What Constitutes accuracy when measuring moisture content of concrete?

One of the worst flooring industry myths, invented by those with vested and conflicting interests, have successfully convinced many in both the concrete and flooring industries that RH Probes measure moisture content of concrete, even though the standard itself doesn't make that claim.

Further this same group providing this misinformation also states that concrete moisture meters, specifically Tramex concrete meter is only useful for determining where to place humidity probes. Such claims are absolute RUBBISH and when I have contested those who make such claims, they had zero empirical data and NOTHING remotely accurate to make such false claims; and YES those claims ARE false!

Worse, these bastions of misinformation actually stated when introducing RH probes as "The answer" if moisture testing was so accurate, why are we still having failures?

A better question is, if RH Probes are the answer, why have failures essentially TRIPLED since the industry adoption of this misguided sales pitch?

Tramex Concrete Meters and Gravimetric

Before heading into gravimetric, it is important to understand that in the waterproofing and restoration professions, Tramex Concrete Meters have been the Gold Standard for accuracy in measuring moisture content.

This article describing the successful Billion dollar Miami Tunnel, completed back in 2014 used the Tramex Concrete Meter to determine moisture content of concrete.

Excerpts from: https://www.miamitodaynews.com/2022/08/02/portmiami-tunnel-blazes-trail-to-future/

"Some 120 feet below sea level the 42-foot-diameter PortMiami tunnel connects the mainland to Miami-Dade County’s second-greatest economic engine, supporting more than 334,000 jobs and contributing $42 billion annually.

Since opening to traffic in 2014 after over four years in construction, it has become a gold standard for tunnels in Florida and in the nation both during construction and now during operations and maintenance.

Now, as local governments are looking at adding other tunnels to increase mobility, the port tunnel’s track record offers guidance for what more tunnels might achieve.

Only a year after opening the $1 billion tunnel – including $668.5 million for design and construction by Miami Access Tunnel Concessionaire LLC in partnership with the Florida Department of Transportation (FDOT), Miami-Dade County, and the City of Miami – the department won the Grand Prize for the Port Miami Tunnel in the 2015 America’s Transportation Awards national competition.

The project was a pioneering public-private partnership (P3) in the state. It was completed on schedule and $90 million under budget, Mr. Hodgkins said. To date, the tunnel has taken out of downtown Miami 80% of the trucks that in the past had to go through the city’s core to get to the port. Traffic inside the tunnel has increased about 265%, Mr. Hodgkins said.

Water tightness of the concrete was one of THE most important factors, and several methods were used to determine concrete maturity, curing progress, and permeability. One device in particular was used and determined to be successful based on the baseline used for this and other methodologies, the baseline used was the Tramex Concrete Meter...you know, the one claimed by producers of RH Probes as not being accurate....with those same producers claiming water vapor can carry alkalies and salts and that water vapor can travel from cool to warm, RH measures the total moisture content of concrete and other non-science claims. I am NOT pulling any punches here. Billions are being needlessly spent on problems that should not exist, and wouldn't if REAL science is brought in.

This is where gravimetric comes in; gravimetric is basically a method where the sample of anything where moisture content is important is weighed, placed in an oven, dried to a constant weight and then the moisture content can be accurately calculated. One of the primary reasons this is so accurate is that liquid water is neither compressible (irrespective of how much pressure is applied, the volume of liquid remains constant) and that the weight of water is also a constant since it ISN'T compressible.

The Gravimetric - Tramex Association

I embarked on a research program I intended to devote at least two years, as an effort to try and find a methodology to measure moisture in concrete that would not be affected by the hydrophilic, hygroscopic, even deliquescent materials that vary in volume and composition.

These materials actively interfere with any form of humidity measurement or any method that is dependent upon free evaporation, such as methods used in both ASTM E 96 and ASTM F 1869.

These water-loving materials will attract moisture and will create a competitive attraction with moisture in a liquid or vapor form. An easy and common example is the industry standard calibration solution which consists of sodium chloride and water. This solution will NOT allow the RH in the immediate air space to exceed 76%, no matter how much salt water is present. The salts in concrete have much greater attraction to water, which is referred to as "critical humidity threshold". An impressive sounding term that refers to what RH is required before a specific salt begins to actively absorb moisture from the air.

Considering that cement is now more alkaline than in the past, and that alkaline material is sodium hydroxide, this prevents some or most of the moisture from being absorbed by other desiccants such as calcium chloride (used in both E 96 and F 1869). How this is known and knowable is due to the critical humidity threshold of calcium chloride which is slightly higher than 18% RH. The critical humidity threshold of sodium hydroxide is slightly lower than 9%. Even the Portlandite (calcium hydroxide) which is created during cement formation has a lower critical humidity threshold than calcium chloride, at approximately 12% RH.

There are "concrete experts" that have claimed the reason calcium chloride test methods are inaccurate is that the calcium chloride "overdrives" the concrete. This isn't true and never has been true, but it is a very effective exploitation of the chemical ignorance that most of us have..so we end up depending on these experts...who just so happen to be giving us bad advice based on bad chemistry.

Gravimetric is not at all affected by these salts. This is why I used gravimetric as my jump off point rather than any other method. NOTE: There are other strange effects that can occur with the different kinds of salts where temperature can create unpredictable variations under different circumstances.

The Finnish Study - Gravimetric Baseline

A few years ago, I was given a copy of a Finnish study conducted by a very well-respected European firm VTT. This firm used a gravimetric method to pre-qualify moisture test methods before bringing them out to site conditions.

Several methods indicated at least some general correlation with gravimetric. These included RH Probes, Calcium Carbide, Concrete Meter (specifically Tramex) and a couple other methods I wasn't familiar with.

Where things got interesting is when taken out of a laboratory, most of the methods began to drift well away from the gravimetric baseline (although not identified by the researchers, I am certain this has a LOT to do with the alkaline salts in the concrete now starting to migrate within the concrete.

The field results were taken at 14 and 28 weeks. The ONLY method that not only had close correlation with gravimetric, but with results that were a near mirror image was Tramex. This was the final confirmation I needed.

Takin It To the Streets

I began to consult with flooring installers and gave them what has been more perfected by Tramex as an "Instant Check". I had each installer use the Tramex CMEX where the room temperature, humidity, dew point were measurable in real time. Using the infrared thermometer, this was critical in ensuring the installation temperature of the concrete was at least 10 degrees warmer than dew point.

We didn't stop at the initial readings, but kept measuring throughout the flooring installation. There were times when windows were open, the humidity in the room spiked and the surface was now within 10 degrees of dew point. Using floor fans, the installer was able to quickly correct these environmental changes and continue with the installation. I have MANY examples of these installations, with NONE of them requiring a moisture mitigation system.

One project in particular was a three story building where ambient conditions created higher moisture content with each successive elevation. The inspector was puzzled why the average moisture readings were higher on the third floor than the second floor and why the second floor was higher than the ground floor. The inspector wasn't familiar with the "stack effect".

I had them bring in fans, the Tramex Concrete meter and an infrared thermometer, we were able to get the moisture levels below 4.5%, which I recommended was their "go number". They kept active air movement within the room as they followed the fans being used to dry the concrete surface.

Instead of spending more than $900,000 for a moisture mitigation system, they we're able to install the floor, open on time and the floors have not experienced any moisture-related issues since time of install, which was completed in 2015.

If Testing Isn't Solving Problems or at least Minimizing them, WHY is the industry insisting on continuing to use what isn't working?

Another great resource is Larry Marvel. I highly recommend watching this video of his experiences with Tramex.

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