All You Ever Wanted to Know About Foundry Sand

How is Foundry Sand Generated and What Are Its Properties?

Metalcasting sand is basically a fine aggregate. Once its 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.

In general, metalcasting sands will be a 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 specific source are related to the type of molding system used in that facility's production. At a basic level, this 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.

Green Sand

More than 80% 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 non-ferrous plants. In green sand systems, high-grade industrial sands are bound together with bentonite clays, into which a small amount of carbonaceous material (such as coal) 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.

Each metalcasting process introduces different amounts of fines in the sand stream, creating unique blends or grain size within the sand mixture. Fine foundry aggregate– or the silica grain size, can often be adjusted by sifting through screen-sized or washing out fines, as is sometimes done at virgin sand quarries. Quality control specifications can usually be met by one of the methods of fines-control; however, they may introduce additional costs.

Resin Sands

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.

Foundry Sand Facts for Civil Engineers- [May 2004, 80-pages]

Foundry sand production is nearly six to 10 million tons annually. Like many waste products, foundry sand has beneficial applications to other industries. The purpose of this document is to provide technical information about the potential civil engineering applications of foundry sand. This will provide a means of advancing the uses of foundry sand that are technically sound, commercially competitive and environmentally safe.

Foundry Sand- Material Description - Recycled Materials Resource Center (RMRC)

Working closely with state DOTs, the RMRC website Includes information to describe foundry sand and the performance record, material requirements, engineering properties, design considerations, construction procedures, environmental outcomes, and proper use guidelines for foundry sand being used in making:

  • Asphalt concrete
  • Flowable fill
  • Portland cement, or
  • Embankment

More Resources

EPA launched a collaborative effort to evaluate the potential risks of using silica-based spent foundry sands produced by iron, steel and aluminum foundries while encouraging beneficial use. Based on the results of the risk assessment, EPA supports the beneficial use of these materials, because the constituent concentrations found in silica-based spent foundry sands from iron steel and aluminum foundries are below the Agency’s health and environmental benchmarks.

EPA's risk assessment for the beneficial uses of spent foundry sands found that that silica-based spent foundry sands produced by iron, steel and aluminum foundries can be safely reused to save energy, reduce the need to mine virgin materials, and reduce costs for both producers and end users. EPA supports the use of silica-based spent foundry sands from these foundry types in the following applications:

  1. As an ingredient in manufactured soil;
  2. As an ingredient in soil-less media (potting soil); and
  3. As a foundation layer of roads (subbase).
  4. EPA estimates that approximately 2.6 million tons of spent foundry sand is beneficially used outside of foundries annually, with iron, steel and aluminum sands representing 96 percent of the foundry sands that are beneficially used. Currently, only about 14 percent of those sands are beneficially used in soil-related applications. EPA believes that there is potential for substantial beneficial use market growth and increased environmental benefits for the applications studied in the 2014 risk assessment.

Foundries and foundry sand recyclers should consult state regulators to ensure that planned uses are consistent with state beneficial use and waste management programs and that the chemical and physical properties of the sand meet applicable state environmental limits, engineering performance criteria and other state requirements.

Use of Used Foundry Sand in Construction

User Guidelines for Waste and Byproduct Materials in Pavement Construction- Federal Highway Administration (FHWA)

One of the largest opportunities to recycle metalcasting byproducts lies in the construction industry. The Federal Highway Administration (FHWA), an arm of the U.S. Department of Transportation, has a policy to increase the use of recycled materials in construction, reconstruction and maintenance of the nation’s transportation infrastructure. Metalcasting sand is one of six target materials for FHWA’s recycling efforts. Transportation is the largest consumer of metalcasting products, so it is fitting that metalcasting byproducts should help to rebuild America’s infrastructure while its products keep the U.S. on the move.

Use of Used Foundry Sand in Concrete: A State of Art Review- [FEB 2014 IJRET]

Using Foundry Sand in Green Infrastructure Construction [Wisconsin specific-2010]