Author: Haroon Khalil
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Alkalis and Metallic Oxides
These materials convert as soluble salts at a low temperature and thereby cause hydraulicity when present in small quantities (5%).
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Magnesium Carbonate
Hydraulicity is rendered to lime when the magnesium carbonate content is about 30% and this can happen even with the absence of clay. But limes containing large proportions of magnesium carbonate are liable to crack. It has the important property of increasing the setting process but reducing slaking.
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Soluble Silica
In order to develop hydraulicity in lime it is necessary to have silica and alumina during chemical combination with limestone. Hydraulicity in lime is caused due to silicates of calcium, magnesium and aluminium. These silicates are inert at low temperatures and they become active to combine with lime at a high temperature.
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Clay
It is the material which gives the property of producing hydraulicity in lime. In small quantity it retards slaking and is also capable of arresting slaking when it is in excess. It gives the property of insolubility for lime in water. In order to get the best quality lime it is recommended to have 8–30%…
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INTRODUCTION
There are several naturally available civil engineering materials or materials directly produced from natural materials. Among them are binding materials, which play a major role. Lime, cement and bitumen are important for civil engineers. Binding materials may be of air binding, hydraulic binding and autoclave binding. Air binding materials, also known as air-setting binding substances,…
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STONEWARE
Stoneware are the products manufactured from refractory clay mixed with crushed pottery, powdered stone, etc. The clay is prepared carefully and moulded to the required shape. The stoneware is then dried under the shade to prevent any cracking or deformation of the product. The dried material is burnt in a kiln, gradually heating to a…
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Porcelainware
Porcelainware or merely porcelain indicates fine earthenware, which is white, thin and transparent. It is also sometimes called whiteware. It is basically prepared from clay and mixed with feldspar, quartz and minerals. The ingredients are powdered and thoroughly mixed. The mixture is moulded to the required shape and then burnt. Porcelain has various uses. In…
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Burning
The dried objects are then burnt in special muffle furnaces. A typical muffle furnace is shown in Fig. 4.3. A muffle furnace has the provision to heat the product without coming into contact with fuels. In order to regulate the drought a damper is provided at the side of the furnace. Figure 4.3 Muffle furnace to…
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Drying
The terra-cotta is allowed to dry in the mould for some days, and then the object in the terra-cotta mould is taken out and then allowed in a room or shed for drying. Gradual drying is to be done failing which the shape of the object may get changed or cracked.
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Moulding
Apart from wooden moulds, special moulds of plaster of Paris or templates of zinc are used. Fine sand is sprinkled on the inside surface of the mould and the clay is then pressed in the mould with the hand.