When dealing with Concrete in testing and diagnosis - Know Thine Chemistry BEFORE Making an Assessment

I have read no less than 12 different studies from around the globe, in the past 3 weeks with researchers stuck on 7 and 28 day "results" in determining "durable concrete".

The convenience of the 28 day has taken precedent over the long term durability of concrete.

A few of the studies only hint at the chemical effects on and within concrete, with some coming agonizingly close to an understanding, then suddenly depart from the underlying chemistry and changes that come with chemical interaction and how so MANY chemicals involving or in use with concrete are not only inadequately covered, but dismissed as the focus becomes myopically linear yet again.

Chemicals - Good, Bad, even if it is the same chemical

As I pointed out in a past article, the latest NIST Concrete Compilation, sodium hydroxide within concrete was identified as an "anti-freeze".

In lower concentrations, this would be accurate, but so many indicators point to sodium hydroxide, particularly in the concrete surface, becoming much more concentrated than what was covered or even suggested within the NIST Report.

It isn't just sodium hydroxide that can behave in seemingly unpredictable ways, calcium hydroxide becomes insoluble as temperatures increase, yet the additives of fly ash, pozzolans and SCM materials ignore this tendency of concrete exposed to elevated temperatures and direct sunlight where the calcium hydroxide will either NOT react with these additives, or do so in such a limited capacity as to negate any perceived advantages with these additives, even worse, actually contribute to negatively affecting the long term durability of the concrete, particularly in the environmentally exposed concrete surface.

Proof? We don't Need no Stinking Proof!

Question: What studies have proven that moisture migrates from the bottom of concrete as a vapor and migrates up through the surface of the concrete?

Answer: NONE

As of this writing, no such studies exist; yet this is considered sacrosanct when evaluating concrete surface moisture issues.

There have been some studies that "suggest" moisture might migrate from the bottom to the top, but from everything I've read, too many data disconnects exist that prove such assertions are ONLY opinions with no basis in fact.

If a study has x amount of moisture moving in and out of point A and there is a close approximation of this moisture moving in and out of point C, without data from point B, the origin of moisture moving from either point A or C is conjecture....PERIOD. If point B remains adiabatic, or even changes at a much slower and/or lower rate than either Point A or C, this disconnect leaves an unbridgeable information gap where assuming A moves to C or C moves to A has no supporting empirical data! This more suggests and actually HAS empirical data that the Point A and Point C surfaces are gradients and respond to their respective environments where the changes in environment govern the moisture ingress and egress, NOT migration THROUGH the concrete. This tendency is even increased as concrete develops hysteresis, where the ingress and egress of Point A and Point C are no longer correlative nor measurable using diffusion models.

Some suggest that a higher temperature with low RH can attract moisture from a cooler concrete surface. That is possible and can happen, but only in a very limited manner, whereas the preponderance of moisture migration is from the warmer ambient air into the cooler concrete.

Those who suggest the migration of a humid cool concrete towards a warmer, drier air do so based on a very linear premise that rarely, if ever exists in field conditions.

ANY and ALL hygroscopic materials within the concrete surface will inhibit ANY movement of moisture from the concrete to the ambient condition, irrespective of the temperature, particularly if any alkaline salts are contained in the concrete surface.

In an unobstructed environment, devoid of hygroscopic materials, moisture can, in a limited fashion, migrate from the concrete to the ambient air as outgassing...this is actually where the difference between moisture in a liquid form versus a gaseous form REALLY needs to be fully understood to be fully appreciated.

From Liquid to Steam then Vapor

Back in the mid 1970's I studied "Fire Science" as I initially intended to become a fireman.

In these studies, one of the lessons taught that was very profound to me was just how dangerous steam explosions were, particularly in a metal processing environment.

The melted metal baths are extremely hot as it was pointed out that a single cup of liquid water can produce the equivalent of 1,500 cups of water vapor/steam if water should somehow contact the molten metal.

An instant displacement like that produces and very forceful and very dangerous explosion....this points out a very important fact that it takes VERY little liquid water to produce a LOT of water vapor!

Water Vapor, By the Numbers

In most manufacturers instructions and within ASTM for flooring installations, the allowable temperature range for a "safe" installation of a flooring material is within a 65oF-85oF range.

Consider that the warmer the air, the more water vapor it can "hold".

Understanding that, let's take the 85oF upper limit since this would potentially produce the highest volume of water vapor at 99% RH. This "high level" is slightly less than 27 grains of water per pound of dry air.

One pound of dry air is slightly more than 13 cubic feet of air space. So this 99% RH equates to 27 grains of water in 13 cubic feet of air space at an 85oF temperature.

