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Pier Problems / complete disaster help.


Adam J

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Had a complete disaster with my pier concrete pour. I stupidly decided to use fast-ish drying concrete mix and it has apparently cracked about two thirds down within the tube that I used as a form. Most likely because it started to go off before I started the second pour leaving an interface between the two. From the way its wobbling I would say this is the likely scenario.

This has left it vibrating about like a spring as the top and bottom sections of the tube are in effect only held together by the plastic form. The whole thing is now attached to the concrete base.

My options as i see it are:

1) Dig the whole thing up including the huge base. This would be a significant job and not something I want to do if at all possible.

2) Cut the form away apply PVA to the pillar and place a larger 12 inch form around the crack creating a coller to strengthen that section from the base of the pillar to about 2/3 of way up the tube...

3) Cut the Original just below where I think the crack is, place the larger from around the stub and use this as a mounting point for the larger diameter pillar.

 

 

peir problems.png

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#3 is my vote, with rebar drilled and epoxied into the base and the concrete poured over the old cut of pillar. A scratch coat of a runny "sand mix" brushed over the concrete where you are going to pour over works as do fancier methods to ensure adhesion.

I use this glue for rebar at times.

http://www.powers.com/product_8486_8490.php

http://www.sakrete.com/media-center/blog-detail.cfm/bp_alias/Bonding-to-Existing-Concrete

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Personally I would take off the top section completely and bolt a steel pier to the base.  It's extremely hard to "adhere" 2 concrete sections in an application where there will be changes in environment and some dynamic loads applied.

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I suppose it depends on how thick it all is.  I'm no builder, but I often help out my brothers projects with different ideas.  With a long masonry drill (I'm pretty sure you can hire these) could you drill through the structure above and below the cracked area and put two bolts through and join each side above and below the crack with a length of metal bolted in place (sort of like a splint).  Maybe do it both ways with the holes at different heights - N to S and E to W.

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Two options:

First, you might be able to "glue" the two parts back together. Polyester resin is an almost magic adhesive for concrete. You could even end up with a joint that is stronger than the surrounding concrete. You could either try a straight "glue joint" or use a angle grinder to cut trenches in the post to hold rebar and glue that in.

Alternatively, check out Twistfix. https://www.twistfix.co.uk/crack-repair Their crack repair technique is strong enough to cope with cracks in houses. It'll cost a couple of hundred £££ but you might feel that is worth it.

Either way, wait until the concrete has fully "gone off" before doing anything,

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1 hour ago, LightBucket said:

Yes get rid of the pier, and bolt steel one to base... :)

Unfortunately I am not currently able to afford a steel pier so this is not really an option. 

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42 minutes ago, Adam J said:

Unfortunately I am not currently able to afford a steel pier so this is not really an option. 

It would not cost that much to get one built by a local fabricator....but I do understand your dilemma, but whatever you do, get it right this time or it could end up costing you more than a steel pier...

i had similar issues hence my advice, i had a plastic tube buried in concrete and 44" above the concrete which was then filled with concrete, and same as you there was a break, lt was not too bad in the winter when very cold, the plastic pipe held it pretty rigid, as the walls were 1/4" thick,  but in summer months when the plastic got hot, it was like a tuning fork....managed to put up with for two years...before I re built.

I bit the bullet in the end and bought a steel one, and will never have to worry again... :) 

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I'm not a concrete expert but I am a Chartered Engineer, and in my experience unless you have a repair done professionally, for what I suspect would be far more costly than a steel pier, then you will struggle to do what you're proposing with the results I imagine you're expecting. Don't forget you are looking for no movement at all, under all conditions, which means some pretty substantial repair. Any resin repair is generally designed to prevent further movement or cracking, not to provide a rigid joint.  It would need to be so stiff it would be brittle. Most resins are actually slightly flexible to help with the bonding process and to prevent further cracking. 

Don't forget this isn't repairing a crack, it's sticking together 2 sections to obtain a totally rigid structure. That's quite a chore. 

Unfortunately some mistakes are costly, I know this myself having broken my Mesu200 mount before I'd even used it, and then had to drive it to Lucas Mesu in Holland to get repaired. 

If you really can't afford a steel pier, which undoubtedly would be the best option, then take off the pier that's broken totally. Make the new post as large a diameter as you can realistically accommodate, and then drill and install with a good chemical anchor 4 x 10mm  reinforcing rods in the base, which will need to stick out to just above the half way point of the new pier, but I would suggest 200mm below the pier top. They need to be set 2/3 out from the centre, and I would suggest at least 1 radial half way up, and one at the top.  

