A few more concrete pier questions

Zachary Hoyt

Well-known Member
I've been asking questions for the last year or more about a set of 20 concrete piers for a new building. I rented a trackhoe and dug the holes today and am getting ready to put in
the forms and the rebar. I am hoping to pour early next week. Each pier will be 5 feet high, 8 inches square on top and 22 inches square on the bottom. I got advice earlier this
spring about rebar and am going to use 4 vertical #4 bars with an L bend on the bottom connected by a square of rebar 12" on a side and another square 6" on a side. I am using
#4 for everything because it and #5 are all that I can get around here. The rebars will be wired together in a bunch at the top. I have anchor bolts to put into the wet concrete too.
I am wondering how to secure the rebar cage inside the wooden forms to ensure that it stays centered in the form while the concrete is being poured in. I can imagine running a
piece of wire from each rebar out through the corners of the forms but I don't know if that would make a pathway for rust to get started on the rebar. On the bottom I plan to place
the "feet" of the rebars on pieces of broken concrete or rocks to hold them up a bit off the bottom of the form. I don't know if that is okay either. The other thing I am wondering
and have not been able to find out is how long I should leave the forms in place after the pour. I can leave them on for a week but if it would be possible to remove the forms and
start backfilling sooner I would like to do that. I know concrete needs to stay wet in order to cure but I am not sure if backfilling and running a sprinkler would be better or worse
than leaving it in the forms and running a sprinkler. Concrete makes me nervous since I am not very used to it, so any advice will be much appreciated. I have poured footers and
slabs before but this pier thing is a new one for me.
Zach
 
Can't help with the rebar questions, but a tapered form like that will try to lift when filled with concrete. Last time I poured piers like that, I used sawed out some aspen boards for the forms. Backfired around the forms. After it was hard I peeled of the above grade boards and left the rest. You can take the forms off as soon as the concrete sets up.
 
As said by first poster, that form design with open bottom will want to lift, like a zombie comeing back to life after being buried, and I don't think that 2x4s transversing the holes and fastened to the forms and staked down will hold them down. I also, believe you will have to back fill the forms before the pour to hold them down. The 2x4s should hold the forms in place when backfilling. What are you using for ancor bolts in the top of the pier. I would seperate the rebar at the top also. A wad of 4 rebars tighed together is never a good idea. If you have an acetylene outfit, cut and bend two squares, one about 4" square for the top and one about 16" for the bottom of each pier, and tie your uprites into the corners with wire twists. Simply cut two peices of bar and form an X half way up. The bent squares will keep the rebar frame much more ridgid. It would also be a good idea to have a vibrator to remove the voids that will form as you are pouring. Good luck with your pour.
Loren
 
Thank you, that sounds like a great idea. I hadn't thought that the forms would lift but I can see how it makes sense that they would. If I backfill first that will make all sorts of things a lot easier. I will have to use an old cheap circular saw blade to cut the above-ground parts of the forms away but that is no problem. The forms themselves have no particular value being made out of willow.
Zach
 
Thank you for your advice. I am planning to bend the squares as you describe except I think I will have to do them cold which may be a little challenging. I have bent rebar before but never that short pieces. I hope to be able to do it with a pipe slid over the outside. The X sounds good in the middle and easy to make. I don't have a vibrator, my plan was to tap with a mallet but I don't know if that will be enough. I have six 3/4" anchor bolts that are about 2 feet long that I plan to use on the corners and the middles of the long sides. The other 14 will just be 1/2 " anchor bolts since that is all the local hardware store or lumberyard carry. I can bend the rebar apart at the top and they should stay separated once they are wired to the squares. I know I am supposed to keep them 2-3" from the edges of the concrete so I will need to be careful not to spread them too far. Do you have advice on how to keep the rebar centered in the form?
Zach
 
To hold the rebar cages centered in the forms, just drill two small holes side by side, on the four sides of the forms, then take a peice of form wire and wrap it around one of the peices of rebar, and thread it through the two small holes and tighten to center the cage in the form. 4 on the bottom and 2 on the top across from each other should surfice.
Loren
 
plastic slip on spacers are used to hold the rebars off the forms--come in various sizes--most common are 1 1/2 or 2 inch
concrete should be moist cured or forms left on for 6 days. a tapered pier needs to be tied down or the concrete poured slowly so there is no uplift from fluid pressure on the forms
 
Zach, I've been planning doing something very similar. I want to use 3/8 plates welded on at the top of the rebar to bolt laminated posts on to the piers. I planned to pour a footer/cookie, then use sona tube up to ground level, and a square form between ground level and the bottom of the plates....and place a horizontal j bolt in the square form for the gravel boards/grade level girts. Kind of like using a Perma column but pouring it in place. Have you looked at Perma Columns? Their web site has some good info.
Chris
 

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