In the January issued of BD+C Magazine, there is an article entitled "13 Tips on Working with ICFs."

You can read the article here:
http://www.bdcnetwork.com/article/CA6627257.html?q=icf

Bruce

Wow, I'm suprised at tip #3.

 

Bunt

Rob Miller, PE, should have his license yanked for his statement. As a Civil PE, seeing a statement like that infuriates me. Increasing the PSI of the concrete mix has no bearing on optimum water to cement ratios and the workability of a mix. Mechanical vibration and admixtures such as Super-Plasticizers are the order of the day for ensuring a void free pour.

I think all he was saying was that because a higher slump is weaker, start off with a higher strength concrete so it remains strong. Also at least through a pump truck the more portland the better it flows, compared to the same mix design and slump with less portland.

Personally I have never added any admixtures in ICF mud. The right aggregate and slump for the form size and design, with vibration as needed. If only the drivers could get the slump right.

The problem with that is that concrete loses strength rapidly once the mix is raised over the optimum water to cement ratio. So, start with a 3500psi mix with the thought that you add some water to lower the slump enough to not require mechanical vibration. You quickly drop your concrete strength below 3000 even 2500 psi, with much more variability in the mix. ICF mud is a great application for a super-P - you should try it. BTW - a driver shouldn't have ANYTHING to do with the slump. That is a component of the mix design that is determined in conjunction with the daily bulk density of the aggregates, the amount of moisture in the stone and sand piles, and a few other things. The only thing a driver ever does by adding water is to weaken the concrete. Finishers love it, but they don't give a crap about the quality of the concrete, just that the top looks smooth.

On too many occassions I have found that minimum PSI strength is ordered and then more water added at the job site to make it easier on the concrete crew.  Crews should concentrate on ordering the correct slump and PSI.

It is nice in theory to order the slump you want. But the ready mix suppliers try to anticipate how much the slump will reduce on the road and so I have better luck in ordering a 4-5" and making it what I want when I have it on site.

Like last week, I ordered a 5" figuring I may have to make it a 5.5-6", but it came at more like a 7". The owner of the ready mix company said next time we will make it a 3-4" slump.

“Increasing the strength of the cement mixture allows you to add more water without deteriorating the mix,” says Miller, whose firm specializes in commercial ICF design and engineering. “The result is a concrete that will flow better and avoid potential voids in the ICF walls.”

Sorry but......LOL!!!


I think the article is decently written but again like others have said #3 is a no-no and is misleading. The infamous block and hammer technique, the external sawsall vibrator or the misconception of 'good' flowing concrete out of the hose are the reasons why the ICF industry unfortunately has had its pitfall/horror stories of bad results. Many (including myself) consider ICFs to be superior to any other wall construction method out there, but proper/accurate placement of the concrete in ICFs is really what the industry and all professionals need to strive toward in perfecting.

We use a special 4500psi - ICF mix from our redi-mix supplier. Most of the time it comes in right at a 5.5-6" slump and pours very nice. I internally vibrate all of my walls, regardless of how 'good' my mix is flowing. It is the only way to minimize segregation of the aggregate at the bottom of the wall and minimize/eliminate the potential for voids.

This should be a must read for all on this board: http://www.cement.org/bookstore/download.asp?mediatypeid=1&id=3871&itemid=RD134 (pdf download)