Reading these posts is a little like listening to pre-pubescent boys bragging about how much stronger is their older brother, or how much faster is their father's car.
If an ICF is so poor that it fails frequently it will quickly go the way of the Dodo.
I have worked with a lot of different ICFs. Some gave me frequent blowouts, some delivered fewer blowouts, and my most recent ICF has not presented me with a blowout in 8 years.
It is not the ICF which dictates what you're to do when introducing concrete, but ACI 318. Follow these directives, finish your pour, deliver your project to your client, relax & go home.
Proselytizing is fine, but knocking someone else because he (she) doesn't agree that your form of choice is the best, tends to be dictatorial (stupid).
In other words, grow up people. Use the form you like and trust , & move on with your lives.
FM

My understanding is that the withdrawal rate of the vibrator is also critical (3" per second). So 16+ seconds for a 4' lift. That's much longer than it sounds.

Jonr,

The withdrawal rate of the vibrator should always be slightly slower than the rate that air escapes the concrete.  I think 3" per second is about right for most mixes.  However, thinner mixes can be vibrated quicker than stiff mixes.

If anyone doe not believe concrete in a narrow wall form congested with rebar needs to be vibrated, then just watch how much the concrete settles down into the form after it is vibrated.  Many times I have seen the concrete settle at least 6 inches in 8" metal forms.  I would suspect that the typical mix of concrete placed in ICF forms would settle more so since the forms are not as slick as metal.

The recomended drop height for concrete is 10 ft after that you start to get graveling with the cement separating from the aggregate, the stones drop to the bottom of the pour with the cement sticking to the form walls. I know Mark Ross has written about this and included pictures. Plus how do you vibrate 20 ft high walls even Arnold couldn't raise and lower a vibrator that much.

Posted By smartwall on 30 Nov 2011 08:36 AM
Accepted practice is 4 foot lifts and somehow Nudura can pour 40 and 35 foot pous in 2 lifts with the concrete magically jumping over the webs. I'm not buying it. The Nudura form has a restrictive web which keeps concrete from flowing as easily as other forms and your telling me that those walls have no voids BS.

It looks like this may have already been clarified by others but I wanted to make sure a couple of things are clear.  

There is no 4 foot lift accepted practice.  This is sometimes misunderstood.   Every now and then I run into a building inspector that wants our installers to pour four feet and send the pump truck home to come back a day or two later to pour four more feet --- and thats just not the ways its done.    Probably what you are referring to is ACI 4 foot lifts per hour.  This has little to do with the block etc, and everything to do with proper vibration.    I never said that I poured 40 feet in two lifts -- I said I've poured 40 feet in two pours.    A pour consists of several 4 foot lifts --- each approximately one hour apart.

Furthermore, should you attempt a high pour make sure you have pour holes (to prevent getting the rebar dirty prematurely) i've built wood chutes in the past a time or two and vibrator holes to insert the vibrator inside the wall.  Also, you will want 4000-5000 psi with a high 6-7 slump.   You can use an excellerator instead of higher psi but the high psi benefit will stay with your wall and may actually cost less than the accellerator.   Don't attempt in 100+ degree weather.

Regarding voids -- these walls were extensively cut open and proded to find no voids -- also this particular job was jam packed full of pilasters.   This is a 16'5" foot wall (Nudura is 18" tall) showing pilasters to the inside.   We have another job in Arlington right now that has exposed pilasters to 55 feet.   When pilasters are fully exposed you know its right.  Regards.

      

 

Here are a few more examples -- the triagular pilaster was 18 feet tall (single pour --several lifts) and rectangular pilaster are currently 16'6" (single pour -several lifts) and on the way to 53 feet.   Regards.

Realistically, what are the consequences of small void areas in 6" or 8" or thicker flat panel ICF walls in residential construction?

Compare that to say a screen grid ICF wall in which 50% or more of the wall area may be void of concrete by design.

