MECHANICAL PROPERTIES OF CONCRETE INCORPORATING USED FOUNDRY SAND
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MECHANICAL PROPERTIES OF CONCRETE INCORPORATING USED
Metal foundries use large amounts of the metal casting process. Foundries successfully
recycle and reuse the sand many times in a foundry and the remaining sand that is termed
as foundry sand is removed from foundry. This study presents the information about the
civil engineering applications of foundry sand, which is technically sound and is
environmentally safe. Use of foundry sand in various engg. applications can solve the
problem of disposal of foundry sand and other purposes.
Foundry sand consists primarily of silica sand, coated with a thin film
of burnt carbon, residual binder (bentonite, sea coal, resins) and dust.Foundry sand can be
used in concrete to improve its strength and other durability factors. Foundry Sand can be
used as a partial replacement of cement or as a partial replacement of fine aggregates or
total replacement of fine aggregate and as supplementary addition to achieve different
properties of concrete.
In the present study, effect of foundry sand as fine aggregate
replacement on the compressive strength, split tensile strength and modulus of elasticity
of concrete having mix proportions of 1:1.45:2.20:1.103 was investigated.
Fine aggregates were replaced with three percentages of foundry sand. The percentages
of replacements were 10, 20 and 30 % by weight of fine aggregate. Tests were performed
for compressive strength, split tensile strength and modulus of elasticity for all
replacement levels of foundry sand at different curing periods (28-days & 56-days).
Test results showed that there is some increase in compressive strength,
split tensile strength and modulus of elasticity after replacing the fine aggregates with
certain percentage of foundry sand so foundry sand can be safely used in concrete for
durability and strength purposes.
Foundry sand is high quality silica sand with uniform physical characteristics. It is a byproduct
of ferrous and nonferrous metal casting industries, where sand has been used for
centuries as a molding material because of its thermal conductivity. It is a byproduct from
the production of both ferrous and nonferrous metal castings.
The physical and chemical characteristics of foundry sand will depend in great part on
the type of casting process and the industry sector from which it originates. In modern
foundry practice, sand is typically recycled and reused through many production cycles.
Industry estimates that approximately 100 million tons of sand are used in production
annually of that 6 - 10 million tons are discarded annually and are available to be
recycled into other products and in industry. The automotive industries and its parts are
the major generators of foundry sand. Foundries purchase high quality size-specific silica
sands for use in their molding and casting operations.
The raw sand is normally of a higher quality than the typical bank run or natural sands
used in fill construction sites. The sands form the outer shape of the mold cavity. These
sands normally rely upon a small amount of bentonite clay to act as the binder material.
Chemical binders are also used to create sand “cores”. Depending upon the geometry of
the casting, sands cores are inserted into the mold cavity to form internal passages for the
molten metal. Once the metal has solidified, the casting is separated from the molding
and core sands in the shakeout process. In the casting process, molding sands are recycled
and reused multiple times. Eventually, however, the recycled sand degrades to the point
that it can no longer be reused in the casting process. At that point, the old sand is
displaced from the cycle as byproduct, new sand is introduced, and the cycle begins
again. A schematic of the flow of sands through a typical foundry is shown in Fig.1.3.
Although there are other casting methods used, including die casting and permanent mold
casting, sand casting is by far most prevalent mold casting technique. Sand is used in two
different ways in metal castings as a molding material, which focuses the external shape
of the cast part and as cores that form internal void spaces in products such as engine
blocks. Since sand grains do not naturally adhere to each other so binders must be
introduced to cause the sand to stick together and holds its shape during the introduction
of molten metal into mold and cooling of casting.
1.2 Types of Foundry Sands
Two general types of binder systems are used in metal casting depending upon which the
foundry sands are classified as: clay bonded systems (Green sand) and chemicallybonded
systems. Both types of sands are suitable for beneficial use but they have
different physical and environmental characteristics
• Green sand molds are used to produce about 90% of casting volume in the U.S.
Green sand is composed of naturally occurring materials which are blended
together; high quality silica sand (85-95%), bentonite clay (4-10%) as a binder, a
carbonaceous additive (2-10%) to improve the casting surface finish and water (2-
5%). Green sand is the most commonly used recycled foundry sand for beneficial
reuse. It is black in color, due to carbon content, has a clay content that results in
percentage of material that passes a 200 sieve and adheres together due to clay
• Chemically bonded sands are used both in core making where high strengths are
necessary to withstand the heat of molten metal, and in mold making. Most
chemical binder systems consist of an organic binder that is activated by a catalyst
although some systems use inorganic binders. Chemically bonded sands are
generally light in color and in texture than clay bonded sands.
Foundries produce Recycled Foundry Sand (RFS) generally in their overall production
volume although there are different sand to metal ratios employed in different casting
processes and products. Most foundries have two sand systems one feeding the external
molding lines and the other feeding the internal core lines. After the metal is poured and
the part is cooling, green sand is literally shaken off the castings, recovered and
reconditioned for continual reuse. Used cores are also captured during this cooling and
shake out process; these break down and are crushed and reintroduced into green sand
systems to replace a portion of sand lost in the process. Broken cores are cores, which do
not break down, are discarded. Depending on the project and implimentationed end use, it may be important
to segregate sand streams at the foundry as each stream can have different characteristics.
Additionally some sand is typically unrecoverable during shake off and finishing
processes. These sans may be contaminated with metals or very large chunks of burnt
cores and will need to undergo some type of segregation, crushing and screening before
1.3 Material Properties
1.3.1 Physical Characteristics of Foundry Sand
Foundry sand is typically sub angular to round in shape. After being used in the foundry
process, a significant number of sand agglomerations form. When these are broken down,
the shape of individual sand grains is apparent.