Attaching rebar in holes

[Roger G Olsson]

Hello! It's about a couple of concrete plinths (15cm thick) that lack rebar. I want to drill some holes into them and insert rebar so they don't break so easily. Ideally, the rebar would have been embedded from the start, but they aren't.

So what should be put into the hole so the rebar stays in place and works as intended? I've looked at Jula's anchor compound, could that be something? Or simply mix some cement with extra concrete? Expanding concrete, but maybe that could crack the plinth?

 

[Marsman80]

I don't think you increase the strength significantly by trying to add reinforcement bars afterward. If it's footings that mainly need to handle pressure from above, then reinforcement is probably not as necessary as in other applications where there is tension in the concrete (like a concrete beam loaded in the middle).

 

[Daniel Barnaniel]

You should not follow any of the suggestions. In theory, the anchor mass thing might work, but hardly in practice. Cast a new proper foundation if you think it's necessary, as we have no idea about its execution or function.
Finally, concrete consists of cement and ballast.

 

[Roger G Olsson]

Yes, it will mostly be pressure from above. There will be a 9m2 storage shed on the pillars with quite heavy stuff in it. I've dug holes for 12 pillars. It might sound like a lot, but the subfloor is built from scrap wood and could have been slightly stronger. So, I thought I’d make it stable through some extra pillars. I will remember to have reinforcement in the other 10 pillars.

By the way, why do you think reinforcement afterward won't be as good as having it cast in from the start?

I don't think you'll increase the tensile strength much by trying to put reinforcement bars in afterward. If they are pillars mainly handling pressure from above, then reinforcement isn’t as necessary as in other applications when there is tension in the concrete (like a concrete beam that is loaded in the middle).

 

[Hallerudsbo]

Anchor compound.
But it's important that it is sealed so the reinforcement doesn't stick out and start rusting.
It's best to leave it be or redo it correctly.

 

[Daniel Barnaniel]

Anchor grout.
But it's important that it is sealed so the reinforcement doesn't protrude and start to rust.
Best is to leave it as is or do it correctly

Exactly, and making it work in practice with full filling and a proper installation I guess will be tricky. I don't actually know how tall the piers are.

 

[Roger G Olsson]

Okay, I've received the same advice twice, so I guess I'll just accept it. I think I'll leave the two plinths as they are; it will probably hold.

Just curious, how do you know it doesn't help to reinforce afterwards?

You shouldn't do any of the suggestions. In theory, the anchor mass thing can work but hardly in practice. Pour a new proper plinth if you think it's necessary; we have no idea about its execution or function. Finally, concrete consists of cement ballast.

 

[Hallerudsbo]

Okay, then I've received the same advice twice, so I guess I'll just have to accept it. I think I'll leave the two brackets as they are, they probably hold.

Just curious, how do you know it doesn't help to reinforce afterwards?

why do you think they have reinforcement before they pour and not just attach it afterward?

The concrete adheres to the steel and creates strength.
Then, depending on what you're casting, the reinforcement needs to be at different depths within the concrete to meet various requirements.

Then you want the reinforcement not to start rusting because that can cause the concrete to crack.

 

[Roger G Olsson]

The plinths are 30 cm above ground and 90 cm underground.

I have a 1-meter long and 12mm thick concrete drill. There was also a 16mm and 24mm drill in the package.

Exactly, and I guess it's going to be tricky to make it work in practice with full filling and a proper assembly. I don't really know how high the plinths are, though.

 

[Roger G Olsson]

I got distracted while casting, and then it was too late to get the rebar into the concrete; it had half set.

Just for the sake of discussion, if we speculate that I would drill a 16 or 24mm thick hole one meter down into the pillar and then pour thin-flowing concrete with lots of extra cement powder. If you then move the rebar up and down so it fills well and then make sure the rebar doesn't stick out of the pillar but is fully embedded? I've never used cement before, so I'm probably missing something everyone knows.

Why do you think they put in rebar before they cast and not just attach it afterward?

The concrete bonds to the steel and creates the strength.
Then, depending on what you are casting, the rebar should be at different depths in the concrete to meet different requirements.

You also want the rebar not to start rusting, as it could begin to crack the concrete

 

[useless]

It is not enough to drill a few holes and insert some iron. For the reinforcement to be effective, it must go through the entire plinth. I don't know how high they are, but I guess it's more than a few dm? If you're going to drill half a meter to a meter, it's probably easier to make a new plinth.

 

[Strontus]

Just for the sake of discussion, if we speculate that I would drill a 16 or 24mm thick hole one meter down into the footing and then pour in thin-flowing concrete with a lot of extra cement powder. If I then move the rebar up and down so it fills well and then make sure that the rebar does not stick up out of the footing but is completely embedded? I've never used cement before so I'm probably missing something that everyone knows.

For it to work well, you need to get the new concrete to bond well with the old one, something that is likely difficult to achieve properly (not that I would be an expert on it).

 

[Hallerudsbo]

It's not enough to drill a few holes and put in some iron. For the reinforcement to be effective, it should go through the entire foundation. I don't know how tall they are, but I'm guessing it's more than a few dm? If you need to drill half a meter to a meter, it's probably easier to make a new foundation.

ts mentioned 30 cm above and 90 cm below ground, so a 1.2 m foundation. Then they talked about drilling up to a meter and adding iron.

 

[Hallerudsbo]

I got distracted when I was casting and then it was too late to get the rods into the concrete, it had half-set.

Just for the sake of discussion, if we speculate that I would drill a 16 or 24mm thick hole one meter down in the plinth and then pour in thin-flowing concrete with a lot of extra cement powder. If you then move the reinforcing rod up and down so it fills well and then make sure that the rod does not stick up out of the plinth but is completely embedded? I've never used cement before so I'm probably missing something that everyone knows.

Given the time and price of a 1 M drill, I would prefer to make a new plinth.
15 cm width should be easy to just lift straight up and in with new concrete.

 

[useless]

ts wrote 30 cm above and 90 cm below ground, so a 1.2 m post.
Then he talked about drilling up to one meter and putting in rebar.

Yess... There was that thing about reading before answering...

But we seem to agree. Drilling a meter into concrete is not fun or easy...