Building the railroad that Went to Sea with photos.
Page 5

Building piers for the concrete arch railroad bridges.

     The concrete Roman arch concrete bridges are fascinating structures. When Henry Flagler was queried about how he was to build so many bridges over the ocean, he replied to the effect, "Well, I will build them one arch at a time." For the purpose of this web site I have separated the construction into two pages. Henry Flagler in effect did the same. The support piers were built first and the arched structure built on top of the piers.

     This was far more complex than the following five photos will explain. To begin with, anything can be built of concrete for which forms can be built. The concrete hardening process is a chemical process - not air drying - therefore will harden under water. Forms, called cofferdams, were built and anchored to the ocean floor. The mud and loose residue were pumped out and wooden piles driven to anchor the mass to the ocean floor. A special strong mixture of "Alsen" cement was poured through a funnel like apparatus to form a seal around the bottom of the cofferdam. Then the water was pumped out and the form filled with a regular mixture of the Alsen concrete mixture with the steel rebar held in place. When hardened, the forms were removed and reused. This process was repeated many times. Alsen cement was a Belgium cement similar to our Portland cement. Tests revealed that Alsen was better for under salt water use. The mixing process was the same as with any concrete. The aggregate rock was shipped in form New England states, that is coral rock was not used in the concrete mixture.  Now to the images.

     Above the cofferdam is shown in place and anchored. Piles are being driven into the ocean bottom.
     Above is a completed series of cofferdams ready to fill with concrete.
     A specially made concrete plant was made to operate close to the cofferdams.
     This is a busy photo, but in front of the work derrick are a series of concrete piers with the steel rebar ends protruding upward. Click on the image to enlarge. On the following page, the remaining part of the arch will be built on top of these piers. 
     But first a comment about on another concrete piers used to support steel trust bridges like the Seven Mile and Bahia Honda Bridges. The construction process was the same except the size and shape of the forms were different. The water was so deep at Bahia Honda that metal cofferdams were used. The photo above is for the Seven Mile Bridge near Knight's Key.
     Let's move on and complete an arch bridge.
Railbed Construction Continued on Page 6
Go to shelf 6

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