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PALESTINE UNIVERSITY BUILDING MATERIAL Chapter No. 9 GLASS , PLASTICS ,BITUMEN
GLASS General Glass has been an important engineering material, since old times. Glass industry has progressed very rapidly and new techniques have been developed with the help of which glass of any type and quality can be produced. The methods of glass manufacture have changed and improved, resulting in higher production rates, superior glass, and large sheet sizes.
GLASS Classification of Glass Glass is a hard brittle, transparent, translucent material. Its structure is amorphous. It is made by fusion of silica with varying proportions of oxides of sodium, potassium, calcium, magnesia, iron and other mineral. All these materials when melted, form a number of metallic silicates. Hence glass may be said as a material consisting of a number of metallic silicates. For the purpose of classification, glass may be grouped into following four categories. Soda-lime glass (Na20, CaO, 6Si02) Potash-lime glass (K20 CaO 6 Si02) Potash-lead glass (K20, PbO, 6 Si02) Common glass.
GLASS Properties of glass It is extremely brittle and is available in beautiful colors. It is affected by alkalis, but not by air or water. It has amorphous structure. It has no definite melting point. It can be polished. It absorbs, and refracts light. It is not easily affected by chemicals. It can be cast into any desired shape. Glass can be welded by fusion.
PLASTICS Introduction Plastic was invented by Schonbein in 1856. He named the product as cellulose. John Wesley Hyatt developed a new material in 1890 and named it celluloid. In this century Dr. Bakeland, a Belgian scientists, produced a product known as Bakelite. The most significant development in plastics occured mainly in the period lying between two world wars. In 1924 an Austrian Scientist Mr. Pollak prepared a substance from urea and formaldehyde. This substance was as transparent as glass.. Now the plastic has been improved to such an extent that it has assumed important place as engineering material.
PLASTICS Composition of Plastic It is an organic substance prepared from natural or synthetic resins in which other materials like fillers, solvents, plasticizers, might have been added or not. In general terms, plastics may be stated as compounds of carbon with other elements such as oxygen, hydrogen nitrogen. Carbon combines with itself and other elements and forms more complicated compounds.
BITUMEN Introduction Bituminous materials have been known and used in road construction since ancient times. They were used as a mortar and water proofing agents. Early bitumen was of natural origin, found in pools and lakes: Many of these pools and lakes exist even to-day. The bitumen lake on the Trinidad island and the Bermudz deposit in Venezuela are the largest known sources of natural bitumen. Now a days bitumen is mainly used in the construction of roads. It is also used in building industry inform of timber preservative, It is also used in so many other fields but its use in those field is not predominant.
BITUMEN Bitumen As per I.S. 334-1951 bitumen is defined as a non-crystalline solid or viscous material having adhesive properties, derived from petroleum either by natural or refinery process. It is substantially soluble in carbon disulphide. The greatest proportion of bitumen is obtained from crude petroleum. It is obtained by fractional distillation process in which the simpler components of the crude petroleum such as white spirit, kerosene, fuel oil, light, medium and heavy lubricating oils which have lower boiling points are evaporated, leaving behind the bitumen. It is black or brown in colour. Bitumen may be extracted by distillation process or cracking process. Mostly distillation process is used.
BITUMEN Straight run bitumen. The bitumen which has been distilled to a definite viscosity or penetration without further treatment is known as straight run bitumen. During processing, by regulating rate of flow and temperature, bitumen from very soft to a very hard consistency grade can be produced. Before this bitumen can be used it has to be processed to reduce its viscosity either by heating, addition of cut, or emulsifying agent. This bitumen is mostly used for road construction.
BITUMEN Air blown bitumen. Special properties can be developed in semisolid bitumen by blowing air through the residue, still in hot condition. This bitumen is sometimes called oxidized bitumen also. This bitumen is not used in paving mixes, but is a useful material for roofing, battery boxes, water proofing, etc. It is widely used, as crack and joint filler material, for concrete pavements.
