Clay is the finess material of soil with finess size 0.002 mm.after the application of water it shows plastic behaviour. It is soft, moist, earthy material that made from eroded rocks. It can be moulded when wet, and is dried and baked to make bricks, pottery, and ceramics.
Bulk specific gravity of clay brick ranges from 1.6 to 2.5.
Bulk specific gravity of clay brick ranges from 1.6 to 2.5.
CLAY
Clay is the most Important Raw Material Used For Making Bricks. It is An Earthen mineral mass or fragmentary rock capable of mixing with water and forming a plastic viscous mass which has a property of retaining it shape with Moulded and dried. when such mass are heated to redness, they acquire hardness and strength. the purest clay consist mainly of kaolinite with small quantity of minerals such as quartz mica, felspar, calcite, magnesite etc. by there origin clay are subdivided as residual and transported clays. residual clay, known as kaolin or china clay, are formed from the decay of underlying rocks and are used for making pottery. transported or sedimentary clays result from the action of weathering agencies. these are more disperse, contain impurities, and free from large particles of mother rocks.
PLASTICITY OF CLAY SOIL
Plasticity is related to deforming a substance continuously under a finite force. Composition, particle size, organic matter and additives may affect clay plasticity. Several techniques are used to determine the optimal water content of clays. Methods for evaluating the plasticity of water-clay systems were reviewed. A consolidated method for measuring clay plasticity still does not exist. but the most accurate mathod for determining the clay plasticity is Atterberg limits.
CLASSIFICATION :
On The Basis Of Resistance To High Temperature :
on the basis of resistance to high temperatures( more than 1580°C),clay are classified as
- Refractory Clay : The refractory clays are highly Disperse and Very Plastic. These have high content of alumina and low content of impurities, such as fe2O3, tending to lower the refractoriness.
- High Melting Clay : It have high refractoriness and contain small amount of impurities such as quartz, felspar, mica,calcium carbonate and magnessium carbonate. These are used for manufacturing facing bricks, floor tiles, sewer pipes etc.
- Low melting clay : It have refractoriness less than 1350 °C and have varying compsition. These are used to manufacturing bricks, blocks, tiles etc.
ADMIXTURE TO CLAY
admixture are added to clay to improve its properties, if desired. Highly plastic clays which require mixing water up to 28%, gives high drying and burning shrinkage, call for addition of lean admixtures or non plastic substances such as quartz sand, chamottee, ash, etc. Item of lower bulk density and high porosity are obtained by addition of admixture that burn out. the example of burning out admixtures are sawdust, coal fines, pulverized coal, etc. Acid resistance items and facing tiles are manufactured from clay by addition of water-glass or alkalies. Burning temperature of clay items can be reduce by blending clay with fluxes such as felspar, iron bearing ores, etc. Plasticity of moulding mass may be increased by adding surfactants such as sulphite-sodium vinasse(0.1-0.3%).
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