"Expected Influences" Can interfere with expected Results.

Far too often, and at this point, unfortunately inserted into nearly every study I have read, there is a taint of an "expected result" or an "expected influence" that often times is noted as "it is assumed" or some other reference to what is an assumed fact, even if such referenced "fact" hasn't been established as a fact.

One particularly irritating unfounded claim: "It is a known fact that water vapor migrates through concrete".

One, it ISN'T a fact and Two, wherever capillary water exists, water vapor cannot migrate or move THROUGH that particular section of concrete, which tends to be in the mid section of concrete.

Water vapor cannot transmit through liquid water since water in its liquid form is in its densest form. Water vapor will evaporate FROM the surface of water, and its efficiency is governed by physical size of the liquid surface, the saltiness of the water and the temperature.

The simple graphic shown is an example of surface area. Irrespective of moisture volume, even a change in surface area can greatly influence measurement of moisture, particularly in its gaseous/vapor state.

The more surface area of a liquid surface, the higher the evaporation volume and the faster equilibrium of humidity is established; IF the water is pure.....which is a massive "if" and using existing industry standards, the rate of available moisture for free evaporation cannot be established.

Wait, it Gets Even MORE Complicated!

There are very few "examples" I find more irritating than when someone cites or uses "scientific examples" in a straight forward and open system and then attempts to correlate the results of that simple system with a system as complex as concrete.

Moisture in concrete can have a higher attraction to certain solids and soluble salts than the water has for itself.

When this happens, "normal" evaporation rates do not apply and that simplistic open system may have no resemblance whatsoever to the onsite activity being experienced by the concrete.

In smaller pores and capillaries, the attraction to the hygroscopic solid is strong enough that evaporation becomes very limited. As the temperatures change and vary from the concrete surface inward, there are situations where the evaporation rate is so slow and gradual, the volume content changes very little. Water vapor CANNOT traverse through these areas.

The attraction to siliceous surfaces is so strong that I will often take two thin glass slides, take a drop of water, attach the glass slides to each other and ask those in the audience to pull them apart. None of the attendees can pull them apart without first sliding them to where there is limited to no contact between the two glass surfaces.....THIS is but ONE force evaporation has to compete against.

If strongly hygroscopic salts such as calcium hydroxide and/or sodium hydroxide are present, the attraction becomes even stronger to where the resistance to evaporation continues to increase as the surface water evaporates and increases the concentration (alkalinity) of the water.

The conditions that would "normally" increase evaporation with an open system, increases in evaporation resistance because as the salts concentrate, the measurable RH diminishes, concurrent to a lower RH, is a lower evaporation rate.

This, and as concrete ages, hysteresis becomes an issue where the constant modifications within the concrete, create a disconnect between the ingress and egress of moisture, in all forms. NOTE: In laboratory studies, hysteresis is so gradual, that most, if not all studies conclude before hysteresis is even noticeable. Without environmental changes, the diffusion models used in these studies remains acceptably accurate..in the field, once hysteresis begins to a noticeable degree, the diffusion models have been rendered inaccurate...yet many labs STILL use these diffusion models due to no, or greatly limited experience with hysteresis models...wondering what is going on and then start adding the evil words "assumption" or "it appears", “may be caused by”, etc.

This is where studies begin to unknowingly apply illusory correlation and assume causation. Then confusion piles on where the numbers don't work and instead of pursuing the seeming anomaly further, the "anomaly" is simply dismissed. The majority of studies are guilty of this...and based on these "facts", the industry applies guidelines and it is usually years down the road, when the contradictions are now too common to ignore, the industry jumps to the next "scientifically proven" hula hoop.

NOTE: BOTH the flooring and concrete industries have done this for decades and in many areas, shows no signs of slowing down.

This is why older concrete can befuddle those who conduct testing and installations where an older concrete measures as "dry", with a prior floor coating fully intact and without problems, but suddenly becomes seemingly impossible to reinstall a coating or flooring material that doesn't have moisture-related bonding issues.

When salts collect, particularly towards the surface (noted in early NSASR (Near Surface Alkali-Silica Reaction) and sweating slab syndrome, using either RH Probes or calcium chloride tests can produce false "low-moisture" measurements due to the lowered evaporation rate/lower humidity, even if the concrete surface itself is nearly saturated with liquid water.

For example, if sodium hydroxide reaches a concentration of 30% in the liquid water, the resulting measurable RH will be 63%, or according to the improperly applied advice/data from the RH Proponents, the concrete is acceptably dry for a a coating or floor installation, when nothing could be further from the truth.

The Truth is Out There

There are many cited "facts" where no confirming empirical data has been produced.

I, like so many others, were convinced by legacy issues and long-held beliefs, that moisture migrated as a gas from underneath the concrete, through to the surface and then cause coating and flooring failures.

This "fact" became undone when I was involved with projects with multiple elevated concrete floors.

