Bitumen and modified bitumen
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Bitumen and modified bitumen
Bitumen andmodified bitumen
Straight run bitumen
BITUMENBitumen is defined as a viscous liquid , or a solid consisting essentially of hydrocarbons and their derivatives, which is soluble in carbon disulphate.
TARObtained by destructive distillation of coal or wood.Tar contain more free carbon which is insoluble in carbon trichloroethylene.They are also readily distinguished by odour.
Natural bitumenNaturally occurring Bituminous binderLake bitumen: They are found in depression in earths surface which have accumulated in lakes.
Rock bitumen: These are deposits of limestone or sandstone naturally impregnated with bitumen.
Artificial Bitumen Straight run bitumenWhen the residue is distilled to a definite consistency without further treatment, the distillation is known as straight running and the residue, is teamed as straight-run-bitumen.
Blown bitumenBlown bitumen is a bitumen obtained by further treatment of straight run bitumen by running it, while hot, into a vertical column and blowing air through it.
Cut backCut back is defined as bitumen whose viscosity has been reduced by the addition of a volatile diluents.Depending upon the diluent used, there are three types of cut-backs.Rapid curing: Bitumen which has been fluxed with a naphtha type of distillate.Medium curing: Bitumen which has been fluxed with a kerosene type of distillateSlow curing: A liquid residue produced in the refining process, containing little or no volatile constituents.
EmulsionEmulsion is relatively stable dispersion of a liquid, subdivided in another liquid in which it is not soluble.Emulsion of bitumen =bitumen+ emulsifier/additives + waterFree flowing dark brown liquidEmulsions of bitumen can be of two type: 1.Anionic - bitumen particle has negative charge 2. Cationic - bitumen particle has positive charge
Properties of bitumen
They contain predominantly hydrocarbons, with small quantities of sulphur, oxygen, nitrogen and metals. They are predominantly soluble in carbon disulphide (CS2) the portion insoluble in CS2 being generally less than 0.1 %. Most bitumens are colloidal in nature. Bitumens are thermoplastic, i.e. they soften on heating and harden on cooling. They have no specific melting point, boiling point or freezing point, though a form of softening point is used in their characterization. Bitumens are insoluble in water.
They are highly impermeable to the passage of water. They are generally hydrophobic(water-repellent), but may be made hydrophilic(water liking) by the addition of small quantity of surface active agents. They are chemically inert.They oxidize slowly.
Advantage of Bitumen
They are more tolerant.They can be used in relatively cold weather.They are ideal for patching and repair work.They are useful for sealing cracks.
Tests on bitumenConsistency test 1. penetration test 2. viscosity test 3. softening point test 4. float testDuctility testFlash and fire point testSpecific gravity testDistillation testWater content testSolubility test
Consistency tests:Consistency defined as the resistance of a material to flow. Since this property changes as the temperature varies, it must be realized that there is no single method of the test that can readily evaluate all bituminous binders for consistency over such a wide range
To determine the penetration grade of bitumen to be used for road construction. It gives the choice to select the grade of bitumen according to the climate condition of the area where the road is to be constructed. Consistency of a bituminous material expressed as the distance 1/10th of mm that a standard needle vertically penetrates a sample under standard conditions of load, time and temperature. Standard test condition: emperature : 25C Load on needle : 100 grams Time in which penetration are recorded : 05 seconds
Procedure : Temperature raised up to 100C above its softening point. Sample is cooled to a temperature of 5C. Place the sample in the penetrometer. Standard needle is approximately 50mm in length and 1.00 to 1.02mm in diameter. At least three penetration are carried out, then the nearest whole value unit the average of the three penetration, whose values do not differ maximum by 8, gives the penetration value of the bitumen.
Viscosity testThe viscosity of a liquid is the property that retards flow so that when a force is applied to a liquid; the slower the movement of the liquid, the higher the viscosity in this sense viscosity is the pure measure of consistency. Procedure: Time is measured in seconds for a fixed quantity of the binder liquid to flow from a cup through a standard orifice under an initial standard head and at a known test temperature. The temperature ranges from 25-100C and generally so selected that the specific viscosity is no more than 45poise The orifice having size of 10mm is used for important physical characteristic of road.
Softening point test
Softening point is not a melting point; bituminous binders do not melt but instead gradually changes from semi solids to liquids when heated. Ring and ball test: Procedure: A steel ball 3/8 inch dia weighing (3.5 +- 0.03) gms, is placed upon a disk of sample contained.The liquid medium is then heated at the rate of 5C increase per minute.The temperature at which the softened bituminous material touches the bottom metal plate placed at a specified distance below the ring is recorded as the softening point.
Float test For the certain range of consistency of the bitumen materials, orifice viscometer test or penetration test cant be used to define consistency of material. Float test measures the material of this group.
Procedure: A float made of aluminium and a brass collar is filled with the specimen material to be tested. Test specimen is cooled to room temp for 15-60 min at 5C and screwed in to the float.
The float assembly is then placed in a water bath at 50C and the time required in seconds for water to force its way through the bitumen plug is noted, as the float test value. Higher the float test value stiffer is the material.
Ductility test The ductility of binder is an indication of its elasticity and ability to deform under load and return to original condition upon removal of load
Procedure: The distance to which it will elongated before breaking when two ends of a briquette are pulled at a specified temp (25C) and speed is measured. Minimum cross section of the briquette before testing is 1sq.cm.
Flash and fire point Flash point: The flash point of a material is the lowest temperature at which the vapour of a substance momentarily takes fire in the form of flash under specified test condition.Fire point: the fire point is the lowest temperature at which the material gets ignited and burns under specified test condition.
Procedure:The bitumen is filled in the cup upto a filling marks and bitumen sample is heated at the rate of 5C to 6C per minute, stirring the material.The test flame is applied at the intervals. the flash point is taken as the temperature read on the thermometer.If heating is continued beyond the flash point vapours ignite in the presence of a flame and continues to burn, indicating the fire point temperature.
Specific gravity testSp gravity is defined as the ratio of the weight of given volume of material at a given temp to that of an equal volume of water at the same temp. Procedure:Take clean and dry sp. Gravity bottle and weigh along with the stopper(weight A)Fill the sp. gr. Bottle with distilled water and keep in water bath having a temperature of 27C+1C for not less then half an hour and weigh it(weight B)Weigh the sp. Gr. Bottle about half filled with the material(weight C)Weigh the sp.gr. Bottle about half filled with the material and other half with distilled water(weight D) Weigh the sp.gr. Bottle completely filled with the material. (weight E)
It is used to find out the quantity and quality of volatile constituents. The amount of non volatile residues presents in road tars, cut back bitumen and binder emulsions.
Procedure: Two hundred millilitres of the sample is distilled in a 500ml flask at the a controlled rate to a temp of 360C for 15 minutes.
Then determined the volume of distillate removed at prescribed standard temp.
Water content test
This test is carried out to know the content of water in a sample of bitumen.Procedure:The specimen of known weight is mixed in a pure petroleum distillate free from water.It is then heated and the water is distilled off.The condensed water is collected and its weight is recorded.The water content of the specimen is expressed as the percentage of the weight of condensed water to the weight of the original sample.The maximum water in the bitumen should not exceed 0.2 percent by weight.
Solubility testProcedure: Different solvents are used in determining the percentage of the binder present in bitumen or tar. In the case of bitumen the accepted solvent is carbon disulphide. A specified quantity of binder usually about 2gms is dissolved in a given quantity of solvent. Filter the solution through a fine porosity filter. Then the residue retaine