Aspahlt mix design with natural bitumen 1

[gegk]

In our project, is used to asphalt wearing course bitumen 50/70 percantage 5.6% in agr. and as additive natural bitumenin percentage 8% in bitumen.This natural bitumen has melt point >180 celcious, asphaltene content more than 50% (rest sand) and is added in the mixer. my question, whta percentage of bitumen to wait in extraction tests. 5.4 in mix or 5.7 in mix. Name of this bitumen is Selenizza from Albania. Thank you

eg attach Selenizza characteristics

 

[deehsmar]

Here you mentioned 5.6% is your optimum bitumen content. By doing the extraction test you have to get back the bitumen percent you added in the plant. ie, 5.6 +- 0.2

Forget about the additives added in the bitumen.

 

[gegk]

thank you deehsmar for your answer
yes, the optimu bitumen is 5.6%. My problem is that the supervisor thinks that additive has inside bitumen (>50%), after the extraction test, we must have bigger value than 5.6 %.
if anybody has experience in the use of this king of additive, i would appreciate his help.
thank you

 

[Hoaokapohaku]

I think we have somewhat of a language barrier, so I'm not totally sure of the situation. To be sure I understand, is the following correct if you are producing 1000 kg of mix?

Where:
T = Total Mix weight in kilograms
Pb = Bitumen Percent of Total Mix
Ps = Percent of Total Bitumen from Selenizza
Psb = Percent Bitumen in Selenizza (remainder sand)

And:
T= 1000
Pb= 5.60%
Ps= 8%
Psb= 50%

Then:
Bitumen from pure source = (T*Pb) - (T*Pb*Ps) = 51.52 kg
Bitumen derived from Selenizza = T*Pb*Ps = 4.48 kg
Total Bitumen = T*Pb = 56.0 kg
Aggregate from Selenizza = Bit. from Selenizza/Psb-Bit from Selenizza = 4.48 kg
Clean Aggregate = T-(T*Pb)-(Pb*Ps) = 939.52 kg
Total Aggregate = T-(T*Pb) = 944.0 kg

If this is the case, your total bitumen content is a blend of two asphalt sources, but the total is still 5.6% of the total mix and that is what should be indicated in the extraction test. However, if the bitumen content is required to be reported as a percentage of the weight of the dry aggregate rather than as a percentage of the total weight of the mix, then the same bitumen content would be expressed as 5.9% (56 kg bitumen/944 kg aggregate) for the same design. Often the two different ways of expressing bitumen content causes confusion, even among some engineers.

In case I misunderstood the situation, I also attached a spreadsheet with the same data as above so you change the variables to correctly reflect the situation. If you do, it would be nice to see the changes in a post.

I tend to disagree with deehsmar about forgetting about the sand fraction of the natural asphalt. Even though the total amount of sand from the Selenizza is only about a half percent of the total aggregate, if that half percent tends to a single size, it can make a significant difference in the mix. Some mixes can be very sensitive to even very small changes in certain particle sizes - which particle size(s) are critical are unique to the void structure of the overall mix. I would treat the sand from the Selenizza as an additional fine aggregate and include it's gradation in the aggregate blend.

Is this mix already being produced and you're trying to explain unexpected extraction results?

 

[gegk]

Thank you Hoaokapohaku for your answer.Yes , the mix is produced and we have discussion about the percentage of bitumen that we must have after extrcaction test. The bitumen content is reported as a percentage of the total weight of the mix . We put 56 kg bitumen plus 8% Selenizza. What result must we have after extraction. Our opinion is 56 kg bitumen, because selenizza is additive.

 

[Hoaokapohaku]

gegk - Ok, your response tells me that I did misunderstand your original post. Given that you consider the Selenizza an additive in addition to the 5.6% neat asphalt, the asphalt content from the extraction test should be 5.8%. I modified my original spreadsheet to show how I arrived at that value and attached it to this post.

I'm not familiar with European mix design methods, so I can't say that the way you are treating the Selenizza as an additive is incorrect. I do know that it would be incorrect using any of the methods in practice in the USA. If it were done that way, it would create many potential problems in the design itself, in the lab, and in the field. If you are getting a value like 5.6 on your extractions, and you are also getting higher than expected values for air voids and VMA on your production testing, I would strongly suspect you may be experiencing some of those problems. I would redo the job mix formula (JMF) so that it reflects the Selenizza as a component in the mix rather than an additive, then verify that the values entered in the plant control are correct per the revised JMF. Then I would check all my lab procedures and analysis and verify they are correct per the revised design.

I would also lab mix the revised JMF using precise proportioning, then perform an extraction on the lab mixed sample and compare the test results vs. known actual. I would probably do this three times and observe if the results are correct on average and the degree of variability between tests. I would also check the gradation of the recovered aggregate against the known gradation of the lab mixed sample.

Do you have the job mix formula in spreadsheet form that you can attach?