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If I'd only known. .

The concrete bridge
By Marc Horovitz
Published: November 22, 2010

Have you learned a painful lesson?

Tell us about it in 300-500 words, with up to three photos. Let us know what you'd do differently if you had it to do over. Send your confessions to "If I'd only known," Garden Railways, PO Box 460222, Denver CO 80224, USA, or e-mail them to mhorovitz@gardenrailways.com
The overall structure as it appears today.
Photo by Marc Horovitz
A pier in the early stages of self-demolition.
Photo by Marc Horovitz
Alas, all is lost.
Photo by Marc Horovitz
My story concerns a concrete bridge I built some years ago. Concrete! The material of the ages! Once poured, never moved! Its very name suggests solidity and permanence. This is part of the reason I like it so much. Another is that it will assume any shape you like, assuming that you can create a suitable mold for it.

And create a mold, I did, as I needed seven identical piers. The finished piers would not be overly large, so I needed a way to anchor them to keep them upright in their ways and evenly spaced, like birds on a wire.

I hatched a plan. I would cast each pier with a pair of iron reinforcing bars in it, the ends of which would protrude from the bottom. Then I would carefully place my seven piers, with their respective irons projecting below, over a mold into which I would cast a large horizontal beam, also with rebar in it. Once solid, the bridge would behave as a single unit, which in fact it would be. This plan was carried out with great success.

While the finished bridge cured for a week, I dug a trench in the place where it was to reside. I then buried them beam there, with only the piers exposed. I laid track across the pier tops, the sun shone, and all was right with the world for several years.

Then, one dark day, I noticed a tiny crack in one of the piers. To my dismay, the crack spread. Similar cracks appeared on the other piers. What was up? The dismal truth finally dawned. It was the reinforcing bars! They were rusting inside the concrete. The relatively small section of each pier was not enough to withstand the irresistible force of expanding iron oxide. The bridge was doomed.

Today, all of the piers are damaged, most of them severely. The entire bridge, which is now surrounded by well-established plant material, is slated to be dug up and bodily removed, and a new structure made and put in its place-a daunting task. I've learned my lesson. No more rebar for me. For all future concrete structures, galvanized hardware cloth (which I've used successfully on other projects) will be my reinforcement of choice.
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HENRY TRUSHEL from OHIO said:
The problem is rain gets in & freezes(expands) in winter. What you need is a sealer.
ROSS MANSELL from UNITED KINGDOM said:
Couple of motorway (interstates) bridges in the UK had the same problem. Idiots use salt on the road here in the Winter!! Dog
THOMAS HUDSPETH from NEW MEXICO said:
Do you really need rebar at all? I mean, the weight of the trains is really light compared to the strength of the basic concrete. Just asking, I have yet to start my GR and I was planning to do without the rebar. Maybe that isn't a good idea?
4 stars
PHILLIP SUGHRUE said:
Just FYI, I hear the concrete guys talking about fiber glass re bar soon to be available. Should be a good alternative. Of course cost will determine that.

Great looking bridge though, very nice castings. Mother nature does do her thing well though.
4 stars
ALLEN JAY from WASHINGTON said:
Evidently, infrastructure problems is not limited to the real world!
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