BITUMEN Cut back bitumen. Cut back is defined as a bitumen, whose viscosity has been reduced by the addition of a volatile diluents. Volatile diluents are gasoline, kerosene and high boiling-point light oils. Cut back is used, when it is essential to have a fluid binder which can be readily poured or sprayed at relatively low temperature. The important features of a cut back are its viscosity at the temperature of its use and also the rate at which it sets. The rate of setting is the rate at which solvent evaporates from cut back.
BITUMEN Emulsions. It is a combination of water, bitumen and an emulsifying agent. Bitumen does not dissolve in water. But when heated bitumen and water are mixed together and agitated. The bitumen disperses in water inform of spherical globules of about 2 micron diameter. To prevent bitumen spheres from coalescing, an emulsifying agent is added in the emulsion which remains dissolved in water. Soap is used mostly as an emulsifying agent. Depending upon the stability of the protective coating of emulsifying agent the emulsion may be classified as Rapid setting (R.S.), Medium setting (MS.) and slow setting (S.S.).
BITUMEN Emulsions. Emulsions are always stored in air tight drums. It is used mostly for the construction of roads. It is not required to be heated, before use and as such are very useful for the places' where heating of the bitumen has to be avoided. Emulsion is mixed with road metal and applied. When emulsion changes its colour from brown to black, it is said that emulsion has started breaking. As the emulsion starts breaking, it starts binding the aggregate. Emulsion can be used for soil stabilization, patch repair works of bituminous roads, etc. Its main feature is that it can be used in wet conditions also.
BITUMEN Tests for Bitumen. In order to ascertain the properties of the bitumen, it may be subjected to tests as follows. Penetration test. This test is used to determine the hardness of the bitumen. This test consists of a needle of standard dimension which is loaded by 100 gm and made to penetrate vertically in the bitumen at 25°C for a period of 5 seconds. The penetration of the needle is measured in units of 1/100 cm. Bitumen is graded according to the penetration. It is written as 30/40, 80/100, 60/70, etc. 30/40 grade bitumen means that under standard conditions of temperature, the needle penetration varies from 0.30 to 0.40 cm.
BITUMEN Tests for Bitumen. Softening point. This test is done to determine temperature susceptibility of the bitumen. This test is done by ring and ball equipment. The softening temperature is that temperature at which a ball of bitumen will flow vertically for 2.54 cm through the ring on which it was placed. This temperature for usual bitumens lies between 35°C and 70°C. As per IS 702-1961 bitumen has been classified into grades such as 62/25, 75/ 15, 75/30, 85/25, 85/40. The first figure gives softening temperature in degrees centigrade and second figure gives penetration in 1/100 cm units at 25°C.
BITUMEN Tests for Bitumen. Ductility Test. This test is carried out to ascertain the ductility of the bitumen. A standard briquette of bitumen is prepared from bitumen and stretched at predetermined rate at 75°C in a stretching machine. The distance of stretch of the briquette, before it breaks determines the ductility of the bitumen. Ductility for various grades of bitumen varies from 5 to 100. For satisfactory use in road pavement, value of ductility should not be less than 50.
BITUMEN Tests for Bitumen. Float test. This test is carried out to determine the consistency of the bitumen. For this test an aluminum float having standard sized hole at the bottom is used. The specimen of bitumen to be tested is filled in the coller fitted in the hole and temperature of the water bath in which this float is left, is raised to 50°C. The temperature of the bath is maintained at 50°C. The time required in seconds for water to force its way through bitumen plug is noted. The higher the float test value, the stiffer is the bitumen.
BITUMEN Tests for Bitumen. Flash point and fire point test. Flash point is the lowest temperature at which the vapour of a bituminous material momentarily catches fire in the form of a flash under specified conditions of test. Fire point is the lowest temperature at which bituminous material gets ignited and burns under specified conditions of test. The knowledge of these points is of interest mainly to the users, since bitumen must not be heated beyond these points. The flash point tells the critical temperature at and above which suitable precautions are required to be taken to eliminate the danger of fire during heating.