The ring and ball test is a widely used method to determine the softening point of bitumen, asphalt, and coal tar. This test involves the use of two brass rings and two steel balls to measure the softening point of various bituminous materials.
The test is conducted by placing a sample of the bituminous material in a ring and applying a specified load to the sample. The ring containing the sample is then immersed in a bath of water or glycerin, and the temperature of the bath is gradually increased at a specified rate. As the temperature rises, the sample softens and eventually flows, causing the two steel balls placed on top of the sample to touch each other.
The temperature at which the two steel balls touch each other is recorded as the softening point of the material being tested. The test is repeated with a second ring and sample to ensure accuracy and consistency of results.
The softening point of bituminous materials is an important property that affects their performance in various applications. For example, the softening point of asphalt is an important factor in determining its suitability for use in road construction. The ring and ball test provides a reliable and standardized method for measuring the softening point of bituminous materials, enabling manufacturers to ensure that their products meet the required specifications.
Softening Point of Bitumen, Asphalt and Coal Tar
The softening point of bitumen or tar is an important characteristic that determines its suitability for use in road construction. This property refers to the temperature at which the material softens to a particular degree. To determine the softening point of bitumen, various standardized tests such as IS: 334-1982, ASTM E28-67, ASTM D36, or ASTM D6493-11 are used.
During the test, a sample of bitumen is placed in a mold, and a standard ball is allowed to pass through it. The temperature at which the ball falls through a height of 2.5 cm is recorded. This is the softening point of the bitumen, and it is expressed in degrees Celsius.
It is crucial for bitumen to have sufficient fluidity before its application in road construction. The softening point of bitumen helps to ensure that it can withstand the high temperatures it will be subjected to during the laying process. If the softening point is too low, the bitumen may become too fluid and not bond properly with the road surface, leading to premature failure. On the other hand, if the softening point is too high, the bitumen may not be workable, making it difficult to apply to the road surface. Therefore, the softening point is a critical parameter that must be carefully evaluated before selecting bitumen for road construction.
Uses of Softening Point
The determination of the softening point of a bituminous binder is essential to ascertain the appropriate temperature to which it should be heated for various road use applications. The softening point is typically determined using a ring and ball apparatus. This equipment measures the temperature at which a bituminous binder placed in a ring-shaped mold softens and allows a steel ball to fall a specific distance under standard test conditions.
The softening point is a crucial property to consider when selecting and designing bituminous binders for road construction. Different types of bituminous binders have varying softening points, and these values dictate their suitability for particular applications. For instance, binders used for high-traffic roads should have a higher softening point than those used in low-traffic areas.
The ring and ball apparatus is a widely used method for determining the softening point of bituminous binders due to its accuracy and reproducibility. By heating the bituminous binder at a controlled rate, the equipment can determine the exact temperature at which it begins to soften, which is a crucial parameter for designing and selecting binders.
In summary, the determination of the softening point of bituminous binders using the ring and ball apparatus is essential for selecting and designing binders for road construction. The softening point provides critical information about the temperature range in which a bituminous binder can be heated for various road use applications.
Apparatus for Softening Point Test
The apparatus used for this experiment is called the ring and ball apparatus. It consists of two steel balls, each with a diameter of 9.5 mm and a weight of 3.5 ± 0.05 g. There are also two brass rings, each with a depth of 6.4 mm. The inside diameter at the bottom of the rings is 15.9 mm, while at the top, it is 17.5 mm. Ball guides are present to guide the movement of steel balls centrally.
There is a support that holds the rings in position and also allows for the suspension of a thermometer. The distance between the bottom of the rings and the top surface of the support is 25 mm.
To measure the temperature, a thermometer is required that can read up to 100° C with an accuracy of 0.2° C. The experiment is carried out in a bath, which is a heat-resistant glass beaker not less than 85 mm in diameter and 1220 mm deep. Lastly, a stirrer is needed to maintain uniformity in the temperature of the bath.
Procedure for Softening Point Test on Bitumen
To prepare a test sample, it is necessary to heat the material to a temperature that is 75-100° C above its softening point. It should then be stirred until it becomes completely fluid and free from air bubbles and water. In case there are any impurities, the material must be filtered through IS sieve 30. The next step is to place the rings, which have also been heated to a temperature similar to that of the molten material, onto a metal plate coated with a mixture of equal parts of glycerine and dextrin. After cooling for 30 minutes in the air, any excess material must be removed with a sharp, warmed knife to level the material in the ring.
Once the sample preparation is complete, the apparatus can be assembled with the rings, thermometer, and ball guides in position. The bath should then be filled with distilled water to a height of 50mm above the upper surface of the rings. The starting temperature of the bath should be 5° C.
Note:
To determine the softening point of a bituminous material, a method is employed which involves the use of a bath filled with liquid. The liquid can either be water or glycerin, depending on the expected softening point of the material. If the softening point is anticipated to be above 80°C, glycerin is preferred over water. The starting temperature of the bath should be kept at 35°C.
Once the bath is prepared, heat is applied to it while stirring the liquid. The temperature of the bath should increase at a steady rate of 5 ± 0.5 °C per minute. As the temperature rises, the bituminous material begins to soften, causing the balls to sink through the rings and carrying a portion of the material with them.
The softening point is determined by noting the temperature at which any of the steel balls with bituminous coating touches the bottom plate. The temperature is recorded for the first and second balls, and the average of the two readings to the nearest 0.5°C is reported as the softening point.
Precautions During Softening Point Test
To ensure accurate results, it is recommended that distilled water is used as the heating medium. The use of impure water can introduce variables that may affect the outcome of the test. Therefore, it is essential to use distilled water, which is free from any impurities.
In addition, it is crucial to avoid subjecting the apparatus to vibrations during the test. Vibrations can cause the equipment to move, leading to inaccurate results. Therefore, it is important to take precautions to minimize any sources of vibration and ensure that the apparatus remains stable throughout the experiment.
Another key consideration is the placement of the thermometer bulb. To obtain precise temperature measurements, the thermometer bulb should be positioned at approximately the same level as the rings. This ensures that the thermometer accurately reflects the temperature of the heating medium and produces reliable data. Taking care to position the thermometer correctly is a simple but important step in ensuring the accuracy and validity of the experimental results.
Observations and Calculations
| Temperature when the ball touches bottom, °C | 1 | 2 |
Results
Softening point of bitumen / tar = °C
Recommended Values of Bitumen Softening Point
Bituminous materials do not have a distinct melting point. Instead, their transition from a solid state to a liquid state occurs gradually over a wide temperature range. The softening point is a crucial characteristic for binders that determines the temperature at which they exhibit the same level of viscosity. This is particularly important for materials that will be used as joint and crack fillers. By having a higher softening point, these materials can maintain their shape and consistency during use, ensuring that they do not flow out of the desired area.
In addition, the softening point has a significant impact on the temperature susceptibility of bituminous materials. The higher the softening point, the less susceptible the material is to changes in temperature. Consequently, bitumen with a higher softening point is more desirable in areas with warmer climates, as it will not become too soft and lose its structural integrity. Therefore, understanding the softening point of bituminous materials is essential for selecting the appropriate binder for a given application, ensuring optimal performance and durability.