Howdy folks
Those of you out there that have cast concrete bridge piers and stuff, any pointers? Since these will be tall (36" some of them) but somewhat thin (5") I assume some sort of rebar? Would welded wire fencing work, or should I use a hunk of rebar? Common wisdom says that the rebar shouldnt go outside the concrete, to keep rust separation to a minimum. Any other pointers? Casting for the lower loop viaduct starts soon!
For casting concrete bridges and piers I use a product called professional non shrinking grout. Home Depot has it. I have been using it for only a couple of years but to date no signs of any effect from acid rain or our winter weather.
If you want to use rebar I would use stainless steel threaded rod.
My tallest concrete pier is only about 20". I only have molds for 12 inch piers so building the higher one took multiple pieces. I used with permission Lone Star castings for the molds but was never able to locate a lower pier section. The Lone Star stuff did not hold up well outdoors.
Hope that helps.
Stan
http://www.flickr.com/photos/23959355@N05/4062866614/in/set-72157622705590588/
Stan
Stan,
Nice layout.
Nico
If the viaduct gets too big for a one piece pour, make it modular it with smaller molds/forms and stack them.
(Like the real viaduct builders do.)
In other words, the piers could be two separate pours and the top deck sections another.
Bob the wire fencing should be enough,but the main point on rebar is keep it about 2" in from the surface of the concrete. The thought of making multiple stacking pieces may make it easier and create a better cast. Frame and cast the first 1’ section and when you level it off place a small piece of foam or wood into the concrete to act as a key for the next pour. When that sets up,remove the key, and extend the frame up for the next pour and repeat until you reach your desired height.
I use the bright wire fencing as rebar in shallow pours - sometimes two layers of it. For thicker pours, I use regular 1/2" rebar. Sometimes both like this last section of roadbed in Deep Cut…
(http://lsc.cvsry.com/Post/DeepCutTunnel-77-800.JPG)
Edit: corrected sentence structure for the grammar police 
Slow down …your stuttering Jon
When I made my concrete viaduct, I cast the whole thing in one piece, using a wooden form. I used 3/8" rebar. I cast it upside down, with the supports sticking up, on our patio, then had to haul the finished piece up to the layout, position it, and pour in cement around the supports to lock it in place. It weighed about 300 pounds, and was a bear to lug up the hill and manhandle it into position. It twisted when we attempted to lift up over the retaining wall, resulting in some small cracks that may eventually cause the rebar to rust.
If I were to do it again, I would cast the deck and supports separately. I also would use some hardware cloth for reinforcement in addition to the rebar, and I would use either stainless steel or aluminum instead of regular rebar.
I have had several cast bridges and one is still on the layout. I cast the abutments and bulkhead as two separate pieces using 4" machine screws sank in the abutment to hold them together. The deck is cast separate. 3/4" PVC pipe makes good molds for concrete piling. A rod in the middle of the piling is matched up with a piece of plastic of water line sank in the bottom of the bridge deck. Makes a good looking bridge.
Ron
Gee - They check my sentence structure, but not my relevance to the topic… CATSING Concrete… like this tunnel portal top…
(http://lsc.cvsry.com/Post/DeepCutTunnel-60-800.JPG)
I used both wire fencing and rebar because I wanted enough strength to be able to lift it out without it cracking…
(http://lsc.cvsry.com/Post/DeepCutTunnel-51-800.JPG)
And that plan almost worked
David Russell said:Actually Jon when I wrote that last night for some reason yours was a double post at the exact same time right down to the second which I thought was odd but funny.
Slow down ...your stuttering Jon
OK - I didn’t see that so I thought you were commenting on my repetitive sentences. You are forgiven, for the moment
Jon Radder said:What's the possibility of a full pardon forever? ;)
You are forgiven, for the moment :)
Jon, 1/2" hardware cloth was used in all of my structures. I used ready mix cement and screened out the larger aggregates using 1/4" wire cloth. With the larger aggregates screened out, the concrete flowed through the cloth with no problems. If you cut and bend one leg of the wire squares every so often in different directions, it will keep it from the sides of the mold. Also, using a piece of wire or a small dowell to agitate the concrete, the air bubbles are removed and it helps the concrete flow in and around the cloth. The concrete was not completely removed from the mold for a week. The sides were removed after 2 days to allow the cement to dry throughly. After the concrete had dried, it was removed and coated with cement to seal it up. I found on one casting, the concrete had been sitting around in the warehouse and after the concrete was removed from the mold, it crumbled. That was a bad day! If your casting weighs a lot, move it on a board if possible so it will have a chance to be broken. Foam insulation make a good cast.
Ron
For small items cast out of concrete I would skip the welded wire fabric and rebar. Instead buy a bag of fiberglass fibers in the concrete section of Home Depot and add them to the concrete as you mix it.
Roger Crooks said:You really want to wear a face mask when dealing with that stuff. Don't breath it.
For small items cast out of concrete I would skip the welded wire fabric and rebar. Instead buy a bag of fiberglass fibers in the concrete section of Home Depot and add them to the concrete as you mix it.