Generally, in asphalt pavement, bitumen is used as a binder for the filler aggregates.
The mix design of asphalt must be done as per the standard for determining the actual binder content.
Hence, at the site, it is necessary to check whether the bitumen content is as per the mix design or not.
Centrifuge Extractor is used for determining bitumen perctegae of bituminious mixtures.
Methods of Bitumen Extraction Test
i. Centrifuge Method
ii. Extraction Bottle Method
The most commonly used method among these two methods is the centrifuge method.
It is also commonly referred to as the cold solvent extraction method.
Centrifuge Method
The apparatus required for conducting the bitumen extraction test are as follows:
1. Centrifuge extractor.
2. Thermostatically controlled oven with a capacity of 2500C.
3. Balance with a capacity of 500 grams and sensitivity of 0.01 grams.
4. Beaker or bowel extraction sample for the collection of the extracted sample.
5. Bitumen Sample
The procedure of bitumen extraction test by Centrifuge Method
The procedure for determining the bitumen content by using centrifuge method involves two primary steps i.e. preparation of the sample and centrifuging the sample. These steps are further explained in brief as follows:
A. Preparation of the sample
The test sample can be collected either from the dump truck or the asphalt plant present at site depending upon the site condition.
Since the age of the sample can affect the test result, the best result is obtained when the sample is obtained directly from the mixtures of pavement immediately after their preparation.
In such a case, the sample may be scraped off using a spatula.
The sample must be soft enough so that it can easily be scraped off else it must be placed on a flat pan and heated in the oven at a temperature of about 1100C till it can be separated easily.
Then, the representative sample is collected from the heated sample as per the size of the aggregate mix, and the following steps are carried out:
1. The sample is taken and weighed to the nearest of 0.05% of its mass and is recorded as W1. It is then placed in the bowl.
2. The sample is then immersed in a solvent for about an hour. The solvent used may be petrol, trichloroethylene, or benzene.
3. A filter ring that has been oven-dried is taken and is weighed. It must be noted that the filter ring has been oven-dried at a temperature of about 1100C.
4. The bowl is taken and its edge is covered by this filter ring.
5. Then, the bowl is covered with a steel cover and is clamped tightly. It is then placed in the apparatus.
6. A beaker or a well cleaned and dried container is placed below the drain outlet of the centrifuge test apparatus to collect the extracted mixture of the bitumen sample and the solvent.
B. Centrifuging the sample
After the completion of the above-mentioned steps, the next step is to centrifuge the apparatus.
The sample is then centrifuged which involves the following series of steps:
1. The bowl is placed in the apparatus and the machine is started to revolve. The speed of the revolution is gradually increased until it attains a maximum speed of 3600 rev/min.
2. The machine is continuously revolved until the flow of mixture ceases from the drain outlet of the centrifuge apparatus.
3. The machine is then stopped and more solvent is added depending upon the quantity of sample previously taken.
4. The process is continued and the solvent is added for about three cycles until the colour of the obtained extract is not clear and darker than light straw colour.
5. The filter paper is then gently removed from the bowl or container that is previously placed below the centrifuge apparatus along with the obtained residue.
6. The residual aggregate collected is then oven-dried at a constant temperature of 1050C to 1100C and cooled down.
7. The aggregate fragments are carefully scrapped and weighed as well as the weight of filter paper is recorded with an accuracy of 0.01 gm.
Standards: EN 12697-1, ASTM D2172, AASHTO T164A, EN 12697-1 clause B.1.2, EN 13108
Used for the determination of bitumen percentage in bituminous mixtures.
It consists of a removable, precision machined aluminium rotor bowl, placed into a cylindrical aluminium box.
The separate control panel incorporates an electronic card fitted with AC drive which automatically drives the bowl speed rotation ramp from 0 to 3600 rpm as requested by Standards, with fast stop bowl rotation at the end of the test.
Supplied complete with speed regulator and digital display monitoring the frequency.
The centrifuge is supplied complete with aluminium bowl+cover and filter discs.
Power supply: 230V 1ph 50-60Hz 600W
Dimensions: 480x330x530 mm
Weight: 50 kg approx.