The sand cone is a direct volumetric replacement method and if done properly, yields accurate results. The nuclear gauge is often compared or "calibrate" to the sand cone method. Both are sensitive to proper methodology in running the tests.
I would say sand cone method is less affected by environmental factors (hydrocarbon contamination, think organics), but the nuclear method is much faster. Sand cone won't give you moisture content, you have to do a separate test for that, and you need a way to dry the sample.
The key is "proper methodology in running the tests".
I can make a case for & against each method.
For either method -- proper equipment, proper calibrations & proper operator technique will produce good results. An experienced operator will recognize oddball soil & site conditions.
The sand cone method has a lot of steps & computations ... mostly simple but potential sources of error, especially if the operator doesn't run the test often.
The nuclear gauge is comparatively simple and yet many operators I've seen tend to be VERY cavalier and thus, sloppy.
As Panars said, nuke gauge is faster. You will need to perform a speedy moisture test or something equivalent to determine the moisture content when using the sand cone.
Military bases in my area can't seem to get away from the sand cone. Personally I believe the sand cone is more accurate, if performed properly. You can turn the nuke gauge 45 degrees and yield a different density.
No question - the nuclear test is faster. Proponents will say that it is more accurate . . yet years ago, I did comparative moisture content (lab vs nuclear) and on our crushed base course, the actual moisture content was 0.7x the nuclear content. This is why Ron states that on a particular site (assuming a big one) you would do a comparative study of the two - and this doesn't always work especially if your operators of both sand cone and nuclear testing are less than honest . . . .
I prefer the sand cone or the rubber balloon method - but, as pointed out, you will need to do drying in an oven (min 18h or standard 24 h) or a microwave (speedy moisture is also used but it should also be "checked" and isn't wholly reliable on all types of soils). In clays, you might consider using the drive tube sample (min 100 mm diameter).
My single caution - regardless of what test you use: ALWAYS and I mean ALWAYS check to ensure that the test result is on the correct side of the zero air voids line. If the manure hits the fan, you will be glad you did.
Hey guys. One source for getting repeat testing work, sent to you via the contractors is knowing the ins and outs of these methods and the fallacy of the nuc being considered as accurate. Once that contractor comes for help when he is not making compaction being "tested" by a competitor with nuc only, and you come to his aid with proof he meets spec, he is a friend forever.
