new asphalt density-cores vs nuclear guage

[clemusc1]

We did Marshall laboratory testing to determine the theoretical unit weight of new asphalt, took 6 inch diameter cores of the road, and determined the density to fail (less than 95-100 percent); the contractor came back and used a nuclear guage to say the density passed. I need backup as to why the nuke is reading too high.

 

[TDAA]

Nuclear gauges need to be correlated to cores.

That core is a physical measurement of the compacted asphalt, the nuclear gauge is not.

FWIW, the density in FAA specs is cores only. The gauge is just used be the contractor to give them a quick idea of if they got it right.

 

[clemusc1]

Thanks-makes sense. The regular protocol for using a nuclear gauge on asphalt is to establish the calibration through a series of roller patterns. Just plopping a gauge on the road after the fact and expecting that number to represent density is no good. Any info on what exactly that gauge reading is telling us and how the machine arrives at it?

 

[Ron]

clemusc1...the process you describe, properly done, is a little more involved. It is called establishing a control strip.

To do that, the contractor uses his process of initial compaction of the asphalt, then the density is checked by nuclear gage and cores. If deficient, another control strip is done with additional compactive effort and the density testing process is repeated. Once it is established that a certain rolling procedure achieves the desired compaction and the density correlation is done, then the nuclear gage is used to check production against the control strip, usually with some specified compaction percentage of the control strip density. Then cores are done less frequently to validate the density correlation with the nuclear gage.