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?
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?
