Completely botched pier rebuild

[vlaiv]

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?

[Craney]

Sorry to hear this Vlaiv.

Before going to the nuclear option and digging it out, can you identify any cracks  that are creating the movement ? 

If so, think about injecting some concrete resin whilst the top half of the pier is plumb vertical.  

It is very strong stuff and may (fingers crossed) lock-in the whole arrangement to the correct and intended position.

[UKDiver]

How cold was it after the concrete was poured? Water is part of the chemical reaction that forms concrete, but if it freezes before the reaction (exothermic in inself) then the concrete will be cracked.

Edited November 20, 2021 by UKDiver

[vlaiv]

7 minutes ago, UKDiver said:

How cold was it after the concrete was poured? Water is part on the chemical reaction that forms concrete, but if it freezes before the reaction (enderthermic in inself) then the concrete will be cracked.

It was cold - but not freezing, I guess around 5-10C at night, 10-15 during day.

[vlaiv]

23 minutes ago, Craney said:

Before going to the nuclear option and digging it out, can you identify any cracks  that are creating the movement ? 

I guess it should be possible.

I'll have a look at it first thing tomorrow morning when there is enough light to thoroughly inspect it.

Builders will also be here so I'll file an official complaint and we'll see why it's happening.

[vlaiv]

25 minutes ago, Craney said:

It is very strong stuff and may (fingers crossed) lock-in the whole arrangement to the correct and intended position.

If I go with such option - how confident can I be that it will be solid and stiff?

Just recently I was looking up building material and I found "repair mortar" - it is fast curing mortar used to repair concrete elements - contains synthetic reinforcement micro fibers.

Will that do the trick?

[jetstream]

1 hour ago, vlaiv said:

If I go with such option - how confident can I be that it will be solid and stiff?

Just recently I was looking up building material and I found "repair mortar" - it is fast curing mortar used to repair concrete elements - contains synthetic reinforcement micro fibers.

Will that do the trick?

Do you have pictures of the pier before they poured the concrete? Was there anything on the pier that the concrete could stick too? Numerous options here, frustrating yes but no big deal. I dont mean to minimize this but its fixable.

 

Edited November 20, 2021 by jetstream

[vlaiv]

1 minute ago, jetstream said:

Do you have pictures of the pier before they poured the concrete? Was there anything on the pier that the concrete could stick too? Numerous options here, frustrating yes but no big deal. I dont mean to minimize this but its fixable.

 

This is from the phase when only foundations were done:

as you can see - there is section of foundations that is only meant for pier and it has rebar for pier put in place

In the mean time - some of it was built - this is image from a week or two ago:

I outlined observation deck that was poured. In this image pier can't be seen - but it rises in the middle of observation deck to the height of about 90cm or so. Walls are at 130cm I think - but slightly higher than pier.

I'll have better images tomorrow to show the extent of problem.

[Franklin]

18 minutes ago, vlaiv said:

I outlined observation deck that was poured.

What supports the observation deck when it was poured? Are they timbers underneath in the picture?

[vlaiv]

4 minutes ago, Franklin said:

What supports the observation deck when it was poured? Are they timbers underneath in the picture?

Yes - it was fully laid with wooden planks - supported by multiple beams and also couple of cross beams (you can see one still sticking out in that picture):

[Franklin]

So the pier rises about 2ft from the floor foundation and then passes through the concrete observation deck about another 3ft with an inch clearance. Meaning the pier in total is about 5ft high from the base. What are the dimensions of the pier? Is the base of the pier as wide as its footing in the first picture or does it just surround the rebar? What thickness is the concrete. 5ft seems very high.

[UKDiver]

Was the pier cast first prior to the separate observation deck? I'm wondering if it was simply knocked against while constructing the second deck, breaking the join between pier and foundation block. It would be quite vulnerable. The rebar would have helped, but it takes concrete about a week to develop about 75% of the specified strength at 28 days, but I think this would not be an issue in your case. I do wonder if the pier might be a bit slender for its height, exposing it to a knock and a fair lever length. It was getting dark, but tomorrow I'd have a look at the join at the base of the pier. If it's gone there, I think breaking it out and starting again will be the best solution. Roughen up the slab under the rebar too. Any reason not to have a steel bolted down pier?

[Franklin]

1 minute ago, UKDiver said:

I do wonder if the pier might be a bit slender for its height, exposing it to a knock and a fair lever length.

Or even strong wind whilst curing. Any movement could have compromised the setting process, If the bond of pier and slab has been breached it would not neccessarily need breaking and recasting. A new, much wider concrete block could be cast around the base of the existing pillar and just kept short of the base of the concrete deck.

