15 Sept 99
historically been less available than glass, but as the amounts of waste glass decreases
this may not remain true.
In the paving industry, crushed glass (cullet) has been used as a replacement for
aggregate in hot-mix asphalt mixtures, known as glassphalt (Malisch et al. 1970, Collins
and Ciesielski 1994). Experience has shown that the cullet can replace up to 15 percent
by weight of total aggregate in hot-mix asphalt. These mixes should not be used in
surface courses (Ahmed 1991, FHWA 1993, and Shelburne and Degroot 1998). The
mixtures containing cullet have been shown to be susceptible to moisture damage. This
effect is only somewhat offset by the use of antistripping agents (West et al. 1993).
Several states add fine glass to paint to increase the reflectivity. The military currently
utilizes the same process on airfield pavements. At least 10 states have experimented
with glass beads as aggregate; however, only one, New Jersey, considers it to be an
acceptable standard practice. One laboratory study investigated the use of cullet as an
aggregate replacement for subbase, base, and embank ment structures. They concluded
that the cullet as an aggregate was strong, clean, safe, and economical. Compaction
results with some cullet gradations showed a flatter maximum dry density versus mois-
ture curve indicating, that in field construction, compaction could occur over a wide
range of moisture conditions (Shin and Sonntag 1994). One small community has used
cullet as a partial aggregate replacement for subbase construction of a city street
(American City and County 1997).
California has constructed an acceptable unbound base course made from crushed
porcelain. The crushed porcelain materials were found to have met or exceeded the
quality requirements for concrete aggregates. The Wisconsin DOT has recently used
broken glass and ceramic waste, along with several other waste materials as partial
aggregate replacement (up to 15 percent) as a highway base course on a state roadway
(Roads and Bridges 1998).
c. Incinerator ash. In the U.S. there are approximately 140 thermal reduction
facilities operating in 32 different states that process municipal solid waste (Collins and
Ciesielski 1994 and Rivard-Lentz et al. 1997). These plants produce heat to generate
electricity and reduce the volume of material by up to 85 percent, resulting in about
8.6 million tons of incinerator ash or residue per year. This will amount to more than 15
million tons by the end of the century (Goodwin 1992). The percentage of incinerator
bottom ash to incinerator fly ash produced varies from 60 to 90 percent depending upon
the properties of the waste and the thermal process used (Lum and Tay 1992, Collins and
Ciesielski 1994, Nicholson and Ding 1997, and Rivard-Lentz et al.1997).
The incinerator bottom ash, specifically that which is water cooled, exhibits physical
properties similar to those of a well-graded gravelly sand, although the specific gravity
will normally be lower than most natural sands (Ahmed 1991 and Kouda 1996).
Incinerator ash has been used successfully as an aggregate replacement in structural fill
applications (Rivard-Lentz et al.1997). A prepared (washed) incinerator ash was used to
replace the fine aggregate fraction in an granite hot-mix asphalt mixture. This resulted in
a very acceptable mixture, although it required a higher asphalt content than found in
normal granite hot-mix asphalt (Ahmed 1991and Lum and Tay 1992). It also reduced