Why is bagged Quick Set concrete "not for structural use"? 3

[Tomfh]

Bagged quick set concrete always says "not for structural use". What is "structural use" in this context of bagged concrete? and why do they warn not to use it? Is it because of the way it tends to be used, e.g. with limited control of water content? Is it because of the speed of set, which make it difficult to place and consolidate prior to it going off? Or it there something about it that really is no good for structural use?

 

[DoubleStud]

Probably because you are not testing the batches? Who knows at what strength it will break and what the air content is.

 

[Tomfh]

Probably because you are not testing the batches?

Nor do you have to with regular bagged concrete, and those bags don't have the warning.

 

[3DDave]

Mainly to eliminate the lawyers coming after the bagged concrete company if something built with it fails.

 

[Tomfh]

Example of what I'm talking about. The red bag says "NOT FOR STRUCTURAL USE". The blue bag has no such warning.

 

[Settingsun]

Does the blue one have any Aust Standard compliance noted? Maybe that's the difference.

 

[Enable]

Having spoken with some technical reps and industrial chemists from the big companies (e.g. KPM) it usually has to do with quality control. The products solid under commercial labels and marketed towards structural repairs have more stringent QC protocols. So even if a mix says it has the same mean air content, and compressive strength, the mix won't be the same in terms of standards.

BTW it is quite common to test bagged mixes where I am at. On any structural repair project we test all concrete pours even if by bagged material. The tests are not primarily to test the bagged mix itself (though they obviously do) but rather they are done to ensure that the contractor mixed the bags correctly.

 

[hokie66]

My guess is that the quick-set stuff has an accelerator which would be incompatible with reinforcing steel. Calcium chloride, perhaps. Are ingredients listed on the bag?

 

[LittleInch]

The " or aluminium products" hints at some sort of chemical or additive which either attacks re bar or compromises strength.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Tomfh]

The safety sheet for the red bagged mentions Soda ash (Sodium carbonate) Na2CO3. That ingredient is missing from the blue bag safety sheet. Presumably that's the accelerator. A quick google says that Soda Ash is corrosive to Aluminium.


I've just noticed that Boral's Quick Set bags have the "not for aluminium" warning, but don't have a "not for structural use" warning. They say "suitable for all general concreting applications" however they warn as follows:

NOTE: Large slabs will be difficult to undertake due to the fast setting
nature of the product. Ideal for smaller slab constructions only.

I'm suspecting now that this is the main issue.

 

[Settingsun]

The datasheet and SDS for the blue product also say it's for non-structural use, without explicitly saying it's not for structural use.

 

[LittleInch]

Yeh, "Sets in 15 mins", whatever "sets" means, but doesn't give you any real time to pour more than one or two bags.

But with 20 kg bags of ready mix, you can't expect to build much in the way of "structural" concrete surely?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hokie66]

Na2CO3 is sodium carbonate, not calcium carbonate, but perhaps it is a bad actor as well.

 

[Tomfh]

Sorry, “calcium” was a typo. Fixed

 

[BridgeSmith]

The quick set most likely compromises the ultimate strength, or at least makes it too unpredictable. Like the warnings on many other products, it's probably a reaction to a lawsuit.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Brad805]

How does the cost of this compare to a structural mix? I suspect Enable is on to part of it, but another is simple marketing. This seems to be marketed to the home builder, a group that is notoriously cost conscious. My BIL is the QC engineer for a large concrete supplier in a Western Canada. He has been in marketing meetings and even in the concrete world they study their markets and strategize how to sell more product. The product sheet (below) is a tad vague.

AUS Mix

 

[LittleInch]

Like anything that is "pre mixed", you're paying for convenience. Great if you just want to have a bit of concrete to put a post in the ground or make a small footing for a shed or something similar, but structural concrete?? Most of the pre mix stuff I ever bought came with a bag of cement which you needed to add to the mix of sand and aggregate. Of course how well you mixed that or whether the cement had started to go lumpy would be one reason to seriously question it's structural strength, not to mention that the elements of the pre mix tend to start to separate in the bag if its's been shaken about too much on its journey from bagging plant to final mixing point.

and yes, who are you going to sue when your building starts cracking when you've mixed the stuff yourself?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MotorCity]

It is interesting that the manufacturer does not trust their product for "structural use", but they do trust the user to determine what is or is not considered "structural". Heck, its such a vague, nebulous term that even a group of engineers could debate what is or is not a structural use.

 

[BridgeSmith]

Heck, its such a vague, nebulous term that even a group of engineers could debate what is or is not a structural use.

If the building falls down when it breaks, it was structural.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[CANPRO]

If the building falls down when it breaks, it was structural.

A lawyer friend of mine once asked me what was the definition of "load bearing". I told him that I suppose that it would be anything that is "bearing load". If you take that definition to the extreme, anything that transfers load other than its own self-weight could be technically load bearing. I didn't pry for context, just answered his question. It was a bit of a "light-bulb" moment for me and I have since started thinking about how I would explain some of my judgement calls in a courtroom, if required.

Point of my story above, and in line with BridgeSmith's comment, is that unless you are making lawn ornaments out of that bagged concrete there is a very good chance that it is "structural" by someone's definition.