Bitumen Viscosity Test – To determine the viscosity of bitumen and tar, a bitumen viscosity test is performed. Viscosity is a measure of resistance to flow.
To choose the right bitumen, it is necessary to know its viscosity. In road construction, if bitumen with low viscosity is used, it does not help to bind the particles. High viscosity also limits the filling of voids between aggregates during pavement construction.
Therefore, by choosing bitumen with appropriate viscosity at a certain temperature, the quality of various applications of bitumen increases.
There are different methods for measuring viscosity based on Indian Bureau standards, such as industrial viscosity, dynamic or absolute viscosity and kinematic viscosity.
Next , we will explain the bitumen viscosity test according to IS 1206 (I), IS 1206 (II), and IS 1206 (III) standards.
Also, Infinity Galaxy has prepared a video where you can learn how to measure kinematic viscosity by using ASTM D2170 (IS 1206) standard, and dynamic viscosity by ASTM D4402 standard.
The dynamic viscosity measured by a cup viscometer is called industrial viscosity.
Using a cup viscometer is a simple method to determine viscosity at a certain temperature.
In this method, first, at a certain temperature, 50 ml of bitumen is poured into the metal cup of the device. Then, the time it takes for the standard volume of fluid to pass through the drain hole or orifice of the cup is recorded.
A cup viscometer is often used to determine the viscosity of emulsions,pure bitumen, and cutback bitumen.
There are different types of cup viscometers . The main difference between them is the size of the orifice of the cup.
To measure industrial viscosity, use equipment such as a tar viscometer, cup, water bath, stirrer, measuring cylinder, thermometer, and stopwatch.
The Procedure of Bitumen Industrial Viscosity Test
* Place the tar viscometer in the cup so that the top surface of the cup is level.
* Heat the water bath to the specified test temperature (The specified test temperatures are 35°C, 45°C, 55°C, and 65°C) . Rotate the stirrer gently.
* Heat the sample to a temperature of about 20 °C over the temperature stated in the test.
* Allow the sample to cool to the test temperature. In addition, rotate the stirrer continuously.
* Clean the orifice with suitable solvents.
* Pour the sample into the cup until the leveling peg on the valve is just immersed. During this, the valve rod should be kept vertical.
* Place the thermometer in the cup. It should be positioned in the center of the tar.
* Let the set stand for 5 minutes. Pay attention, during this time, the temperature of the set should not change more than 0.05 degrees Celsius from the specified test temperature.
* Remove the thermometer.
* At this stage, when you read 25 ml in the cylinder, turn on the stopwatch
* When the reading on the cylinder reaches 75 ml, stop the time and record the time in seconds.
* Repeat this test several times. The average recorded times show the final result.
Dynamic or Absolute viscosity is measured by different types of vacuum capillary viscometers. Capillary viscometers consist of narrow tubes through which bitumen flows. These pipes have thin and wide sections and there are two or more marks on them to show the volume and amount of flow.
The equipment will be required including:
* Capillary viscometer
* Water bath
* Vacuum pump
Note that three types of capillary viscometers can be used to measure dynamic viscosity:
* Cannon Manning Vacuum Viscometer
* Asphalt Institute Vacuum Viscometer
* Modified Koppers Vacuum Viscometer
The Procedure of Bitumen Dynamic Viscosity Test
* Heat the sample slightly higher than the approximate softening point temperature, so that it should not be more than 60°C and 90 °C for tars and bitumens, respectively.
* Fill the viscometer with melted bitumen to line E and maintain it at a temperature of 135 °C. Also, allow trapped air bubbles to escape during this time.
* Place the viscometer vertically in the water bath with the help of the holder.
* After creating a vacuum of 30 ± 0.05 cm Hg with the help of a vacuum pump, connect the vacuum system to the viscometer.
* Allow the assembly to stand in the water bath for 30 minutes. Open the valve and allow the bitumen to flow into the viscometer.
* Measure the time required for bitumen to pass between the two sequential pairs of the timing marks in seconds. An accuracy of 0.5 seconds is required.
* The viscosity value is obtained by multiplying the recorded time with the viscometer calibration factor.
Kinematic viscosity is obtained by dividing the dynamic viscosity of a fluid by its density. Kinematic viscosity is measured by different types of capillary viscometers.
Cannon-Fenske Viscometer and BS U-Tube Modified Reverse – flow Viscometer are used to determine kinematic viscosity.
For cutback bitumen, first, stir the sample for 30 seconds to remove the air bubbles. Then heat the sample to 60 °C.
For bitumen and tar, it is necessary to heat the samples until it becomes completely uniform. The required temperature should be higher than the softening point. The temperature of the tars and bitumens should not be higher than 90°C and 60°C, respectively.
The Procedure of Bitumen Kinematic Viscosity Test
In this test, the crossing time of a certain volume of liquid between two specified points inside the capillary tube of the viscometer is measured at a controlled temperature.
According to the type of viscometer used in the test process, some details of the test are different. In the following, we will review the test process in general.
* Fill the viscometer according to the viscometer instructions.
* Place the viscometer in the bath until it reaches the test temperature.
* Measure the time required for the liquid to travel the distance between the first and second marking lines in the tenths of a second.