FOUNDRY SANDUser Guideline

Portland Cement

Note: The use of foundry sand in Portland cement and Portland cement concrete mixtures is an emerging application area. Published research and case studies on this subject are limited. As such, the use of foundry sand for this application is not well documented, and any use of foundry sand in Portland cement should be considered somewhat experimental. Publication of such uses and laboratory research would aid in the understanding of the performance of foundry sand in Portland cement.

INTRODUCTION

Portland cement concrete is a commonly used paving material that consists of approximately 45 percent coarse aggregate, 25 percent fine aggregate, 20 percent cement and 10 percent water.⁽¹⁾ It has been shown that foundry sand can be used in concrete production as a replacement of the fine aggregate portion of the mixture.⁽¹⁾ The following guideline was developed to provide the foundry sand user a comprehensive summary of foundry sand in terms of its physical properties as well as additional design considerations when incorporating foundry sand into Portland cement mixtures.

MATERIAL PROPERTIES

Various characteristics of foundry sand can affect the quality of concrete produced. Because foundry sand properties vary depending on the source from which the foundry sand was produced, it is important that adequate testing of the sand is performed. The material characteristics that are most relevant in Portland cement applications include particle size distribution, dust content, density, specific gravity, organic content, and grain shape.⁽¹⁾ These characteristics are described in further detail below.

Particle Size Distribution: The fine aggregate particle size distribution of Portland cement is an important characteristic as it can affect concrete workability, porosity, shrinkage and durability. In particular, too many fine particles can lower the concrete strength and adversely affect durability. ASTM C33⁽²⁾ requires that the fine aggregate used in concrete have a fineness modulus, an index of aggregate fineness, in the range of 2.3 to 3.1.⁽¹⁾ The fineness modulus of foundry sand typically ranges from 0.9 to 1.6.⁽¹⁾ Generally foundry sand is too fine to permit full substitution. The sand has to be blended with a coarser material to meet this specification. In some areas, natural sands lack finer material. Foundry sand can be blended with them as a partial replacement to satisfy the specification.

Dust Content: Dust content is a concern when using foundry sands in Portland cement. A large dust content can interfere with the bonding of cement to the surface of the aggregate and can also increase water demand. As a result, increased dust content reduces the durability of hardened concrete. ASTM C33 allows a maximum of 5% fine aggregate particles to pass the No. 200 sieve.⁽¹⁾

Density: According to ASTM C330, the density of fine aggregate must be a minimum of 1.20 to 1.76 g/cm³ (75-110 lbs/ft³).⁽¹⁾ A higher density aggregate is required when the concrete will be subjected to high compressive loads.

Specific Gravity: The specific gravity of foundry sand varies from 2.5 to 2.8, depending on the source, which compares very favorably to natural sands.⁽¹⁾ Although specific gravity does not directly relate to concrete quality, it can be used as a quality control indicator.

Organics Content/Deleterious Materials Content: According to ASTM C33, the maximum amount of clay lumps and friable particles allowed is 3%.⁽¹⁾ Organic content is restricted because it interferes with hydration of the cement and its subsequent strength. The organic content of aggregate can be measured by a color test.⁽¹⁾

Grain Shape: Foundry sand particles are typically angular to rounded.⁽¹⁾ Round particles are desired as they need less water and cement to coat their surface, and they produce a mixture that is more workable. In contrast, angularity increases water demand and cement content to maintain a workable mix.

PROCESSING REQUIREMENTS

Prior to reuse, foundry sand must be processed to ensure optimal performance. In particular, spent foundry sand should be screened and crushed to obtain the desired gradation, and magnetic particles should be separated. These processes will also remove waste and deleterious materials, such as tramp metal and core pieces, preventing technical problems when mixing the cement components.⁽¹⁾

MIX DESIGN

Although there are no specific requirements for mix design of Portland cement using foundry sand, the selection of aggregate used in concrete is of great importance as aggregate properties strongly influence the concrete properties, before and after hardening. Aggregates are classified based on particle size. Fine aggregates consist of sand or crushed stone with particle diameters smaller than 3/8 inch.⁽¹⁾ Coarse aggregates are gravel or crushed stone with particle diameters ranging between 3/8 inch and 2 inches.⁽¹⁾ To achieve optimal performance, aggregate must be:

Clean and free of objectionable materials, including organic material, clay and deleterious contaminants, which can affect bonding of the cement paste to the aggregate
Strong, hard and durable
Uniformly graded

Foundry sand can be used in combination with all types of cementitious materials including mixes containing chemical admixtures. ⁽³⁾ Retarders and water reducers are compatible with most foundry sands. As with natural sands, any organic material in the foundry sand may affect the dosage and effectiveness of air entraining agents. Trial mixtures should be examined for any potential compatibility problems.⁽¹⁾

ENVIRONMENTAL CONSIDERATIONS

In casting some non-ferrous metals (such as copper, bronze, and brass), lead is often used to decrease the permeability and increase the machineability of the finished casting. As a result, lead concentrations in spent foundry sand from these processes can exceed the EP toxicity criterion for lead set by the U.S. Environmental Protection Agency.⁽³⁾ Fortunately, applying foundry sand in Portland cement stabilizes the material and can render it non-EP toxic by means of both physical and chemical mechanisms.⁽³⁾ Cement not only coats the sand particles to physically prevent leaching; cement is also alkaline which causes it to neutralize acids in the mixture which could leach the lead.⁽³⁾

UNRESOLVED ISSUES

Because spent foundry sand is black, it may cause finished concrete to have a grayish/black tint, which may not be desirable. A 15 percent or less fine aggregate replacement with foundry sand typically produces a minimal color change. In addition, if foundry sand is used in precast manufacturing, the foundry must be able to meet the quantity requirements of the manufacturer.⁽¹⁾

In general, further investigation is needed to determine appropriate mix designs of Portland cement that account for the variability in material properties of foundry sand.

REFERENCES

A searchable version of the references used in this section is available here.
A searchable bibliography of foundry sand literature is available here.

Federal Highway Administration. Foundry sand facts for civil engineers. Federal Highway Administration (FHWA); 2004 May 2004. Report nr FHWA-IF-04-004.
ASTM C33-03 standard specification for concrete aggregates. In: Annual book of ASTM standards. West Conshohocken, Pennsylvania: ASTM; 2003.
Zirschky J, Piznar M. Cement stabilization of foundry sands. J Envir Engrg 1988;114(3):715-718.

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Last Update 7/28/08