Float Test Of Bitumen

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A Float test of Bitumen is generally used to determine the consistency of a highly viscous bitumen sample. The consistency of bitumen is an important property of bitumen to find out before using. The float test of bitumen gives us an idea about how the bitumen sample behaves in temperature changes and resistance to flow.

Let us discuss this practical in detail.

Aim:

To determine the consistency of the bitumen by float test.

Significance

The float test of Bitumen measures the consistency of the bitumen when it is not possible to determine the consistency by penetration test or viscosity test. Consistency of Highly viscous bitumen is tested by float test. The distillation residues and residues from emulsion are tested by float test.

Consistency of bitumen is an essential parameter to analyse the quality of bitumen. Consistency measures the susceptibility of the bitumen to temperature change and resistance to flow.

The bituminous binder used in the pavement should be able to resist the deformations applied to it. and consistency affects the ability of bitumen to resist deformations. Hence, it is important to ascertain the consistency of bitumen before its use.

Important Terms related to Test

Consistency of Bitumen: The consistency of bitumen measures the susceptibility of the bitumen to temperature change and its resistance to flow.

Apparatus:

The apparatus used in the float test of bitumen are described below:

Floating apparatus:

1. Float– Float is made up of aluminium alloy. The details and normal measurements of its various parts are as follows:

Weight of Float = 37.9 ± 0.2 gram
Total Height of Float = 35.0 ± 1.0 mm
Height of Rim above the lower side of shoulder = 27 ± 0.5 mm
The thickness of Shoulder = 1.4 ± 0.1 mm
Diameter of Opening = 11.1 ± 0.1 mm

2. Collar: It is made up of brass. The details and normal measurements of its various parts are as follows:

Weight of Collar = 9.8 ± 0.2 gram
Overall Height of Collar = 22.5 ± 0.2 mm
Inside Diameter at Bottom of Collar = 12.82 ± 0.10 mm
Inside Diameter at Top of Collar = 9.70 ± 0.05 mm

3. Thermometer: To measure the temperature of water in the ductility apparatus. Its range should be from -2 to 80 °C.

4. Water Bath: Its dimensions are as follows:

Float Test of Bitumen | Apparatus, Procedure & Result — Water Bath

Minimum Internal Diameter– 185 mm
Minimum Water Depth– 185 mm
Height of Container above Water Level– 100 mm

5. Calibration Assembly: The assembled float and collar in which collar is filled until bottom weighing 53.2 gram in total should float in the water such that its rim remains above the water level by 8.5 ± 1.5 mm.

6. Other accessory apparatus include:

Knife or spatula
Heating oven
Beaker
Stopwatch

Materials for Float Test of Bitumen:

Bituminous material- cutback bitumen or asphalt or tar products
Glycerine
Dextrine

Precaution:

Following precautions should be taken while performing the float test of bitumen to obtain accurate results:

The collar should be tightly fitted to the float to ensure that no seepage of water takes place between them
The melted bitumen should be stirred thoroughly before pouring in the collar to ensure its homogeneity
No air bubbles should be entrapped in the specimen while pouring the melted bitumen in the collar

Procedure for Float Test of Bitumen:

The procedure to carry out the float test of bitumen is described below:

Sample Preparation:

Take the bitumen sample in a beaker and heat it to the lowest possible temperature. Allow the bitumen to melt until it is converted completely into a liquid state sufficient for pouring.
Stir the bitumen sample thoroughly to get a homogenous sample free from any air bubbles.
Prepare a mixture of glycerine and dextrin in equal proportions. Mix it well.
Take the brass plate and coat it with the mixture prepared in the above step. Then place the smaller end of the brass collar on the brass plate.
Pour the air-free homogenous bitumen sample into the collar as per your convenience till it is filled slightly above the top.

Asphalt and Asphalt Products–

Allow the specimen to cool down at room temperature for about 15 minutes.
Then place the specimen in the water bath for 5 minutes and maintain the temperature of 5 °C.
Remove the sample from the water and trim the sample from the top of the collar with the help of a slightly-heated steel knife or a spatula.
Place the collar and base plate with the sample again in the water bath for at least 15 minutes at 5°C. Care should be taken that the duration does not exceed 30 minutes.

