This article discusses the concept of ductility in bitumen, which refers to its ability to stretch without cracking under traffic load during road construction. A ductility test is conducted to measure the distance in centimeters that bitumen can elongate before it breaks. The test requires specific apparatus and follows a particular procedure, which includes precautions to ensure accurate results. Observations made during the test are important for reporting and determining recommended values for bitumen ductility.
Ductility Test on Bitumen
The purpose of conducting a ductility test on bitumen is twofold. Firstly, it is used as a means of measuring the amount of ductility exhibited by a particular sample of bitumen. This information is useful for understanding the physical properties of the material, as well as for ensuring that it meets the necessary requirements for its intended use.
Secondly, the results of the ductility test can also be used to determine whether or not a particular sample of bitumen is suitable for use in road construction. This is because the ductility of the material is a key factor in determining its ability to withstand the stresses and strains associated with heavy traffic loads and other environmental factors.
Overall, the ductility test is an important tool for assessing the quality and suitability of bitumen for use in road construction. By providing information on the material’s physical properties, it allows engineers and other professionals to make informed decisions about its use in various applications.
Apparatus Required for Ductility Test on Bitumen:
The apparatus described in the IS: 1208-1978 standard for testing bituminous materials consists of four components: a briquette mould, a water bath, a testing machine, and a thermometer.
The briquette mould is made of brass and has circular holes at both ends called clips to grip the fixed and movable ends of the testing machine. When properly assembled, the mould forms a briquette specimen with specific dimensions: a total length of 75.0 ± 0.5 mm, a distance of 30.0 ± 0.3 mm between clips, a width of 20.0 ± 0.2 mm at the mount of slip, a width of 10.0 ± 0.1 mm at the minimum cross-section (halfway between clips), and a thickness of 10.0 ± 0.1 mm throughout.
The water bath is designed to maintain a temperature within 27.0° ±0.1°C of the specified test temperature and contains not less than 10 litres of water. The specimen is submerged to a depth of not less than 10 cm and supported on a perforated shell less than 5 cm from the bottom of the bath.
The testing machine is used to pull the briquette specimen apart continuously while it is submerged in water. Any apparatus may be used as long as it is constructed to ensure that the specimen remains continuously submerged in water and that the two clips are pulled apart horizontally at a uniform speed of 50 ± 2.5 mm per minute.
Finally, a thermometer is required for the test with a range of 0-44°C and readable up to 0.2°C.
Theory of Ductility Test on Bitumen
The ductility test is a crucial tool for evaluating the adhesive properties of bitumen and its ability to stretch. This test plays an important role in designing flexible pavements, as it helps determine whether the binder material can form a thin, ductile film around the aggregates, thereby improving physical interlocking. Bitumen binders with insufficient ductility are prone to cracking under the repeated loads of traffic, leading to a porous pavement surface.
To measure the ductility of a bituminous material, a standard briquette specimen of the material is subjected to a pull-apart test at a specified temperature and speed. The test measures the distance, in centimeters, to which the material can elongate before it breaks. This distance is an important indicator of the material’s ductility and its ability to withstand the stresses of repeated traffic loads. Ultimately, the goal of the ductility test is to ensure that the bitumen binder used in pavement design is strong, durable, and able to maintain a stable surface over time.
Procedure of Ductility Test on Bitumen
The procedure for testing the ductility of bituminous materials is as follows:
Firstly, the test material is heated at a temperature of 75°C to 100°C above its approximate softening point until it becomes thoroughly fluid. The fluid is then strained through an IS sieve 30.
After stirring the fluid, it is poured into a mould assembly and placed on a brass plate. To prevent the material from sticking, the surface of the plate and the interior surfaces of the sides of the mould are coated with mercury or a mixture of equal parts of glycerine and dextrine.
After about 30-40 minutes, the plate assembly along with the sample is kept in a water bath maintained at a temperature of 27°C for half an hour. The sample and mould assembly are then removed from the water bath, and the specimen is trimmed by levelling the surface using a hot knife.
