# Foam Culvert/Bridge



## docwatsonva (Jan 2, 2008)

I was going to comment on Yogi's adobe building technique but I decided to create a new post that describes my experience with concrete on foam so as not to take the thunder away from another of Yogi's excellent tips.

It is my opinion that creating structures by layering concrete onto rigid foam is an excellent method for building. You can create structures that will stand the test of time. Evere since I learned the technique from Kevin's father many years ago, I've felt that this was the way to go for some things. My first attempt was the building of 2 tunnel portals for my old RR in Virginia. Not only did the portals last for the 9 years I operated that RR but, when it was time to move, I removed them and brought them with me.

Here's a photo of one of the portals:











In the construction of my new RR here in western NC, I decided to use this technique to build a culvert/bridge for my water drainage project. The process involves cutting a foam form to serve as the basis of the culvert ends. The form is about 24" wide by 8" high with holes cut for the drainage pipes. I sat the form on a large piece of foam and surrounded it with foam strips that were 1/8" higher that the thickness of the foam. I used a felt tipped pen to mark the foam dams to indicate where I wnted to create the lines representing the stones that I would later carve into the concrete.










Here's a close up of the form with the surrounding strips. Noticed that I also gouged a bunch of holes into the foam. This was to provide a little more "grab" for the concrete.











Next I cut 2 short pieces of PVC pipe 1/8" longer than the thickness of the foam. These were to serve as inside edges (dams) for the concrete.











I then mixed a batch of vinyl concrete patcher about the consistency of a thick pancake batter and spread it onto the form.












After getting the layer of concrete smooth and even, I used a straight to first cut the horizontal lines and then I used a short piece of 1/2" wide by 1/16" thick styrene to create the vertical lines. I used an artist's palette knife to do the horizontal line cutting.











Here's a picture of one of the culvert ends after drying overnight.











After completing the initial layer, I taped off the finished surface, created another set of foam edging pieces, and layed on another layer of concrete to create the top cap stones. Then I cut circles out of a piece of 1/8" plywood equal to the diameters of the drainage pipe trim and layered on some more concrete to form these.

Here's a photo of a completed end.










After finishing another end piece. I cut lengths of PVC pipe and glued them into the ends. I glued pieces of 2"X2' aluminum angle the the backs of each end to provide a little extra rigidity. Maybe not necessary.

Here's a photo of the completed culvert/bridge.











Hope this can be of some help to those of you who may be considering using this technique for outdoor structures.

Doc


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## Jerry Barnes (Jan 2, 2008)

Nice work Doc! I made a bridge, just using the foam, scribing in the patterns. Critters liked to eat the top of the foam, so I did use the concrete vinyl patch on the top edges, that seemed to solve that problem. IF I had it to do over again, and I probably will, I would follow your excellent example.


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## dltrains (Jan 2, 2008)

Really nice Doc. Looks like it should serve you well.Is it going to support track, roadway, or foot traffic? 

Dave


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## docwatsonva (Jan 2, 2008)

Thanks Jerry and Dave.

Dave, the culvert is intended to support 3 tracks on a 20 ft. dia. curve. The 2 ends are about 27" apart. After I set it in place, I'll fill in around it with 1" stone and then cover it with stone dust to set the track. I'll blend it into the surroundings with some carved concrete rock walls.

Doc


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## lownote (Jan 3, 2008)

Doesn't it set too fast to do the vertical lines? My limited experience with the vinyl concrete is that it starts to set up really fast

That looks great, by the way


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## docwatsonva (Jan 2, 2008)

Mike,

The work time seems to be between 20 and 30 min. The other variable is how wet the mixture is. The wetter it is the longer the setup time. If you're working on a flat surface, with dams, the mixture can be made a little wetter, however; if it's too wet, it could make the final product structurally weaker. It took a little practice on some test pieces before I got it right. For the ends of the walls, I mixed the batch a little stiffer. But, since the edges were only 8" long and about 1" thick, it didn't take that long. BTW, the edges were done freehand by slapping the mixture on the sides with a narrow trowel and sort of hand carving the stones.

I think the size of the piece was about as big as you'd want to go. Any bigger and I think you couldn't finish in time. This technique does have it's limits.

In a project like this one, having the spacing markings already in place allows for a quicker work time. I think it took me about 8 - 10 minutes to get a nice even surface and about another 5 minutes to cut the horizontal lines. By the time I finished the vertical lines, about 20 minutes had gone by. The concrete was beginning to set up but, since I was using the piece of styrene to actually push the lines into the concrete, it seemed to work OK.

Doc


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## astrayelmgod (Jan 2, 2008)

Ambient temperature maks a huge difference in the set up time. In hot weather, in direct sunlight, I have had cement get too hard to work in 15-20 minutes. Another time, I had to do some last minute work before a meet when the temperature was in the low 60's, and after six hours the batch still wasn't set. I don't know how long that batch took: it got dark, and I had to give up.


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## docwatsonva (Jan 2, 2008)

I did all the work in my workshop where the temperature is about 70 deg. So all the times are based on that. I've never done any of this stuff outdoors.

Doc


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