Model 3440 5–9
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 ¢6² at the Setup menu.
The gauge displays:
Nomograph: OFF
1. Enable
2. Disable
3. Chg/View Data
From this menu, the operator may enable, disable, or change the
Nomograph function, as described in the following sections.
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