What unit is viscosity expressed in according to IS 1203?

It is expressed empirically in 'seconds', representing the total time taken for 50 ml of the sample to flow through the viscometer orifice.

What orifice sizes does the standard tar viscometer use?

It uses standard cups equipped with either a 4 mm or 10 mm diameter orifice, depending on the expected viscosity of the sample.

Is this test suitable for standard paving-grade (penetration) bitumen?

No, it is generally used for liquid binders like cutback bitumens and road tars. Absolute or kinematic viscosity using capillary tubes (e.g., IS 1206) is used for standard paving bitumens.

IS 1203

: 1978

Methods for testing tar and bitumen: Determination of viscosity

CurrentSpecializedTesting MethodTransportation · Waterproofing and Damp Proofing

Archive.org BIS Portal Google

This code specifies the empirical method for determining the viscosity of road tars and cutback bitumens using a Standard Tar Viscometer. The viscosity is measured as the time taken in seconds for exactly 50 ml of the bituminous binder to flow through a standard 4 mm or 10 mm orifice at a strictly controlled temperature.

Describes the method for determining the viscosity of cutback and road tars by means of a standard tar viscometer.

Quick Reference Values

Volume of flow measured50 ml

Tar Viscometer orifice sizes4 mm and 10 mm

Water bath temperature tolerance± 0.1°C

Unit of measurementSeconds

Practical Notes

Viscosity of bituminous materials is highly sensitive to temperature. The water bath must maintain the test temperature strictly within ±0.1°C.

The 10 mm cup is typically selected for highly viscous materials, whereas the 4 mm cup is used for more fluid materials.

Never use metallic objects (like wires or pins) to clean the orifice, as scratches will alter the diameter and permanently ruin the calibration.