Bitumen Tests

Bitumen tests have been introduced to the market with the aim of facilitating the application of bitumen in various industries. Bitumen that we use in road construction, for instance, loses its desirable properties after being exposed to traffic and change in temperature. In order to make the properties of bitumen more predictable in the time of application and after aging, we have various test methods that help us much.

Tests that measure the consistency of bitumen are penetration, viscosity, and ductility test. These methods of testing evaluate one of the most important features of bitumen, which is its resistance to flow.

With the help of these tests, we can predict the stiffness of bitumen in various temperatures.

Penetration and viscosity test are also the main basis for grading various types of bitumen. Click for more information on bitumen penetration grades. Viscosity test is also reliable in grading bitumen based on its temperature susceptibility. For more information on various grades of viscosity visit here

There are also tests that have been introduced to the industry, to enhance the safety of bitumen application. Flashpoint test is one of them which is obligatory in many countries.

In what follows, we take a look at these different bitumen tests, their goals, and their procedure.

Higher values of penetration in this test indicate that the bitumen is softer. Harder types of bitumen have a better performance in hot temperatures and heavy traffic loads, whereas softer bitumen that gives a better performance in cold weather.

In this test, the softness of bitumen is measured by evaluating the permeability of the sample at 25° C. In the lab, we penetrate a standard needle in a sample of bitumen and measure the speed of penetration to indicate how stiff the substance is. This is the easiest way we can predict the behavior of bitumen on the pavement.

Apart from describing the physical characteristics of bitumen, this test is also useful in grading bitumen for a better application in various temperatures. Bitumen penetration test leads to one of the most widely used grading systems for bitumen, which is penetration grade and includes the well-known range of bitumen 40/50, 60/70, 80/100, and 85/100.

What is the significance of Penetration Testing of Bitumen?

The penetration test is the simplest way of classifying various types of bitumen based on their softness at a specific temperature. By classifying bitumen to four categories of pen grades, we predicting the softness level of each grade in the refinery. 

This testing method is also used in the specifications table of other types and grades of bitumen.

Please note that the penetration test must be lined up with a ductility test, in order to ensure that bitumen has the right stickiness or consistency.

It is also necessary to know that penetration testing of bitumen is not useful for evaluating softer types of bitumen, like cutback or emulsion. For these types of bitumen viscosity test is recommended.

How We Measure the Penetration Value of Bitumen?

The test equipment needed for running a penetration test on bitumen is a penetration test apparatus, thermometer, spatula, hot water bath, two small containers of different size and a stopwatch.

The test method for measuring penetration is simple. First, we heat a sample of bitumen to about 60° C. This container has a diameter of 5.5 cm and a height of 3.5 cm. Care must be taken to ensure that the bitumen surface is perfectly smooth and without bubbles.

We then place the container of bitumen in the laboratory air to cool the bitumen. Then place the bitumen container in a warm water bath with a temperature of 25° C to balance the water in the bath after an hour and a half. After that, we can remove the pan from the hot water bath and dry the surface with a cotton swab.

Then we place the container under the penetration device so that the tip of the needle and the tip of the image overlap on the glossy surface of the bitumen.

Now we set the degree of the device to zero, and by starting the stopwatch, the needle, which weighs 100 grams, is released within 5 seconds, and the amount of needle penetration on the device dial can be read and recorded.

It is also necessary to perform the test 5 to 10 times for each sample (each container) and the resulting values are recorded. Note that the values obtained are in tenths of a millimeter. A bitumen with a penetration value of 30 to 40 mm (which is called bitumen pen grade 30/40) is the hardest type of bitumen, while a bitumen with a penetration value of 85 to 100 mm is the softest one.

Bitumen viscosity test measures the bitumen resistance to flow

Viscosity Test of Bitumen

Bitumen viscosity is a quantity that determines the behavioral properties of bitumen at high temperatures.


The internal resistance of liquids that impede their movement and flow is called viscosity. This viscosity is measured for fluids in terms of poise, which is the same as Pascal-seconds [Pa/s].

