Insulated concrete forms and concrete placement

[markross]

In another website, there has been a tremendous amount of discussion about the type of concrete mix design to use in an ICF or insulated concrete form system (walls only). The concern is that there are no standards yet set for this. There is one unique aspect to a concrete form that causes standard water reducers and plasticizers to be detrimental during pours, and that is that the additive generates a co-hesive aspect to the mix, and as we cannot use release agents due to the form material components, it tends to cause a greavelling or seperation on initial placement at the bottom of the wall system. Even with proper consolodiation, which only packs large amounts of course aggregate at the bottom of the concrete mass, there is still a fair amount of seperation. Due to the interior structure of the forms, there is little room to manover a hose in the interior of the wall system (typically only 6" wide with substancial ties every 8" vertically and horizontally). We have reccomended standard 4" slump mixes and proper internal consoldation, however many of the form produced are not capable of taking the pressures induced on the system, blow outs and/or form bulging is common. Wet mixes enhance the bulging/blowout problems inversly with increased slump mixes. What mix designs allow for sufficient workablility with the lowest hydraulic stress placed on the forms??? These are typicall poured in lifts.

 

[borandin]

What are the defects in concrete due to the effect of the wether. I mean the effect after casting the concrete due to wether aspects like temperature, gases (like carbon dioxide) and others...etc.?

 

[jheidt2543]

I am not very familiar with the ICF system, but here are a few thoughts:

1. In my experiance, a 6" wall seems thin for a foundation wall, 8" is by far the most common.

2. If the addmixtures are causing the problem, I would revise the mix design.

3. Again, in my experiance, the two main causes of wall blowouts are pouring the concrete into the forms too fast and vibrating too much against the forms.

4. Whatever the form system used, the recomendations in ACI's Manual of Formwork Design, by Mary Hurd are still the best and surest way to form concrete.

Hope this helps in some way.

 

[markross]

Borandin. Actually, its mainly for residential use, so the effect of weather and such are negligagle. The EPS foam covers both the interior and exterior surfaces.

Jheidt: The problem is that the ICF's have a differing specification that is not covered in the ACI manual of formwork design. They may be the best and surest way to form concrete, however ICF construction is an animal unto its own. People purchase it mostly for the energy efficiency.

 

[jheidt2543]

Markross:

With all due respect, I think we are missing each other's points.

1. Any new structural system must be approved by the code authority and in the process the system manufacturer must produce supporting data. No matter what the system of construction is, it still must meet the local building code. Virtually all building codes refer to existing, proven, standard specifications and when it comes to concrete, ACI is the standard.

2. If a new system can't show that it meets existing codes it doesn't get approved and therefore eventually leaves the construction market to proven systems.

3. I would think the FIRST thing the ICF system would have to show is that you can pour concrete into it, used as formwork, in a safe way, without blowouts. The fact that your getting blowouts indicates something is wrong with either the way it is being used (most likely) or the way the system is designed (not as likely, but possible).

So, my comments were not meant to knock the product, but to help explain what I think could be the causes of the blowouts you noted, based on my experiance. After all, we are all captives of our experiance.

However, to say that because "ICF's have a differing specification that is not covered in the ACI manual of formwork design" misses the whole point of specifications! Any new system just can't make up it's own specification irrespective of existing codes.

Perhaps doing away with the admixtures and using a tremi (elephant trunk) when pouring would reduce the segregation of the mix?

Regards,

 

[markross]

No offence taken, I think I had better clarify.

The NES, BOCA, ICBO, Miami Dade and such approvals given to ICF forms, generally include a mix design which asks for a 6" Superplasticized slump of a 3/8" stone, standard 3,200 PSI (in most cases). The problem is that upon placement, the concrete gets dropped over 9'3" in most cases (normal wall height for these). The fluid pressures the ICF forms are asked to take, typically exceed 500 lbs per square foot. The forms are designed for about 400 Lbs per square foot. Then the vibrator starts its work, and the problem is enhanced.

As a huge supporter of ACI, We pour ours with a 3-1/2" slump, no additives, and vibrate properly with a pencil vibrator, then spot check the wall by removing foam in known trouble areas.

This has solved the problem for us, however most installers have problems with "graveling" at the bottom of the wall, voids and aggregate seperation. The plasticizer makes the portland co-heasive, and this causes all the course aggregate to collect in pockets at each lift of each pour. We have learned that standart ACI installation methods work well, however the approvals all state otherwise, and dont work as well. There are key differences between the two types of forms, and I just dont know if there is a catch all, since a lot of ICF is installed by unqualified contractors, who tend to go with the approved methods, without understanding them.

Thank you for your reply, I look forward to your new responce.

 

[jheidt2543]

markross,

Thanks for the added clarification. I agree and I think you have hit the nail on the head. The problems result from untrained concrete crews pouring too fast and without the proper equipment.

 

MarkRoss's observations are correct, and I do concur with all the related postings found on this thread. All of the "quality I.C.F.'s" have acheived the necessary applicable #'s as well as the code approvals. That being said, everything looks great on the drafting table and the specifications given for the mix design. Unfortunately( in my opinion) things do change when it is time for placement.
In almost every I.C.F. project, the placement of concrete is delivered via a pump from the chute of the ready mix truck- and time being money- it is expected that this be done quick. The truck dumps into the pump hopper which holds approx. 5 c.yds, and the pump delivers via hose to the wall. In my experiences, this is the problem of the initial segragation that can occur (irregardless of the slump)as the stone sinks to the bottom-and is the 1st thing that enters the pump inlet-and also the walls. My solution is to not let the hopper be filled more than it can deliver(in a timely manner). But alas, this always raises objections from the operators-because time is money, But so are blow outs and that is my bottom line. Take care all, Great site- Thanks ALL,Sincerely.

 

[jheidt2543]

Sorry, but I can't agree to blame the mix segregation on the pump! I've watched thousands of yards pumped into footings, walls, beams, columns and slabs; below grade, at grade and 3-4 stories above grade. If the concrete mix becomes too "stoney" it will plug the pump, which requires stopping the pump, pulling the pipe apart, cleaning it and then starting over. If the mix is too wet, the same thing happens, because the water is pushed through the mix and leaves the stone behind. It takes a well designed mix with a good cement "creme" to keep the concrete flowing through the pump lines. Whether you are using a 2" grout pump, a 4" or 6" concrete pump the mix design is what makes the difference. Communication between the ready-mix supplier and the field is one major key.

I do agree that mixing of various additives can cause some unintended problems and I agree that pouring the concrete too fast into the forms can cause form blowouts. In my experiance, when using new systems or methods it pays to have the manufacturer's representative on the site. A pre-pour meeting to layout the "game plan" before hand and some inspection and coaching during the pour is a real help to a crew that is working with a new system.