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2,000 – 3,000 psi:
11,000 fps
3,000 – 4,000 psi:
12,000 fps (default value)
4,000 – 6,000 psi:
13,000 fps
6,000 – 8,000 psi:
14,000 fps
Note that these values are general guidelines which will increase the accuracy of the
measurements to 5% of full scale for cases where a direct calibration cannot be done.
Note that the accuracy of the unit improves to 2% if a direct calibration can be done.
Pan Pour:
When testing a corrugated pan pour slab, test in a straight line that is
transverse to the direction of the corrugations, making note of the “thinner” concrete
zones and the “thicker” concrete zones. Note that the areas between the thin zones and
thick zones may produce data with two peaks or more. Data from these areas will
probably not be useful. After the thick zones have been identified, test parallel to the
corrugations in the thick zone if you want to identify the maximum thickness of the pan
pour. Position the axis of the CTG-2 unit parallel to the direction of the corrugations.
Calibration of the CTG-2 on slab on metal deck (pan deck) concrete
:
The CTG-2
has the greatest accuracy (typically 2%) if a test at a known-thickness location is
conducted and used to calibrate the concrete velocity. However, for the special case of
pan-deck slabs, it is also possible to obtain a reasonable calibration (typically about 4%
or better) by using the known dimensions of the metal deck pan.
To measure the velocity of the concrete in a pan deck slab, take a minimum of two
thickness readings using the default velocity value of 12,000 ft/sec. One should be
centered over a “Thick” part of the slab (D1 below) and the other centered over a “thin”
part of the deck (D2 below). Find these locations by performing a series of close-spaced
(0.5 to 1 inch) tests along a line to find points which are at the centers of typical thick
and thin sections of the slab. Then, using the known deck height variation (H1 as shown
below, from specifications or from direct measurement on the slab bottom), use the
following equation to compute the calibrated velocity (Vc):
Vc = 12,000 * (H1/(D1-D2))
(where 12,000 fps is the default velocity and Vc is the new calibrated velocity)
