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Asphalt is a black brown complex mixture composed of hydrocarbons of different molecular weights and their non-metallic derivatives. It is a kind of organic liquid with high viscosity. It is liquid with black surface and soluble in carbon disulfide. Asphalt is mainly divided into petroleum asphalt, coal tar asphalt and natural asphalt three kinds, used for pavement, energy chemical industry, coatings, plastics, rubber, new material research and development and other industrial uses. Asphalt viscosity is very large but has fluidity, Australia University of Queensland physics professor Parnell carried out an asphalt dripping experiment. The experiment is very simple, a funnel, a beaker, a glass cover, and a timer, and then put a few pieces of asphalt on the funnel cup, and then the experiment began! The experiment took a total of 93 years. Well, you read that wrong! It was’ 93!! Each drop of asphalt takes about 8-9 years to fall. This experiment proved to us that the asphalt used to pave the road, although it looks hard, is actually a very viscous liquid. According to the latest data, asphalt is 20 billion times more viscous than water. The experiment was recognized by the Guinness Book of World Records as the world’s longest running experiment.

An introduction to measuring methods of asphalt viscosity

viscosity

When there is a velocity difference between adjacent flow layers, the fast flow layer tries to increase the fast flow layer, while the slow flow layer tries to slow down the fast flow layer. This interaction is intensified with the increase of the interlayer velocity. This characteristic of the flow rate is viscosity.

The force between layers is called internal friction or viscous force. The viscosity of the liquid is due to molecular gravity. When the liquid flows, the molecules of the fast layer try to pull the molecules of the slow layer forward, and the slow layer tries to pull the molecules of the fast layer back. These interactions between the fluid molecules allow motion to be transferred layer by layer, and maintain the velocity difference between the layers, presenting the viscosity of the fluid. According to the expression meaning of viscosity and different measurement methods, it can be divided into the following types.

An introduction to measuring methods of asphalt viscosity

Classification of viscosity

1 Dynamic viscosity

Viscosity is the degree of viscosity, also known as dynamic viscosity, which characterizes the resistance of a fluid to deformation and increases with the rate of deformation. The resistance generated when two areas of 1 square meters are taken in the fluid, 1m apart, and the relative moving speed is 1m/s is called dynamic viscosity (Pa.s, a measure of flow resistance).

2 Kinematic viscosity

Kinematic viscosity: the ratio of the dynamic viscosity of the fluid η to the density ρ of the fluid at the same temperature, called kinematic viscosity. Kinematic viscosity can be easily measured by gravity capillary viscometer.

In the ASTMD445 standard, kinematic viscosity is used to calculate dynamic viscosity, that is, dynamic viscosity (Pa.s) = density (Kg/m3) × kinematic viscosity (m2/s).

3 conditional viscosity

The conditional viscosity is the ratio of the flow time measured under certain conditions using a specific “viscometer” to the flow time of the standard liquid used. The conditional viscosity of asphalt used in road engineering includes Ngla viscosity, Saibolt viscosity, asphalt standard viscosity and so on

An introduction to measuring methods of asphalt viscosity

4. Engla viscosity

The ratio of the time required to flow 200ml of test liquid from the Engla viscometer to the time required to flow the same volume of distilled water at 20 ° C.

5. Saibolt viscosity

Time required to flow 60ml of test solution from Saybolt viscometer at test temperature.

6. Standard viscosity of asphalt

The time required to flow 50ml of asphalt from a standard viscosimeter at a given temperature.

In general, there is no theoretical relationship between dynamic viscosity and kinematic viscosity and conditional viscosity, and the relationship between them and kinematic viscosity is only an empirical relationship.

An introduction to measuring methods of asphalt viscosity
Viscosity test method

According to the physical meaning of viscosity reaction and the means of testing, the test methods of liquid viscosity include capillary method, rotation method, falling method, vibration method, slide method, outflow cup method and so on. According to the different temperature range and purpose of measurement, the commonly used viscosity measurement methods of asphalt in highway engineering are mainly as follows. The dynamic viscosity of asphalt at 60℃ was measured by vacuum vacuum capillary method. Countercurrent capillary viscometer and Brookfield viscometer are used for 135℃ and higher temperatures. In order to evaluate the low temperature performance of asphalt, the falling column and sliding plate viscometers are generally used. In order to reflect the flow performance of asphalt under specific conditions, the use of viscometers are road asphalt standard viscometer, Engla viscometer, Saibert viscometer and so on.

1. Capillary method

Capillary capillary method is based on the stable laminar flow of liquid in the capillary, which can be divided into gravity capillary and pressure capillary according to the external force exerted by it. Gravity capillary viscometer is the time required for a certain volume of liquid to flow through a capillary under the action of gravity. The basic requirements of a viscometer are a method of having a long enough capillary tube and a timing ball to measure the results of the liquid’s kinematic viscosity. The standard method of measuring viscosity of asphalt by two capillary measuring methods is listed in the Test Code of Asphalt and Asphalt Mixture for Highway Engineering. The viscosity classification in the ASTM standard also uses the above two methods to measure the viscosity of asphalt. In the capillary viscosity measurement, attention should be paid to ensure that the test tube is not tilted, so as not to cause the change of the effective height of the liquid, and the incorrect filling method will also lead to the test error.

2, the rotation method
The principle of viscosity measurement by rotation method is based on the rotation of objects immersed in a fluid, or when these objects are stationary and rotate with the surrounding fluid, these objects will be affected by the viscosity moment of the fluid, the size of the viscous moment is proportional to the viscosity of the fluid, and the viscosity is obtained by measuring the viscous moment and the rotational speed of the rotating body.