Both viscosity and penetration tests measure the stiffness of bitumen, so what is the significance of doing a viscosity test? After many years of research and experience, engineers found that two bitumen that has the same degree of penetration at 25oC behave differently at higher temperatures. That’s why they found it necessary to perform an experiment to show these differences. Find more details about the difference between viscosity and penetration of bitumen.

What is the significance of Viscosity Testing of Bitumen?

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What is the significance of Viscosity Testing of Bitumen?

The viscosity value of bitumen is directly related to the stability of asphalt with temperature changes. Bitumen that we use on a road surface may become unstable after a while and experience rutting in hot weather and fatigue cracking in cold winters.

If the viscosity of bitumen is very low, it causes the asphalt swell and become billowy under a load of traffic in hot summers. On the other hand, a bitumen with very high viscosity causes cracks in the asphalt when the weather is very cold.

By measuring the viscosity level of bitumen in a lab, we can predict the resistance of bitumen in various temperatures.

Viscosity level is also an indicator of the bitumen’s ability to compact better on a road surface. With predicting both viscosity of bitumen under two different temperatures, 60° C and 135° C, we can have sufficient information about the best temperature we should mix and compact bitumen. The higher viscosity may lead to bitumen’s resistance to compaction and leaves many air voids in the final asphalt, which reduces the durability of asphalt significantly.

In brief, with controlling the viscosity of bitumen, you can experience better resilience, reduction in maintenance costs, lower fatigue cracking, and less temperature susceptibility.

How We Measure the Viscosity of Bitumen?

How We Measure the Viscosity of Bitumen?

The viscosity of bitumen is tested at two different temperatures. At first, the absolute viscosity of bitumen sample is measured in 60° C. To make sure that the bitumen viscosity is suitable for being mixed under a higher temperature, we do another test that measures the kinematic viscosity in 135° C. For more information about the difference between absolute and kinematic viscosity, visit here.

Viscosity of bitumen is tested in two different temperatures.

What is the Apparatus for Viscosity
Testing of Bitumen?

There are various types of viscometers that can be used to determine the viscosity of the bitumen. The most used ones are the Saybolt Furol (also called efflux), Brookfield (or rotating spindle), and the Capillary tube (Cannon-Manning vacuum). Each one of these viscometers is used for measuring the characteristics of different types of bitumen.

The most common device for measuring the viscosity is saybolt furol or efflux viscometer

Saybolt Furol

Also known as efflux viscometer, this equipment is used to measure the time that is needed for a specific amount of bitumen to flow through an orifice with a specific size. This apparatus of viscosity testing is recommended for both cutback and emulsion bitumen.

In this test, the amount of bitumen sample is 60 ml and the temperature of the device is 135o C. The time required for passing bitumen from an orifice shows the viscosity of the bitumen. The higher the viscosity of bitumen, the more time will be needed for the sample to flow.

Brookfield Rotational Viscometer

Road constructors and bitumen experts believe that the force that is needed for a liquid substance to rotate within a certain time is an indicator of viscosity value. That’s why a rotational viscometer is equipped with a spindle that can be immersed in a sample of bitumen and become twisted afterwards. The only thing that a rotational viscometer needs to do is to measure the bitumen resistance to rotate and convert it into the viscosity.

Modern rotational viscometers have the ability to measure the viscosity of bitumen in a wide range of temperatures (between 120 and 180 o C).

Capillary tube viscometer is very common for testing paving grade and cutback bitumen

Capillary Tube Viscometer

The most common application of capillary tube viscometer is for testing paving grade and cutback bitumen at both 60 o C (absolute viscosity) and 135 o C (kinematic viscosity).

In capillary tube viscometer the orifice in saybolt furol viscometer is substituted with a long tube. This capillary tube is marked by two or more indicators. When the testing starts, the flow of bitumen through the tube is measured; the time that is required for bitumen to reach the marked points, shows the viscosity of bitumen sample.

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