Viscosity test on road Tar and Bitumen as per IS 1206

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Viscosity test on road Tar and Bitumen as per IS 1206

OBJECTIVE:
To determine the viscosity of road tar/bitumen.

APPARATUS/EQUIPMENT'S REQUIRED:
Ten millimeter orifice viscometer is specified for testing road tar and is called tar viscometer, 4.0 mm orifice is used to test cutback grades, 0 and 1 and 10 mm orifice to test all other grades. The apparatus consists of main part like cup, valve, water bath, sleeves, stirrer, receiver and thermometers, etc.

THEORY:
Viscosity is the measure of resistance to flow. It is measured by recording the time in seconds taken by 50 c.c. of the material to flow through a specified orifice of standard dimension into a receiver at specified temperature.

PROCEDURE:

• The tar cup is properly leveled and water in the bath is heated to the temperature specified for the test and is maintained throughout the test. Stirring is also continued.
• The sample material is heated at the temperature 20°C above the specified test temperature, and the material is allowed to cool.
• During this the material is continuously, stirred.
• When material reaches slightly above test temperature, the same is poured in tar cup, until the leveling peg on the valve rod is just immersed.
• In the graduated receiver (cylinder), 20 ml of mineral oil or one percent by weight solution of soft soap is poured.
• The receiver is placed under the orifice.
• When the sample material reaches the specified testing temperature within ± 0.1°C and is maintained for 5 minutes, the valve I opened.
• The stop watch is started, when cylinder records 25ml.
• The time is recorded for flow up to a mark of 75ml. (i.e., 50ml of test sample to flow through the orifice).

The viscosity test on road tar is carried out using 10 mm orifice and the standard test temperature for road tar grades RT1, RT2, RT3, and RT4 are 35, 40, 45, and 55°C respectively. In case the viscosity test is being carried out to classify a given sample of road tar of to find its grade, then the test should be first conducted at the lowest temperature of testing road tar, i.e. 35°C; if the time taken for 50ml of the tar sample to flow through the 10 mm orifice is more than 55 sec, of if the sample does not flow freely test may be repeated at the next higher temperature, till the viscosity value falls in the specified range.

The viscosity test on cutback bitumen is carried out using 4.0 mm orifice for grades 0 and 1 (SC– 0, MC – 0, RC – 0, SC – 1, MC – 1, RC – 1, at 25°C). The test for cutback grades 2 and 3 are carried out at 25°C using 10 mm orifice and those for grades 4 and 5 are carried out at 40°C using 10 mm orifice. For details of requirements of cutbacks see Tables 23.1 – a, b & c. if the viscosity of an unknown grade of cutbacks, is to be determined, the orifice size and the trial test temperature may be chosen using judgment. If the viscosity value of the trial test does not fall within the specified range, test should be repeated by altering the test temperature or orifice size of both suitably.