3d Printed Concrete Forms for Architectural Post Tensioned Concrete Sculptures

[cjh83]

I am looking at the feasibility of 3D printing concrete forms to make a staircase that goes up a 4’ retaining wall. The forms would be cylindrical, split in half, and during the pour would be supported using a wood support system.
Ideally I would have one main highly curved support “column” (think more of a snake or spaghetti noodle) with then stairs that slide in via a mortise and tenon type connection. The stairs would be poured individually in a separate production process than the main support.
I plan on using a combination of a wire mesh, rebar and tension cables for the concrete reinforcement. The tension cables would run the length of the main support beam and would be hydraulically tensioned just before the formwork was removed.
I have ample concrete experience as a civil engineer and a construction manager but this idea seems like I need some outside input.
Does anyone have any experience 3d printing concrete forms. What is the best material that will hold up to the moisture and high alkalinity of concrete?
At this point I have no real conceptual drawings but I’m looking to see if any similar projects have been attempted and hopefully learn and improve on them!

[MaddieG]

Very interesting idea! I hope some of our community members have some insight here.

[wirlybird]

First thing is it will really be impractical. The scale at which you’d need to print will make it cost prohibitive probably.
You’d need to find a very large printer and I think the cost of filament and time would be through the roof.
To do this on more “normal” sized printers would take doing the form in many parts then assembling all of the parts would bring its own challenges.
The forms would have to be very thick to reduce warping or bending and to just handle the shear weights involved.
Theoretically it is doable but first the files need to be designed and then how to print. Ambitious project.

[cjh83]

I intend on breaking the forms into 2-part 10" sections. Each section will have multiple hose clamps around it to hold the hydrostatic pressure of the wet concrete. Each section will be temporarily supported via 2"x4"s and other temp bracing structures. I’m going to design the forms so there is a point to attach the bracing onto it.

Also I intend on pouring concrete at around 2’ vertically per hour. Basically slow enough that the concrete cures to a sufficient slump that it does not blow out the lower forms as I pour vertically, but fast enough that the concrete bonds and does not over cure and create cold seams.

The sculpture will start of a 1’ dia sono tube buried 3’ to 4’ down. The 3d printed forms will start on surface where the sono tube is then taper down to about a 6" dia at the top.

[wirlybird]

What kind of dimensions are you talking about for each part of a form? I was thinking this was going to be rather large.
PLA, ABS or PETG would probably work ok. The parts would just have to be thick enough to not deform under weight/pressures.
ABS and PETG will handle higher temps if it is a factor and will be stronger than PLA.
PLA and PETG will be the easier ones to print with. PLA would work I think as long as there isn’t much of any twisting or bending moment. PLA can be brittle and break easily if bent or twisted.

[cjh83]

By the end of the week I’ll have some concept drawings and site photos. I think this will help visualize what I am trying to achieve.

Let me add the the forms are not designed to take the structural load of the concrete and they will be heavily braced and reinforced for 28 days until the concrete is cured and I can tension the cables. There will also be quite a bit of standard rebar reinforcement.

Here is an article about post tensioned concrete slabs: https://www.concreteconstruction.net/how-to/construction/post-tensioned-slabs_o

Once I have a more refined concept drawing I am going to do a full structural analysis to make sure that if I get the completed structure in place that it will stand. I think that post tension cables are going to be the only way that I can get the required strength out of the size of formwork I can realistically print.

[cjh83]

[cjh83]

[rickparker]

Great design - testing the boundaries of what is possible with concrete!

Looks feasible to me. A bit of design work is needed to break the forms into printable lengths with good joints to maintain strength and the surface finish in the concrete. I say go for it!