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.

The short-term aging properties of neat bitumen can be investigated using the rolling thin film oven to simulate these aging phases by the use of only one equipment. The empirical tests, which include penetration and softening points, are conducted to ascertain the binder consistency before and after this aging process. The test is conducted at 163 0 C for 70min, 85min, and 100min in function of the standard used. Due to aging the viscosity increases, the binder penetration decreases and the softening point increases compared to the neat bitumen properties.

Two ovens can be used to simulate the short term aging:

• ROLLING THIN FILM OVEN
• THIN FILM OVEN

Different bitumen properties can be analyzed thanks to the use of a Ductilometer, a machine capable of applying a sample elongation at a fixed speed.

1) Ductility:

The ductility is a measure of tensile properties of bituminous materials.

It is measured by the distance to which a bituminous material will elongate before breaking when two ends of a briquet specimen of the material are pulled apart at a specified speed and at a specified temperature. The specimen will be continuously immersed in water, while the two clips are pulled apart at a uniform speed.

2) Elastic Recovery:

The elastic recovery of a bitumen is expressed as a percentage of the distance between the ends of the half-threads, which has developed 30 min after the division relative to the elongation length of 200 mm.

A bitumen specimen is stretched at a temperature of 25 °C and a constant rate of 50 mm/min to a predetermined elongation (200 mm). The bitumen thread thus produced is cut in the middle to obtain two halves of thread. After a predetermined time for recovery has elapsed, the shortening of the half threads is measured and expressed as the percentage of the elongation length. This value is especially applicable to bituminous binders modified with thermoplastic elastomers.

3) Deformation Energy:

The deformation energy is the energy supplied by test pieces, until a certain displacement of the moving element is achieved. For each test specimen, the energy calculation is accomplished from the computerised data of couples force/elongation.

Appropriate ductilometer permits the following measurements to be made:

• tensile force exerted on the specimen, by calibrated load cells;
• elongation of the specimen, by following the movement of the attachment points.

The softening point of bitumen can be determined through the use of a ring-and-ball apparatus immersed in distilled water (30 to 80°C) or USP glycerin (above 80 to 157°C). The softening point is reported as the mean of the temperatures at which the two disks soften enough to allow each ball, enveloped in bitumen, to fall a distance of 25 mm (1.0 in.).

The softening point is useful in the classification of bitumens, as one element in establishing the uniformity of shipments or sources of supply, and is indicative of the tendency of the material to flow at elevated temperatures encountered in service.

The penetration is measured with a penetrometer by means of which a standard needle is applied to the sample under specific conditions.

The penetration test is used as a measure of consistency. Higher values of penetration indicate softer consistency. The value of penetration obtained is also used to classify the bitume in a range of penetration grade.