Nuclear Gauge FAQs

Do I have to have a target density (Proctor, Marshall, Voidless) programmed into the gauge in order for it to work?
No. The target value is only used by the gauge to calculate the percent of compaction that has been achieved. The gauge will still give Wet Density, Dry Density, Moisture and Percent Moisture results without the target density entered. The percent compaction can be calculated at a later time if necessary.

Example:
(DD/Proctor) x 100 = %Proctor or (WD/Marshall) x 100 = %Marshall

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How will frost (frozen material) affect the gauge readings?
The percent moisture result will be elevated and the dry density read by the nuclear density gauge will be lower if the material contains frost. Therefore, the tests will fail. When the water freezes it expands and takes up a larger volume in the material beneath the gauge. Because water is less dense than the measured material, the density will be lower and the percent moisture will be higher. It is commonly written in engineering specifications that "no fill may be placed over frozen material". In extreme cases, settling could occur if frozen material is covered and thaws at a later time.

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My gauge readings do not match my sand cone readings.
Usually they will not. There is a lot of room for operator error when performing a sand cone test. There is really no way to prove which test is more "accurate" because there is no absolute test for soil density. The best way to compare the two test methods is to take at least three 4 minute nuclear gauge measurements at different locations (preferably direct transmission @ 6 or 8 inches) and at least 3 sand cone tests (at the same locations as the gauge readings). Find the difference at all locations and average them.

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Should I take a backscatter or direct transmission reading on aggregate base? (usually 4"- 6" in thickness)
Either one would be acceptable. The best thing to do is try one of each. Ideally the direct transmission will give a more representative reading, but it may also disturb the larger aggregate and lower the density. If you try both in the same spot (backscatter test first) and see which gives a better reading you can make the decision for yourself. If the material thickness is over 4", direct transmission is more appropriate in order to get a representative measurement.

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Can the gauge read the moisture of a concrete slab?
It can read the moisture as a relative reading; in other words it will give an indication of a problem area, but will not give a definite moisture content. There are constituents in concrete that can cause the moisture readings to be in error, but as long as the concrete is homogeneous, the error will be constant. Example: If the slab reads approximately 12% moisture in all areas but one area is approx. 20%, it can be assumed that this is a problem area. This will give an indication of where a core sample should be taken for investigative purposes.

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My 3411 gauge is giving the ERROR 30 message.
This message means that the gauge cannot calculate the test results. Usually this is due to the fact that there is no standard count in the memory. Also, this could mean that the depth switch is not correctly set; if the depth switch is set at a value much different that that which is actually being measured, the calculated results will be too large for the gauge to calculate. Try taking a new standard and checking the depth switch before taking a measurement.

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Why is my gauge moisture result higher/lower than the oven dry/speedy moisture results?
The oven dry tells the true moisture content by removing all water from the sample. The gauge measures the hydrogen present in the material; which is usually in the form of water. If the material contains naturally occurring hydrogen or bound hydrogen, the gauge will measure the moisture falsely high in many cases. (Some of these materials are: mica, lime, fly ash, cement, organic materials, gypsum, coal, phosphates, etc.) A false low reading can also occur but is less common (causes include: high salt or iron oxide content or boron, lithium or cadmium present). A moisture offset will adjust for this problem.

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How often do moisture/density gauges need to be calibrated?
We recommend that the gauges be properly evaluated for accuracy or calibrated every 12 months.

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What are the ASTM and AASHTO standards written specifically for moisture and density testing?

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My gauge displays tube error. What's the problem?
Take the gauge to a clean, dry environment and remove the control panel or "scaler". Check for loose hardware inside the gauge that could short the high voltage. Check for moisture inside the gauge and, if moisture is present, remove the scaler and dry overnight with a fan.

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When I try to get my density, I get nothing but +'s. Why?
Obtain the gauge's most recent calibration printout and check that the calibration constants in the memory match those on the printout. Also, verify that the depth strip is functioning correctly. Check for correct standard counts.

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Why are my gauge readings off?
Ensure you have a good standard count. Verify you are at the correct depth. Check to make sure no offsets are enabled. Make sure that the handle is clicked into the notch (depth position) properly. Do not pass notch or push up on the handle after positioning it.

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Why is my gauge hard to index?
Magnalube is the recommended lubricant. Place a small amount on the source rod and exercise the rod up and down. Check the bottom of the gauge to make sure dirt has not accumulated in the sliding block or base plate area.

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My gauge is locked up and there is no keypad response.
Press and hold the OFF button for 15-30 seconds until the gauge turns off. If it does not turn off, remove the scaler and unplug the ribbon cable from the baseboard. Plug the cable back in and turn the gauge on allowing it to go through its 5 minute self-test.

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