Structural Fills & Embankments
Summary
The largest volume of waste foundry sand is used in geotechnical applications. These applications are concerned with the engineering properties of earth materials and construction, and include embankments and structural fills as well as road bases, landfills, highway construction, and barriers.
Foundry sands have been used as embankment and structural fill material for many years. This practice ceased in the U.S. when new environmental laws were introduced. However, Ham et al. (1990) concluded that foundry wastes from ferrous foundries are generally non-hazardous. This study and other research has lead several states to issue general exemptions or blanket policies for the beneficial reuse of many types of foundry sands in embankment and structural fill applications.
Most states, however, place restrictions on locations of such applications and require some type of encapsulation of the foundry sand.
The specifications for using foundry sands as fill materials generally have been the same as the specifications for typical backfills. These specifications consist of compacting the material in layers to a minimum percentage of the maximum dry unit weight. Of course, for these applications and others, foundry sand is required to be separated from other foundry by-products. Raw foundry sands are usually of higher quality than natural sands used for construction site applications which means that spent foundry sands are more consistent than natural sands for these applications.
Engineering
Embankment and structural fill materials are typically classified by grain size distribution, Atterberg limits, soil type, bentonite content, shear strength (friction angle), specific gravity, moisture-density relationships (compaction), permeability, and their susceptibility to frost. Such information is usually needed by designers before any consideration for beneficial reuse.
There are three main elements that determine foundry sand quality and their success in geotechnical applications. Foundry sands typically demonstrate high durability. Chemical composition is important and may affect performance, and variability can be controlled when the sands are produced in the same foundry; a consistent product is important to customers. A good way to ensure a high quality sand is to require testing and certification with the shipments so they meet state and application standards.
In addition to having a quality product that meets standards and expectations, foundry sand suppliers must have a source of supply that is abundant enough to maintain a steady and sufficient inventory to meet the demand of the customer. If this cannot be achieved, the operation becomes unattractive and uneconomical.
Application Practices
Foundry sands behave similarly to traditional construction materials such as natural and manufactured sands and soils. As with these materials, foundry sand can be stored inside or outside exposed to the elements. Delivery (covered trucks) and site preparation is the same as for soil materials. On-site storage is an option as long as the foundry sand is kept moist and covered. The sand is spread in a conventional manner with traditional equipment, with moisture content again being important, as with traditional materials. The sands are durable and not usually sensitive to over-rolling. They can also withstand a greater range of moisture content than natural sands.
Things to Consider for a Successful Project
1. Consider foundry sand availability.
- There must be sufficient available supply of high quality sand to complete the job.
2. Assess site conditions.
3. Evaluate the Properties of the Foundry Sand.
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Study the physical, chemical, and engineering properties of the foundry sand to determine how the sands will behave. Standard laboratory techniques used for testing soils are acceptable. Foundry sands normally contain trace elements, but the concentrations mirror those found in other construction materials such as native soils and fly ash. State regulatory agencies can provide information about testing procedures and water quality standards.