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Measuring moisture in concrete slabs with DeFelsko PosiTest CMM and PosiTector CMM IS
Measuring moisture in concrete slabs with the DeFelsko PosiTest CMM and PosiTector CMM-IS (In Situ)
Related products:
PosiTest CMM, PosiTector CMM IS
There are various methods for testing the moisture content of concrete. The two most common are, firstly, measurement with non-destructive electronic impedance meters and secondly, in situ relative humidity (RH) probes. This article looks at electronic impedance meters, how they work, and demonstrates that the DeFelsko PosiTest CMM Concrete Moisture Meter is the simplest, most durable, and most accurate way to measure moisture content in concrete slabs per ASTM F2659.
What exactly are concrete moisture meters and how do they work?
Non-destructive concrete moisture meters (or electronic impedance meters) measure concrete moisture using the principle of electrical impedance of concrete, which is related to concrete moisture. An AC electric field flows from the device's transmitting electrodes through the concrete and is intercepted by the receiving electrodes. The impedance is measured, with increasing moisture content leading to an increase in the impedance value. Using concrete standards of known moisture content, the meter can be calibrated to show concrete moisture in units.
Concrete moisture meters give an instant result without having to drill into the concrete (ie with in situ probes).
However, impedance can also be affected by changes in concrete composition or the presence of rebars in close proximity to the surface. These meters measure moisture near the surface of the concrete, i.e. in the top ¾" of the slab. Non-destructive concrete moisture meters are ideal for use as a comparator to locate areas of relatively high moisture within the slab. They combine well with Vor Combine local RH probes such as the PosiTector CMM IS.
Watch the PosiTest CMM information video for more information:
How is the moisture content of concrete measured with the PosiTest CMM?
The PosiTest CMM is a fast, non-destructive impedance meter ideal for inspectors who want to quickly assess the moisture status of concrete slabs. With a convenient four-button user interface, innovative measurement modes and 3 measurement ranges, measuring moisture content is easy.
1. Turn on the device.
2. Select the desired scaling - Concrete 0-6%, Carbide 0-4% or Relative 0-100%.
3. Select the desired measurement mode
- Continuous measurement mode is the default mode and continuously updates the display with the current reading. Maximum hold mode displays the maximum reading until the store button is pressed to store it or the power button is pressed to discard it innovative Maximum hold and store mode waits for the reading to stabilize, then automatically stores it in memory and resets the display without the need to press a button.*Maximum hold and store mode is particularly suited for use with the Telescopic extension that screws into the meter's tripod mount. The telescopic extension is perfect for quickly measuring and recording concrete moisture over large areas without having to bend down or kneel.
4. Check the accuracy of the meter
A check standard is included to verify the accuracy of the meter. Simply place the check standard on a flat, non-conductive surface and press down firmly on the meter until the pins are pressed together. If the displayed reading is within the range specified on the check standard, the meter is functioning properly.
5. Surface preparation
Make sure the surface to be measured and the pins on the PosiTest CMM are free of dirt, dust, and other contaminants. The pins of the PosiTest CMM Concrete Moisture Meter must be in direct contact with the concrete surface to provide an accurate reading.
6. Measurement on the concrete surface
Place the moisture meter on the concrete surface and press down to fully compress the sensor pins. The sensor pins are designed for accurate measurements on smooth, rough or uneven concrete surfaces. The moisture reading is displayed until the meter is lifted from the concrete surface, depending on the measurement mode selected.
Testing a concrete slab for moisture content according to ASTM F2659
ASTM F2659 outlines and procedures guide the user through performing the relative humidity test in concrete using an electrical impedance meter. They define the environmental conditions and describe the preparatory tasks that must be carried out before the measurements can be carried out.
This section summarizes the general procedure for complying with ASTM F2659-"Standard Guide for Preliminary Evaluation of Comparative Moisture Condition of Concrete, Gypsum Cement and Other Floor Slabs and Screeds Using a Non-Destructive Electronic Moisture Meter".