Liquid water is 7,000 grains per pound, a gallon of water weighs 8.34 lbs, which equates to slightly more than 58,000 grains of water.

If a calcium chloride test is used and measures 3 lbs. of moisture emitting from a concrete surface, that surface is considered "dry" and safe for a flooring installation.

Here is where the difference becomes startling; 3 lbs. of moisture equates to 21,000 grains of water...and that is a safe level, yet, when using an RH Probe, 27 grains of water is the upper measurable limit within the capacity of an RH sensor, and is somehow found its way into virtually ALL flooring manufacturer's guidelines!

A "dry" calcium chloride measurement, suitable for a flooring installation contains more than 700 times as much moisture as an "excessive" and "unsafe" moisture level when measured by a RH probe, according to manufacturer's requirements.

Nonsense/Non-Science facts

One very poor example used by those who don't really understand concrete very well, is the claim that calcium chloride "over-dries" the concrete and exaggerates the volume of moisture in the concrete.

For those who claim that as a "fact"; calcium chloride has a critical humidity threshold of 18% RH, which means is will absorb any moisture when the humidity is above 18%. The two main alkaline components in concrete have much lower critical humidity thresholds than calcium chloride, with calcium hydroxide at 12% and sodium hydroxide at less than 9%...which means these will absorb moisture an time the RH is above 9% and then 12%.

This "tag-team" prevents the calcium chloride from removing all the moisture from the concrete, the alkaline salts will retain moisture that calcium chloride is incapable of absorbing...in other words, alkaline concrete will prevent a calcium chloride test from absorbing moisture as it is also fighting the natural hygroscopicity of other concrete components that reduce the ability of calcium chloride to readily absorb moisture. Hygroscopic materials resist free evaporation, which in turn reduces the volume of moisture that can be absorbed by the ASTM F1869 procedure in the 60-72 hour time frame. NOTE: As moisture is extracted from the concrete surface, this also increases the concentration of alkalinity, which increasingly diminishes the ability of either calcium chloride and more so, the RH Probes from measuring the moisture content of concrete.

One more Example

A basic example used in classrooms to demonstrate the humidity buffering capacity of fabrics shows how deceptive a "quantification" claim and why RH measurements are NOT "quantifiable" as incorrectly noted in ASTM F2170.

A 2 cup container is humidified until it reaches 90% and is sealed to preserve the moisture content. If kept at a constant temperature, the humidity remains at 90%.

However, when a small amount of cotton, weighing 10 grams is added to this container, the RH is reduced dramatically to around 60%.

So according to the RH sensor, there is less moisture in the container, even though the moisture volume remains EXACTLY the same. Cotton is hygroscopic, so it attracts water vapor that is no longer measurable with ANY form of RH measuring device.

Did You Know?

We are incorrectly taught that chemical reactions are linear...that is seldom, if ever an accurate assessment:

Low concentrations of sodium hydroxide can reduce the freezing point of water down to -20oF and conversely, high concentrations of sodium hydroxide can raise the freezing point of water to over 100oF?

Calcium chloride at 2-3% can accelerate the hardening of concrete by as much as 300%, yet at concentrations of calcium chloride lower than 0.05%, the rate of hardening is reduced to less than half.

High concentrations of sugar dissolved in water can greatly retard the rate of concrete hardening and is an "old school" method of creating a decorative exposed aggregate surface. Yet in low concentrations, this same sugar will accelerate rather than retard the set of the concrete.

In the presence of sodium hydroxide, the solubility of calcium hydroxide can be severely retarded, preventing pozzolans or SCM from effectively reacting to form additional and beneficial cementitious products. The pozzolans and SCM material can NOW become deleterious since these are hygroscopic materials that DIDN'T form the needed functions and can accelerate autogenous self-desiccation, increasing the permeability, porosity and weakening the concrete surface.

Basics NEED to be taught in Certification Schools

There are so many basics that are NOT being taught in certification schools, most are given a certification and sent out to test and measure a substrate they have little or no understanding of.

This article is only the very "tip of the iceberg" to what is needed before ANYONE can properly interpret test data, much less recommend any form of remediation.

A project 10 years ago, I received a near panic phone call where a three story project was stated to have excess moisture on all three floors and the inspector recommended a moisture mitigation system that would have delayed the opening of the building by 3-4 months and cost over $900,000 to install.

Following my advice, over the phone and not needing to be physically present after all the pertinent data was conveyed to me, the procedures corrected the site conditions, which were continuously monitored during the entire installation.

The result? No floor failure, even 10 years later.

Would the mitigation have worked? I am sure it would have...but a cost of close to a million dollars when a nearly no-cost (and no delay) alternative was available.