15 Sept 99
not having to landfill or otherwise treat the material is a large consideration. Other
factors affecting use include the cost of treating the waste to make it environmentally
acceptable and the relative cost of local aggregates (Ahmed 1991).
d. Foundry wastes. Foundry wastes include foundry sands, furnace dust, and arc
furnace dust, with sands being the largest volume of waste produced. In 1992, the yearly
production of these wastes was between 10 and 15 million tons (Collins and Ciesielski
1994). Foundry sands have been the only foundry waste used in pavement construction,
with the majority of this being as a fine aggregate for hot-mix asphalt. It has also been
used as an embankment material, as a pipe bedding material, and as an aggregate
replacement in base course construction for a roadway (Roads and Bridges 1998). One
study successfully used foundry sands in flowable fill mixtures (Bhat and Lovell 1997).
Prior to any application, the sand must be investigated for possible trace chemicals which
could cause environmental problems (Collins and Ciesielski 1994 and Bhat and Lovell
Another material similar in properties to foundry sands is waste sands that are generated
as a by-product of the casting industry. The sands are normally reused several times,
depending upon the casting process involved, until they are sufficiently altered and
become waste sands. One study using waste sand from a green sand molding of gray iron
products found that a replacement of up to 15 percent o f the fine aggregate in a hot-mix
asphalt did not adversely affect the mixture's properties (Javed et al. 1994). Another
study successfully used the same type of sands to construct two roadway embankments.
This study examined possible environmental problems relating to metallic elements as
well as other possible contaminants using the toxicity characteristic leaching protocol
(TCLP) procedure and other tests. After more than one year of monitoring the water
quality, no pollutants were detected (Fox et al. 1997). It should be noted that these
foundry sands may require some cleaning or washing prior to use.
g. Non-ferrous slags. Non-ferrous slags are produced from the thermal processing
of copper, lead, zinc, nickel, and phosphate ore. The majority of these smelters are in the
western half of the U.S. Approximately 10 million tons of slag is produced each year, the
majority of which is either copper or phosphate slag. The slags are produced in either
air-cooled or granulated form, and each contain some concentration of the metals from
which they were produced (Collins and Ciesielski 1994).
Non-ferrous slags have been used successfully in asphalt and PCC mixtures, base
courses, and as railroad ballast. Only a few states have used non-ferro us slags, despite
the relative success of mixtures containing these slags. Some state DOTs have concluded
that some zinc and copper slags should not be used for PCC mixtures (Collins and
Ciesielski 1994). In the early 1970's the use of zinc smelter residues was investigated for
use in stabilized base courses, hot-mix asphalt, and PCC. The results of this study
indicated that the material was suitable as aggregate in stabilized mixtures and hot-mix
asphalt, but not for PCC because of an unacceptable cement-aggregate reactivity (Hughes
and Halliburton 1973).