The Technology Exists, Why aren't we using it? Durable Concrete, What Needs to Change.

After reading yet another study that discusses "durable concrete", I was frustrated yet again by another hamster wheel of logic that continuously revolves, creating a lot of effort with very little, if any true progress.

Stepping On Toes

I realize that much of what I write is uncomfortable for many whose livelihoods depend on, or are based on the various industries being and remaining confused and uncertain about what should be done. If I step on a lot of toes, I remain unapologetic.

Rules and Requirements versus Reality and Progress

A few years ago, I was hired as a consultant for a concrete company that had a legitimately sound approach to creating what was essentially, a waterproof concrete.

Their carefully controlled approach created some very impressive results in laboratory and most importantly, field conditions.

Yet, due to incredibly myopic and flat-out wrong requirements, there were architectural firms that disallowed them from bidding on jobs since their product retained an internal humidity for several months.

Even though there was solid proof that no free water existed in this concrete, the obstinate refusal to budge from the "excessive" moisture of 90+% RH as a requirement, kept this viable technology from gaining traction.

A Work Around - Tricking the RH Probes

I was contacted to see if there was anything I could do to help. No matter how many facts I gave these architectural groups, they refused to move away from what everyone else was doing.

So rather than keep beating our heads against the wall, I suggested we "trick" the humidity tests since measurable humidity can be reduced by incorporating different salts into an interior environment.

When working with different industries, one of the most sophisticated when dealing with control of humidity and temperature control are museums.

Many rare and fragile artifacts can be easily damaged or even destroyed by sudden spikes in humidity. As a result, many of the encased artifacts have various methods of maintaining a fixed humidity, even as humidities would otherwise fluctuate.

I suggested adding a salt that could maintain an internal humidity between 80-85% RH, which would not only comply with the unyielding requirement by these architectural firms, but would also allow continued cement development.

NOTE: RH of lower than 80% will NOT allow formation or development of cement, which in and of itself undermines the ridiculous "requirement" by some to try and achieve an internal humidity of 75%. If 75% RH is achieved with newer concrete, congratulations, you've just created a permanent concrete problem!

Once we found a percentage of added salt that remained in this range, they began to add this to their product. Side-by-side, with the exact same amount of water, the concrete with the added salt had an internal humidity of 80-85%. The samples without the added salt retained a humidity level greater than 90% for 6 months.

So, did complying with this requirement create any benefit? NOPE...all it did was to bring into compliance with a moisture form not proven to cause flooring failures.

This product began to be used, but sparingly since the cost as compared to a standard Portland cement-based concrete was nearly three times the cost.

Fast-Forward to Now

In a recent PBS article, there is increasing interest in what is termed UHPC (Ultra high performance concrete) that is WAY more expensive, and in my view, only incrementally more durable than the concrete mix design mentioned above, but far less expensive.

The increasing pressure on sustainability has basically started a trend of looking at even prohibitively expensive technologies, where efforts to bring down costs are a priority.

Form the PBS article: UHPC, which was first developed several decades ago in Western Europe, is not just stronger than traditional concrete. It's also much more durable and less brittle, and the material is nearly impenetrable to water and chemicals like deicer.

UHPC has now been used in bridge projects in 28 other states and the District of Columbia, but mostly on a small scale. One of the main reasons? Cost. Traditional concrete is roughly $100 per cubic yard. Commercially available UHPC costs about $2,000 to $3,000 a cubic yard.

UHPC's current price tag makes it unaffordable for most government-funded infrastructure projects, but researchers around the country and here in Iowa are now working to bring those costs down.

Missing the Point

This ultra high performance concrete may be 5 to 10 times stronger, but will it be 5-10 times more durable? Not likely.

Current studies keep missing the point and focus on what they've always focused on, the 28 day compressive values.

These studies ALL, without ANY exception I've seen, haven't given much thought, if any as to WHY Portland cement concrete is less durable than in the past.

The other studies that ARE on the right track are those that focus on the initial curing of the concrete, why? Because these focus on the two most important issues governing concrete quality; Water to cement ratio and proper curing. The compressive strength tests do not!

Self Cure - Internal Cure

The surface gradient of concrete is the most important factor in environmental durability. A poorly cured surface allows ingress of water and contaminants, irrespective of how strong the concrete might be.

There have been promising studies regarding methods of internal curing and creating self-curing concrete. The biggest challenge for most of these promising steps is the uneven distribution of moisture, which can cause internal (differential) restraint for those areas that have little to no moisture containing particles or aggregate.

The most promising, and something I am solidly behind are nano colloidal silica.

The Promise - The Risk

One product I believe is way ahead of its competition is a company out of Indiana called Specification Products. I point them out due to the impressive amount of data and the millions of square feet and years of use to support the claims of a more durable concrete.

I consulted with them for a little over a year, and even though I am no longer a retained consultant, my interest in improving our various industries maintains my enthusiasm.

Place, Monitor, Prove

likewise, I have been approached by several companies that have or claim to have nano colloidal silica products, but the data is scant or non-existent....I'm sorry, but I am decades past the "trust me" phase and without sufficient proof, I will not accept any claims until proven.

