Foundry Sands in Portland Cement Concrete

Portland cement concrete, herein referred to as "concrete," consists of a mixture of approximately 30% sand, 50% gravel, 15% cement, and 55% water. Concrete can be either cast-in-place, or pre-cast into concrete products such as bricks, pipes, blocks, etc. The fine aggregate portion used in the production of concrete is of particular interest if foundry sands are to be beneficially used in concrete production. Several studies have also been performed to investigate the suitability of foundry sands in Portland cement production.

The specification for Portland cement concrete depends on the specific use of the concrete, such as bridge deck, pavement, blocks, etc. When foundry sands are used as a partial replacement for fine aggregates in the production of concrete the combined fine aggregates should have the following gradation recommended by ASTM C33:

Table 3. Typical Gradation for Fine Aggregate in Concrete Sieve Size (Number)

ASTM C33 requires that the fineness modulus for the combined fine aggregate be 2.3 to 3.1, and not vary by 0.2 from the approved aggregate source. Most specifications also require that the percent loss in a sodium sulfate soundness test be less than 10%. In addition to these requirements, the concrete must meet project-specific strength requirements.

Using foundry sand as a partial replacement of fine aggregate in Portland cement concrete is a large market that could use all of the foundry sand being produced in the U.S. Core sand can replace as much as 45% of the fine aggregate in concrete. Green sand, however, can replace only 9 to 15% of the fine aggregate, depending on the amount of fines in the green sand. This percentage can be increased if the foundry sand is processed and fines are removed.