About 24 hours are required for the relative humidity in the cylinder to equalize with that in the surrounding concrete. Then a device is inserted into the cylinder to measure the temperature and relative humidity inside. These probes can be purchased from electronics equipment suppliers. This relative humidity corrected to a standard 750 E indicates the internal relative humidity of the concrete, but does not directly indicate absolute moisture content. Further research is needed to establish a relationship between the measured internal relative humidity of concrete measured and the actual moisture content.
Several methods are available for measuring the internal moisture content of concrete in service.
Here, a dew point hygrometer is being used to measure the relative humidi ty of a concrete slab covered with floor tile. A similar method involves drilling the hole to nearly the depth where a measurement is desired, cleaning out the hole, then drilling into and just through the zone of interest. The concrete powder from this zone is collected and sealed in a container. After about 24 hours, when the humidity of the air and powder equalize, a probe is inserted into the container to measure the relative humidity and temperature. These measurements are comparable to those made directly in the field.