Bitumen, a substance commonly used for pavement construction, is derived from crude petroleum through a process of partial distillation. This black or brown mixture of hydrocarbons is insoluble in water and is composed of 87% carbon, 11% hydrogen, and 2% oxygen by weight.
Obtained in either a solid or semi-solid state, bitumen is a versatile material used for a variety of applications such as surface courses for roads and roof coverings. Due to its properties and characteristics, various laboratory tests are conducted to determine its quality and different properties, such as its ability to withstand various conditions and loads.
These tests are essential in ensuring that the bitumen used for pavement construction meets the required standards and specifications. Through these tests, the quality of bitumen can be assessed and the appropriate measures taken to ensure that the pavement construction is of the highest quality possible.
Tests on Bitumen to Check Quality and Properties for Pavement
Bitumen is a material widely used in the construction industry for various purposes, such as road pavement and roofing. To ensure its quality, several tests are performed to evaluate its properties and characteristics.
One of the tests performed is the Ductility test, which measures the ability of the bitumen to stretch before breaking. This is an important test as it determines the ability of the bitumen to withstand the tensile stress it will experience during its application.
Another test performed is the Flash and Fire point test, which determines the temperature at which the bitumen can ignite and sustain a flame. This test is important for safety purposes and to ensure that the bitumen can withstand high temperatures without igniting.
The Float test is also conducted to determine the purity of the bitumen. This test involves placing the bitumen in a solution of water and observing whether it sinks or floats. Impurities in the bitumen cause it to float, indicating a lower quality material.
The Loss on heating test is performed to determine the amount of volatile matter in the bitumen. This test involves heating the bitumen to a specific temperature and measuring the weight loss due to evaporation. The result of this test is used to determine the suitability of the bitumen for specific applications.
The Penetration test is used to measure the hardness of the bitumen. This test involves measuring the distance a standard needle penetrates the bitumen sample under specific conditions of temperature, load, and time. The result of this test is used to classify the bitumen based on its hardness.
The Softening point test is another important test that determines the temperature at which the bitumen softens. This test is important for determining the application temperature range of the bitumen.
The Specific gravity test is performed to determine the density of the bitumen. This test is important for determining the amount of bitumen needed for a specific project.
The Viscosity test measures the resistance of the bitumen to flow. This test is important for determining the ability of the bitumen to be pumped and spread during its application.
Lastly, the Water content test is conducted to determine the amount of water present in the bitumen sample. This test is important as water reduces the quality and performance of the bitumen.
1. Ductility Tests on Bitumen
Ductility is the property of bitumen that allows it to stretch or elongate before breaking. This property is measured by the distance in centimeters to which a standard specimen of bitumen will elongate before breaking, at a specified temperature and speed. To measure the ductility of bitumen, a sample is first heated to 75-100oC and melted completely. The molten bitumen is then poured into an assembled mold that is placed on a brass plate. To prevent sticking, both the mold and plate are coated with glycerin and dextrin.
After filling the mold, it is left at room temperature for 30-40 minutes and then placed in water for 30 minutes. Once removed from the water, any excess bitumen is cut with a hot knife, and the surface is leveled. The entire assembly is then placed in a water bath of a ductility machine for 85 to 95 minutes. The brass plate is detached, and the hooks of the mold are fixed to the machine before operating it.
The machine pulls the two clips of the mold horizontally, which causes the bitumen to elongate. The distance between the starting point and the point of breaking is noted as the ductility value of the bitumen. The minimum required value for ductility is 75cm.
2. Flash and Fire Point Tests on Bitumen
The flash point and fire point of bitumen are important parameters that are used to assess the risk of fire accidents in areas coated with bitumen. The flash point is defined as the lowest temperature at which bitumen will catch vapors of a test flame and ignite in a flash. On the other hand, the fire point is defined as the lowest temperature at which the bitumen will ignite and burn for at least 5 seconds under specific test conditions.
These tests are important for determining the appropriate bitumen grade to be used in areas with high temperatures. By knowing the flash and fire points of the bitumen, it is possible to choose a grade that is suitable for the specific environmental conditions. This can help to reduce the risk of fires caused by the use of bitumen in construction and other applications.
3. Float Tests on Bitumen
The consistency of bitumen is typically determined through the use of penetration test and viscosity test, except for certain ranges of consistencies. However, the float test can also be used to determine consistency. To perform the test, an apparatus is utilized that consists of an aluminum float and brass collars. The collars are filled with melted bitumen sample and cooled to 5°C, after which they are attached to the aluminum floats. The assembly is then placed in a water bath at a temperature of 50°C. The time in seconds from the moment the float is put on the water bath until the water breaks the material and enters the float is recorded.
