The Undermining of Concrete Research - Example: NIST 1999 State of the Art Report on Concrete

Having gone over the mostly useful report published by NIST, which included concrete research from all over the globe, there are consistencies within the studies that produces a ceiling that should not exist when gathering and evaluating data for analyzing concrete, particularly for methods and materials that can help us to better understand why concrete doesn't last as long as it did in the past, and why the "improved" concrete designs in the field are NOT performing as indicated from laboratory studies.

Truncated Data Used for a "Non-Truncated" Reality

My ongoing issue with laboratory work, is when elements are controlled as closely as they are, this is an inherent truncation of influences that can and usually ARE critical to understanding what is actually happening in the field.

In the past, laboratory tests were used primarily to better understand what would be observed in the real world. As testing became more sophisticated, laboratory work revealed much of what we didn't understand.

This somehow morphed into products, methodologies, processes, etc. being tested BEFORE use, and using laboratory testing as the bar that must be cleared BEFORE a product, process or methodology is used.

This over-reliance of "qualifying" under lab conditions has been at least as curtailing to progress as it has been to understanding of how things "work".

My favorite example (I will not use any names to protect the innocent and "not-so-innocent") involved a Transportation Department who decided on a sweeping upgrade to their qualification (testing) programs.

This department had successfully been using an "old school" product that had proven to be a benchmark standard that gave them excellent results for an acceptable amount of time.

It was decided to run this product through the new qualification program..there was a problem....the successfully used product failed and failed BADLY under this new program.

They wondered if it were some anomaly and repeated the testing another two times, same result and in comparison to some of the products that failed, this product with a proven track record was near the bottom of the failed products...in other words, if they hadn't already had decades of experience with this product, it NEVER would have been used.

Rather than scrap the "new and improved" testing program, they simply "grandfathered" this product through and from my understanding, continue to use a product that would have failed their "new and improved" evaluation!

Self Desiccating Concrete Issue

The 1999 report very clearly produced some excellent information of how the lower water-cement ratio concrete that SHOULD be a significant improvement over the higher water-cement ratio concrete of the past, have not proven to be anything but more expensive.

The durability goals are not and WILL NOT be met until these researchers and those requesting such research pull their collective heads out of the sand.

Until recent studies that incorporate embedded humidity measurements and thermocouples have been used to evaluate the progression of concrete curing and with the study conducted by the Texas Transportation Institute, it was thought (ASSUMED) that curing the concrete with water (preferably) for several days, or the application of a topical curing agent would produce a durable concrete surface.

Adding to the problem(s) and complexities, speculative theorems were injected into the collective hive mind where speculation became facts, at the expense of producing a more durable concrete directive.

Some of the collateral damage included absorptive aggregate, where articles in industry respected magazines and journals, incorrectly identified absorptive aggregate as detrimental to concrete quality and that absorptive aggregated increased the water-cement ratio of concrete...neither speculation was accurate.

Without admission of "gee we screwed up" we are seeing more and more research on materials that WILL hold water independent of the designed water-cement ratio and that the absorptive aggregate, when properly used, helped to reduce the effects of self-desiccation.

Most of these technologies have proven to be helpful, but the only SURE way to correct the self desiccation is to make concrete self/internally cured.

Again, we find researchers tripping over each other by repeating one of my pet peeves, which is myopically directed research. The key(s) to correcting self-desiccation are are multi-directive, NOT a single directive. Many of the SAP's (Super Absorptive Polymers) reduce the self-desiccation, but having no other value than to provide additional moisture and too much can weaken the concrete and too little can cause uneven restraint within the concrete....along with a question I've yet to get a viable answer to: "what happens to these organic SAP's when they begin to degrade within the concrete, what potential detrimental effects might exist that hasn't been addressed in ANY of the research I've read?.

As I said...myopic approaches are a pet peeve of mine.

Matured Technology that worked in the past are likely more detrimental than helpful.

The problem with self-desiccation is simple...not enough water to physically contact the unhydrated clinker to form cement.

The default to make concrete denser, silica fume. slag, fly ash are used....this is yet another indication of a myopic view.

ALL of these additives require WATER....rather than helping to reduce self-desiccation, these make it worse! These are secondary/supplementary cement producing products that depend on the initial hydration of the primary cement to be effective!!!!

Adding these without the needed reaction produces a more permeable concrete since these pozzolans/SCMs are simply a fine aggregate that has been added to concrete that not only won't function properly, these will COMPETE for the available water, further reducing the moisture needed to form the primary cement. If something doesn't have enough water to begin with, WHY are we adding even MORE powder??? If anyone stops to think it through...there'd be a LOT of forehead slapping and the sound of Homer Simpson-like "dohs"!

Modern Problems are not solvable with technology developed for concrete we no longer use

When curing was first proposed and used, the cement of those days was very coarse and did not produce a lot of heat.

When it was found that a finer grind would gain strength faster and there was a targeted compressive value, less cement was needed. In the UK, the volume of cement decreased by 34% when a finer grind was introduced.

A benchmark of 28 days was established as sufficient to establish the serviceability and load bearing capacity of the concrete. Thus entered one of the then most useful, but now one of the most detrimental measurements in establishing durable concrete.

Enter the Dragon - More sodium hydroxide in cement

The EPA began to require CKD (cement kiln dust) be reincorporated back into cement production, which proceeded to make ALL cement more alkaline.

This alkaline was identified as sodium hydroxide, which FINALLY brings us back to the illustration and NIST reference.

The NIST identified sodium hydroxide in a very limited way and by the use of truncated data, has managed to throw off virtually every researcher that depends on such information to be factual and true.

According to the NIST, sodium hydroxide acts as an antifreeze and quickly dismissed it as any kind of influence, much less a detrimental influence (with many assuming a pH of 12.5 was "normal and assumed this high pH was the presence of calcium hydroxide, again a misjudgment/assumption caused by use of truncated data!!!!

The NIST ASSUMED sodium hydroxide remained in a somewhat dilute form, and when diluted, will lower the freeze point of water (acting very similarly to a deicing salt)...however, as the sodium hydroxide continues to become more concentrated (such as a lower moisture volume at time of curing would produce), the sodium hydroxide switches roles and becomes a freeze initiator!

At 40% concentration, sodium hydroxide will raise the freeze point of water to 59oF, at 60%, the freeze point is raised to over 120oF.

What happens to the available moisture is a three-pronged monster for cement hydration, 1. a 20% concentration will reduce the RH of concrete to 78% cement formation ceases when the RH drops to below 80% RH; 2. The increased alkalinity temporarily binds the water, making it unavailable to the unhydrated cement and 3. The presence of sodium hydroxide reduces the solubility of calcium hydroxide, making any and all dry-added pozzolans and SCM's unable to react with calcium hydroxide.

Believe it or not, even the second portion of the graphic is truncated. Higher concentrations of sodium hydroxide in water can raise the freeze point to a point higher than the normal boiling point of water! NOTE: Those who distribute bulk sodium hydroxide do so where the sodium hydroxide is at an approximate 40% concentration. The tank and lines are heated to 70oF to keep the product from "freezing" in the lines or during storage.

Conclusion

Laboratory results are NOT sacrosanct, one of my first "wake-up calls" in this was a lawsuit where I hired a very well respected petrographer in California. There were two other petrographers brought in...with all three having contradictory conclusions and the arguments over who was right or wrong got quite heated.

This forced us to bring the mediator out to the jobsite....all samples were cored at location directed by the respective clients, and two of the three samples were not truly representative of the problem as the cores were extracted from areas that were not in the direct area(s) of concern.