Air Void Content - problems with BS EN 12697-6 2

[iandig]

I have recently been involved with a project, but just looking at the sub-grade and re-engineering of the materials below a pavement.
Once my involvement with the project finished, the pavement was surfaced in the normal manner, but subsequently the binder course was found to be saturated. After coring through the pavement and extracting a series of cores, the main contractor did a simple test on the binder course by pouring water through the compacted layer, into a bowl below and he asked me “is it normal for a blacktop layer to be permeable”. My answer was no, not unless it was designed to be porous. The material should have been equivalent to a dense(graded) bituminous layer, and I have not seen material that behaves like this in the past. You pore water onto the surface, and within seconds it runs through 120mm and pores out of the base of the core.
I suggested calling in a lab, coring the pavement and testing the material for air void content, then checking the results against the requirements from the SHW. The test results came back with air void contents between 6 and 8%, based on a measured Maximum Density of the mix. From my own inspection of the cores before testing, I was expecting air void contents in excess of 10%, so as you can imagine I was very surprised by the results from the lab, jumped in the car and went to inspect the cores myself. When the lab had determined the density, (volume by water displacement) they had waxed the cores. Due to the surface voids on the top, base and cut sides of the core, wax had penetrated into the core via the voids and pores, and thus the volume determined by water displacement was less than the actual volume.
When I queried why they had not used a medium to block the pores (i.e. filler/plasticene etc…) I was shown the latest version of BS EN 12697 which now only talks about paraffin wax, or other sealing materials such as latex or foil. The standard does state that using wax (and other similar sealing materials) might penetrate internal voids, and thus lead to an overestimation of bulk density and lower air voids. I am sure this is what has happened, but because of the manner in which the standard is written, and a similar disclaimer is levelled against other materials (either under estimation of density when using foil or overestimation of density using sealing materials) how can this standard be used to identify either compliance or failure in the layer. The supplier of the material has done his own tests, come up with identical values, followed the standard and all done by an independent UKAS lab and neither of the labs can prove a failure or a pass.
The real problem in this instance is that the surface of the pavement does not properly dry (this is the UK after all) and the pavement is being used as a testing facility for motorcycle tests. The new EU motorcycle test requires an unqualified (they are doing their test after all) rider to swerve at 30 MPH, and with a wet/damp surface it does not bode well for a novice rider.
My question is, has anyone else experienced this problem, and if so how did you deal with it?

 

[Ron]

iandig...I think you're right about the air voids, but I would bet you have a very low asphalt content for the gradation of the mix.

As for the parafin, they are probably getting it too hot and it is penetrating too deeply into the cores. Have them do the same with Saran wrap just to check.

 

[BigH]

iandig - the point I get from your post is that reliance to the strict lettering of the code and not being able to (or not willing to) use common sense and engineering judgment - will get you in trouble! Codes cannot always be all to all things. This is a point I have pondered on codes - say I follow the code, get some scheisse answer that make no sense but I use the code anyway. I have problems, but, I followed the code because I don't want some "auditor" to ding me for not following the code. I've seen many times where it is reported that an engineer has been reprimanded for "not following the code" although there is absolutely nothing wrong with the behaviour of his design. As for your post - and wax, Ron's comments about using wax "just above" the melting point as a "thick paint" might be tried rather than lowering (?) the viscosity and making it more liquidy.

 

[iandig]

The fundemental problem I am finding is that the Supplier's lab have stated that they followed the standard (which I don't doubt) and they have provided results which show the material passes. A second independant lab have repeated the testing, and returned near identical values. Everyone appreciates that the material probably has too high an air void content, but the 'party line' is that the testing was done in accordance with the standard, and the material passes. Being able to re-test the cores and using a different sealent does show failures, but this 'alternative' but 'standard' method of sealing has a similar caveat, only this time that the method of sealing may under-estimate the bulk density.
It is not an issue of whether or not we can demonstrate the air void content is too high, it is the 'fact' that the new European standard is unable to be relied upon to identify it and as such you can't use a test method 'in accordance with BS EN 12697-6' and therefore not acceptable in cases of dispute.
The question was really put out there to see if anyone else had come across the same problem with black-top testing and the 'new' European stanards. We had a similar problem which we are still suffering from when the grading requirements for sub-base were converted from the old BS to the new Eurocode, which resulted in a grading which was slightly finer. Slightly finer does not seem much, but it had a disproportional effect on the ability of site plant to traffic the unbound stone, as there was insufficent stone in the middle of the grading to lock together.
If there is a problem with the standard(s) then it is approrpiate to report this back through BSi, but it always helps to have supporting evidence and additional cases to back up your arguement. That I guess was the real purpose behind the original post, the bulk of the post was explaining the situation, the question was has anyone esle had a similar experience?

 

[BigH]

No, Ian, I've not have had a need to use the new European standard - I have used wax before on rock cores that would have dissolved in water. Maybe Mccoy can answer? eh?