Practical Determination of Bitumen content in mix - Bitumen Extraction

Dnyan Deshmukh

Staff member
Determination of Bitumen content in mix by Bitumen Extraction at Project Site
Bitumen extraction test is most important test in Road Construction Project as it mostly gives assurance of bitumen content in mix and the Quality of mix on which you can rely.

The Bitumen extraction test should be done at the time of placing of bitumen mixes on road.
Bitumen paver.jpg
Benefits of doing bitumen extraction test during construction of road;
- Complete Quality Control and Assurance Guaranteed.
- Contractors wont cheat to make extra money.
- Life of the road drastically improved due to use of quality and correct quantity materials in mix.

Bitumen is a costly material and if the client is not smart enough to understand how contractor can make you cry, contractors gonna punish clients and going to loot huge money by spoiling the life of road.
Bitumen content need to be checked in every pour of road, the sampling of bitumen mix can be done from a loaded truck, or from a Paver or from a freshly laid layer of Road.

Bitumen in mix purely depends on the design of pavement, size of aggregates / stones, client should specify the bitumen content to be poured in mix along with other size aggregates and percentage of each ingredient in mix.

test is done mostly as per IRC: SP 11 –1988 (Appendix - 5) and ASTM D 2172.

for doing test you need to have centrifuge extractor along with bowl, filter paper and solvents like Trichloroethylene or benzene which is available commercially.

Trichloroethylene is recommended to use for doing test due its property, Trichloroethylene is non-flammable liquid and have clear transparent color.

While doing testing at site you need to ensure, all equipment required for testing are available and are in working condition.
Take a sample of bitumen mix from either laid layer of road, from paver hopper or directly from a loaded truck. Mix the collected sample thoroughly.

bitumen sample.jpg

You need to take the weight of empty bowl before pouring sample in it. (this may not be required in most of the cases)
empty weight of cone.jpg

Record the weight of empty bowl and pour the sample of bitumen mix into bowl in quantity either 500 grams or 1000 grams or base on you centrifuge extractor capacity.
Do ensure you weight exactly the correct quantity with accuracy to a gram or lessor is better.
there is nothing hard and fast rule to take sample exactly weighing 500 or 100 gram you can take nearby it to keep the authenticity of sample correct, mainly when we say we need exactly 500 grams, people tries to remove excess quantity by disturbing the sample which may give false results.
So try to get 500 or 1000 gram and take nearest sample size without disturbing it.
bitumen weight.jpg
After Taking the required sample size in bowl, put bowl in centrifuge extractor, it have a small hole on its bottom plate which allows the draining of mixture of solvent and extracted bitumen from it, you need to ensure equipment have mild slope towards hole to ensure drainage.
extractor drain.jpg

Put bawl in the equipment and add benzene or Trichloroethylene at 200ml per 500 gram sample. benzene starts its works as soon as it comes in contact with bitumen (testing with benzene will be much faster). Trichloroethylene might required more time to get start reacting, might be an hour and may cycles of it.
softening of bitumen.jpg

After addition of solvent, put filter paper on top of bawl to ensure no escaping of finer material from mix due to gap between cap and bowl. You can also record the weight of filter paper before fixing it on top of bowl.
filter paper.jpg

after putting filter paper, put a cap on bowl and do tight the nuts correctly.
cone top lid tighening.jpg

after that put a centrifuge extractor top lid and tighten it, this ensure if you are new and did not tighten bowl cap correctly during revolving process, it protects your cloth and skin from getting a spray of bitumenous solvent and also protects you from safety point of view.
top lid tightening bitumen extraction.jpg

There is a possibility that the fine materials might go out during process, so better put beaker below the drain of centrifuge extractor, after completion of test, you can check if any material is collected here and add that in remained mix.
Once the top lid is fixed, you can start revolving the bowl by spinning handle. speed should be increased gradually by starting slowly and reaching to maximum of 3600 rpm.
It should be continued until you do not see any solvent coming out from the drain.
bitumen extraction going on.jpg

Remove the lids and do check for bitumen removal from the mix, if bitumen had got removed from mix, you can able to see a clear color aggregates in it. in case of Trichloroethylene aggregates in mix may not be seen clearer.

road sample after bitumen extraction.jpg

at this stage the bitumen had extracted from mix completely, the aggregates now do have absorb the solvent so we need to dry it before taking its weight, we can do that by heating it in oven at 100 to 110 degree centigrade for an hour. in case of benzene you can fire it directly which will remove all benzene remain from it (do this with precaution and at your own risk, it might cause an accident).
sample fired to make it dry.jpg

Once the sample is dried in oven or fired you will record following
- weight of dried sample remain.
- weight of dried filter paper along with stuck fine material to it.
- weight of dried fines collected in beaker through the drain.

Finally you need to arrive at following

- weight of sample bitumen mix taken for test - 500 or 1000 or recorded value during testing -> A.
- Total weight of dried sample remains after extraction test -> B.

So the Bitumen content in mix can be calculated as below

[(A-B) / A] x 100

Bitumen content is stated as % in total mix quantity purely on weight basis.

Important points to be consider during test.
Each gram have a very high value in this taste so accuracy in recording of weights is highly important.

a gram error in 1000 gram sample can lead to variation of 0.1% quantity of bitumen.
a gram error in 500 gram sample can lead to variation of 0.2% quantity of bitumen.

Bitumen in mix is varies from 2.5 to 5.5 or may be some higher quantity.

so 0.1 or 0.2 in values of Bitumen makes a lot of difference.

Before taking bitumen mix for construction of road do make terms of acceptance for mixes with acceptable limits for variation.
Do ensure the vehicle which does not meat the criteria which is mutually agreed by purchaser and supplier should be rejected straight a way.

You might not be aware of, contractor purposefully did a mix with low content and sent vehicles just to check, is low content is accepted or not after testing.
If such things got accepted, you will get more mixes with leaner combination which spoils the whole life of road, just due to you haven't taken any action after observing it.

So be very sensible in case of bitumen mixes and take actions on time to time for ensuring healthier roads are built by you.

Hope you would like this article.