In MANY instances, the elevated concrete had higher measurable moisture than the concrete on-grade/ground.

Three studies by the Portland Cement Association, Florida Solar Agency and the Army Corps of Engineers, made/found no link between soil originated moisture and flooring failures, but TWO of the studies DID indicate that the moisture content within the concrete remained constant throughout the duration of the test, stating the concrete in the middle was adiabatic.

Adiabatic: An adiabatic process is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment. In an adiabatic process, there is no heat transfer. The term "adiabatic" means occurring without gain or loss of heat.

Revelation Upon Revelation

Temperature changes are inextricably bound to moisture movement within a building envelope...if no temperature change (absent of intentional bulk water flow where temperatures are manually controlled), no moisture movement.

Concrete Gradient - Global Consistency

In my insistence upon empirical data, few things have been more compelling than studies being conducted, particularly with ZERO knowledge of the others being conducted, yet arrive at similar if not nearly identical conclusions.

With more sophisticated testing, it was discovered in the field and shockingly, in laboratory environments, the concrete surface is consistently weaker and more permeable than the remainder of the concrete. This section is called the surface gradient and has been consistently noted to be the most pronounced in the top 0.75-1.0 inch depth into an environmentally exposed concrete surface.

Technically speaking, the concrete is enveloped by a surface gradient, with the top surface as the most susceptible due to the settling of the concrete where bleed water transports to the surface. This is much less pronounced at the sides of concrete and minimal to non-existent with the underside.

The earlier discoveries that led to establishing salt collection at the concrete surface could cause NSASR and Sweating Slab Syndrome ends up correlating very strongly with the newer, more sophisticated testing where it was discovered that the top 0.75-1.0 inch of the concrete can self (autogenous) desiccate in the first 2-3 weeks after placement.

This self desiccation has reached RH measurements much lower than the 80% RH needed to create cement. The lower and longer the desiccation effect lasts, the less cement is formed.

IT would be extremely difficult to separate or compartmentalize this activity from the key reason for premature deterioration of concrete, coating/flooring issues, NSASR and Sweating Slab Syndrome.

Interestingly enough, some studies have blamed the formation of cement as the primary cause for the self desiccation of the concrete gradient. That conclusion is compelling ONLY if the concrete is a high performance to an ultra high performance concrete where under the best of circumstances, there is barely enough water to effectively form cement.

The "Cures" are often Worse than the Problem

In a lab environment, there is no sunlight exposed surface, nor moisture differentials that exist from one portion of the concrete to the next where the temperature and humidity fluctuations are considered.

In a benign environment such as a laboratory setting, an SCM or pozzolan will function very well as an adjunctive producer of cement. In the field however, is a different story altogether.

Field concrete can be exposed to elevated temperatures that will initially increase cement formation, then quickly retard cement formation. As the initial cement hydration is formed the alkalinity increases and the RH falls below 80%.

Once the RH falls beneath 80%, cement formation ceases...and then the SCM and/or pozzolan become a deleterious additive rather than a beneficial one.

BOTH SCM's and pozzolans are very small in particle size, AND require water to dampen these particles in order to be available to the cement hydration by-product; calcium hydroxide.

Unfortunately, in the presence of heat, calcium hydroxide becomes less soluble...AND in the presence of sodium hydroxide, calcium hydroxide becomes INSOLUBLE and rather than creating more cement, these can end up inhibiting the initial cement of the Portland cement.

Now add something like a high limestone cement to this equation, this can be a recipe for disaster!

Expected Influences - Interfering with Expected Results

Now we come full circle to where we are taught legacy issues are facts, told what results we should have, yet we consistently do not achieve the expected results that we witness in laboratory setting, but seldom able to duplicate in field conditions.

Concrete is a fascinating, yet complex material that continues to defy full understanding....cement formation, even to this day, is incompletely understood.

Now we add other changes and complexities to where whatever understanding we had for concrete placed in the 1920's, the 1950's 1980's and concrete prior to 2002 are no longer applicable to the concrete we have today.

The current plasticizers and cement grinding aids did not exist when curing standards were developed.

Compressive values were placed prior to the finer grind, lower cement content modern concrete contains.

ONLY after several years using a finer grind cement, did we realize that curing became an even more important aspect of a quality concrete to where water/cement ratio and curing were given nearly equal weight in placing a high quality concrete.

NOTE: Curing of a coarser cement in concrete was much more efficient due in part to the lower heat of hydration and the more relaxed construction schedules at the time.

We even emphasize convenience over durability since elevated temperatures have PROVEN to reduce the long term strength of concrete, but give a very good 28 day compressive value.

As a result, each study concentrates on the 28 day goal, yet again and again ignoring the long term durability, suggesting the current approach is proof of insanity. "Insanity is doing the same thing over and over and expecting a different result".

Trivia Note: Although the insanity quip is often referred to as originating from Einstein, there is no evidence he ever said it and the actual origination may be from Al-Anon and Narcotics anonymous.