15 Sept 99
1994). Central Florida, Louisiana, and southeastern Texas are the locations where the
majority of phosphogypsum is produced and stockpiled in the U.S. There are also sizable
stockpiles of this material in various other countries, including Australia and Japan (Taha
and Seals 1992).
Phosphogypsum has been used in several experimental cement stabilized road base
applications. Laboratory studies have also shown that phosphogypsum can be used
successfully in stabilized mixtures (Taha et al. 1992). Louisiana State University has
investigated the use of a phosphogypsum slag, a by-product of a sulfuric acid production
process, as an aggregate in hot-mix asphalt (Taha and Seals 1992b). Another research
study found that the slag aggregate would perform well as a coarse aggregate in PCC for
pavement applications (Foxworthy et al. 1994). In 1989 the Environmental Protection
Agency (EPA) issued a ban on the use of phosphogypsum, due to concerns related to
radon gas emissions (Lea et al. 1992). This ban covered research studies as well as any
other applications and there are no current or planned research projects.
d. Quarry waste. Quarry waste consists mainly of excess fines generated from
crushing, washing, and screening operations at quarries. These wastes are normally
stockpiled or exist in ponds and therefore generally require dewatering prior to use.
Quarry waste is being generated, at a rate of about 175 million tons per year (Collins and
Ciesielski 1994). The material properties of this waste vary with the source, but are
relatively constant at a particular site.
A 1994 survey showed that six states have used quarry waste in pavement applications
(Collins and Ciesielski 1994). One study of potential uses of quarry waste recommended
its use in cement-treated subbase and flowable fill as well as mineral filler in hot-mix
asphalt and as slurry seal aggregate (Kumar and Hudson 1993). Another study found that
combining 10 percent quarry tailings (waste) with a mixture of municipal solid waste ash
would provide an effective landfill cover material (Lee and Nicholson 1997).
e. Spent oil shale. There are large deposits of oil shale on federal lands in
Colorado, Utah, and Wyoming. These deposits may contain up to several billion barrels
of oil (Collins and Ciesielski 1994). During the oil crisis of the 1970's several projects
were established to remove the oil from the shale, resulting in an oil shale ash. This ash
was mainly granular with some particles up to 75 mm (3 in.) in diameter (Miller and
Collins 1976). These facilities all closed in the 1980s; however, several million tons of
the ash are stockpiled, mainly in northwestern Colorado. The only documented research
regarding use of this material as a pavement construction material found that replacing
various percentages of the asphalt cement in a hot-mix asphalt resulted in improved
mixture stiffness and reduced stripping potential (Khedaywi 1988).
f. Washery rejects. This category includes by-products of the phosphate and
aluminum industries. These wastes are very fine clay-like materials, which are produced
in slurry form (Collins and Ciesielski 1994). These materials have proven very difficult
to dewater and after many years of stockpiling still have a relatively low solids content
(Collins and Miller 1976). The phosphate wastes are located mainly in central Florida,
with some in North Carolina and Tennessee. The alumina wastes are located Louisiana,