Ready Mixed Concrete
Field: Cast-In-Place Performance
Miracon’s® system dramatically helps reduce the number of variables that are often major factors in the making and delivery of everyday air entrained concrete. For starters, re: ToughAir® or CapCell®, none are affected by the most common factor that affects all other air entrainers – i.e. temperature changes. A 20⁰F swing – which is easily recorded in every market on virtually every day – will change the loading requirement of ALL other air entrainers to some uncertain amount ; and this could mean changing the loading or dosage rate of the air entrainer by a factor of 2 times…..and this is always just a guess. But guess wrong and the air in the concrete could miss the design spec by the same factor, i.e. by 2 times.
The impact of this constantly moving target is often routinely documented by variations in strength and/or Freeze-Thaw failures due to insufficient (good) air volume. Miracon’s® ToughAir® or CapCell® are not affected by climate temperature changes – at all . There is a pretty long list of other factors which predictably make all other air entrainers unpredictable; most of these, again, have little, if any, effect on Miracon’s® products.
Major changes in the Carbon within fly ash can have some effect any air entrainer – but with our’s it is many times less than any other air entrainer. Cement volume in a mix design is not a factor in determining the dosage or loading rate of ToughAir® or CapCell®. All other air entrainers require attachment to the cement particle(s) to stabilize…. which in turn makes the concrete sticky and drag. Miracon’s® air entrainment products do not require attachment to the cement particle – and they are simply loaded on a volume basis. So, in a particular mix, if cement is increased or decreased (in that same mix) no change in the loading rate of our product will be needed.
So, what does affect our entrainment system? It has been observed that very low slump concrete (i.e. 2”and below) will often require a higher loading rate of Miracon®; however, typically past this point, changes in slump, say going from a 3 1/2” slump to a 7 1/2” slump does not require a loading rate change of Miracon’s® air entrainer product. Note that entrapped air may change due to material properties, slump and/or other changes, and while this is not considered “good air”, it needs to be identified for performance re: freeze-thaw, pumping, etc. to be optimized.
For the most part, the most influential factor in determining the required loading rate of “good air” such as ToughAir® or CapCell® has to do with the (sand and rock) matrix. It is this matrix which supports any/our air entrainer and will therefore have an effect on the yield. Importantly, though, with our system this is not a fine line to walk – at least from the standpoint that if the sand and/or rock F.M. changes a little or the blend of sand and rock changes by only several percentage points – typically no change in ToughAir® or CapCell® is observed. So, based upon these guidelines, once the dosage or loading rate of Miracon’s® product is determined for a given mix, then that dosage/loading rate should be repeatable – Winter, Spring, Summer, Fall.
Above is a picture taken during placement of a concrete job at Pearl Harbor. A nuclear submarine docking station wall was built by placing 4,000 cu. yds. of 68pcf (55% entrainment) concrete – all placed underwater at depth of 28 feet at the base of the wall.
Air Stability With Transit Time
Besides the influence that any change in temperature has on ALL other air entrainers, the other routine/unpredictable variable has to do with transit time and/or transit time combined with delays or simply time on the job. And while we accept that if a mix is unstable from a design standpoint it is difficult to make anything predictable, including entrained air, stability with transit time/time on the job is just not typically a problem with ToughAir® or CapCell®.
Our products should be very predictable and stable - from the time they are batched to the time they are placed. Again, entrapped air can and is often lost through transit time or pumping or other, but if a mix is relatively balanced in terms of its design, then Miracon’s® products should be predictable not only at the plant, but on the job as well.
Controlled Low Strength Concrete. This is a product category that exists and is needed in every market , every day. D.O.T.’s often need to dig in roads/streets to repair or replace utilities. Ability to excavate and fill quickly, all with the idea that probable future excavation means the concrete fill needs to designed to be excavatable with a backhoe.
• What really differentiates our product is how fast it applies. Because our product has sheer-thinning/visco-elastic properties it goes on a vertical surface and then thickens and does not want to sag. So, the applicator can go much faster. And because it thickens immediately as it goes on the wall, there is a significant reduction in rebound.
Drill shafts that are more than 70 or 80 feet deep and more than 5 or 6 feet wide can be really difficult because they typically use a tremie application where initial concrete is placed at the bottom and the pattern of the mix placement is from bottom to top. So flow or rheology is really important. Either after, or even before the concrete is placed in the shaft, a steel rebar reinforcement cage is lowered through the concrete mix.
The primary, universal, reason for using air entrainment in Bridges/Bridge Decks is very much the same as to why it is used in all other concrete infrastructure – i.e. to relieve internal pressure in any concrete when it freezes.
Most concrete producers, even those that routinely make structural lightweight, find this category of product extremely challenging not only to make, but to control. In fact, this is the category where Miracon® ToughAir® or CapCell® are ideally suited to optimize for certainly strength, other performance properties, and ease of predictably manufacturing end-product.
With ALL other air entrainers, producers need to guess at how much entrained air will be lost when going through a pump. With Miracon’s® polymer air entrainer products, typically the only air lost through the pump is the entrapped air.