Scabble the base heavily to provide a good key, and then poor a strong but wet mix. My biggest recommendation by far is to vibrate the new mix to make absolutely sure it is keyed and has no air pockets, just prodding and poking with a stick is no good at all.  You can get a cheap poker on eBay or Amazon for about £40.

Finally leave it at least 6 weeks before you do anything with it as the wet mix will take a fair bit longer to firm up, and whilst it may look set, it will be green inside. Leave it as long as you possibly can to drill it. 

The above should work fine, but whatever you do, you need to accept that wherever you join concrete you will always have an inherent weak point, no matter how you do it. 

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 You could remove existing pillar, us impact hammer to take out the bit in the base (I understand it's insulated by foam on the sides so no need for expensive circular diamond drill-bit) and just pour concrete. Depends on what tools you have lying around, I suppose. Or how good your relations with local tool rental (or, if you work in construction - site manager) are. Personally I wouldn't leave anything wobbly/cracked in the structure that must be vibration free, might cause problems in the future. 

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6 hours ago, Adam J said:

Unfortunately I am not currently able to afford a steel pier so this is not really an option. 

I had a local sheet metal worker construct a 6'6" by 6" square steel pier which cost me £35. After painting it with red lead and sinking it into a concrete base, the whole thing cost around £70. That was about 6 years ago! Having a pier manufactured rather than buying the expensive, ready made affairs, is a much less costly venture.

Mike

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Ok as an update I went for option 1 and am currently breaking the whole thing up. I know where I went wrong. Having removed the form from the pier there was a layer of crumbing concrete that for what ever reason (too much water / not sufficiently mixed) had just not fused properly. Nothing was going to fix it. Am going to get a impact hammer and break up the main block over the weekend and then start again using a much stronger concrete mix and raising  the bottom of the form to the surface of the concrete so that the form is not within the sub base. I think from what i saw it was a valid method though and would have worked if not for the issues with the concrete mix.

I am also going to ask the local fabricator for a quote on a steel pier but I suspect this will come out too expensive.

To be honest with you I am fairly relaxed about the whole thing its not going to be so hard to fix as I had originally thought and what with some of the things going on in the world its not worth getting upset about it. One way or another I will end up with a good quality obsy in the end even if I have to have a few attempts at some aspects to get it 100% up to my standards.

3 hours ago, Peter Drew said:

What size/type of telescope is this pier to support?    :icon_biggrin:

At the moment its only for a HEQ5 and a 130PDS but I am leaving room for expansion I want to to support a EQ8 if I get one at some point down the line.

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  • 3 weeks later...

I am not an imager yet but a couple of years ago I built a pier- actually I copied the late Per Frejval's design with his blessing. It only cost me about 100 bucks for the material and a few minutes to weld up. Somewhere there is an old thread with his pier illustrated. Something like this might be worth consideration. I just pulled it out of the bush where its been sitting- they are very tough...

 

 

propane pier 008.JPG

propane pier 009.JPG

propane pier 010.JPG

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If money is tight then I would go for picture option two. But I would cut the first pillar down to the point of the cracked section and use new pipe inside the new larger section..if this makes sense.

I would also use some rebar or stud bar horizontally going through the new inner section to the outer section and maybe drill some in vertically into what is left of the first pillar.

 

 

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Sorry guys this thread seems to have resurrected itself, I dug the whole thing out weeks ago and replaced it with another concrete pillar better reinforcement and 300mm and high strength concrete its working great this time around. However, thanks for your comments. :)

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On 15/06/2017 at 03:21, jetstream said:

I am not an imager yet but a couple of years ago I built a pier- actually I copied the late Per Frejval's design with his blessing. It only cost me about 100 bucks for the material and a few minutes to weld up. Somewhere there is an old thread with his pier illustrated. Something like this might be worth consideration. I just pulled it out of the bush where its been sitting- they are very tough...

 

 

propane pier 008.JPG

propane pier 009.JPG

propane pier 010.JPG

If you do this, don't make the top square. I host four of the posts like (and including) Per's and they are very good, actually made by Jonas Grinde, but I would recommend round as much less of a hassle for snagging and collision. We've had to do a few work arounds with the square tops.

The OP could take off the pier entirely and then make something like the one I've just made. It uses four pre-formed concrete cylinders filled with concrete. The cylinders are epoxy bonded to the concrete base and rebar is bonded into the base, rising up into the concrete fill. I like the preformed cylinders because they hold still in construction and give a strong outer structure to help the poured concrete.

594589a8ccbee_PREVIEWWEB.thumb.jpg.7470829b1a609928f1832d7dc447098d.jpg

Olly

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