Are we really getting
viscosity graded (VG) paving bitumen in India
It is very unfortunate that many Indian highway engineers still do not know that it is illegal and unethical to specify, produce, and use penetration graded paving bitumen such as 60/70 and 80/100.
The Bureau of Indian Standards (BIS) revised IS:73
Specification for Paving bitumen in July 2006. The revised specification IS:73-2006
outlawed the old (more than 100 year old) penetration grades such as 60/70 and
80/100 and adopted new viscosity grades (VG) such as VG-30 in lieu of 60/70 and
VG-10 in lieu of 80/100. [Prof. Prithvi Singh Kandhal was instrumental in
introducing the viscosity grading of paving bitumen in India in 2005 with the
assistance of 10 Jan Path, New Delhi.]
The Ministry of Road Transport and Highways (MORTH) issued
Circular No. RW/NH-33041/3/2001-S&R (R)-Vol. III on 04/08/2008 to all the state PWDs, NHAI etc.
reminding them to implement the new bitumen viscosity grades as soon as
possible. According to the circular, the user must substitute VG-30 in lieu of
60/70, substitute VG-10 in lieu of 80/100, and substitute VG-40 in lieu of
30/40 or 40/50 grades. Is that really hard to do? Just changing the
nomenclature in tender notices or project reports is not a rocket science!
If the user would like to know more about viscosity grades
(VG), please read the following IRC paper:
Kandhal, P.S. An Overview of the Viscosity Grading System
Adopted in India
You can download this paper at the following link by clicking or copying and pasting the
following URL in your internet browser.
The BIS has further revised IS:73-2006 Specification for
Paving Bitumen in April 2013. The revised IS:73-2013 has the following
significant changes. Instead of specifying a penetration range for each VG
grade, only minimum penetration values have now been specified. For example:
minimum penetration of 80 for VG-10 and 45 for VG-30. Instead of specifying the
minimum absolute viscosity at 60 C, viscosity range has been specified for each
VG grade. For example: 800-1200 poises for VG-10 and 2400-3600 poises for
VG-30. These revisions were warranted and justified as explained in the IRC
paper above.
Progressive user agency (be it PWD, contractor, consultant,
testing laboratory or university) must purchase the viscosity testing equipment
as soon as possible to monitor the grade and quality of the VG bitumen supplied
by the oil companies. Research study completed by IIT Madras for BIS in 2011 determined
that a significant percentage of VG-30 bitumen samples obtained across India
were actually either VG-20 or VG-10; that is, softer viscosity grades which may
cause premature rutting/bleeding in the asphalt pavements. Therefore, the user
agencies must test at least the absolute viscosity at 60 C to ensure right VG
grade is being supplied to the project. Only the vacuum capillary viscometer
(and not the Brookfield Brookfield
Click at the following link (or copy and paste the following
URL in your internet browser) to access Prof. Kandhal’s technical note on
equipment details and testing procedure:
