In April, the new RT 103333 technical guideline on measuring the relative moisture content of concrete was published, updating the measurement guidelines as the previous version was already more than 10 years old. The measurement methods outlined in the card have, in practice, become established at the national level as guidelines for conducting measurements to assess the readiness of concrete for coating. The most notable changes include practices to improve measurement accuracy, as well as better instructions for utilizing sensors embedded within the concrete.
In this blog post, we’ve compiled the most important changes for construction sites. You can learn more about the contents of the new RT card in our from the summary.
Analysis of Measurement Uncertainty
Even under the best conditions, measurement results are not exact, and this must be taken into account in the future by ensuring that the moisture limit for the coating product is not exceeded, taking into account measurement uncertainty, which is also essential to consider when planning the drying schedule. In practice, this means that even with the most accurate measurement methods, the uncertainty class is approximately ±1–2%RH; thus, for example, concrete to be waterproofed with a limit value of 90% must be measured at a moisture content of 88–89%RH prior to coating. An accuracy class of ±1%RH already requires nearly laboratory-like conditions for measurement, and ±2%RH is likely to be the accuracy class aimed for when evaluating coating suitability under site conditions. Due to various sources of uncertainty, the accuracy class may also be, for example, ±4 or 6%RH.
A measurement point suitable for assessing paveability
Previously, it was common practice to measure concrete in wet areas using a single sensor at a single depth, and in dry areas at two depths, using a total of two sensors. According to the new guidelines, ”When assessing coatability, measurements must always be taken at a minimum of two depths at each measurement point… The most critical measurement depth shall be measured using at least two parallel boreholes/test tubes.” In other words, for each measurement point used to assess surfacability, measurements must be taken at two depths, using a total of three sensors.
Temperature during borehole logging
Borehole measurements The lower temperature limit has been raised from 15 degrees to 18 degrees, with the acceptable range now set at 18–25 degrees in accordance with the new guidelines. The aim is to ensure that the measurement results better reflect actual operating conditions.
Sensors installed in the casting
Various types of sensors designed to be embedded in concrete, which enable longer-term monitoring, have been available on the market for a long time, and now clearer requirements have been defined for them for different purposes and levels of accuracy. However, the document notes that ”The actual coating thickness measurement should be performed with an accuracy class of at least ±2 % RH, typically using the sample patch method or the drill hole method under stable thermal conditions on new drill holes,” meaning that traditional methods are not yet being abandoned, but here at Vertia we are also closely monitoring the development of various measurement techniques.
Other
It should be noted that the refinements aimed at improving measurement accuracy mainly concern measurements taken to assess the suitability of concrete for coating. For example, measurements for monitoring drying or surveying areas affected by water damage may continue to be performed with lower measurement accuracy.
While striving for greater measurement accuracy, measurements in accordance with the new RT card can be implemented immediately; however, in practice there is a transition period, and construction will initially proceed according to the guidelines that were in effect at the time the building permit was applied for. However, potential impacts on longer drying times for concrete structures, as well as under favorable drying conditions, should already be taken into account in future projects.
The matter has been discussed in greater detail in our summary.
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