Determination of the viscosity of bituminous binder.

Determination of the viscosity of

bituminous binder.

Theory:Viscosity of a fluid is the property by virtue of which it offers resistance to flow. Higher the viscosity, the slower will be the movement of the liquid. The viscosity affects the ability of the binder to spread, move into and fill up the voids between aggregates.Aparatues required:As per IS: 1206 (Part I)-1978, following equipment is required: Tar viscometer (shown in Fig.1)Receiver: A 100 ml graduated cylinder, having an internal diameter of not more than 29mm and it has markings on 25ml and 75ml levels. Thermometer and a stop watch or other timing device capable of being read up to seconds.Procedure:Select the test temperature from the table. Heat the water in the water bath to the temperature specified for the test and maintains it within 0.1C of the specified temperature throughout the duration of test. Warm and stir the material under examination to 20C above the temperature specified for test.Pour the tar into the cup until the leveling peg on the valve rod immersed when the latter is vertical. Pour into the graduated receiver 20ml of water and place it under the orifice of the tar cup. Place the thermometer in the tar and stir till the temperature of the water bath and the tar is equal.Allow the assembled apparatus to stand for five minutes during which the temperature should be maintained/remained withn 0.05C of the specified temp.After that lift the valve and suspend it on valve support. Start the stop watch when the reading in the cylinder is 25ml and stop it when it is 75ml. note the time in seconds.Report the viscosity as the time taken in seconds by 50 ml of tar to flow out at the temperature specified for the test.

Observations:Test Temperature = ................C .

2. Time taken to flow 50 c.c. of the binder = ...........Sec . 3. Viscosity =...................(in Seconds).

Precautions:The tar should be cleaned gently with non-corroding solvents such as light tar oils free from phenols.

The orifice size should be tested at frequent intervals with a gauge having appropriate diameters

Conclusion:The determination of time of flow of binder through the orifice gives an indirect measure of viscosityThe viscosity of the particular grade of road tar or cutback bitumen should fall within the range as given in table 1 or table 2.Binder having low viscosity can be advantageously used in exceptionally cold weather condition. High viscosity binder have to be heated before their application.

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