Test Importance
In all bituminous works bitumen is required to be heated up to a definite temperature, so that the specific grade of bitumen may reach at its proper viscosity label, so that it can be mixed correctly with the aggregates to get a homogenous mix.
Definition of Kinematic Viscosity
It may be defined as the proportion of the absolute or dynamic viscosity divided by the density of the liquid under test; both at the same temperature. The CGS unit of Kinematic viscosity is the Stoke (centimeter square per second). For petroleum products the kinematic viscosity is usually expressed in Centistokes (cSt) which is 1/100 th of a Stoke.
Objective
Objective is to determine the properties that may contributed towards the viscosity grade of bitumen.
Apparatus
(i) Cannon-Fenske Viscometer
(ii) Thermometer
(iii) Bath
(iv) Timing device (stop watch)
(v) Required u-tubes of different types
Sample preparation
The sample need to be heated to not greater than 90% above the respective approximate softening point temperature of sample bitumen until it attains pouring consistency. Mix it rigorously and pour approximately 20 ml in a 30 ml container. Local over heating and entrapped air in bitumen sample must be avoided.
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| Cannon-Fenske Viscometer |
Process for Cannon-Fenske Viscometer
For charging of the Carmon-Fenske viscometer turn the wrong way up the viscometer and put in suction to the tube L, submerging tube N within the liquid sample. Pull liquid through tube N filling bulbs D to fill mark G, wipe excess sample out tube N and again turn upside down the viscometer to its normal position. Align the viscometer vertically in the bath. Visual observation is adequate. However, it can be done more precisely and rapidly by suspending a plumb bulb in the tube L. Allow the viscometer to continue in the constant temperature bath for a enough time to warrant that the sample reaches temperature equilibrium. It generally takes about twenty minutes at 38°C, twenty five minutes at 100°C and thirty minutes at 135°C. When the test temperature is touched, remove the stopper within the tubes N and L respectively and allow the sample to flow by gravity. Measure to the nearest 0.1 s the time required for the foremost edge of the meniscus to pass from timing mark E to timing mark F. If this efflux time is less than 60 sec, choose a viscometer of smaller capillary diameter and again repeat the operation.
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| U- tube for viscosity test |
Result & Conclusion
Determine the kinematic viscosity up to three significant figures, Kinematic viscosity cSt = Ct , Where , C = calibration constant of the viscometer in centistokes per second which is generally varies with manufacturer , t = Efflux time in seconds
Report all the time the test temperature along with the results as follows :
Kinematic viscosity at 135°C = ‘x ‘ cSt
Source- (IS-1206 -1978, Part –III)
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