Concrete Moisture Issues - An example of Misapplied Assumptions

Starting even before I left my former company in 2009, I began to realize that there were MANY issues I was dealing with that were no more than assumptions, based on prior assumptions, which were even based on other prior assumptions.

As it turns out, many of the resolutions was no different than a blind squirrel finding a nut now and again...pure blind luck, yet my company and many others would chalk this "accomplishment" up to another "success", completely unaware of the continuation of myths that become fact when repeated often enough.

Legacy Issues, Assumptions and Refusal to Recognize Fact

There were many "tests" and procedures I used in my line of work that were considered unimpeachable facts and used dutifully, even by the most sophisticated researchers and testing firms. This, ironically became my realization of just how easy it is to fool or misdirect even the most intelligent of these organizations and companies. Most, if not ALL of this is due to legacy issues, where there is a line of trust we place in those who we THINK know and understand the information being conveyed, where in reality, the person(s) we take this information from may have been just as reliant upon others before them who KNEW and understood this information.

Concrete Moisture Damage

It is a sobering realization that concrete, being one of the oldest known building materials, also is one of the least understood when it comes to moisture damage.

Some examples of recent revelations, which STILL contain disturbing information gaps, is that cement in Portland Cement concrete is weakly crystalline and can redistribute in concrete under certain circumstances. This discovery was reported by MIT in 2015. The dramatic differences in Roman concrete versus modern Portland cement was also a recent discovery, with the explanation I am not fully on board with, but the singular difference pointed out was pretty dramatic.

Moisture Damage, on, in and through Concrete

Although there were earlier studies of concrete slabs on ground (on-grade), arguably the most referred to is the oft cited "Brewer Study" conducted by the Portland Cement Association and published in 1965.

I, like nearly everyone else, was told this study established and confirmed the dangers of moisture migration through concrete, causing surface coating failures.

Because this is how it was conveyed, EVERYONE I knew understood this to be factual, only it wasn't. How I happened to re-read and dissect this study came by pure accident when I was doing research on an even older procedure, used for MANY decades that could identify if concrete had "carbonated".

The common perception of carbonated concrete is that the calcium hydroxide formed during the initial hydration process that creates the cementing process is quite alkaline and considered an important factor in protecting any contained metals, particularly reinforcing steel. Calcium hydroxide is highly alkaline with a pH of 12.45-12.5. This high pH creates what is known as a "passivating effect" where the reinforcing steel will not corrode (rust).

Although exceptions, particularly with chloride contamination (from de-icing salts, sea air exposure, etc.) will create conditions that can create corrosion, even with a higher pH if there is sufficient chloride contact with the steel reinforcement. NOTE: This prompted a design consideration that reinforcing steel should be at a minimum depth from the surface as an attempt to keep the chlorides from reaching the reinforcing steel.

It was found that as the concrete surface absorbed carbon dioxide from the atmosphere, or from petroleum-based exhaust (i.e. propane heaters) could react with the calcium hydroxide to form calcium carbonate. The identification of this was established by using a chemical called phenolphthalein. Phenolphthalein will give a visual indicator in a pH range of slightly higher than 9, upwards to a pH slightly higher than 12, becoming colorless below a pH of 9 and a pH of 13 or higher.

When calcium hydroxide reacts with carbon dioxide, and forms calcium carbonate, the calcium carbonate is nearly insoluble. Coupled with the low solubility of phenolphthalein, this results into a no color change. When the color change occurs, it is ASSUMED the concrete is NOT "carbonated" and the reinforcing steel remains in a sufficiently alkaline environment. Well, as I began experimenting, this turned out to be an assumption, NOT a fact! To say I was stunned is putting it mildly. MANY projects have used this indicator to give a "safe" qualification for structures that may be suffering from corrosion of the steel reinforcement, as this goes unrecognized!

What was Missing in the Phenolphthalein Indicator Assessment

What I discovered was that IF calcium hydroxide were the only consideration in determining whether concrete is carbonated or not, the assessment would be adequate, even if not ideal. However, forgotten or lost in the field assessments is the presence of sodium hydroxide. Sodium and sometimes potassium hydroxide can actually be present in much greater volume than calcium hydroxide. However, unlike calcium hydroxide, sodium and/or potassium hydroxide do NOT become insoluble after reacting with carbon dioxide. These materials become sodium carbonate and/or potassium carbonate. BOTH these newly formed compounds will react vigorously with phenolphthalein, forming a bright red coloration that gives a reading that the concrete is NOT "carbonated", when in fact, it could be VERY carbonated and the reinforcing steel is inadequately protected, causing corrosion that is in turn ignored due to this false positive. The reading is accurate, but our interpretations are NOT!

I Don't Want to hear This

As I recovered from being stunned by this revelation and confirming repeatedly the reaction of the soluble carbonates, I also dug deeply into other test methods I had taken for granted and simply accepted what I was told since everyone else had accepted these "facts".

Before I jump into the dynamics of concrete moisture, I want to emphasize that revealing this information was not enthusiastically received, with some refusing to accept the information, even to the point of refusing to conduct even simple bench tests. For better or worse, that is human nature, where Samuel Clemens so aptly put; "It is easier to fool someone than it is to convince them they've been fooled".

Well, folks, we've been fooled, often and repeatedly. There has been a very strong resistance to the information given regarding moisture movement and concrete, along with our legacy-created mistakes that refuse to go away.

Dissection of The Brewer Study

Part of my research included the Brewer Study which as I read through it, it became increasingly obvious, all the way to the point of the Study Conclusions that the entire concrete and flooring industries have been misled.

