Bitumen Tests

A Complete Overview of Test Procedures, Goals, and Required Equipment Bitumen
Quality Tests
A Complete Overview
of Test Procedures, Goals
and Required Equipment

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.

Flash point 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.

Using viscosity grade bitumen with globally approved standards penetration test on bitumen Viscosity Test on bitumen with a viscometer softening point test on bitumen Softening Point Test Flash Point Test Viscosity Test ductility test on bitumen Ductility Test Flash point test on bitumen Specific Gravity Test on Bitumen Performance Test on bitumen Specific Gravity Test Performance Test Penetration Test

Slide penetration test on bitumen Penetration Test of Bitumen Bitumen penetration testing is used to determine the relative hardness or consistency of various kinds of bitumen

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 are as below:

  • penetration test apparatus,
  • thermometer,
  • spatula,
  • hot water bath,
  • two small containers of different size, 
  • 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 millimetre.

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.

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.

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:

  • Saybolt Furol (also called efflux),
  • Brookfield (or rotating spindle), 
  • 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 bitumen emulsion.

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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softening point test of bitumen

Softening Point Test of Bitumen

The primary purpose of the softening point test is to specify the temperature at which the bitumen starts melting

ring and ball test method

Bitumen is a viscoelastic material that under a specific temperature, becomes softer and less viscose. To use this material properly, we must know at what temperature it softens.

The primary purpose of the softening point test is to specify the temperature at which the bitumen starts melting.

Bitumen with a lower softening point tends to melt on the road in summer and start flowing under the impact of temperature and traffic.

Subsequently, when the bitumen cools down at night the road surface loses its original shape and becomes wavy.

This kind of road’s deformation is referred to as rutting. To guarantee a suitable rutting resistance, we must consider its softening point in addition to penetration value and viscosity.

The softening point of bitumen is most of the time tested by a ring-and-ball apparatus.

By using this device, we heat bitumen in a water bath gradually and measure the temperature at which bitumen softens and starts to flow.

We provide further details about the softening point test here.

What is the significance of the Softening Point Test?

Although the softening point test is an old test based on empirical standards, not scientific ones, it is still used for identifying the melting temperature of bitumen.

The objective here is to understand how much we should heat the bitumen at the moment of application.

Just like penetration and viscosity tests, this method of testing is used to determine the temperature susceptibility of a bitumen sample.

A bitumen with a higher softening point has a higher viscosity, which should be considered when we mix bitumen with aggregates.

By using the results of the softening point test, one can guarantee that the mixture of bitumen and aggregates will not flow during the application.

If you have doubt about which type of bitumen better suits your area, pay attention to the temperature on the hottest day of summer.

The softening point of the bitumen that you buy might not exceed this temperature, this way your bitumen will not dramatically soften and bleed after application.

Softening Point vs Viscosity Test on Bitumen

Both softening point and viscosity testing are standardized methods for measuring the consistency of bitumen.

For maximizing the performance of bitumen during and after application, we must take the consistency of this material into account.

In the bitumen industry, the amount of asphaltene indicates the consistency of bitumen well enough.

With an increase in the asphaltene content of bitumen, bitumen becomes harder, with a higher softening point, lower penetration value, and higher viscosity.

In brief, the relation between softening point and viscosity could be that a higher softening point is an indicator of higher viscosity as well.

Secondly, when various kinds of bitumen reach their softening point, they all have the same viscosity (about 1300 Pa.s).

It is also worthwhile to mention that the softening point test is suitable for harder grades of bitumen, just like the penetration test. When it comes to softer grades of bitumen such as cutbacks and emulsions, a viscosity test is preferred.

Softening Point vs Penetration Test on Bitumen

Both the softening point and penetration test are traditional and empirical methods for testing the properties of bitumen.

In harder grades of bitumen, these two tests accompany each other to ensure a fixed temperature susceptibility for various applications of the product.

While penetration testing is a globally popular way of grading bitumen , it is used as a valid way of grading oxidized bitumen, along with a softening point test.

For instance, 85/40 grade of oxidized bitumen has a softening point of 85° C and a penetration value of 40.

What Factors Affect the Softening Point of Bitumen?

softening point test bitumen

What Factors Affect the Softening Point of Bitumen?

As we mentioned before the asphaltene content of bitumen is the main factor that has an influence on the softening point of bitumen.

The softening point of bitumen may also change by weathering and aging of bitumen. Some studies show that aged bitumen has a higher softening point than a virgin one.

The degree of polymerization in modified bitumen will have an influence on the stiffness and softening point of bitumen.

With an increase in the amount of polymer in the bitumen, the softening point will rise.

The softening point itself is influential on the storage stability of polymer modified bitumen.

To measure the stability, the difference between the softening point of the top and the bottom section of a sample is measured.

If the difference is less than 2.2 °C, the polymer modified bitumen is stable for storage.

How We Measure the Softening Point of Bitumen?

How We Measure the Softening Point of Bitumen?

The test equipment needed for running a softening point test are two balls, two brass shouldered rings with 6.4 mm depth, a heating device, a spatula, a beaker (water bath), a lamp, and a thermometer.

First of all, we slowly pour the hot bitumen into the two brass rings so that the ring is completely filled.

If a little more is poured, we let the bitumen cools and then smooth the surface with a spatula to remove the excess bitumen of the rings.

softening point test apparatus

As you can see in the pictures, we then fix the place of bitumen rings in the apparatus (called ring holder).

To start the softening point test, we immerse the sample in the water bath and put them in a heater so that the water temperature inside it reaches 25°C.

Now we take the beaker out of the heater and put the balls on the bitumen in the center of the rings and put the water bath on the lamp.

At this stage, we must increase the temperature of the water from 30 to 80°C.

Since this test is very sensitive to heat, it is necessary to increase the heat consistently.

Therefore, we adjust the temperature in a way that the water temperature increases by 5 degrees per minute, using a thermometer in all stages of the test.

By an increase in the temperature of the water bath, the balls will soften the bitumen and fall until they reach the metal blade which has a distance of 25 mm from the rings.

The balls and the time needed for them to reach the blade will show us the tendency of bitumen to flow at a certain temperature.

In the end, the temperature at which each container of bitumen softens under the pressure of the ball will be considered as the softening point of bitumen.

The softening point of pure bitumen 60/70 is usually 45 to 54 degrees Celsius.

Do you know why we use two rings containing bitumen?

Simply we do this to prevent the test results from errors. If the difference between the two results exceeds 1°C for, the test must be repeated.