pH Testing of Concrete - How it can be made more meaningful

In the past and currently, many flooring and adhesive manufacturers have required pH testing, which has produced confounding results since damage to flooring materials isn't always aligned with the pH test methods.

In the past, the ONLY reason I would perform pH testing was to ensure that whatever surface was being evaluated was actually concrete by using a pH of 9 as the low number to ensure the surface was indeed exposed concrete.

I sat in the audience where pH was inadvertently taught incorrectly, where slide depicting a pH over concrete ranging from 7-8 was a suitably prepared surface for CaCl testing and other forms of evaluation. The pH of a fully carbonated concrete is approximately 9.45-9.5 or slightly higher. I have seen in print and mentioned often that carbonated concrete surfaces can have a pH lower than 9.

Although that assessment is accurate, it is also misleading.

If the pH is lower than 9, the concrete that is exposed is contaminated. There are few interior surfaces that will pick up environmental contaminants ranging from dust to dandruff more efficiently or effectively than concrete. When soil, oil or other contaminant is present, even in trace amounts, this contamination becomes imbedded.

Because much or all of this embedded contamination isn't visible as someone would see on kitchen counters, desktops, etc., imagine those surfaces left for months without dusting. Even a weeks worth of dust if you wipe a finger or cloth over it, adheres tenaciously to the finger or cloth. ALL that accumulated contamination MUST be removed before unadulterated concrete surfaces are exposed.

Elevating the methodology in pH Testing to include the relative alkalinity contribution

Fully carbonated concrete can have a range of pH between 9 and 12. That isn't a misprint.

Most have established 9 as "carbonated concrete" with a pH of 12 being considered "non-carbonated" concrete, which is an errant assumption.

There are two hydroxyl ions common to concrete; calcium hydroxide (cement by-product) and sodium hydroxide (in higher volume since EPA requirements have been enacted for addition of CKD - Cement Kiln Dust).

When calcium hydroxide absorbs carbon dioxide, which is generally a slow process, the calcium hydroxide absorbs carbon dioxide to produce calcium carbonate. Calcium carbonate for practical purposes is nearly insoluble, so adding water should NOT produce a measurable pH. However, as calcium carbonate is exposed to cooler water, this can convert at least SOME of the calcium carbonate to calcium bi-carbonate, which has a pH ranging from 8-10. In an open environment, the pH can be lower, but in an alkaline environment such as concrete, this condition would likely manifest only in matured concrete that has been in place for a couple decades or longer.

So when the carbonated layer reveals a pH of 9, that is an indirect measurement of calcium carbonate. Temperatures can effect the pH readings, which is yet another reason pH measurements can be confusing.

When evaluating carbonated concrete, the elephant in the room is sodium hydroxide. When sodium hydroxide reacts with carbon dioxide, it also converts to a carbonate form; sodium carbonate. Unlike calcium carbonate, sodium carbonate is VERY water soluble and can have a pH averaging in the range of 10-12.

Under normal environmental conditions, any sodium carbonate tends to wash out of a concrete surface due to its high solubility and high mobility. THIS is seldom if EVER considered in ANY evaluation of concrete, or its effect on moisture testing!

Elevating the pH Method to include presence of alkalinity

Way too many believe that high pH and high alkalinity are interchangeable terms, even as these terms mean something COMPLETELY different; with these differences having a profound effect in all levels of moisture testing, site conditions and suitability for the flooring components.

I was recently involved with a project where a sodium silicate was used as an admixture, purportedly to "prevent excess vapor emission or moisture related flooring failures". First off, such claims are absolute BULLSHIT!

Adding a sodium silicate to concrete as an admixture will increase the sodium ion content, along with an increase, NOT DECREASE in alkalinity (another BULLSHIT claim).

Additionally, sodium silicate will tend to thicken the concrete mixture and accelerate the concrete set, particularly in elevated temperatures. This will produce areas of variable sodium ion content that can range from little to no effect on a flooring assembly through the production of significant and dramatic damage to the flooring assembly.

The project brought in one of the three largest concrete testing firms in the U.S., with the client asking me to give them a script for information needed to gather in either proving or disproving the variability of the sodium content and its relationship to the damaged flooring assembly. Unfortunately this lab could not differentiate sodium carbonate from sodium hydroxide, which was a bit of a dissapointment to me, but the crux of the matter actually dealt with BOTH forms of the anticipated sodium content consisting of sodium carbonate and sodium hydroxide.

I had them core areas where there was no evidence of flooring distress (to establish a relative baseline), areas where there was some visible distress as well as areas where the flooring distress was significant.

We numbered the samples with no identification of from where these were removed to prevent any form of predisposition of what we SHOULD find versus what we actually DID find.

The pH test was set-up as follows: for each area, I had them place over-the-counter "plumber's putty to the concrete surface in an area approximately the size of a US quarter. In each area, 0.5 mL of water (distilled) was added and a pH indicator was used (hydrion strips, for uniformity) to test the pH. I cannot emphasis enough to NOT use tap water, EVER!.

After adding the 0.5 mL of water and the initial measurement, an additional 0.5 mL of water was then added and retested.

These steps were repeated until a notable drop in pH to what would "normally" constitute a carbonated concrete was reached.

Although there was some variability, there appeared to be a reasonable consistency in the amount of added water needed to bring the pH down to 9, relative to the visible damage to the flooring assembly.

In the non-damaged areas, adding 0.5 mL between 1-3 times decreased the pH to 9. In the moderately damages areas, it took between 5-7 additions of the 0.5 mL water to bring the pH to 9, and in the severely damaged areas, it took between 8-15 steps using the 0.5 mL water to bring the pH down to 9.

This is a practical and useful way to clearly indicate the differences between high pH and highly alkaline concrete. Even when the initial pH reading appeared to be identical, the repeated additions of water clearly indicated the buffering/concentration of the sodium ion in that specific area.

ASTM F 710 Committee, are you listening?

In its current form, pH testing has been of questionable value, even as it does produce potential red flags in a site condition.

In my view, the pH methodology has MUCH more potential in establishing a meaningful standard, or at the very least, can establish ranges suitable for the different types of flooring assemblies.

By creating repeatable methodology, a manufacturer, installer, inspector, etc. can quickly and easily determine if a pH of 13 is a concern, or even if a "lower" pH of 11 is a concern.

REMEMBER: pH, much like RH measurements can reveal the presence of, just not how much is there.

Precaution: NOT taught, yet can be vitally important is to note color changes that may occur before the "final pH" measurement has been completed. These can indicate other influences can be otherwise obscured if ONLY the final color change is noted.

NOTE: I am going to ask Carl Bredl to comment here, he has extensive experience and MANY photos showing multiple if not outright bizarre color changes using litmus paper.

Additional Precaution(s): Depending upon the type, location and volume of an alkaline component, the concrete and air temperature can produce vastly different pH results as some of the calcium components become more soluble as temperatures decrease, whereas sodium components become more soluble as temperatures increase, with the sodium inhibiting the calcium components as temperatures increase, creating potential areas of cross over where the conditions at time of installation may be outside of the temperature ranges that were present during the pH testing.