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Commingled plastic has been used with steel pipe to produce composite piles (Heinz
1993 and Shelburne and Degroot 1998).
e. Residual material from water treatment plants. Treating water normally requires
the removal of fine solid particles, organic matter, and cations of various materials such
as calcium, iron, and aluminum (Raghu et al. 1997). The high water content and
resulting low shear strength and high compressibility of the residual materials removed
during this process prevent direct application for construction. A study by Raghu et al.
(1997) showed that blending topsoil with this material would provide a suitable fill
material for construction purposes. In their case, the fill served as a landfill liner. As
with any construction involving fill, control of the water content was critical in achieving
good engineering properties such as density, strength, and durability.
f. Sewage sludge. There are more than 15,000 municipal water treatment plants
throughout the country that produce in excess of 8 million tons of dry solid sewage
sludge annually (Collins and Ciesielski 1994). This sludge is normally composed mostly
of organic materials such as nitrogen and phosphorus, with minor amounts of various
contaminants. About 20 percent of this material is incinerated with equal amounts of the
remainder either composted, used in land applications, or placed in sanitary landfills.
Sewage sludge disposal is regulated by a combination of state and federal EPA
regulations. In 1989, there were 282 incinerators burning sludge in the U.S.; however,
burner emission considerations have become a limitation on this type of process (Morse
1989). Incinerator ash has been used in pellet form as a coarse aggregate for concrete
and in ash form as a filler for hot-mix asphalt (Collins and Ciesielski 1994, Bhatty et al.
1992). Concrete made with the pellets has achieved compressive strengths up to
15 percent greater than comparative concrete when they made up 35 percent of the
aggregates in the mixture. In those laboratory tests, fracture occurred through the pellets,
indicating lower strength when compared to the limestone aggregate used in the tests.
The pellets have a relatively low unit weight making them useful where lighter weight
concrete is desirable (Bhatty et al. 1992).
Dewatered sewage sludge has been used mainly as an additive to topsoil. One study
using dewatered sewage sludge with soil, lime, and fly-ash additives in different
proportions, found that the material, when properly modified with the additives, could be
used in embankments, provided the water content was kept low (Wang et al. 1992).
g. Used motor oil. Over two billion gallons of lubricating oil is produced every
year. About 90 percent of what is reclaimed is burned as fuel. At least 3 DOTs have
experimented with burning the oil in asphalt plants (Collins and Ciesielski 1994).
h. Used tires. The estimated amount of used tires that are discarded annually varies
between 235 to 300 million (Papp et al. 1997 and Shelburne and Degroot 1998). Current
trends to smaller and longer-wearing tires have resulted in a relatively small increase, if
any, in number of tires from about 240 million in 1990 (Ahmad 1991). The disposal of
waste tires is as follows: approximately 80 percent of the tires were placed in landfills,
10 percent were used as fuel, about 8 percent used the tire whole or shredded for
pavement applications and other miscellaneous uses related to pavements, and about