See the following comparison of the structural load resistance of various types of ICF walls vs. Steel & Wood-Frame walls:

http://www.cement.org/homes/brief08.asp

Posted By arkie6 on 01 Dec 2011 02:28 PM
Realistically, what are the consequences of small void areas in 6" or 8" or thicker flat panel ICF walls in residential construction?

Compare that to say a screen grid ICF wall in which 50% or more of the wall area may be void of concrete by design.

See the following comparison of the structural load resistance of various types of ICF walls vs. Steel & Wood-Frame walls:

http://www.cement.org/homes/brief08.asp

It can be significant depending WHERE the void is. If the void is small and somewhere in the middle of a wall that is not bearing any load/2nd floor, the consequences would be non-existent. If the void was somewhere that a 2nd story floor joist would attach to, then the consequences would be major. It could cause the joist attachment to fail and cause the floor joist to drop. This can cause some serious injuries, death or structural failure. A void in a corner can be catastrophic.

The structural load of ICF is only as good as the concrete pour itself. If it is full of voids, the structural load can be LESS than that of a steel or wood framed wall. ICF walls and their thickness/weight can be detrimental just as much as they can be beneficial when voids are present. Concrete is only as strong as the sum of its entire structure.

I would rather take a 2x6 wood framed wall that was sheared with OSB than an ICF wall that is full of voids. The wood frame wall would outperform and be safer than that ICF wall full of voids.

I talked to guys who worked with concrete their entire lives, especially in commercial fields. To them, vibrating concrete is not optional, it is mandatory when poured into forms. When I told one such guy that in some ICF applications, they don't vibrate, he was shocked to hear that.

According to concrete engineers:

"Concrete, when placed in a form will not flow into a homogeneous solution and fill all voids and hollows. Left alone, it will leave large air gaps, especially around wire mesh and re-bar. Wet concrete may have as much as 20% of it's volume made up of trapped air. This trapped air reduces the density of the concrete, which equates to lower strength and an increase in the concrete's ability to have water permeate through it."


Think about that, 20% of wet concrete's volume can be trapped air. I am confident in Portland Cement's study on ICF and the potential for voids within ICF's. To them, as for me, vibrating ICF is mandatory and utilizing internal vibrating techniques is the way I would go.

Otherwise, why risk failure? Might as well go back to the tried & true 2x6 wood construction. What you see is what you get with wood construction. No guessing what is behind the EPS, 6" of concrete or a big gaping void of air.

At the risk of getting bashed for double posting here is what I wrote in the "Storm Shelter" thread.

When we were pouring the walls of my house I grabbed the vibrator and started to vibrate. The concrete contractor said not to do that, the risk of blow outs was too great. He used the vibrator at the corners and to flow the concrete under the windows. He ordered the concrete so it would around 6" slump out of the hose and with 3/8" aggregate. He had the plant make it a 6 bag mix. The heavier cement content aided in the flow. I found no voids anywhere with a probe or when putting anchor bolts into the wall. I'm sure the concrete had some air entrained in it, but I have to ask, "So what?"

Let's look at the impact on strength by entraining air, having voids, or using a high slump mix. The target is generally around 3000 psi or greater, right? As we all know, concrete has strength only in compression. On my house the gable wall at one end is 14' high. The total load, live and dead, at the footing is roughly 4500 psf, max. That is equal to 31 psi! Even if the concrete strength is reduced to 1500 psi by the air, voids, and slump, it still is 50 times greater than the load it is bearing. Why all the fuss about the effect of air, voids, and slump on concrete strength? Lateral strength is provided by the rebar and that changes very little regardless of concrete strength.

Based on my experience with one house, I say flowability is the paramount parameter to be concerned with. Vibrate as needed, but don't get wrapped around the rebar about vibrating. It ain't worth it.

No offense intended to anyone installing ICFs who maintains that with good concrete flowability you don't need to vibrate at all (and dmaceld- I concur in your defense that you did said vibrate as necessary) For those of us who have to tech support these jobs for a living and walk the line between residential and commercial, I ascribe more to the internal vibration line of thinking than not, as it goes back to ACI practices and company liability when and if you EVER encounter even ONE job that went sour because of voids. It's pretty cliche but here ---- Best offense is a good defense. A strong enough form system and following the manufacturers instructions for required form support and vibration techniques makes the use of an appropriately sized internal vibrator on your installation a much smaller risk than attempting an install without it.

