AIM:
To determine the viscosity of bitumen using tar viscometer
APPARATUS:
Tar viscometer, cup, valve, receiver, thermometer etc.
THEORY:
Viscosity is the inverse of fluidity. The degree of fluidity at the application temperature greatly influences the ability of bituminous material to spread, penetrate into voids and also coat the aggregate and hence affect the strength and characteristics of resulting paving mixes. At high fluidity or low viscosity, bitumen binder simply lubricates the aggregate particles instead of providing an uniform film thickness for binding action. Low fluidity or high viscosity does not enable the bitumen to coat the entire surface of aggregate in the mix easily and also resists the compactive effort and resulting mix is heterogeneous in character.
PROCEDURE:
The tar cup is properly levelled and water in the bath is heated to the test temperature. Stirring is also continued. Material is heated to 20°C above the test temperature and material is allowed to cool. During this material is continuously stirred. When temperature reaches 40°C, it is poured into cup of the tar viscometer until levelling peg on valve rod is just immersed. Receiver is placed under the orifice. Valve is opened after applying kerosene in the receiver. Stop watch is started when cylinder records 50 ml. Time is recorded for flow upto a mark of 100ml.
RESULT:
Viscosity of cutback bitumen = ---------seconds.
RECOMMENDED VALUES:
| 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 |
| Test Temperatures(°C) | 25 | 25 | 25 | 25 | 40 | 40 |
| Viscosity Ranges | 25-75 | 30-250 | 10-20 | 25-75 | 14-45 | 60-140 |