Test for Bitumen Specific Gravity: Definition and Method
A specific gravity test determines how much bitumen weighs in relation to the same amount of water. The Pycnometer method and the Balance method can both be used to determine the specific gravity of bitumen.
Pure bitumen has a specific gravity in the range of 0.97 to 1.02. Tar has a specific gravity of about 1.20.
It is clear that bitumen is lighter than water when the specific gravity number is less than 1, and bitumen is heavier than water when the value is greater than 1.
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Specific Gravity Value < 1 => Bitumen is lighter than Water
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Specific Gravity Value > 1 => Bitumen is heavier than Water
When the value is less than 1, bitumen has a tendency to float on the water's surface more. Additionally, when the value is greater than 1, it usually settles down.
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Here is an illustration of a bitumen grade's softening point using the Indian Bureau's standard procedure (IS 1205):
Why Is the Bitumen Specific Gravity Test Important?
It is possible to categorize bitumen using a specific gravity test. It is beneficial to know the type of bitumen. Bitumen 80/100, for instance, has a different specific gravity than bitumen 30/40.
We use the specific gravity of bitumen to regulate its quality as well. By doing that, the bitumen impurity can be seen. due to the increased specific gravity of impure bitumen.
Bitumen combined with aggregates is used in road construction. The right amount of bitumen must be utilized in order to produce an appropriate and stable Bitumen. Bitumen becomes sticky when bitumen levels are too high. Additionally, the aggregates do not adhere to one another when there is insufficient bitumen.
The area between the aggregates should be thoroughly coated with bituminous binder. We must therefore determine the density of vacancies.
The density of the bitumen and the density of the aggregates influence the volume of the voids.
The Marshal Mix Design is used to perform these computations.
Marshal Mix Design needs the amount of bitumen. When we combine bitumen and aggregates, the volume is changed to mass. because it is simpler to measure weight than volume.
Weight = Specific Gravity * Volume
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International Standard Procedures for Bitumen Specific Gravity Testing
The following conventional techniques are offered to calculate the specific gravity of bitumen:ASTM D 70
IS 1202 | EN 15326 | AASHTO T 228 | IP 549
The Specific Gravity Apparatus Components and Test Procedures
We outline two approaches for estimating specific gravity in the sections that follow:
Pycnometer method ( ASTM D70 ) 2. Balance method ( IS 1202 )
I. Pycnometer Method
Apparatus
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Specific Gravity Bottle (Pycnometer): The ordinary specific gravity bottle shall be used for materials that remain fluid at 25 °C. On the other hand, the wide mouth capillary type shall be used for materials that remain semi-solid or high viscous at 25 °C.
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Oven | Heater | Water bath | Thermometer | Electronic balance
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Wide-mouth capillary bottle with specific gravity.
Common bottle for specific gravity.
Procedure
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The Pycnometer's specific gravity container should be washed and dried in the oven. With its stopper, weigh it. Assume that the value is A.
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Insert the stopper after adding distilled water to the pycnometer. Wait for it to warm up by placing it in a water bath set to 25 °C. After that, remove the pycnometer from the bath of water and pat it dry with a towel. Assign the weight B after recording it on the balance.
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To make bitumen entirely liquid, heat it between 75 and 100 °C. Bitumen should be placed in one-half of a clean, dry pycnometer. Make sure that no air gets into the sample.
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At room temperature, let it cool. After that, put it in a water bath that has been heated to 25 °C to reach bath temperature. Dry it fully before weighing it and assigning a C value.
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Next, add distilled water to the remaining half of the bottle. To get it to the same temperature as the water bath, put it in a water bath set at 25 °C. Weigh it after drying. Take the value to be D.
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Finally, it is determined how much bitumen-filled pycnometer weighs. Think of that number as E.
The specific gravity can be calculated using the formula below:
For Solid And Semi-Solid Bitumen: Specific gravity = (C-A)/[(B-A)-(D-C)] | For liquid bitumen: Specific gravity = (E-A)/(B-A)
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A = Pycnometer mass
B = It is the mass of the pycnometer when it is filled with water
C = It is the mass when it is about halfway filled with bitumen.
D = Mass of the pycnometer with the material filled approximately halfway and distilled water in the remaining space.
E = It is the bitumen-filled pycnometer's mass.
II. Balance method
Apparatus
1. It has a Balance Straddle that is large enough to accommodate a beaker. The specimen's weight in water ought to be accurate to measure.
2. Thermometer. 3. Analytical balance scale. 4. Cubic brass mould. 5. Waxed silk thread.
Procedure
1. Bitumen Sample Preparation:
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Warm it up gradually. Apply a dextrin and glycerin mixture to the brass cubic mold.
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Fill the mold with the specimen after pouring it in. Filling it out a little bit more than necessary is preferable. Then use a hot knife to trim the extra.
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Place the specimen in a cool, dark place to cool. Then, take it out of the brass mold.
2. Test:
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Conduct a test by tying a piece of wax silk thread to the balance. The thread's length should be sufficient to reach the pan.
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Weigh the sample after attaching it to the thread.
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Place the sample in a water bath set to 25 °C while it is suspended from the thread, then weigh it.
Determine the material's specific gravity using the formula below:
Specific Gravity = A/(A-B) | A = Mass of the dry specimen | B = Mass of the specimen when immersed in distilled water.
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