NOTE: While reviewing the Brewer Study, I reviewed a 1974 study from the Army Corps of Engineers that gave further credence to how misunderstood and miss-translated the Brewer Study had become.

In the Brewer Study, when the samples were being constructed, more than 40% of the initial samples were determined to be unusable for the intended study since leakages and other factors created conditions that couldn't be controlled. While reading that portion, I thought to myself, "well, welcome to the real world where placement of concrete isn't perfect".

Of the samples that were considered acceptable, measurements were conducted where moisture absorbed from the bottom surface and the top surface were compared. Samples of concrete were evaluated with and without underside vapor retarders. Some of the results were surprising. It made little difference in the results where a vapor barrier was used versus concrete without a vapor barrier, with some results suggesting a vapor barrier was beneficial while in other results, the vapor barriers led to an increase in moisture outflow through the concrete surface. To be fair, I found neither conclusion to be be very persuasive.

That being said, the shocker in all this; the conclusions were the OPPOSITE of what I and virtually BOTH the flooring and concrete industries were led to believe.

In the conclusions, it was very specifically pointed out; moisture emanating from the concrete surface was the cause of moisture-related flooring failures.

Conspicuous by its absence, was ANY mention of moisture originating from the underside of the concrete through to the surface to cause flooring failures.

Now We Mix in Modern Studies and the Second Law of thermodynamics into the assessment of moisture-related Flooring Damage

Now that field studies have become increasingly sophisticated, we are finding out that nearly ALL moisture-related damage is created within the top one inch of concrete that is exposed to the environment. This is consistent, irrespective of where in the world these studies have been conducted. My earlier articles cover much of this in more detail.

Now, when we add what we've been taught, how moisture migrates from the underside of the concrete to reality, what we have been taught to believe is actually embarrassing!

The portion of where the average concrete slab on grade is cooler at the bottom of the concrete, gradually becoming warmer through to the surface and the ambient conditions tend to be warmer than the concrete surface (this is generally accurate, with the exception of desert and tropical climates).

Now, what we have been incorrectly taught and goes AGAINST the second law of thermodynamics, moisture is migrating from the cool underside to the warm concrete surface. Moisture migrates from cool to warm, NOT from warm to cool. The second law of thermodynamics is the opposite of what we were taught as fact in seminars and certification schools...moisture moves from warm to cool...period. Even as it is stated as such in other studies, this fact is somehow ignored when it comes to moisture-related flooring issues!

Obvious, but ignored confirmations are with multi-story buildings, particularly those that aren't yet climatized. MANY inspectors have expressed surprise when concrete on the 20th story of a building has a higher moisture content than the on-grade concrete. If one considers warm air rises and warmer air can contain more moisture than cool air, this makes perfect sense.

But What About.....

In a discussion I had with an inspector on LinkedIn, that person's knowledge base is unfortunately too typical. Portions of the Brewer Study were brought up that were taken out of context, to which I pointed out, then YOUR conclusions are different from the study, please justify YOUR conclusion - silence.

Even worse, talking with some "experts" that give "educational presentations all over the U.S. and in published articles, it has been stated (and I am NOT making this up):

1. Moisture only moves through concrete in vapor form, that's why they make dams with concrete.
2. Water vapor carries alkaline salts and acids through concrete.
3. Humidity measurements can be used to measure the total moisture content of concrete.
4. RH Probes are ONLY qualified to measure between 10% RH and 90%. Yet in publications and educational seminars, RH probes are being used to assess humidity measurements outside their accuracy levels. Worse, these are being USED for qualify or disqualify a warranty or material replacement for moisture issues these have NOT been qualified for! RH Probes tested are qualified ONLY for the initial mix water in concrete - of which I still take issue with, but that is a debate for another time.
5. I asked an inspector with approximately 40 years experience to please cite even ONE report where there is empirical data on moisture moving from ground moisture through to the surface of concrete. Since that is supposedly a "fact" why is there no data? There's no data because the second law of thermodynamics states otherwise.

Diffusion and Moisture Content

It is vital that we understand the difference between moisture migration and diffusion. Diffusion can and will distribute soluble components even as the moisture itself does not move, nor does it have to. So when contaminants can eventually reach the surface (which places the concrete quality itself in question), it is due to diffusion, NOT migration. This is where things can get VERY complicated since the now contaminated moisture can interfere with most testing methods, giving us an accurate measurement, again, even as the interpretations are misunderstood.

If an RH probe or calcium chloride method is used, any salts within the top surface will reduce the measurable moisture recordable by EITHER method, with the humidity method most susceptible to altered moisture measurements. This does NOT mean these are inaccurate, it is simply a limitation created by the chemistry within the top surface of the concrete. Unfortunately, the current methodology in the F 2170 is nearly meaningless since it completely by-passes the problematic area. NOTE: I HAVE seen RH information where the concrete surface is 74% and the lower portion of the concrete is at 90%. These differences can co-exist due to the relative equilibrium in a given area. This isn't unlike the unfair BS given to cementitious underlayments that have a higher moisture content than the underlying concrete, this should be expected, not a surprise. The key here is the relative "normal" state of each. This is no different than wood species all having their respective different moisture content...it would be unfair and dangerous to try and uniformly require a singular moisture level for the different wood species, as it is unfair and dangerous to require a singular moisture level for the different cementitious species. Again, I have no issues with the majority of test methods, BUT I have a significant concern over the consistent misinterpretation of the test method results and what they actually convey.

Conclusion

We need to get back to the basics and clean house on the legacy issues that are misleading and will continue to mislead. We cannot move forward using data KNOWN to be incorrect, or at the very least, misleading due to misinterpretation of the data. One of the hardest things to do is to first UNLEARN, so we can LEARN the right way.