IS: 1206 (Part 2) – Method for Testing Tar and Bitumen Materials: Determination of Absolute Viscosity
The following testing equipment is needed to measure absolute viscosity of viscosity graded paving bitumen (IS:73-2006) at 60 C in accordance with IS:1206 (Part 2) (similar to ASTM D 2171), which uses a vacuum capillary viscometer. It should be noted that any other viscometer such as rotational viscometer cannot be used to measure the absolute viscosity at 60 C since the bitumen in non Newtonian in nature at this temperature.
While obtaining quotations specify the following requirements. Although Asphalt Institute vacuum viscometer and Modified Koppers vacuum viscometer can also be used, the following refers to Cannon-Manning vacuum viscometer only.
Complete Absolute Viscosity Testing Equipment conforming to IS:1206 (Part 2) Method for Testing Tar and Bitumen Materials: Determination of Absolute Viscosity with the following components:
Constant Temperature Bath – A suitable bath for immersion of at least 6 vacuum capillary viscometer tubes with a digital temperature controller. The accuracy of the temperature in the bath should be +/- 0.1 C throughout the bath.
Silicone Bath Oil suitable up to 150 C
Vacuum System – Capable of maintaining a vacuum within +/- 0.05 cm of the desired level up to and including 30 cm of mercury. The system shall consist of vacuum pump, moisture trap, vacuum regulator, manometer with electronic controller, bleed valve, all interconnecting tubing/piping, and any other accessories as needed to complete the vacuum system.
Thermometer for Bath – Mercury in glass, range 37.8 to 82 C, and graduations of 0.2 C.
Timing Device – A stop watch or stop clock capable of reading up to ½ second.
Cannon-Manning Vacuum Viscometers– With manufacturers’ calibration certificate, viscometer holder and silicone cork. Size 12 and Size 13 (one each) [Size 12 is suitable for testing VG-10 and Size 13 is suitable for testing VG-20, VG-30, and VG-40 bitumen.]
Viscometer Stand – for holding 6 viscometers.
Installation of the quoted instrument in client’s laboratory and operational training.
Note: Only the Cannon-Manning viscometer tubes need to be imported at this time, the remaining equipment such as bath and vacuum system are available in India.
However, be aware of water bath and vacuum control systems manufactured in India, many do not give the accuracy and consistency needed for the test (viscosity is very sensitive to small variations in temperature and vacuum level). Try them out carefully before buying them. If not satisfactory, these systems may have to be imported.
Preparation of Sample:
Heat the bitumen sample to a temperature not more than 90 C above its approx. softening point until is has become sufficiently fluid (like motor oil) to pour easily (Pic-1).
Transfer about 20 ml into a suitable container (Pic-2) and maintain at a temperature of 135 +/- 5.5 C stirring occasionally to allow entrapped air to escape.
Pour the hot bitumen in the Canning-Manning vacuum viscometer through the larger diameter filling tube A so that bitumen is within +/- 2 mm of the fill line E. Place the charged viscometer in an oven or bath maintained at 135 +/- 5.5 C for a period of 10 +/- 2 minutes to allow larger air bubbles to escape.
Maintain the test bath temperature at 60 +/- 0.1 C. Place the charged viscometer vertically in the test bath with the help of a holder so that that the uppermost timing mark is at least 2 cm below the surface of the bath liquid (Pic-3).
Establish a vacuum of 30 +/- 0.05 cm of mercury in the vacuum system and connect to the viscometer with the valve closed. After the viscometer has been in the bath for 30 +/- 5 min, open the valve and allow the bitumen to flow in the viscometer.
Measure the time required (to within +/- 0.5 sec) for the leading edge of the meniscus to pass between successive pairs of timing marks (Pic-4 and 5).
Report the first flow time which exceeds 60 sec between a pair of timing marks, noting the identification of the pair of the timing marks.
Calculate (Pic-6) and report the absolute viscosity in poises to three significant figures as follows:
Viscosity in poises = K t
K = Calibration factor in poise per second supplied with the viscometer tube for the pair of timing marks where the flow time exceeded 60 seconds.
t = flow time in seconds
Report the test temperature and vacuum level with the viscosity test results such as viscosity in poises @ 60 C and 300 mm mercury vacuum.
Note: Kinematic viscosity at 135 C also needs to be determined for the paving bitumen as specified in IS: 73-2006. At this temperature, bitumen flows readily so no vacuum needs to be applied. Follow IS: 1206 (Part III) Methods for Testing Tar and Bituminous Materials: Determination of Kinematic Viscosity, to select the proper viscometer tube given in there. The same oil bath as used for absolute viscosity can be used, just the viscometer tube will be different (Pic-7). As an alternate, one can also use a rotational viscometer which will also give the same results because the bitumen is Newtonian in nature at 135 C. The purchase and use of rotational viscometer is encouraged because it can also be used for modified binders and also for Superpave Performance Graded (PG) binders, which are expected to be adopted in the near future. Again, rotational viscometer cannot be used to measure the absolute viscosity at 60 C.