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
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. |