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Compare Moisture and Humidity Tests to Get the
Complete Picture

THURSDAY, DECEMBER 29, 2016

By Andrew Rynhart, Tramex Ltd.


A large contributing factor to many of the moisture problems we currently face in the concrete flooring industry is the oversimplification of the science and overcomplication of the method of moisture testing. During the last 10 years we have been subjected to a lot of marketing aimed at selling one type of relative humidity (RH) test, which has been claimed as a measurement of the “total moisture content" or “true moisture condition” of concrete. The same marketing language has been used to discredit other types of testing because they do not always give the same results as the RH testing.

It is important to properly understand the differences between
test results in order to obtain the most meaningful information.

The measurement of RH as a stand-alone test can only really be a measurement of the total vapor in concrete and, as such, is arguably the least useful information when taken out of the context of other tests. Therefore, initial decisions should be based on at least three easily performed, complementary test methods, such as:

  1. Instant and non-destructive impedance testing of moisture content;
  2. Ambient relative humidity and temperature testing along with the surface temperature
    of the concrete; and
  3. In-situ relative humidity testing.

Each of these testing methods, included in the demonstration video below, has its own validity and provides results that will give us more understanding of the origin and extent of a moisture problem, when it is understood in the context of other testing methods. These different testing methods are not all time consuming and can actually reduce the time spent testing overall.

Identifying the Problems

The severity of the effect of moisture issues can differ depending on a number of variables. These variables range from the quality and density of the concrete itself to the ambient site conditions and even the seasonal and regional climate. Without using a combination of the tests, it may not be possible to determine the source of the moisture or the extent of the issue.

There are times when moisture problems clearly exist or clearly do not exist, and any one moisture test will most likely confirm either situation. There are other times when single-testing data may be inconclusive or raise further questions, and the benefits of multiple testing will help provide a more complete understanding. In many cases, making critical decisions based on single pieces of data will lead to incorrect decisions that can be costly and time consuming for both the contractor and client.

There are a number of different international tests available to test concrete including: ASTM F2170 In-Situ RH; ASTM F2659 Impedance Moisture Meter; British Standards Hygrometer Box; German Standards Calcium Carbide; and the ASTM F1869 Calcium Chloride test.

At Tramex, we favor the combination of three tests, as stated above. While the following trio of tests is by no means the only method for measuring moisture correctly, it is both a practical and easy way to gather information.

Instant and Non-Destructive Impedance Testing of Moisture Content

Tramex impedance testing ASTM F2659

By performing preliminary non-destructive impedance moisture testing, as per ASTM F2659, the inspector can obtain an instant and precise evaluation of the moisture conditions within the top inch of the slab, as well as build up a moisture map of the entire slab, showing how wet the slab is and identifying the wettest locations. This is done using an impedance moisture meter, which gives a percentage measurement of moisture content by weight.

This method helps identify moisture problems from within the concrete or originating from the surface, such as dew point and condensation issues or leaks. It also helps the user determine where it is best to locate the RH sensors for in-situ testing as per ASTM F2170.

The Tramex CME instant test for concrete is completely non-destructive and specified by many floor-covering manufacturers around the world, in part because of its simplicity and the repeatability of the results.

Ambient Relative Humidity and Temperature Testing

Measurement of the ambient conditions also provides some key information and will allow the inspector to get a more complete picture of the moisture condition of the concrete slab.

For example, by comparing the moisture map with the on-site ambient RH readings and surface temperature, it is possible to distinguish dew point and condensation issues from other potential moisture problems and deal with them separately.

Tramex ambient conditions testing

Another example is when testing to ASTM F2170 at “in-service” temperature and humidity. ASTM F2170 states (in section 9.1), “Concrete floor slabs shall be at service temperature and the occupied air space above the floor slab shall be at service temperature and service relative humidity for at least 48 hours before making relative humidity measurements in the concrete slab,” making it critical for inspectors to understand the necessity for stable temperature and humidity during the testing period. Potentially serious errors can occur if this is not properly understood.

The problem is that even small temperature changes will provoke converse changes in in-situ RH values. If the equilibrium is unsettled, it can take hours of stable temperature to allow for conditions to return to equilibrium, and only then can reliable and meaningful RH readings be achieved from the tests.

If a building is not in “in-service” condition but in-situ RH testing is required, it is advisable to take two separate in-situ readings, two hours apart. The first recorded readings of ambient temperature and relative humidity as well as the in-situ values should be the same as the second recorded readings in order to demonstrate their accuracy and to be sure that there isn’t any instability.

Alternatively, the use of non-destructive impedance testing as per ASTM F2659, combined with ambient temperature and RH and concrete surface temperature testing will give instantaneous and meaningful information when testing in-situ conditions that do not allow for F2170 testing.

Tramex in situ relative humidity testing ASTM F2170

In-Situ Relative Humidity Testing

After the user has mapped out the slab with the preliminary non-destructive impedance testing and located the wettest locations, as well as acquired “in service” conditions, in-situ RH testing can be performed as outlined in ASTM F2170.

To perform this in-situ type RH test with the Tramex Hygro-i system, simply drill a hole in the concrete, 40 percent of the thickness of the slab. Push the sleeve into the hole, insert the Tramex Hygro-i probe into the sleeve and cover with the cap. Leave for the standard test period. When taking readings, plug the interface into the Hygro-i probe and instantly read the relative humidity, temperature and dew point simultaneously on the clear display. When testing is complete, the Hygro-i probes can be removed with the extraction tool and used repeatedly. The user must be mindful of all the proper safety precautions as mentioned in the ASTM standard.

When performed alongside the other test methods, as outlined above, the internal RH reading becomes more meaningful.

Conclusion

When relying on only one testing method, false assumptions regarding the moisture conditions of the concrete can be made due to a lack of more valuable, holistic and meaningful data.

When using a combination of testing methods, and when understanding the testing methods themselves, the inspector can minimize the risk that goes with not seeing the complete picture. D+D

*Claims or positions expressed by sponsoring authors do not necessarily reflect the views of TPC, Durability + Design or its editors.

ABOUT THE AUTHOR
Andrew Rynhart, Tramex Ltd.

Andrew Rynhart is CEO of Tramex, founded in 1974 and recognized as an international leader in the design and manufacturing of moisture and humidity meters. Rynhart says he is proud to helm the company that not only invented, patented and developed the first ever non-destructive moisture meters but continues to innovate and produce meters to the highest standards of precision and durability.

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Tagged categories: Climate Control; Climate monitoring; concrete; Equipment manufacturers; Floors; Good Technical Practice; Humidity and moisture; Moisture detection; Quality control; Site/field testing; Tools

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