4. Loss on Heating Tests on Bitumen
To determine the level of loss of bitumen when heated, a test can be performed. Initially, the weight of the bitumen sample should be recorded with an accuracy of 0.01gm at room temperature. The sample is then heated in an oven at a temperature of 163oC for 5 hours. Once the heating process is complete, the sample should be allowed to cool to room temperature before recording its weight again with an accuracy of 0.01gm. By comparing the two recorded weights, the loss of mass can be calculated. If the loss of mass is greater than 5% of the total weight, it is not suitable for construction purposes due to its brittleness and susceptibility to damage.
5. Penetration Test on Bitumen
The penetration value of bitumen is determined by measuring the distance in tenths of a millimeter that a standard needle would penetrate vertically into a bitumen sample under standard testing conditions. This test helps to determine the hardness or softness value of the bitumen.
To conduct the test, the bitumen is heated above its softening point and then poured into a container with a depth of 15mm. The bitumen is stirred to remove any air bubbles and then cooled to room temperature for 90 minutes. After this, it is placed in a water bath for an additional 90 minutes.
Next, the container is placed in a penetration machine, and the needle is adjusted to make contact with the surface of the sample. The dial reading is set to zero, and the needle is released for exactly five seconds. The penetration value of the needle for that five seconds is noted down. This process is repeated three times, and the average value is recorded.
6. Softening Point Test on Bitumen
The softening point of bitumen is the temperature at which the substance becomes soft to a specific degree under particular test conditions. To conduct this test, a small sample of bitumen is taken and heated to a temperature between 75 to 100 degrees Celsius. The test is conducted using a ring and ball apparatus. To prevent the bitumen from sticking to the rings, glycerin is applied to the rings. The rings are then filled with bitumen and any excess material is removed using a hot sharp knife.
The apparatus is assembled, with the balls arranged in a guided position on top of the bitumen sample. A beaker is filled with boiled distilled water and placed below the bitumen sample. The temperature is increased gradually at a rate of 5 degrees Celsius per minute. As the temperature rises, the bitumen softens and the ball slowly moves downwards until it touches the bottom plate. This point is noted as the softening point of the bitumen.
7. Specific Gravity Test on Bitumen
The specific gravity of bitumen is an important indicator of its quality as a binder. It is defined as the ratio of the mass of a given volume of bitumen to the mass of an equal volume of water at a specified temperature. To determine the specific gravity of bitumen, the pycnometer method can be used.
This method involves using a clean and dry specific gravity bottle. Firstly, the weight of the empty bottle is measured (w1). Secondly, the bottle is filled with distilled water and placed in a water bath for 30 minutes. After this, the weight of the bottle with water is noted (w2). Next, the bottle is filled halfway with the bitumen sample and weighed (w3). Finally, the bottle is filled halfway with water and halfway with bitumen and weighed again (w4).
Using the values obtained, the specific gravity of the bitumen can be calculated using a formula. By determining the specific gravity of bitumen through this method, it is possible to gain insight into its quality as a binder.
8. Viscosity Test on Bitumen
Bitumen is a material commonly used in road construction, and its viscosity is a crucial factor in determining its performance. Viscosity refers to the fluid property of bitumen and influences its ability to spread, penetrate into voids, and coat aggregates.
If the viscosity of bitumen is high, it can result in a reduction in the compactive effort of the material, leading to a heterogeneous mixture. Conversely, if the viscosity is low, it can help lubricate the aggregate particles. Therefore, it is essential to measure the viscosity of bitumen accurately.
The tar viscometer is a device commonly used to determine the viscosity of bitumen. The test involves measuring the time taken for a 50 ml sample of bitumen to pass through the orifice of a cup under specific test conditions and at a specified temperature. The viscosity of bitumen is expressed in seconds, with higher values indicating a more viscous material and lower values indicating a less viscous one.
In summary, the viscosity of bitumen is a crucial property that affects its performance in road construction. Accurate measurement of viscosity using a tar viscometer is necessary to ensure optimal material selection and usage.
9. Water Content Test on Bitumen
Foaming of bitumen can occur when it is heated above the boiling point of water. To prevent this, it is important to ensure that the bitumen has minimum water content. The water content in bitumen is determined using the Dean and Stark method. In this method, a bitumen sample is placed in a heat-resistant glass container with a capacity of 500 mL. The container is then heated to just above the boiling point of water. As the water evaporates from the bitumen sample, it condenses and is collected. The collected water is expressed as a mass percentage of the sample. The acceptable limit for water content in bitumen is not more than 0.2% by weight.