[vlaiv]

22 minutes ago, Franklin said:

So the pier rises about 2ft from the floor foundation and then passes through the concrete observation deck about another 3ft with an inch clearance. Meaning the pier in total is about 5ft high from the base. What are the dimensions of the pier? Is the base of the pier as wide as its footing in the first picture or does it just surround the rebar? What thickness is the concrete. 5ft seems very high.

I think that total height of pier is about 6ft and it is 8" x 8" square.

Observation deck was poured first but there were wooden planks already placed for encasing the pier (and some very thin polystyrene sheets as spacers to the deck).

[vlaiv]

10 minutes ago, Franklin said:

A new, much wider concrete block could be cast around the base of the existing pillar and just kept short of the base of the concrete deck.

That is interesting option provided that problem is near base.

 

[M40]

Before I cut it half and made a pier out of it, we had a steel reinforced concrete washing line post about 2M high and 100 x 100mm at the top. Solid as a rock and no way would it twist, even when I broke away all the concrete just leaving the steel reinforcement, I couldn't twist it. The only thing I can think of is that the pier has become separated/broken from its fixings and is sitting loose on the foundation which seems unlikely or is it the mounting plate that is loose?

[vlaiv]

19 minutes ago, UKDiver said:

Was the pier cast first prior to the separate observation deck? I'm wondering if it was simply knocked against while constructing the second deck, breaking the join between pier and foundation block. It would be quite vulnerable. The rebar would have helped, but it takes concrete about a week to develop about 75% of the specified strength at 28 days, but I think this would not be an issue in your case. I do wonder if the pier might be a bit slender for its height, exposing it to a knock and a fair lever length. It was getting dark, but tomorrow I'd have a look at the join at the base of the pier. If it's gone there, I think breaking it out and starting again will be the best solution. Roughen up the slab under the rebar too. Any reason not to have a steel bolted down pier?

Observation deck was poured first but there were wooden planks already placed for encasing the pier (and some very thin polystyrene sheets as spacers to the deck).

Concrete pier seemed as simpler solution that just works, but apparently it is not the case. I did not even look for steel piers to be honest.

[vlaiv]

2 minutes ago, M40 said:

The only thing I can think of is that the pier has become separated/broken from its fixings and is sitting loose on the foundation which seems unlikely or is it the mounting plate that is loose?

At this point, I'm not even sure what you are asking. Sorry - too much building technical terms that I need to look up.

We did not use any sort of fitting - rebar was left sticking out of foundation and wooden casing was built to measure around it and concrete poured inside.

One possibility is that concrete did not bond well with foundation for some reason - or as mentioned above - that something happened during curing time that caused it to crack at the base.

[UKDiver]

8 minutes ago, vlaiv said:

Observation deck was poured first but there were wooden planks already placed for encasing the pier (and some very thin polystyrene sheets as spacers to the deck).

Concrete pier seemed as simpler solution that just works, but apparently it is not the case. I did not even look for steel piers to be honest.

Perhaps the pier was broken while removing the planks, even with the spacers. Whatever the reason, I hope the solution is simple.

[M40]

When you look at your concrete base and steel reinforcement picture, once set, you would not be able to twist the top of the steel. It may vibrate but twist? wouldn't think so. My thoughts are that either your steel reinforcement has broken which seems unlikely, or could it be that the mounting plate at the top of the pier is loose? Did the pier twist or was it just the mounting plate?

[vlaiv]

1 minute ago, UKDiver said:

Perhaps the pier was broken while removing the planks, even with the spacers. Whatever the reason, I hope the solution is simple.

I wonder how one breaks 8" x 8" concrete reinforced pier

[Tomatobro]

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.

[M40]

1 minute ago, vlaiv said:

I wonder how one breaks 8" x 8" concrete reinforced pier

You and me both

[Franklin]

13 minutes ago, vlaiv said:

6ft and it is 8" x 8" square.

I think that's the problem Vlaiv, the pier at that height needs to be much wider at the base. I would make the base 1/3rd of the height. Get your builders to drill into the foundation around the pier and epoxy resin in some more rebar. Then knock up some form work 2ft square, at least, around the base and cast a new block. The wider, the better. Good luck.

[vlaiv]

1 minute ago, M40 said:

When you look at your concrete base and steel reinforcement picture, once set, you would not be able to twist the top of the steel. It may vibrate but twist? wouldn't think so. My thoughts are that either your steel reinforcement has broken which seems unlikely, or could it be that the mounting plate at the top of the pier is loose? Did the pier twist or was it just the mounting plate?

Mounting plate was welded for some steel rebar (same diameter as used for pier itself) and sunken into freshly poured concrete.

Whole thing did not twist - but rather bend. Force needed to bend it was not very big - I sort of just grabbed it with one hand and managed to get it swaying left / right with tug or two - it was easy to get its resonant frequency. Top moved an inch left / right when I was doing that.