4–24
Asphalt Surface Preparation
It is possible, but usually not necessary, to take direct
transmission readings on asphalt. Drilling a hole in asphalt can
be difficult, and may require the use of a proper drill (not the
drill rod) if the asphalt has cooled and hardened.
Under normal conditions, a backscatter reading provides an
accurate measurement of asphalt density. To prepare the site:
Find a smooth location on the asphalt. You may want to fill
the voids on open mixes with sand or cement. Take care to
leave the asphalt exposed. The gauge base must rest on
the asphalt, not the fill material!
Ensure that the gauge does not “rock.” It must remain
steady.
If rocking occurs, find a more suitable test site. If taking a
measurement around a core, the gauge may be moved up to
a few inches to any side of the hole.
NOTE
These directions also apply to taking a backscatter
measurement on soil.
MARK FOR SCRAPER
PLATE CENTER
MARK FOR DRILL
ROD CENTER
Figure 11. Marking the Test Area
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