Think about that, 20% of wet concrete's volume can be trapped air. I am confident in Portland Cement's study on ICF and the potential for voids within ICF's. To them, as for me, vibrating ICF is mandatory and utilizing internal vibrating techniques is the way I would go.

I think you need to see some experienced ICF contractors do their pours. Conventional forms are very forgiving, allowing you to just flow the concrete in and vibrate to take care of any problems caused by lazy technique. On an ICF pour, the hose is kept moving all the time The concrete is "placed", not so much "allowed to flow", it probably goes in more slowly than you are used to. You SEE everywhere that the concrete is going. There is very little chance for error except when attention is allowed to wander. If the pump truck operator is trained well, he will stop the flow if he sees that happening.

Moreover, if you suspect a void, it's not the end of the world. You just pop a hole and squeeze some grout in to fix it.

Hi Lbear, You ask how one can fill a wall without voids? In 2004 I was on a site and they used 3000 psi grout, not concrete. No voids. No vibrators used. Would I recommend this? Probably not due to cost, but the installers were used to masonry and that is what they ordered....hope the pic attach ok - shows the height of the pour and how well the wall filled. Lowest void visible at the 8 foot mark. Cheers,

no pic, sorry. less than 100kb, no luck, sorry guys. not letting me insert the 64kb file....

Draftman56,

Very well stated.  Kind and diplomatic.  No one should take offense.

I see this forum is about more than advertising a product or service.  I see this forum as a great place to learn how and why others are using the methods and products they do.  Experienced professionals sharing hard-earned insight can be valuable to the tradesmen and building owners.  I think sharing of knowledge on this forum should be encouraged more so than pushing one product for every need.

Posted By Alton on 02 Dec 2011 10:25 AM
Draftman56,

Very well stated.  Kind and diplomatic.  No one should take offense.

I see this forum is about more than advertising a product or service.  I see this forum as a great place to learn how and why others are using the methods and products they do.  Experienced professionals sharing hard-earned insight can be valuable to the tradesmen and building owners.  I think sharing of knowledge on this forum should be encouraged more so than pushing one product for every need.

I agree. I think in my case had we vibrated everything I wouldn't have been so long on the concrete we ordered. The concrete contractor was pushing me toward to end to decide whether or not to call for the last load. I wanted to wait because it looked like the walls were filling faster than expected. I relented and called for the last load of 6 yds. You guessed it, we were six yds long. The entire load got dumped back at the plant. I went back and refined my wall volume calculations by accounting for window and door openings right down to the exact inch. I refined the block volume numbers and reduced them by 25 cf. In total, I reduced the volume calc from 44 cubic yds to 41 yds. I suspect the other 2 - 3 yd difference was because of the air that was trapped in the concrete. Don't recall what we added for pump loss and contingency. Probably a yard. Like I wrote above, I could not find any voids that would have explained the discrepancy. But when I did strip some foam off I could see all kinds of pin head and pencil eraser sized bubbles in the concrete. But again, in this kind of application I don't see where that is a problem.

I am going to see some ICF construction this week in person. Curious as to see them stack and re-bar it. They will pour this week also, so I will hopefully see them vibrate the mix and report back.

Keep an eye on our secure buildings web page. We will be updating it as the project progresses. This will illustrate how Polycrete handles extensive rebar. www.polycrete.us/Secure_Buildings.html

Is using an 8" slump common practice with ICF pours?

Posted By Lbear on 08 Dec 2011 07:24 PM
Is using an 8" slump common practice with ICF pours?

I hope not.  That's a code violation.  I believe a 6" slump is the highest allowed slump.  How did they achieve an 8" slump?  Water or admix?  Lemme guess, no vibration . . .