Vaisala SHM40 - Manual (Page 17)

Chapter 3 ____________________________________________ Humidity Measurement in Concrete
VAISALA _______________________________________________________________________ 15
CHAPTER 3
HUMIDITY MEASUREMENT IN
CONCRETE
This chapter describes the borehole method of concrete humidity
measurement.
Humidity Measurements in a Borehole
SHM40 kit is designed for measuring humidity in concrete using the
borehole method. In the borehole method, a hole is drilled to a suitable
depth in the concrete structure to be measured. After the drilling, the hole
is cleaned and covered, and air humidity in the hole is allowed to
equalize with the humidity in the concrete. The airspace humidity will
reach humidity equilibrium with the concrete in about three days. After
this, the humidity measurement is made.
For successful humidity measurement using the borehole method and the
SHM40 kit, the following points are vital when preparing the hole:
- The hole must be  16 mm and reach to proper depth. See section
Measurement Depth on page 16.
- After drilling, the hole must be cleaned from the drilling debris.
- The hole must be allowed to cool down from the drilling, and the
humidity in the concrete must be allowed to equalize with the air in
the hole.
- The hole must be sealed during the equalization time. The plastic tube
and rubber plug in the SHM40 kit are used for this purpose. Ideally,
the probe should be inside the plastic tube during this time.
NOTE For reliable results, it is recommended to have several measurement
points.