# Complex concrete arch bridge question



## SE18 (Feb 21, 2008)

I'm angling to start one of these this weekend as the weather seems to be warming slightly


http://www.marklin-users.net/forum/default.aspx?g=posts&t=11788

It's obviously for large scale and will be pretty big.

I'm having trouble thinking this through regarding the mold.

I'm thinking to make the mold of many sections that can be unscrewed to demold and a latticework of wire, connecting each segment; building it on its side and then uprighting it.

Before I do anything, I was wondering if anyone has done anything this challenging using concrete.

It doesn't need a brick or block pattern and in fact would be more prototypically done just as a concrete dealy

Thanks in advance

Dave V 


Oh, it's the last photo (4th photo) down in the initial post


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## SE18 (Feb 21, 2008)

oh, I don't want it to be made out of styrofoam, as it will be holding a lot of weight and be walked on


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## Totalwrecker (Feb 26, 2009)

Welded steel and a off white powder coat. 
Was with the cast crete until you said walked on... that structure supports linear weight not vertical. 
It would be a shame for one too many pizzas to cause it to crack and crumble! 

John


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## jake3404 (Dec 3, 2010)

Couple things I could say is: 

-Pour it in place. It is going to be real heavy, especially with the rebar reinforcement you'll need so it can support your weight. Would hate to have you make this beautiful bridge and then have to hire a crane to get it into place. If your going to pour it all in one piece. 

Are you going to leave the inside of the spans open, like in the prototype? If so, I would maybe use forms carved out of high density foam. Make small pieces and then glue them in place with (PL Landscape block adhesive, this stuff is extremely strong). I would look at trying to make forms to make each "side" that includes the arches, then pour some "cross-supports" to glue in-between the "side" pieces and thus making the bride more open like the prototype. Word of warning, find ways to reinforce the sides with rebar when your pouring them, so they will hold your weight.


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## Cougar Rock Rail (Jan 2, 2008)

Neat bridge project--similar viaducts have definitely been done already in large scale so it's doable...just can't find the links when I need them! They have done them for sure in Germany/Switzerland--keep Googling! 
As Jake says, definitely pour in place and the foam knockouts are a good idea too. You may even want to investigate whether fibre-reinforced concrete is available locally, as long as the aggregate size isn't too big. For those thin beams a fine but high strength mix is what you need and maybe polymers added to. With those thin sections it will help to use a vibrator (such as a palm sander) on the forms to minimize air/segregation at the surface. 
If I find anything I'll post the links. 

Keith


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## SE18 (Feb 21, 2008)

Thanks. I'm writing down your tips, especially regarding the cross-members, and I'm thinking the prudent thing to do would be to construct a test span and then do the jump test on it with a stomach-full of pizza  

I'm not familiar with PL block adhesive but do have some Gorilla glue. If directions are followed (matching surface, water, pressure etc), I'm wondering if it would stand the test of time. Having glue fail would be a major headache


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## jake3404 (Dec 3, 2010)

I get it at my local Menards, ACE Hardware and Lowes. PL is the brand and its call "Landscaping Block Adhesive". It comes in a tube so you will need a "caulk gun" to use it. It is the strongest stuff I have ever seen. I used it on a landscape block retaining wall. I had glued one row down and then let the glue set up. I then realized that the row was crooked so I tried to take the row apart. No matter what I did I could not get the glue apart. End up having to scrap two rows of blocks. 

Afterwards I was curious how much this glue would take. The concrete would break before the glue would let go. That, in my opinion, is some very strong stuff.


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