There are even some that try and baffle me with BS, with some being unaware that I have decades of chemical and formulary experience with silicates, silica and concrete. NOTE: If a product has a pH in excess of 10.7, it CANNOT be a colloidal silica, it is a silicate, which behaves in a significantly different manner and should NEVER be used as a concrete admixture.

A TRULY effective nano colloidal silica is easy to monitor and prove based on some earlier theories I had developed that have shown a lot of promise as a quality assurance procedure for any specifier and/or owner.

It seems counter-intuitive that a product that adds water to concrete can actually produce concrete with lower moisture content than products that do not add water to concrete.

Without going into the why, how and what, the quickest way to ensure the rapid moisture reduction even as the concrete "should" register a higher moisture content is to use a Tramex concrete meter.

In two projects where the Tramex Concrete Meter was used, the E5 colloidal silica reduced the moisture content of the concrete to less than 5% within 14 days.

There was one project where some of the concrete did not get the E5 dosing, along side concrete that did; after 14 days, the areas with E5 were measuring less than 5%, whereas the concrete without were well over 6%.

Tp put this in perspective, several moisture insensitive adhesives that can be placed over a concrete surface with a Tramex Reading of 5% or lower.

Unlike poorly cured standard concrete surface where an increase of moisture will occur after placing the adhesive, this will NOT occur with the E5. The trend of lower moisture content due to ever increasing cement.

Therein lies the "secret". What would normally be unreacted cement and free moisture, is now chemically bound and now pat of the structure within the newly formed cement.

The ever reducing moisture volume has another un-researched beneficial effect, where these reactions take place on a nano scale, the moisture given off creates an evaporative cooling effect. The uniform dispersion and evaporative cooling effect are two reactions that have been ignored, even though these are critical to a durable concrete, particularly in elevated temperatures.

This is also why the other pozzolans and SCM materials cannot prevent the self-desiccation of the concrete surface, these COMPETE with the moisture available for primary cement development and do NOT add moisture within this critical area.

As the moisture content is consumed by the cement particle = more solids within the surface that cannot be dampened and will concentrate alkalinity = reduced RH = reduced cement formation = reduced pozzolan/SCM reaction.

Missing Pieces in Research

There are critical areas that HAVE to be explored for continuing research to provide remediation, or better yet, prevention of the accelerating issues;

1. Add 365 day compressive strength tests to the 28 day.
2. As proven by the Texas Transportation Institute (Dr. Zollinger), the top one inch of the concrete needs to be evaluated and compared with the full depth compressive strength tests.
3. The RH and temperature of the concrete, particularly the top one inch of the concrete needs to be evaluated immediately after placement and for several weeks afterwards.
4. The DRH (Deliquescent Relative Humidity) and ERH (Efflorescent Relative Humidity) of the salts contained in the concrete needs to be explored. "Deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH), the two parameters that regulate phase state and hygroscopicity of substances, play important roles in atmospheric science and many other fields." Yet these fundamental effects are NEVER considered. In fact, most concrete studies don't even differentiate that calcium hydroxide and sodium hydroxide respond in nearly diametrically opposition to each other with temperature, yet are consistently put in a nice, neat pile ignoring the temperature response differences and the solubility inhibiting effect sodium hydroxide has on calcium hydroxide.
5. Establish CRH (Critical Relative Humidity) AND the Humidity Fixed Points of salts solutions within concrete. There are already established humidity fixed points, which are used for the standard salt solutions used to calibrate humidity and moisture measuring devices. We don't have to re-invent the wheel, but we DO need to install these wheels onto this vehicle that isn't going anywhere!

Getting Technical

As illustrated in the photo accompanying this article, there are various conditions where water will NOT behave in a predictive manner, yet the researchers continue to ASSUME it does.

Salty water will not always mix readily with a fresher water, even vapors (including water vapor) can have their own gradients where differences will exist, yet again, it is assumed these simply go into equilibrium.

There are two phases of water that DO NOT behave in the same manner as water in a free system, and are heavily influenced by the chemistry of the concrete, this is adsorbed moisture and absorbed moisture.

Even chemicals when mixed can alter their properties dramatically. Calcium hydroxide becomes insoluble in the presence of sodium hydroxide.

The fertilizer Industry has noted that the CRH of chemicals can be dramatically altered to produce dampness whereas the non-combined components wold not create dampness (condensation).

TSP has a CRH of 80% RH at a temperature of 30oC (86oF), but when mixed with ammonium nitrate, the CRH decreases to 50%! In layman's terms, the TSP would liquify at RH values above 80%, but when mixed with the ammonium nitrate, the TSP would now liquify at a RH of 50%.

The Necessity of Modernization

Concrete is a material that has undergone MANY changes in cement grinding, cement additives, concrete additives, different aggregates, etc. But so little information exists on the long term effects, with many detrimental effects not being noted for months, years and even decades.

Even when discovered, some debates as the the mechanisms of damage are then debated for several more years, even decades.

What IS known however, if we modernize our testing and re-evaluate traditional testing and if some of these even have a place in our world, we can start improving the concrete.

In too may studies, where studies may claim 20 years of research, it is more like one year of research repeated for 20 years. If we dumb-down the research we also dumb down the concrete quality.