Which concrete for casting a playhouse?

[messijah]

Hi, I have built 2 towers for the children to play with, but what type of concrete should I use to cast the footing irons I plan to cast in place? There's rock close to the surface in some places, so I might not be able to go very deep in certain areas. I'm mostly concerned about the frost in winter.

 

[C.Lundin]

Concrete is not damaged by cold once it has set, so regular coarse concrete in bags will do just fine.

 

[Ludvigjohnsson]

Concrete is not damaged by cold once it has cured, so regular coarse concrete in bags is perfectly adequate.

Not true. Concrete that is exposed to freezing should have air-entraining additives to withstand the exposure class. This is to create cavities that the water can expand into when it freezes. There is ready-mixed concrete in bags that can withstand freezing. /The Constructor

 

[useless]

So all plinths, house foundations, retaining walls, etc. that people cast at home without these additives freeze and break?
I think it's risk-free to skip it in a playhouse.

 

[Ludvigjohnsson]

So all foundations, house bases, retaining walls, etc. that people cast at home without these additives freeze and break? I think it's risk-free to ignore it in a playhouse.

What does it matter if “all” freeze and break or not?

It depends on what you mean by the risk, doesn’t it? If you intended to cast foundations for a playhouse from the start, you probably don't want it to freeze and break so the work was in vain? So yes, the risk is unnecessary work in that case. I don’t understand where you’re going with this...

 

[useless]

How long does it take for the plinths to freeze and crack?

 

[C.Lundin]

Incorrect. Concrete exposed to freezing should have an air-entraining additive to withstand the exposure class. This is to create cavities where the water can expand when it freezes. There is pre-mixed concrete in bags that can withstand freezing. /The Designer

Now we're talking about two different things here. Sure, the concrete should be designated XF2, maybe even XF3. But what I said was that the concrete won't be damaged, which it won't be.

 

[Ludvigjohnsson]

Now we're talking about two different things here.
Sure, the concrete should be specified as XF2, maybe even XF3. But what I said was that the concrete won't get damaged, which it won't.

I don't understand what you mean. We are indeed talking about the same thing. If you have those exposure classes, then you have air entrainment, and the concrete won't get damaged, no. If you ignore it, there's of course a risk it will freeze and crack at a point when the concrete is very wet. However, if the concrete is not exposed to freezing (insulated) or if it is always dry, it can't freeze and break.

 

[Ludvigjohnsson]

How long does it take before the ground anchors freeze and break?

I don't answer stupid questions. It's like asking how many years it takes before a roof collapses from the snow load.

 

[useless]

That's not a stupid question. Lots of people cast e.g., plinths for patios every year with self-mixed concrete without additives. Should they be afraid that the patio will collapse in 5, 10, 50 or 100 years?

 

[Ludvigjohnsson]

Hi, I've built 2 towers for the children that they will play with, but what type of concrete should I use to cast the plinth iron I plan to cast? There is rock close to the surface in some places, so I probably won't be able to go deep in those spots. I'm mainly thinking about the frost in winter.

To answer your question. Buy any pre-mixed concrete in a bag as long as it states that it can withstand freezing. If you have rock so close to the surface, there is likely a high risk that it will often stand in water unless the rock is heavily cracked. If you're unlucky, it will freeze properly once when it's thoroughly wet, and then you'll have to redo everything. There's no reason to skimp on it. Don't listen to DIY enthusiasts. That's my advice to you, completely free. / The Engineer

 

[C.Lundin]

To answer your question. Buy any pre-mixed concrete in bags as long as it says it can withstand freezing. If you have rock so close to the ground, there is probably a high risk that it's often in water unless the rock is very cracked. If you're unlucky, it will freeze properly once when it's thoroughly wet and then you'll have to redo everything. There's no reason to skimp on it. Don't listen to DIY builders. That's my advice to you for free. / The Engineer

You are being way too theoretical now, which you confirm by repeatedly claiming that you are an engineer.
In that case, you need to go all the way and explain everything that applies if he's going to cast with XF2, such as the max w/c ratio he can have for the additives defining the exposure classes to even be effective.

Or, just accept the situation and realize that if he casts some pillars, they will not be damaged even without any added agents.

 

[Ludvigjohnsson]

You are being far too theoretical now, which you confirm by repeatedly claiming that you are a designer. If so, you need to go all the way and tell everything that applies if he is going to cast with XF2, such as what maximum w/c ratio he can have for the agents that define the exposure classes to even be effective.

Or, just accept the situation and understand that if he casts a few plinths, they will not take damage even without any added agents.

Exactly, I am a designer, are you? People pay me 1000 SEK an hour to answer this type of question. Do they do that with you too? So tiring with all the amateurs who can't learn to listen to someone who actually has competence. You can't stand just doing what someone else says.
XF2 doesn’t really seem like the most likely exposure class. Not very common to salt under a play equipment. XF3, however. You manage that with C28/35 if you have 5% air. A ready-mix concrete in a bag that is supposed to withstand freezing should reasonably not have a lower strength class than that.

 

[C.Lundin]

Exactly, I'm a designer, are you? People pay me 1000 kr per hour to answer these types of questions. Do they do that with you too? So tiresome with all the amateurs who can't learn to listen to someone who actually has competence. You can't stand just doing what someone else says.
XF2 doesn't seem like the most likely exposure class. It's not common to salt under a playground. XF3, on the other hand. You can manage with C28/35 if you have 5% air. A pre-made concrete in a bag that should withstand freezing can't reasonably have a lower strength class than that.

It's pretty obvious that you don't have any competency around concrete, you're just presenting what you learned from the books you read in school.
Amateur, I don't know, I work with only concrete daily and have done so for many years. I'm in daily contact with people developing concrete recipes based on different requirements in outdoor environments, cooling, and foundational environments.
I also have daily contact with designers who hand over all relevant information concerning concrete recipes to those who actually can. They do it without blinking and it's nothing they're ashamed of, because in turn, they're doing something they're really skilled at.

Now you're probably mixing up the classes. XF has nothing to do with salting, maybe you meant XD.
But to answer your question - no, I'm not a designer. However, that doesn't mean I can't.
If people would pay 1000 bucks if I were to be hired out? Not far off, why that would be relevant.

 

[Ludvigjohnsson]

It is quite obvious that you have no expertise in concrete, you only present what you've learned from books you studied in school.
Amateur, I don't know. I work exclusively with concrete daily and have done so for many years. I have daily contact with people who develop concrete mixes according to different requirements for both outdoor environments, cooling, and foundation environments.
I also have daily contact with designers who hand over all relevant information about concrete mixes to those who actually know. They do it without blinking and it's nothing they are ashamed of since they are, in turn, doing something they are truly skilled at.

Now you must be mixing up the classes. XF has nothing to do with salting, perhaps you meant XD.
But to answer your question - no, I'm not a designer. However, that doesn't mean I can't.
Would people pay 1000 kronor if I were to be hired out? Not far off, why it would be relevant now.

I have quite a lot of expertise in concrete and work daily with concrete issues. What we're discussing is not complete recipes. We are talking about concrete structures exposed to freezing. A designer prescribes exposure classes and also air entrainment if it involves freezing since air entrainment results in a different strength class compared to w/c ratio than if there was no air entrainment.

Okay, I understand. You have daily contact with people who know about concrete. But that doesn't mean you do.

No, I'm not mixing up any exposure classes. Which XF class it becomes has to do with the availability of water and whether there is de-icing agent or not. XF3 = high water saturation without de-icing agents.