Technical Overview
Metalcasting sand is basically a fine aggregate. Once properly screened and segregated from other metalcasting facility discards, these sands are usable in most of the same applications where conventional construction sands are used. From an engineering standpoint, metalcasting sand has several characteristics that make them a good fit for many applications. In a handful of cases, those characteristics may limit their value in substituting for other sands.
Proven market applications for metalcasting sand generally break down into three groups:
- Highway and Construction Uses – many types of construction projects require granular materials to level construction sites, create berms or retaining walls, build embankments, or backfill structures. Properly prepared metalcasting sands have been shown to perform well in all of these applications, as well as in bases and subbases under roadways, paved surfaces and structures. In pavement surfaces, foundry sands are also used in hot mix asphalt, and in portland cement concrete products. Metalcasting sand also performs extremely well in controlled low-strength material (CLSM), commonly referred to as flowable fill.
- Aggregate Substitutes – in these applications, recycled foundry sands substitute for other fine aggregates in a product that is bound together in some manner. The highest volume uses in manufactured products are: feedstock for Portland Cement kilns, fine aggregate in hot mix asphalt and fine aggregate in flowable fill. Although there are fewer examples of full-scale commercial use, metalcasting sands have also been shown to be useful fine aggregates in products such as ready mix concrete, pre-cast concrete, bricks, blocks and pavers, grouts and mortars, ceramic tiles and other manufactured products where sand is a raw material.
- Manufactured Soils – metalcasting sand is an ideal candidate for soil blending because of its composition, color and consistency. In urban areas, soil scientists in nursery and landscaping companies are manufacturing soils by blending a range of recycled materials with organic matter. It is particularly important to check with your state regulatory agency before contemplating this use as many states have different rules for soil-based applications than for construction applications.
In general, metalcasting sands will be finer sieve analysis than construction sands. The sands from an individual facility will usually be a uniform grain size. For some applications, it may be necessary to source material from several metalcasting facilities or blend facility sands with other aggregates to achieve the desired grain size distribution or specification.
Most of the characteristics that determine the fit for metalcasting sand from a particular source are related to the type of molding system used in that facility's production. At a basic level, that relates to whether the metalcasting facility uses clay to bind the sand grains together in the manufacturing process. Many facilities generate two or more different sand streams from different places in the casting process. In determining which sand streams fit local market requirements, it is helpful to think about whether the clay is likely to be an advantage or a disadvantage in the ultimate application.
More than 80 percent of casting volume in the U.S. is produced in iron and steel metalcasting facilities, collectively referred to as ferrous facilities. The most common molding technique used for ferrous casting is called green sand. Some aluminum facilities cast in green sand, although other molding systems are generally more prevalent in nonferrous plants. In green sand systems, high-grade industrial sands are bound together with bentonite clays, into which a small amount of carbonaceous material and water are added. Green sand is black in color, adheres together and has some percentage of material passing the 200-sieve size, depending on the facility's internal sand handling process. Green sands look and feel much like a silty soil. Most of the large-scale construction projects that have been field-tested are designed using green sands because they are the most prevalent types of sands produced.
The combination of the sand, clay and moisture content makes many green sands particularly suitable for geotechnical applications such as structural fills and base courses. The presence of the clay appears to improve the performance of these sands relative to other granular materials in parts of the country subject to freeze/thaw cycles. Additionally, green sands can often be placed in construction projects in colder climates long past the point in the construction season where other granular materials can be moved and graded. Green sands generally require only screening to remove tramp metal and sand lumps in order to be market ready. In its evaluation of foundry sand as a construction material, the Federal Highway Administration also pointed out that foundry sands can be transported, placed and graded using conventional construction equipment.
Research has shown that these same green sand properties will provide a good substructure for manufactured soils, a growing need in many parts of the nation. The U.S. Department of Agriculture undertook a major research study to determine whether ferrous and aluminum foundry sands can safely be used in soil blending. The results were favorable. Conversely, the presence of the clays may be a limitation in the amount of green sand that can be used as fine aggregate in hot mix asphalt or ready mix concrete.
Different metalcasting processes introduce different amounts of fines in the sand stream. It is sometimes possible for facilities to exclude most of the passing 200 material from their “fine foundry aggregate” – or the fines can be washed out, as is sometimes done at virgin sand quarries. Both of these fines-control techniques may introduce additional costs for metalcasting sand processing.
Resin sands are similar high-grade industrial sands that are bound together with a variety of proprietary chemical formulas. Chemically bonded sands are always used as the “cores” in castings that have hollow void spaces. Some foundries, generally steel or non-ferrous facilities also use chemically bonded sands as their external molds. These sands, absent the clay and the carbon, are usually lighter in color and coarser in texture than clay-bonded sands. That may make them more suitable for use in certain concrete products where the dark color of the green sands can be detrimental to the finished product. Used sand molds from chemically-bonded (resin) sand systems will often require crushing before screening to produce a uniform granular material.
APPLICATION DESCRIPTIONS
Additional information relating to high volume applications for metalcsting sand may be found on the following pages of this website. Each of the individual Application Pages contains a listing of primary references.
Construction Uses
Manufactured Soils
Asphalt
Bases and Subbases
Cememt Manufacturing
Concrete
Embankments
Flowable Fill
Landfill Construction
Structural Fills
Case Studies
Tools and Resources
Because metalcasting sand behaves in most respects like other sands, there are numerous other products and applications where the sand can be substituted for virgin aggregates. Prospective users are encouraged to search the Metalcasting Library and then to contact us to see if there is experience in the industry with an application not described on this website.