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Completely botched pier rebuild


vlaiv
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3 minutes ago, Tomatobro said:

concrete takes weeks to go off properly and freshly poured should not be disturbed at all. My pier centre block had 4 weeks before I stood on it, same for the outer standing pad.

I think it was at least a week if not two before they started removing planks few days ago. I did not go near it up until tonight.

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7 minutes ago, vlaiv said:

Top moved an inch left / right when I was doing that.

It's pivoting on the rebar at the base. You need to recast around the base to secure it or break and start again.

Edited by Franklin
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8 minutes ago, Franklin said:

It's pivoting on the rebar at the base. You need to recast around the base to secure it or break and start again.

Yep.

I just went out to examine it again (armed with torch and all :D ) - it is really easy to move it as it is completely detached from base. It simply did not bond for some reason with the base.

It is holding only by rebar which is flexible so whole thing can bend.

You can't see crack - but I was on platform moving it and my wife says that it can be seen that it is detached at the bottom (she came along for inspection).

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Vlaiv, in your first pic showing the foundation, where the polystyrene square is around the rebar. You need to extend that square up to just below the base of the observing pad. A huge 2ft square concrete block to secure your pier. That's what I would do and I'm a builder.🙂

I would also fit more rebar in the base around the pier to fix block to foundation. How you pour it with that pad above presents another problem. Cut out a notch in the form work to get access for filling.

Edited by Franklin
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1 minute ago, Franklin said:

Vlaiv, in your first pic showing the foundation, where the polystyrene square is around the rebar. You need to extend that square up to just below the base of the observing pad. A huge 2ft square cocrete block to secure your pier. That's what I would do and I'm a builder.🙂

I'll consult with builders tomorrow.

Whole deal is rather upsetting. Same people built my house. If this can happen, I wonder if they managed to mess up anything else.

So far everything is standing upright, but one never knows ...

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The problem with making concrete piers is that after pouring excess water can migrate down to the bottom which weakens the mix at the base.  Its a bit like when the mix is tamped down and water appears on the top surface but in this case gravity does the reverse.

Having done a lot of civil engineering I have learnt that there is generally a work around for most problems that present themselves.  How about some steel "L" plates, one for each side, drilled and bolted to the floor and the pier using resin bonded bolts. I am guessing that wooden battens will be screws to the floor and a false wooden floor put on top of the base to allow for underfloor cabling etc so the steel brackets would be mostly hidden.

Best I can suggest as a solution

 

 

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6 minutes ago, vlaiv said:

I'll consult with builders tomorrow.

Whole deal is rather upsetting. Same people built my house. If this can happen, I wonder if they managed to mess up anything else.

So far everything is standing upright, but one never knows ...

Its all good vlaiv, the house is fine.

Some steps taken, not taken with this pier design could be at fault. I mean this respectfully.

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1 minute ago, jetstream said:

I mean this respectfully.

I know you do. There is no need to mention it.

I'm not sure I understand what you said there though. Do you think pier design is poor? Maybe too thin or something?

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1 minute ago, Franklin said:

Yes. A 6ft high concrete pier needs to be 2ft square at the base not 8". It is not able to support itself.

To be honest, I find that hard to believe, but I'm not going to argue since I know nothing about construction.

 

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4 hours ago, vlaiv said:

I just noticed something and I'm infuriated.

My observatory is in the middle of the build. Crude works have been completed. It has observing deck (concrete slab) and pier made out of reinforced concrete - those two are decoupled (about inch of space between them). Pier has its own foundations.

I did not inspect it previously, but since work around the house is (hopefully) coming to an end - I went outside to see what has been done today and decided to check out the obsy as well - climb on observing platform (it is about meter of the ground) and see the skyline / horizon.

I also then inspected the pier and mounting plate. It has been exposed to elements for few days and rust started to show up and I wanted to check how to best protect it - and then I realized.

Pier is loose!

I have no idea what has happened - but I can move it couple of centimeters left right with one hand. This thing should be rock solid and it's bending like piece of rubber.

Dark was starting to set in so I could not really identify the problem, but I think that concrete pouring did not go well - or some sort of crack formed next to foundation.

Now I'm wondering what would be best course of action in attempting to make it stable. My initial gut feeling says - break and remove that one and redo concrete pouring for it again?

Will that work? How to make sure it is solid and does not budge? (I'm really confused with how this happened in the first place so I'm worrying in advance that it will happen again).

Anyone has any ideas how to best proceed on this one?

So a crack at the join at the base, this happened to me you need to add PVA to the mix and a layer at the join, especially the case with rebar I find as concrete shrinks as it sets and if a piece of rebar is going though it then it can actually pull itself up on the rebar and leave a tiny gap at the join. Differential shrinkage between two layers spanned by the rebar that is no going to move itself. 

Edited by Adam J
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12 minutes ago, vlaiv said:

I know you do. There is no need to mention it.

I'm not sure I understand what you said there though. Do you think pier design is poor? Maybe too thin or something?

The concrete pier should have been poured "as one" with the bottom slab. Then rebar should have been in place in pier, wired in to the rebar in the top slab. Even still, the disconnect (shrinkage etc) still may allow for small movement and vibration.

I would consider Per Frejvals design .

 

Edited by jetstream
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6 minutes ago, Franklin said:

Yes. A 6ft high concrete pier needs to be 2ft square at the base not 8". It is not able to support itself.

I think I'm going to disagree there. 6' fence posts are far more slender, cheaply made yet support themselves. I also take it that the base is the larger section surrounded by polystyrene. I see multiple 12" columns with far more load than this pier will ever get close to, albeit only ever dead load and no torsion.

I do agree with you that the repair is best done with more mass concrete and rebar joining the original base.

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Just now, jetstream said:

The concrete pier should have been poured "as one" with the bottom slab. Then rebar should have been in place, wired in to the rebar in the top slab. Even still, the disconnect (shrinkage etc) still may allow for small movement and vibration.

I would consider Per Frejvals design .

 

Yes that's the ideal. But not always possible. I did find my pva method to work well, it's not load bearing after all. I make mine 40cm X 40cm though so a much larger contact area. 

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2 minutes ago, Franklin said:

A fence post is just part of the structure of the total fence.

As I said - I'm not very versed in building materials or structural stuff - but we have here 5-6 meter high 250mm concrete posts for electricity.

Those things weigh half a ton and manage to stand still in high winds and all kind of weather.

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