A viscosity is measured indirectly by the penetration of a standard needle under standard conditions of load, time and temperature. The test measures the hardness or softness of bitumen in terms of penetration expressed in units of mm/10 of the standard needle. The standard conditions are:
Temperature : 25oC
Load : 100 gm
Time over which penetration is recorded : 5 secs
A diagram of the set-up is given in Figure.
Figure: Penetration Test for Paving Bitumen
Bituminous of the following penetration grade are available in India: