NOMOGRAPH
In some cases, the gauge may be used to determine the density of
thin asphalt overlays. This measurement may be performed with the
gauge in backscatter mode and using the Nomograph method of
density measurement. It should be noted that this method is not as
accurate as a true thin-layer gauge. However, this method may
produce satisfactory results under many conditions.
When a nuclear gauge is used in backscatter mode on overlays
under 3 in. (7.5 cm), several effects must be overcome to produce an
accurate reading. With most gauges, the primary problem is the
result of photons from the source penetrating deeper than 3 in. (7.5
cm) and scattering back to the gauge. These backscattered photons
from the underlying material will adversely influence the reading.
Obtaining an accurate overlay density with the Nomograph method
requires that the density of the bottom layer and the thickness of the
top layer be determined. The simplest method of determining the
density of the bottom layer is to take a nuclear gauge measurement
prior to applying the top layer or overlay. With the overlay applied
and compacted, the depth of the layer should be determined. At this
time, the gauge may be used to calculate the overlay layer density.
To access the Nomograph function, press 〈6〉 at the Setup menu
shown on page
5–3. The gauge displays:
From this menu, the operator may enable, disable, or change the
Nomograph function, as described in the following sections.
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