Viscosity and fluidity are opposite to each other( i.e. Viscosity is the oppose in the flow of liquid and fluidity is the encouragement to the flow of liquid ). When the temperature is increased viscosity decreases which mean fluidity increases. The viscosity of bitumen is determined by using a viscometer. Viscosity test is the measure of resistance to flow (fluidity). Higher the viscosity of liquid bitumen, the more nearly it approaches a semi-solid state in consistency.
Procedures in the Viscosity Test:
1. The tar cup is first properly levelled and water in the bath is heated up to the required test temperature.
2. Continuous stirring is carried out.
3. The material is then heated above 20 degree Celsius withy continuous stirring and allowed to cool.
4. When the temperature reaches 40 degree Celsius, it is then poured into the cup of viscometer.
5. The receiver is then placed under the orifice.
6. The valve is opened and the stopwatch is started when the cylinder records 50ml. Time is recorded for flow up to 100ml.
7. Finally, the obtained value in seconds is compared with the recommended value.
The viscosity of cutback bitumen = ………….seconds.
Recommended values for viscosity
|Cutback bitumen SC, MC, RC of grades||0||1||2||3||4||5|
|Orifice Size (mm)||4.0||4.0||10.0||10.0||10.0||10.0|
Meanings of technical terms used above:
a tough, flexible branch of an osier or other willows, used for tying, binding, or basketry