It is common to conduct the penetration test on bitumen as part of the material’s viscosity grading. Penetration bitumen is a semi-hard, black substance known as petroleum-grade bitumen. Bitumen is graded into subgroups according to the climatic conditions in which it will be used and the type of construction. To prevent softening, lower penetration grades are desirable in warmer regions. To prevent the occurrence of excessive brittleness in colder regions, more penetration grades like 180/200 are used. Spray application works often require higher penetration grades.
Permeation grading’s basic theory is that a needle will penetrate deeper into asphalt that is less viscous. When bitumen is produced in a vacuum bottom production unit by oxidation, it penetrates into specific groups and is classified into different grades. Permeation grade bitumens exhibited a thermoplastic property, meaning they soften at high temperatures and harden at lower temperatures. It is important to evaluate the relationship between temperature and viscosity when determining the adhesion, rheology, durability, and application temperatures of bitumen.
The penetration value of bitumen is determined by applying the needle vertically to it at 25 degrees celsius for 5 seconds with a 100-gram load. In decimillimeters (0.1 mm), the needle movement is measured. The deeper the needle penetrates the bitumen, the higher the grade of the bitumen.
Penetration testing is used to determine how consistent the bitumen is. A higher penetration value indicates a softer consistency. Various grades of bituminous materials are classified using this test throughout the world. Different penetration grades of bitumen are used according to the climate and type of construction. There are three grades commonly used: 30/40, 60/70, and 80/100. Warmer climates tend to use lower penetration grade bitumen, while colder climates utilize higher penetration grade. The consistency test is not meant to include materials softer than cutbacks, which are usually graded with a viscosity test
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A thin layer of bitumen is melted, stirred well, and placed into the containers for testing. At least 15mm of bitumen is kept in the container over what is expected to penetrate. Once the samples are placed in the water bath, they are kept at 25 degrees Celsius for one hour.
The needle is brought in contact with the surface of the bitumen sample after one hour, and the dial is read when the needle is in contact with the surface. At that point, the reading of the dial is set to zero or the dial reading is noted when the needle has been brought in contact with the surface of the bitumen sample.
The needle is then released and allowed to penetrate for five seconds before reading the final result. It is recommended to perform a minimum of three penetration measurements in that sample at distances at least 10 mm apart. It is a must that the needle gets disengaged after each test, wiped with benzene, and dried. The penetration test is the main value of the three measurements.
Pouring temperature, needle size, weight on the needle, and test temperature influence the accuracy of the test. Bitumen grades are determined by their penetration values. 30/40 grade bitumen, for example, indicates that the penetration value of the bitumen is between 30 and 40 when tested under standard conditions.
In a penetration test of bitumen, a loaded needle is inserted vertically against a sample of bitumen at 25 C for five seconds in order to determine the degree of hardness or softness.
Depending on the type of bitumen used in road construction, penetration values can range from 20 to 225. The most common grade bitumen used for road construction is 30/40 and 80/100, depending on the type of construction and weather conditions. Bitumen 30/40 is preferred in hot climates.
A bitumen grade 80/100 will sink as deep as 8 to 10 mm in the bitumen when the bitumen penetration test is conducted, proving that this grade of bitumen is 80/100.
Penetrometers measure penetration of the sample by applying a standard needle under certain conditions to the sample. A sample of asphalt cement is measured by the depth at which a needle penetrates. The penetration is measured in millimeters (dmm).