Bitumen Tests

Bitumen is a material with different properties. In order to choose proper bitumen for road construction and other industries, bitumen tests are introduced. 

Bitumen tests, help us to determine the properties of bitumen and examine its quality before using it, during the application, and after aging. It can also be used to classify bitumen by its physical properties.

Cracks in asphalt can be caused by factors such as traffic and temperature changes. This reduces the quality and life span of the asphalt. We can reduce the risk of cracking and damage on the asphalt by using bitumen tests and checking the quality of the bitumen binder, then choosing the right bitumen for desired conditions.

 

Following is a list of bitumen tests:

  1. Penetration test
  2. Softening point test
  3. Ductility test
  4. Viscosity test
  5. Specific gravity test
  6. Solubility in TCE
  7. Flash and Fire point test
  8. Loss on heating test
  9. Spot test
  10. Drop in penetration after heating

 

Tests that measure the consistency of bitumen are penetration, viscosity, and ductility tests

These methods of testing evaluate one of the most important properties of bitumen, which is its resistance to flow. Also, with help of them, we can predict the hardness or elasticity of bitumen in various temperatures.

Penetration and viscosity tests are also the main basis for classifying various types of bitumen.

Viscosity test is also reliable in classifying bitumen based on its temperature susceptibility.

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 required in many countries.

 

See the penetration grade and viscosity grade of bitumen articles to get more information about them.

 

 

Following is a summary of different bitumen tests, their goals, and their procedures:

1. Penetration test of bitumen

Penetration test of bitumen measures the consistency of bitumen. This test is used for grading bitumen based on penetration value or in other words its hardness.

This grading system helps to select the right bitumen for the desired temperature. 

Harder types of bitumen have a better performance in hot temperatures and heavy traffic loads, whereas softer bitumen gives a better performance in cold weather.

 

Procedure:

To perform a bitumen penetration test, a needle with a load of 100 grams vertically penetrates into the bitumen for 5 seconds at 25 degrees celsius.

The amount of needle movement is determined in  0.1 mm. 

The higher the penetration of the needle in the bitumen, the higher the bitumen grade.

 

Read our article for detailed information on the bitumen penetration test

 

 

penetration test of bitumen

Figure 1: Bitumen penetration test

2. Softening point test of bitumen

Bitumen does not have a distinct melting point. The temperature that bitumen starts to melt is the softening point.

Viscosity is an important factor that causes the aggregates to stick well together. 

As the temperature rises the bitumen gradually softens and its viscosity decreases. As a result, asphalt softens and loses its uniformity.

Consequently, we must know at what temperature bitumen starts to melt and becomes softens.

 

Procedure:

The laboratory method of measuring the softening point is the ring and ball method. 

To perform the test, the bitumen sample is taken in two brass rings. Two steel balls are placed on the bitumen samples. 

The assembly is placed in a water bath and heated. 

The temperature at which a steel ball with a bitumen coating hits the bottom of a glass beaker is called the softening point temperature.

 

Read our article about softening point test of bitumen.

 

 

ring and ball

Figure 2: Softening point test of bitumen

3. Ductility test of bitumen

One of the important properties that affect asphalt quality is the ductility of bitumen.

If a bitumen binder is ductile enough it can tolerant the traffic load and expand and contract due to temperature changes. As a result the possibility of cracking decreases and the life span of asphalt increases.

During this test, bitumen is stretched to determine its cohesive strength.

Procedure:

A liquefied sample of bitumen is poured into the tester. Then the tester with bitumen is placed in the water bath. 

Then it is pulled with a speed of 5 cm/min at a temperature below its softening point. Ductility is the length before tearing apart of a stretched bitumen.

 

Read the ductility test of bitumen article for detailed information.

 

 

start the ductility test

(a) start the test

ductility test

(b) during the test

Figure 3: Ductility test of bitumen

4. Viscosity test of bitumen

The viscosity test measures the bitumen resistance to flow. A higher amount of viscosity shows that it flows harder.

After many years of research and experience, engineers found 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.

Viscosity also indicates a bitumen’s ability to compact the aggregates better together to have a uniform asphalt.

By 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 with aggregates.

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

Procedure:

Bitumen viscosity is generally tested by placing a sample in a viscometer, then measuring the flow-out time under specified conditions. To calculate viscosity, multiply the calibration coefficient of the viscometer by the time in seconds.

 

Visit the viscosity test of bitumen article for more information

 

 

schematic of viscosity test

(a) shematic of test

apparatus of viscosity test of bitumen

(b) apparatus of viscosity test

Figure 4: Viscosity test of bitumen

5. Specific gravity test of bitumen

A specific gravity test measures the ratio of bitumen weight to the weight of the water with the same volume.

Each bitumen has a unique specific gravity, thus allowing us to classify it. specific gravity can help to recognize the impurity of bitumen because impure bitumen has a higher specific gravity.

