How to make 3" concrete "legs" via reusable casting structure?

Question

I have a design for a (set of) planter(s) I'm trying to make, and to make the design I have in mind, I need an 18" long 3" OD leg with a bit of rebar in them. (let's say 100 of these bad boys in toto)

My initial thought was to cast it using PVC pipe and cut the pipe off, but pricing that off the top of my head has the cost of PVC to be about $60 in cost. I wanted to make the legs round, but would settle for square if that would be less cost prohibitive.

If I use PVC with endcaps, can I fabricate the legs in such a way that after "casting" I can neatly slide the legs out of the PVC pipes, thus allowing me to reuse the PVC repeatedly, or is there a better method for making over 100 18" 3" OD concrete (with rebar inserts) concrete columns than using PVC during the pour process?

_{If it matters, I was going to use quikrete crack-resistant concrete, but am totally open to ideas.}

Answer 1

Yes, you could use 3" PVC schedule 40 pipe such as This one from The Home Depot. Cut it to length, then cut it lengthwise on one side and use duct tape to hold it together... This single cut will keep the round shape and when it has set, it will give you the ability to flex the pipe enough to have your cast come out. I would not use a PVC end-cap, but I would just make a duct tape one. Cutting ten foot length pipes will make you six molds per pipe @ ~$9 per pipe.. 100 casts in 8 batches for < $20.

Answer 2

Consider using a super-plasticizer, also called a water reducing agent. This makes the concrete highly flowable with very little water, so it maintains its strength.