Tar Products–

Immerse the tar products in the water of the water bath immediately for 5 minutes and maintain the temperature of 5 °C.
Remove the sample from the water and trim the sample from the top of the collar with the help of a slightly-heated steel knife or a spatula.
Place the collar and base plate with the sample again in the water bath for at least 15 minutes at 5°C. Care should be taken that the duration does not exceed 30 minutes.

Preparation of Warm Bath:

Heat the water bath to the temperature required for testing of the sample- 50 °C.
Maintain this temperature throughout the test without stirring. Variations up to ± 5°C from the specified temperature are allowed.
Ensure the temperature by immersing the thermometer in the water. The bulb of the thermometer should be immersed below the top of the water level to a depth of 40 ± 2 mm.
Heat the water for a minimum of 15 minutes and not more than 30 minutes.

Testing of the Specimen:

Remove the collar along with the sample from the base plate.
Place the sample along with the collar to the aluminium float and fix it with a screw.
Immerse this assembly in water for 1 minute at 5 °C.
Take out the assembly from the water and remove the water from inside of the float, if present inside.
Hover the assembly immediately into warm bath prepared previously of temperature about 50 °C ensuring that the collar is tightly attached to the float. No seepage of water should occur at the time of testing between the collar and float.
Take a stopwatch and start the timer as soon as the assembly is introduced into the warm bath.
Note the time in seconds at which the water breaks through the specimen with the help of a stopwatch. This time gives the float value.

Observation:

As the specimen is kept in warm water, the water slowly breaks through the specimen in some time.

The time at which the thread of the bitumen breaks is to be noted down for both the specimen.

Observation Table for Float Test of Bitumen:

Following observations are to be recorded during the float test of bitumen

(A sample observation table for float test of bitumen is drawn below)

Observations	Specimen – 1	Specimen – 2
Time in Second

Float Value = Average float value of 1 and 2.

Result:

The average of the float values to the nearest whole value obtained from the two samples is the float value of the given bitumen specimen.

Conclusion:

By performing the Float test of Bitumen Practical, we can determine whether the given bitumen sample meets the specification requirements for penetration as given in the standards.

Higher the float value, stiffer is the bitumen specimen.

Consistency in terms of penetration time is one of the measures of the quality of bitumen along with other measures such as ductility value and so on.

Summary:

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Test Procedure
	The bitumen sample is heated in a beaker at the lowest possible temperature till it is completely melted into a fluid. The sample is stirred to obtain a homogenous fluid sample.
	Glycerine and dextrin are mixed together in equal proportions.
	The above mix is applied to the brass plate to prevent the bitumen from sticking to it. Then both the collars are placed on the plate with its smaller end in contact with the plate.
	Melted bitumen is poured into the collar till it is completely filled by ensuring no air is entrapped. Both the collars are allowed to cool at room temperature for 15 minutes for asphalt and asphalt products. While this step is skipped for tar products.
	The whole assembly is placed in the water bath having iced water at 5 °C for 5 minutes. Excess bitumen is cut off by a pointed sharp-edged knife to obtain a leveled surface at the top. The whole assembly is placed in the water bath at 5 °C for at least 15 minutes and not more than 30 minutes. The thermometer is placed inside the water bath with the bulb immersed to a depth of 40 ± 2 mm to ensure a constant temperature.
	The collar along with the sample is separated from the base plate. The collar is then attached to the aluminium float and the screw is tightened.
	The assembly of float and collar is immersed in iced water for 1 minute at 5 °C. Then it is taken out and any water-filled in the float is removed.
	The assembly is put in a warm bath of 50 °C ensuring water does not seep in-between float and collar. The stopwatch is started as soon as the assembly is introduced in the water.
	The time is noted in seconds from the stopwatch at which the water forces out of the bitumen plug.
Result
Float value of the sample	The time when water forces out of the collar.

Float Test of Bitumen | Apparatus, Procedure & Result