Impurity is an important factor for construction. Impure bitumen binder causes low-quality pavement.

The pycnometer method, and the Balance method, are two methods for calculating specific gravity.

In the following, we describe the pycnometer method.

Procedure:

To perform the test measure the following then use the equations:

A= mass of pycnometer

B= mass of the pycnometer that is filled with water

C= mass of pycnometer about half-filled with the bitumen

D = mass of the pycnometer about half-filled with the material and the rest with distilled water

E = mass of the pycnometer filled with the bitumen.

For solid and semi-solid bitumen:

Specific gravity= (C-A)/[(B-A)-(D-C)]

For liquid bitumen:

Specific gravity=(E-A)/(B-A)

 

Do you need more information? check out the specific gravity test of bitumen article.

 

 

specific gravity test of bitumen

Figure 5: Specific gravity test of bitumen

6. Solubility in TCE test of bitumen

The solubility test of bitumen is a method of measuring the inorganic content of bitumen. In another word, this test shows the impurity of the bitumen sample.

For a construction to be of high quality, bitumen without impurities must be used.

There is no uniform and stable asphalt made with a bitumen binder that is less than 99% soluble in trichloroethylene.

Procedure:

To do the solubility test of bitumen at the first step, dissolve the 2 grams of bitumen sample in 125 ml of trichloroethylene. 

Weigh the solution then filter it. Then wash the insoluble matter, dry it, and weigh it again.

The percentage of insoluble material calculate as follows:

Insoluble matter (%)= mass of insoluble materials/mass of bitumen sample

 

You can find more information in the solubility test of bitumen article.

 

 

solubility test of bitumen

Figure 6: Assembly for solubility test of bitumen

7. Flash and Fire point test of bitumen

When flammable or combustible materials are heated, the vapor is generated near their surfaces. Flash point is the lowest temperature at which the vapor burns in the presence of an ignition source with an instant flame.

The fire point is the temperature higher than the flash point. Its flame lasted more than 5 seconds.

To measure the flash and fire point two famous instruments are used:

  1. Pensky-martens
  2. Cleveland open cup tester

Procedure:

For Cleveland open cup tester, at first fill the test cup with bitumen. Then heat it and the temperature rises. Test flame moves over the surface of the test cup. At the flash point temperature, the sample vapor is fired. 

The fire point is determined by continuing to heat the sample until a flame appears above it. The flam must last for at least 5 seconds.

 

Detailed information is in the flash and fire point test of bitumen article.

 

 

cleveland open cup sys

Figure 7: cleveland open cup system

8. Loss on heating test of bitumen

The loss on heating test of bitumen measures the percentage of bitumen volatile components.

If the bitumen sample has a high amount of volatiles during the heating process for paving, it becomes hardened, less flexible, and brittle. 

The asphalt produced by using this type of bitumen does not have a high durability to temperature changes and traffic loads.

In construction, the loss on heating of bitumen binder must be below 1%.

Procedure: 

To perform the loss on a heating test of bitumen, 50 g of bitumen sample is heated in the oven at 163 degrees celsius. After that, the bitumen sample is weighed.

The percentage of loss on heating is calculated as follows:

Loss on heating (%) = [(Initial weight – Final weight)/Initial weight]*100

 

For detailed information visit the loss on heating test of bitumen article.

9. Spot test of bitumen

A spot test of bitumen is used to indicate that the bitumen is not damaged during the refinery’s overheating. 

The bitumen with cracking damage does not have a proper stickiness to hold the aggregates well together. Moreover, it can not tolerate the aging process.

 

Procedure:

Put 10 ml of a solvent in a flask containing 2 grams of bitumen sample. Rotate the solution for 5 seconds. Place it in boiling water for 55 seconds. Repeat those steps until the bitumen is dissolved completely.

After it cools at room temperature, put a drop on filter paper.

If the trace of the drop is brown the test is negative. Inversely if the drop is brown with a black center the test is positive and the bitumen is damaged.

 

Check out the spot test of bitumen article for detailed information.

negative spot test

Figure 8: Negative spot test

10. Drop in penetration after heating test of bitumen

Drop in penetration test measure the hardness and volatile content of bitumen. 

As bitumen is heated for construction, the volatile component evaporates and it becomes hard. Hardness after heating increases as the bitumen has a higher volatile content.

Procedure: 

To perform the drop in penetration after heating test, put the bitumen in the container. At the next step apply the needle with a load of 100 grams for 5 seconds. Note the amount of penetration in 0.1 mm.

Place the bitumen sample in the oven at 163 ͐degrees celsius for 5 hours.

After that remove the sample and let it cool. In the next step repeat the penetration test.

Drop in penetration value (%) = 

[ difference between 2 amount of peneration/initial amount ] * 100

 

You can find more information on the drop in penetration after heating test of bitumen article.