The mould assembly is then replaced in the water bath for 80 to 90 minutes. After this time, the sides of the mould are removed, and the clips are carefully hooked onto the machine without causing any initial strain.
The pointer is adjusted to read zero, and the machine is started. The clips are pulled horizontally at a speed of 50 mm per minute. The distance at which the bitumen thread of the specimen breaks is noted.
The ductility value is calculated as the mean of two observations rounded to the nearest whole number.
Note:
The machine has the capability to accommodate multiple molds at once, allowing for the simultaneous testing of three specimens. By fixing two or more molds onto the machine, it becomes possible to conduct multiple tests in a shorter period of time. This not only increases efficiency but also reduces the time required for testing.
The use of multiple molds is particularly useful in cases where time is of the essence or when there is a large quantity of specimens that require testing. By allowing for the simultaneous testing of three specimens, the machine is able to provide quicker results and expedite the testing process.
Furthermore, the ability to test multiple specimens at once can also improve the accuracy and consistency of the results. By testing multiple specimens under the same conditions simultaneously, it becomes easier to identify any variations or inconsistencies in the testing process.
Overall, the provision to fix two or more molds onto the machine for simultaneous testing is a valuable feature that can greatly improve the efficiency and accuracy of testing procedures.
Precautions for the Test
Paragraph 1: The plate assembly on which the mould is positioned must be completely flat and level. This is necessary to ensure that the bottom surface of the mould remains in constant contact with the plate throughout the molding process.
Paragraph 2: It is essential to exercise caution when filling the mould to prevent any deformation of the briquette. Additionally, it is important to ensure that there are no air pockets present within the molded sample. Any such pockets could compromise the structural integrity of the briquette and affect its overall quality. Therefore, it is imperative to carefully inspect the moulded sample to ensure that it is free from any air pockets.
Observations of Ductility Test
The given context mentions four different parameters related to bitumen: Bitumen Grade, Pouring Temperature, Test Temperature, and Period of cooling in minutes.
The first parameter, Bitumen Grade, refers to the quality or type of bitumen being used.
The second parameter, Pouring Temperature, is the temperature at which the bitumen is poured or applied.
The third parameter, Test Temperature, refers to the temperature at which the bitumen sample is tested for its properties.
The fourth parameter, Period of cooling in minutes, is the time taken for the bitumen sample to cool down after being heated. This cooling process can be done in air or in a water bath, and there are two different temperatures associated with the water bath method: one before trimming and one after trimming.
Overall, these parameters are all important factors in determining the properties and quality of bitumen, which is commonly used in road construction and other applications where a durable and waterproof material is needed.
| Observations | 1 | 2 | 3 |
| (a) Initial Reading | |||
| (b) Final Reading |
Result of ductility Test on Bitumen
Ductility value =
Recommended Values of Bitumen Ductility
When assessing the suitability of bitumen for a particular application, it is essential to consider both the type of bitumen and the intended use. Different types of bitumen possess unique properties that make them more or less suitable for specific purposes. One important factor to consider when selecting a bitumen type is its ductility value, which refers to the ability of the material to stretch without breaking. In cold weather, bitumen with low ductility values may become brittle and crack, rendering it unsuitable for certain applications.
To ensure that bitumen meets the required quality standards for a given application, minimum values for ductility have been specified by the Indian Standards Institute (ISI) for various grades of bitumen. These values represent the minimum level of ductility that bitumen must possess to be considered suitable for a specific purpose. By adhering to these minimum values, manufacturers can help ensure that their bitumen products will perform as intended and meet the needs of their customers.
| Source of paving bitumen and penetration grade | Min ductility value (cms) |
| Assam Petroleum A25 | 5 |
| A35 | 10 |
| A45 | 12 |
| A65, A90 and A200 | 15 |
| Bitumen from sources other than Assam Petroleum S35 | 50 |
| S45, S65 and S90 | 75 |