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BITUMEN: is defined as “A viscous liquid, or a solid, consisting essentially of hydrocarbons and their derivatives, which is soluble in trichloroethyelene and is substantially nonvolatile and softens gradually when heated. It is black or brown in colour & possesses waterproofing and adhesive properties. It is obtained by refinery processes from petroleum, and is also found as a natural deposit or as a component of naturally occurring asphalt, in which it is associated with mineral matter.
Bitumen or bituminous binder available in India is mainly of the following types :
Penetration Grade :
Viscosity Grade :
Paving grade bitumen is the bitumen obtained from refineries and conforms to IS 73. Recently, the third revision of Indian Standards for Paving Bitumen Specifications IS 73:2006 has been released by Bureau of Indian Standards. Three grades of Bitumen confirming to IS 73: 1992 are manufactured in India. In this third revision grading of Bitumen is changed from penetration grade to viscosity grade. To improve the quality of Bitumen, BIS revised IS-73-1992 Specifications based on viscosity grade (viscosity @ 60 deg. C) in July 2006. As per the Specifications, there are four grades VG-10, VG-20, VG-30 & VG-40.
With the current revision several key issues are addressed, like :
Performance at high temperatures by adopting a viscosity-graded bitumen specification (based on viscosity at 60 ºC), in place of the current penetration-graded specification (based on penetration at 25 ºC)
Issues relating to compaction, which the tender asphalt mixtures create as push and shove under the roller wheels, have also addressed by having a requirement of minimum viscosity at 135ºC, it will be helpful in minimizing the tender mix problems in the field.
Adoption of viscosity-graded paving bitumen specifications will also reduce the number of total tests to, without compromising the quality of bitumen and also no new tests are required in implementing this specification.
Viscosity grades Bitumen are categorized according to Viscosity (degree of fluidity) grading. The higher the grade, the stiffer the Bitumen. In Viscosity Grade, Viscosity tests are conducted at 60 deg. C and 135 deg. C, which represents the temperature of road surface during summer and mixing temperature respectively. The penetration at 25 deg. C, which is annual average pavement temperature, has been also retained in Specifications.
Viscosity Based System
The actual tests conducted are as follows:
Viscosity at 135 Deg.C is a fair indicator of the ability of bitumen to coat the aggregates properly. In order to get best coating the viscosity has to be optimum. Too viscous bitumen would result in inadequate and non-uniform coating of the aggregates. Very low viscosity would again result in inadequate coating as the bitumen will tend to bleed. Therefore viscosity at 135 Deg.C is a true reflection of the quality of bond that is likely to be formed with the aggregate. Various testing equipments like Capillary Viscometer, Cup Viscometer, Tar Viscometer, etc. can be used for testing the viscosity.
Viscosity at 60 Deg.C is a very good indicator of the resistance of bitumen to melting/flowing on the road. It is considered to be replacement test for Softening Point test. Some specifications have replaced softening point test with Viscosity at 60OC. However, at many :
places both the tests are carried out as both the tests are empirical and have their own limitations.
METHODOLGY FOR PROCESSIG OF BITUMEN VG10 TO VG40 :
The Theory of Air Blowing
The Process of Air Blowing
Following procedural steps are involved for blowing process:
METHODOLGY FOR PROCESSIG OF BITUMEN VG30 TO CRMB60 :
BITUMEN SPECIFICATION AS PER IS 73:2006
|Softening point, Deg C, min||40||47||50||IS 1205:1978|
|Penetration at 25 Deg C||80 - 100||50 – 70||40 – 60||IS 1203:1978|
|Flash point, Degree C, min||220||220||220||IS 1209:1978|
|Solubility in trichloroethylene, %, min||99||99||99||IS 1216:1978|
|Absolute Viscosity, 60 Deg C, poises, min||800||2400||3200||IS 1206 (P2):1978|
|Kinematic Viscosity, 135Deg.C, CST, min||250||350||400||IS 1206 (P3):1978|
|Tests on residue from thin film over test / RTFOT:|
|Viscosity ratio at 60 Degree C, max||4||4||4||IS 1206(P2):1978|
|Ductility at 25 Deg. C, cm, min, after thin film over test||75||40||25||IS 1208:1978|
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