Preparation for the ASTM F2659 test
- The concrete floor slab must be at operating temperature for at least 48 hours prior to the moisture content test. The air above the concrete slab must also be at operating temperature and the relative humidity should be at levels expected under normal use. If these conditions are not met, the tests should be carried out at 24°C ±5°C and a relative humidity of 50 ±10%.*No liquids, dirt, coatings, floor coverings, adhesives or other contaminants.*See PosiTest DPM Dewpoint Meter for environmental monitoring.
Conducted ASTM F2659 test using the PosiTest CMM Concrete Moisture Meter
Before beginning the test, ensure that the PosiTest CMM is turned on and set to the desired measurement mode in order to use the device correctly.
1. Determine the test centers.
The ASTM F2659 standard stipulates that a minimum of 8 tests must be carried out for the first 100 square meters and a minimum of 5 additional test points for each additional 100 square meters.
It is recommended that the inspector examines the entire concrete slab to correctly assess the moisture condition inside. Look for areas suspected of having high moisture levels that are not exposed to direct sun or other heat sources. These are areas roughly in the middle of the concrete slab and near the outer walls.
2. Measurement process
A In accordance with ASTM F2659, relative humidity, air temperature and dew point are recorded over the test sites. Measure the concrete surface temperature at a distance of 200 mm from each test point. PosiTector DPM dew point meters are accurate and reliable tools for the job.
Use the PosiTector DPM to obtain surface and ambient air measurements per ASTM F2659.
B. Using the concrete moisture meter, take 3-5 measurements within a 929 cm2 (1 ft2) area at each test location. Report the maximum reading at each point. To perform this task quickly and easily, use the PosiTest CMM's Hold Max or Hold Max and Save mode.
Use the Max Hold or Max Hold and Store modes of the PosiTest CMM to obtain the required 3 to 5 readings per measurement point.
Note: Chlorides, carbonates, rebar, and other materials can affect the accuracy of readings from a concrete moisture meter. Be careful when using these or similar materials. Non-destructive devices are best used in conjunction with on-site moisture probes such as B. the PosiTector CMM IS used to ensure the best accuracy when determining the moisture status of a concrete slab.
*Use Hold Max or Hold Max and Save with the telescope extender to measure even faster without having to bend or kneel.
3. Message
When the inspection is complete, use the built-in USB port and included cable to quickly and easily download, view and print stored readings in professional PDF reports using PosiSoft Desktop.
ASTM F2659 requires the following data to be reported:
- Locations of the test areas on the concrete slabThe highest moisture content at each test pointThe relative humidity, ambient air temperature and dew point temperature above each test pointAdditional information about the location, the tester and additional observations shall also be recorded. A full description can be found in ASTM F2659.
Example of a concrete moisture inspection report created with PosiSoft Desktop software for Windows and MacOS
When other DeFelsko instruments such as the PosiTector CMM IS In Situ Concrete RH Probes, PosiTector DPM Dew Point Meter or the PosiTector 200 Concrete Coating Thickness Gage are used on the same job, the measurement data can easily be summarized in one report. Fully customized reports can also be created to match existing paper forms or layouts.
DeFelsko PosiTest CMM - the ideal solution for measuring concrete moisture
The PosiTest CMM Concrete Moisture Meter is the simple, professional and accurate way to measure moisture content in concrete and screed. With its easy-to-use interface, high measurement speed, large memory and free report generation software, the PosiTest CMM is the best solution for concrete moisture measurement according to ASTM F2659.
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Justus-von-Liebig-Strasse 17a
50374 Erftstadt (Gymnich)
49 2235 987170 info@mtv-messtechnik.de
Justus-von-Liebig-Strasse 17a
50374 Erftstadt (Gymnich), Germany
+49 2235 987170
info@mtv-messtechnik.de