Utilization of Recycled Materials in Illinois Highway Construction
Waste Foundry Sand
- Waste foundry sand (WFS) is a by-product of the foundry casting process of ferrous and nonferrous metals; 95 percent of this material is generated from the ferrous casting process. The automotive industry and its suppliers are the primary generators of this material. The presence of heavy metals is of greater concern in nonferrous foundry sands. WFS generated from brass or bronze foundries may contain high concentrations of cadmium, lead, copper, nickel, and zinc (1, 15).
- Physical Properties:
- WFS prior to its use in casting, consists of high quality silica sand or lake sand coated with a thin film of burnt carbon, residual binder, and dust. This material is sub-angular to rounded and has an overall uniform grain size distribution, where the gradations tend to fall within the limits for a poorly graded fine sand. WFS contains metal casting pieces, partially degraded binder, and may also contain some leachable contaminants, including heavy metals and phenols (1).
- Engineering Value:
- WFS grain size distribution is more uniform and somewhat finer than conventional concrete sand. The fineness of this substance contributes to good suspension limiting segregation in flowable fills, which are manmade self-leveling, self-compacting backfills. This material displays favorable durability characteristics with resistance to weathering in bituminous concrete paving applications. The high amount of silica found in this material may result in stripping of the asphalt cement coating aggregate, which contributes to pavement deterioration (1, 15).
- Potential Application:
- The commercial use of this material is extremely limited in the United States. In conjunction with a northwestern Indiana foundry, Indiana DOT has completed a cooperative venture utilizing WFS as embankment material. The major concerns were environmental risks associated with leaching of heavy metals, compaction of the material, foreign object damage to equipment, and dust control. As a result of careful environmental testing and planning, the material performed satisfactorily. Purdue University conducted a study with bituminous concrete samples containing up to 30 percent WFS; this study concluded that including more than 15 percent WFS lowered the unit weight, increased air voids, decreased the flow and stability of the mixes, and reduced the indirect tensile strength (1, 15).
- Department Concern:
- The environmental safety of WFS depends on chemical additives and casted metals utilized with the sand. The Department does not allow use of ferrous foundry waste sand because it is often contaminated with traces of hazardous elements.