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CHAPTER 11.1.1 Cement:

1.1 INTRODUCTION

Cement is an extremely good material having adhesive and cohesive properties which provide a binding medium for discrete ingredients. It is obtained from burning together in a definite portion a mixture of naturally occurring argillaceous and calcareous material to partial fusion at high temperature (about 1450c) .The product, called Clinker, is cooled and ground to the required fineness to produce the material known as cement. Depending upon the location of the cement manufacturing plant available materials are pulverized and mixed in proportions such that the resulting mixture will have the desired chemical composition. The lime stone, clay are the basic ingredients, the proportions will be approximately four pats of limestone to one part of clay. Depending upon the wide variety of raw material used in the manufacturing of cements, the oxide composition of ordinary Portland cement is as follows: Table 1: Oxide composition of ordinary Portland cement: OXIDE Lime, CaO Silica, SiO2 Alumina,Al2O3 Iron oxide Fe2O3 Magnesia MgO Sulpher trioxide, SO3 Soda and/or potash Na2O+K2O 1.1.2 The various types of cement are: Rapid-hardening Portland cement Portland slag cement Low heat Portland cement Portland Pozzolona cement 1 PERCENTAGE 60-65 17-25 3-8 0.5-6 0.5-4 1-2 0.5-1 AVERAGE 63 20 6 3 2 1.5 1

High strength Portland cement Super Sulphate cement High alumina cement Waterproof cement White Portland cement Coloured Portland cement Hydrophobic cement.

1.1.3 Storage of cement bags: It is often necessary to store cement bags for long period, although cement retains its quality almost its quality almost indefinitely if moisture is kept away from it. The cement exposed to air absorbs moisture slowly and this causes its deterioration. Absorption of 1 or 2 % of water has no appreciable effect but further amount of moisture absorption retards the Hardening of cement. Cement in bulk can best be stored in bins of depth 2m or more. Usually a crest of about 5cm thick forms and this must be removed before cement is taken for use. The bagged cement can also be kept for months, if stored in water proof shed, with non porous walls and floors and windows being tightly shut. Once the cement has been properly stored it should not be disturbed until it is to be used. 1.2 Natural Sand: Sand is a loose, fragmented, naturally-occurring material consisting of very small particles of decomposed rocks, corals, or shells. Sand is used to provide bulk, strength, and other properties to construction materials like asphalt and concrete. It is also used as a decorative material in landscaping. Specific types of sand are used in the manufacture of glass and as a molding material for metal casting. Sand was used as early as 6000 B.C. to grind and polish stones to make sharpened tools and other objects. The production of sand for construction purposes grew significantly with the push for paved roads during World War I and through the

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1920s. The housing boom of the late 1940s and early 1950s, coupled with the increased use of concrete for building construction, provided another boost in production. Today, the processing of sand is a multi-billion dollar business with operations ranging from very small plants supplying sand and gravel to a few local building contractors to very large, highly automated plants supplying hundreds of truckloads of sand per day to a wide variety of customers over a large area. Sand that is scooped up from the bank of a river and is not washed or sorted in any way is known as bank-run sand. It is used in general construction and landscaping. The definition of the size of sand particles varies, but in general sand contains particles measuring about 0.063-2.0 mm in diameter. Particles which are smaller than this are classified as silt. Larger particles are either granules or gravel, depending on their size. In the construction business, all aggregate materials with particles smaller than 6.4 mm are classified as fine aggregates. This includes sand. Materials with particles from 6.4 mm up to about 15.2 cm are classified as coarse aggregates. Sand has a density of 1,538-1,842 kg per cubic meter. The trapped water content between the sand particles can cause the density to vary substantially. [9] 1.3 Foundry Sand: Foundry sand is a high-quality silica sand that is used to form moulds for ferrous (iron and steel) and nonferrous (copper, aluminium, brass, etc.) metal castings. The most common casting process used in the foundry industry is the sand cast system, in which the sand moulds, chemically bonded sand cast systems are used. These systems involve the use of one or more organic binders in conjunction with catalysts and different hardening/setting procedures. Chemical binders include phenolic, furfuryl alcohol, and other inorganic binders. Foundry sand makes up about 97 percent of this mixture. Chemically bonded systems are most often used for "cores" (used to produce cavities that are not practical to produce by normal moulding operations) and for moulds for nonferrous castings.

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Excess foundry sand is typically generated because varying amounts of the previously mentioned additives must continually be reintroduced to the foundry sand to maintain its desired properties, resulting in a larger volume of sand than is needed for the foundry process. Addition, heat and mechanical abrasion eventually render the sand unsuitable for use in casting moulds, and a portion of the sand is continuously removed and replaced with fresh unused sand. The spent sand is either recycled in a non-foundry application or land filled. Of the 6 to 10 million tons of spent foundry sand generated annually, less than 15 percent is recycled. Thus in order to reuse this foundry sand, attempts have been made in using this foundry sand in replace to the natural sand in the concrete technology for the reasons such like,Concrete is a mixture comprised of cement (10-15 percent), coarse and fine aggregates (60-75 percent) and water (15-20 percent) by volume. Foundry sand can be used as a fine aggregate substitute in concrete. Fine

aggregates are generally smaller, while coarse aggregates are in diameter. Foundry sand meets two of the critical requirements for concrete aggregates as it is uniformly graded, and is strong, hard, and durable. A foundry is a manufacturing facility that produces metal castings by pouring molten metal into a preformed mold to yield the resulting hardened cast. The primary metals cast include iron and steel from the ferrous family and aluminum, copper, brass and bronze from the nonferrous family. [1]

1.3.1 Manufacturing of Foundry Sand: Foundry sand is high quality silica sand that 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. 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 mould 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

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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, 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. . 1.3.2 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 chemically bonded systems. Both types of sands are suitable for beneficial use but they have different physical and environmental characteristics. Green sand moulds are used to produce about 90% of casting volume. Green sand is composed of naturally occurring materials which are blended together; high quality silica sand (85-95%), betonies 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 and water. Chemically bonded sands are used both in core making where high strengths are necessary to withstand the heat of molten metal, and in mould 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 sand. 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 moulding 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. B

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