Water Content Test of Bitumen is one of the important tests of bitumen. In case when bitumen heated above boiling point there are chances of foaming of bitumen and to prevent that sufficient water content in bitumen is essential.
So, before using bitumen for any purpose determination of water content of bitumen is required.
To determine the water content of tar and bituminous products.
Bitumen types include asphalt bitumen, fluxed native asphalt, crude coal tar, road tar, cutback bitumen and others.
Significance of Water Content Test of Bitumen:
When bitumen is heated to a temperature above its boiling point, foaming of bitumen may take place.
To prevent this foaming, minimum water content is desirable in bitumen.
Hence, the water content test of bitumen is performed to know this amount of water.
Important Terms related to Water Content of Bitumen:
Water Content: The amount of water present in a material in terms of percentage by weight of the material is termed as water content.
The Water content test of bitumen works on the principles described below:
Distillation: It is the process of separation of constituents that has different boiling points from a mixture.
Condensation: As the liquid evaporates on reaching boiling point, it is condensed on the surface of the condenser tube. These droplets are then collected to isolate them from the mixture.
In this practical, water is isolated from the bituminous mixture to determine the amount of water present in the sample.
Following apparatus required in water content test of bitumen-
1. Dean and Stark apparatus:
- It is made up of heat resistant glass and its capacity is 500 ml.
- A metal flask may also be used alternatively. Then, the receiver without a ground joint is used.
- The top of the neck is ground forming socket of a ground glass joint.
- It is made up of heat resistant glass.
- ts shape and dimension details along with tolerance are shown below:
- It is made up of heat resistant glass.
- It consists of upper chamber, side tube whose ground glass joint leads to the flask and graduated tube.
- Its dimension details along with tolerance are tabulated below:
|Capacity in ml At 20 °C||Graduation interval in ml||Numbering at every graduation||Maximum error in ml|
|2||0.1-2 in 0.05||0.5 ml||± 0.2|
|10||1-10 in 0.1||1 ml||± 0.6|
5. Heater: Gas burner or electric burner may be used.
6. Graduated Cylinder of 100 ml capacity
Materials for Water Content Test of Bitumen:
- Tar or bituminous products like asphalt bitumen, fluxed native asphalt, crude coal tar, road tar, cutback bitumen or others
- Solvent: Take any one of the following as a solvent or carrier liquid.
- Petroleum or coal tar naphtha which is free from water- Its yield should not be more than 5 % distillate at 125 °C and should not be less than 20 % at 160 °C.
- Petroleum spirit- Its boiling range = 100-120 °C
- 20 % of toluene by volume of industrial grade and 80 % of xylene by volume of industrial grade blended together
Following precautions should be taken while performing the water content test of bitumen to obtain accurate results:
- A loose plug should be fitted at top of condenser tube after heating else atmospheric moisture will start condensing and the accuracy of the result will be affected.
- While using metal flask, care should be taken that an airtight connection is formed between flask and receiver.
Following steps are involved in water content test of bitumen-
- Accurately weigh 100 gram of the sample and take it in a flask.
- Add 100 ml of the solvent to the flask.
- Attach this flask to the dean and stark condensing and collecting system.
- Heat the flask at such a rate that the condensate falls from the end of the condenser at 2-5 drops/sec. continue heating the flask till no condensed water is visible in the flask except at the bottom of the graduated tube. Before stopping the heating, also check that the volume of water remains constant for at least 5 minutes.
- Remove the ring of condensed water inside the condenser tube if it is present. This can be achieved by increasing the rate of distillation by a few drops/sec.
- Wash the water droplets adhering at the lower end of the condenser tube with the help of a spray tube filled with solvent or carrier liquid.
- Insert a loose cotton plug at the mouth of the condenser tube to prevent the water condensation because of moisture present in the atmosphere.
- Determine the amount of water collected in ml.
For 100 gram of sample, water content collected in the receiver is calculated. Its accuracy for measurement is mentioned below:
- For a 2 ml receiver, the water content is reported to the nearest 0.05 %.
- For a 10 ml receiver, the water content is reported to the nearest 0.1 %.
The water content of the specimen calculated should not be more than 0.2 % by weight.
By performing the water content test of bitumen, we can determine whether the given bitumen sample meets the water content requirements as given in the standards.
The water content should not exceed 0.2 % by its weight.
Water content present in the bitumen holds importance as excess water may result in foaming.
|1. 100 gram bituminous sample is taken in a flask and 100 ml of solvent is added to it|
|2. The flask is attached to the condenser and collector of Dean and Stark apparatus|
|3. The flask is so heated that the rate of fall of condensate is 2-5 drops/sec Heating is continued until water droplets are left only at the bottom of the graduated cylinder|
|4. Using a spray tube filled with solvent, the droplets adhering to the lower end of the condenser tube are washed|
|5. A loose plug is inserted at the top of the condenser tube|
|Water Content of the sample ≯ 0.2 % by weight of the sample|