AIM:
To determine the viscosity of bitumen using tar viscometer
APPARATUS:
The Tar viscometer is a device used to measure the viscosity of tar. It typically consists of a cup that holds the tar sample, a valve that controls the flow of the tar, and a receiver that collects the tar as it flows out of the cup. Additionally, a thermometer is often used to measure the temperature of the tar during the viscosity test.
THEORY:
The ability of bituminous materials to spread, penetrate voids and coat aggregate, greatly depends on their degree of fluidity at the application temperature. Viscosity, which is the inverse of fluidity, plays a critical role in determining the strength and characteristics of the resulting paving mixes.
When the fluidity of bitumen binder is high or its viscosity is low, it simply lubricates the aggregate particles. As a result, it fails to provide a uniform film thickness for binding action, which can negatively impact the mix’s overall strength.
Conversely, when the fluidity of bituminous materials is low or their viscosity is high, they cannot easily coat the entire surface of the aggregate in the mix. Additionally, high viscosity resists the compactive effort, making the resulting mix heterogeneous in character.
Therefore, it is crucial to carefully monitor and control the fluidity or viscosity of bituminous materials during the paving mix production process. Proper control of fluidity or viscosity can help ensure uniform film thickness for binding action, improve the overall strength and characteristics of the mix, and produce a high-quality paving surface.
PROCEDURE:
To conduct the tar viscosity test, it is important to ensure that the tar cup is properly levelled and that the water in the bath has been heated to the desired test temperature. Stirring must also be continued throughout the test to ensure uniformity in the material being tested.
Next, the material is heated to a temperature that is 20°C above the desired test temperature. The material is then allowed to cool while being continuously stirred. Once the temperature reaches 40°C, it is poured into the cup of the tar viscometer until the levelling peg on the valve rod is just immersed. A receiver is placed under the orifice, and kerosene is applied to the receiver.
The test is initiated by opening the valve when the cylinder records 50 ml. At this point, the stopwatch is started and the time is recorded for the flow of material up to a mark of 100ml. This data is important in determining the viscosity of the material being tested.
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 |