The resistance of a liquid in flowing is defined as the viscosity of that fluid.
The viscosity can be defined as the ratio of shear stress applied to the rate of shear strain. It is measured in Pascal Seconds. The dynamic viscosity can also be calculated in terms of kinematic viscosity in units m2/s or mm2/s.
Based on absolute or kinematic viscosity requirement, the bitumen viscosity can be measured by a variety of devices. The specifications kept for measurement is the absolute viscosity at 60 degree Celsius and a Kinematic viscosity at 135 degree Celsius. Bitumen tend to soften, when subjected to a temperature rise and will harden when the temperature falls.
The vacuum capillary tube viscometer is used to find absolute viscosity. Atmospheric capillary tube viscometer is employed to measure the kinematic viscosity.
Another method to measure the viscosity is the use of a rotational viscometer where a torque required to rotate a spindle at constant speed while immersed in the sample fluid. Dynamic viscosity is proportional to this measured torque.