on the surface of the particles while increasing their crush resistance. The results of this investigation indicate that asphaltic concrete mix designs in which bottom ash represents from 5 0 to I 00 percent of the aggregate fraction can be achieved.