The Viaduct

I've always had an interest in the Roman aqueducts. So, I thought, why not a stone viaduct for the railroad?   

If cost were no object I'd have purchased the necessary molds, etc. from Stoneworks

However, we're still dealing with the real world, so it was off to "Plan B." Much procrastination ensued as well as debate on a thread on MyLargeScale.  With the basic questions answered it was off to find construction materials for forms. I wanted an arch diameter of about 6 inches. A coffee can would have worked, except it was about an inch too short  Hmmmm.  PVC pipe? Probably too hard to get it out after the pour. Sonotube? No 6" available locally. As a sage once observed "There is always a third alternative" and that came in the form of galvanized vent pipe. Seven inch diameter x 24 inch long pieces. So I get 3 sets of forms from each stick.

OK, that's solved, so onto pouring the base.

Some measuring with the string to determine radius of curve, some spray paint, some shoveling....

Vertical pairs of rebar will reinforce each pier. String line is approximate height of railhead. Got a little carried away with the shoveling, so bricks form one side of the excavation.

Mix 200 pounds of concrete, pour, level, go back to engineering in the garage, where it's 65 degrees, not 92 like it is outside!                                 

Stove pipe has been fastened to 1/4 masonite, cut in wedge shape so bottom of pier is wider than top. Other pieces were cut similarly for the sides. Concrete mix poured in, but just half-way up the arch. Sides from this point are vertical.

Foam insulation board cut and sandwiched so it just slightly overlaps the poured piers. 1/4" threaded rods go through the pipe and clamp the entire mold together. The stuff bends easily, and has a plastic film on the sides. Should make it easy to release it from pour when cured.

Notches were cut into board to allow placement of line poles so they'd be surrounded by a decent amount of concrete. Used 1/8" and 3/16" steel rod from local hardware store (They didn't have enough 3/16" in stock!!!) Primed and painted black.

In the center of the pour are 5 pieces of foam board, each about an inch square. They were glued at one end, then bent to form a center channel. Wedges help to keep them more or less centered. Concrete was poured to about an inch and a half of the top of the sides. Then cement was put down about a half-inch thick, then the center form "squoze" into place. Added cement to top of form to make side parapets. Result is at right, after center form removed. Going to need some touch up, or maybe not if I opt to install stone veneer.

Things cleaned up a bit. Trough isn't exactly centered. Thinking more about using vinyl concrete mix to make cast stone veneer.

Overall, this is how things look. Used a cut-off wheel in the drill to smooth out some of the irregularities in the walls. The stove pipe forums came out easily as I had left the crimped seam at the bottom of the circumference, meaning all I had to do was reach in and un-pop it to release it from the pour.  Weather continues unbearably hot and sticky for Western Pennsylvania -- we're not supposed to have a heat index of 97 in July -- that's August weather!!


Note: Never did bother with any veneer dressing of the sides. The concrete has weathered nicely. There's been some spalling around the line poles, and several sections of the edging have broken off. -- possibly from the freeze-thaw cycle. The missing parts may be replaced with tie cribbing. Those should look reasonably prototypical for cash-starved trolley line.