Checking the quality of bitumen means subjecting it to various tests to determine its quality, consistency, viscosity, temperature sensitivity, and safety. The characteristics of bituminous materials can be evaluated using a variety of tests.

The following tests are typically performed to evaluate various properties of bituminous materials.

• Penetration test
• Ductility Test
• Softening point test
• Viscosity test
• Flash Point Test
• Density and Distillation Tests

Penetration Test

The penetration test is probably the most popular traditional test in binders, as it is used to grade bitumen by measuring the depth in tenths of a millimeter to which a standard loaded needle will penetrate vertically in 5 seconds.

The 100g needle set and a mechanism to unlock and lock the needle set in any position make up the penetrometer. The bitumen is heated to a pouring consistency, stirred thoroughly, and then poured into containers to a depth that is at least 15 mm greater than the expected penetration.

The test must be performed at the designated temperature of 25°C with a very strict tolerance. It should be noted that any errors in pouring temperature, needle size, weight on the needle, and test temperature have a significant impact on the penetration value. In hot climates, a lower degree of penetration is preferable.

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Ductility Test

The ability of bitumen to undergo significant deformation or stretching is known as ductility. It can also be defined as the distance in cm to which a standard sample or briquette of the material can be stretched without breaking.

Ductility equipment was originally designed to evaluate the ductility of pure binders. The cross-section of the briquette thus formed is exactly 1 cm square. The bitumen sample is heated and poured into the mold set placed on a plate. These molded samples are air cooled and then in a water bath at 27°C , a hot knife is used to level the surface and cut off the extra material.

The mold with the mounted sample is then held in the water bath of the ductility machine for about 90 minutes. The sides of the mold are removed, clamps are attached to the machine, and the machine is then started. The ductility value, which is given in cm, is the length to failure of the wire. The ductility value is greatly affected by factors such as the pouring of the bitumen, the test temperature, and the entrainment rate.

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Softening point test

The softening point denotes the temperature at which the bitumen reaches a particular degree of softening under the condition specified in the test. The test is performed using the Ring and Ball apparatus.

A brass ring containing a bitumen sample is suspended in liquid such as water or glycerin at a given temperature. A steel ball is placed over the bitumen sample and the liquid medium is heated at a rate of 50°C per minute. The temperature is recorded when the softened bitumen touches the metal plate that is at a specified distance below.

The term “softening point” refers to the temperature at which the bitumen softens to a specific degree under the given test conditions. At a specific temperature, a brass ring containing a bitumen test sample is suspended in a liquid, such as water or glycerin.

The liquid medium is heated at a rate of 5°C per minute while a steel ball is placed on top of the bitumen sample. When the softened bitumen touches the metal plate below at a specific distance, the temperature is recorded. Generally, a higher softening point indicates less susceptibility to temperature and is preferable in warm climates.

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Viscosity Test

The liquid quality of bituminous material is known as viscosity, and serves as a standard for flow resistance.

This characteristic has a substantial effect on the strength of the resulting sidewalk mixtures at application temperature. Lower stability values were observed when mixing or compacting materials with low or high viscosities.

The low stability values are caused by the high viscosity, which resists compaction and results in a heterogeneous mixture. Also, with low viscosity, it will lubricate the surfaces of the aggregate particles rather than forming a uniform film on the aggregates. Different types of viscometers are available, but for deducing the viscosity of liquid binders such as cuts and emulsions, orifice-type viscometers are used.

Under standard test conditions and at a predetermined temperature, the time it takes for 50 ml of bituminous material to pass through the hole of a cup is the viscosity, which is expressed in seconds.

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Flash Point Test

The flash point is the lowest temperature at which a flame causes the vapors of a material to ignite, like a flash, under specific test conditions. These volatiles ignite, which is extremely dangerous, so it is crucial to specify this temperature for each grade of bitumen

The lower the flash point temperature, the greater the susceptibility of the material to catch fire. In other words, the higher the flash point temperature, the safer the material.

Density Test and Distillation

Usually, the consistency of bituminous material can be measured either by penetration testing or by viscosity testing. But for a certain range of consistencies, these tests are not applicable and the float test is used.

The apparatus consists of an aluminum container and a brass collar filled with bitumen to be tested. The sample in the mold is cooled to a temperature of 50C. The total test set is floated in the water bath at 50°C and the time required for the water to pass through the sample plug is noted in seconds and is expressed as the oat value. Distillation tests are critical to identify the presence of volatile constituents and the amount of non-volatile residues in the bitumen.

The Dean Stark device is used to determine the presence of water, which needs to be kept to a minimum to avoid foaming problems. Finally, the Fraas apparatus can be used to determine the low temperature breaking point of binders. Find out how we can help with Density Testing and Distillation.

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