Vaisala SHM40 - Manual (Page 25)

Chapter 3 ____________________________________________ Humidity Measurement in Concrete
VAISALA _______________________________________________________________________ 23
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Figure 7 Plugged Tube in Fresh Concrete
4. When the concrete has hardened, remove the plug and the flange
from the tube. Leave the tube in place.
5. Use a flat-head screwdriver or other suitable tool to crack the
concrete at the bottom of the tube. This is necessary because during
the curing of the concrete a solid surface forms in the bottom of the
tube. Cracking this surface helps the air in the tube to reach
equilibrium with the humidity in the concrete. See Figure 8 below.
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Figure 8 Cracking the Concrete at the Bottom of the Tube