3D Printed Concrete Walls

[jerseyshore]

Have a potential project where the owner wants to utilize 3D printed concrete walls. We'll have a traditional footing 3 ft deep, then 2 ft of below grade (non-retaining) printed foundation walls plus about 10 ft of ground floor printed walls with a two story wood house on top.

Anyone have any experience with these? Any tips or advice if this thing goes forward?

The owner said they spoke to someone who has done this before and is willing to provide some guidance. I said I wouldn't even start the project until I saw ICC reports and the building department pre-approves it as a method of construction.

 

[Factoter]

Wish I could say I knew something practical about this, but am still largely baffled by it. Think I understand shotcrete and prefabs’ but not so much the ribbon of mystery mix cement. It seems to be a variety of adobe, slump wall.

https://en.wikipedia.org/wiki/Reinforcement_in_concrete_3D_printing

 

[phamENG]

They should probably go through the company that will build it (sorry). These are highly specialized and the builders generally have their own engineers. The highest profile builds are happening in Texas (look up Icon 3d printed concrete), but there's been at least one here in Eastern Virginia. Not sure who built it, though.

Just looking at the process, it's probably most comparable to URM.

 

[jerseyshore]

The owner wants to purchase a couple of the 3D printers and build it themselves so that throws another wrench into things obviously. I'm not sure if my insurance company would even cover me for something like this even if it was approved by the town.

 

[SWComposites]

Run far far away. Let the owner and the 3D printer company sort this out.

Even most of the 3D printing stuff I have seen in the aerospace industry is what I consider to be in the “research” phase.

 

[milkshakelake]

I'm a bit more risk-taking, so I think you should take the job. I'd only agree to do this job after receiving a lot of documentation about the testing and specifications. I'd imagine it uses fiber reinforcement or metal shards instead of rebar. I'm not too familiar with it, but last time I checked, there is an ACI code on this. I attended some webinar about alternatives to rebar, so there's research about it out there. Also, there should be some contingency about what happens if the construction fails to meet requirements.

The concrete itself should comply with compression strength testing using cylinders taken from the site. I don't think the bending needs to be tested. I'm not sure how one would test/inspect the fiber reinforcement, but the testing/inspection procedure for that should be noted as well. It might be on their ICC reports. I'd also look into things like how they test for slump, air content, and vibration during pouring/3D printing. Since this is a pretty new thing, I'd look deeply into every aspect of the design mix and how things are verified, and what the building department would be willing to accept as far as testing and specification.

Then there's the question of the limitations of the 3D printing. I know that regular 3D printing has limits on things that can be printed and even requires "formwork" for certain things. So all of that needs to be considered in the design. If it's just footings or piers, I wouldn't worry. But if it's a shear wall with openings or even a floor slab, I'd look into it.

I'm guessing they have their own engineers but would need an EOR in Jersey to sign off on things. So you have to do your homework and coordinate with the building officials. If New Jersey is anything like New York, the building departments vary from town to town, so you'd have to do it in multiple areas (possibly using one area's letter of acceptance to influence the others). Obviously, you charge the owner for all this legwork. But it's kind of a one shot deal for each building department.

From an entrepreneurial standpoint, I think your client is trying something bold. And if you pull it off, jerseyshore will be the go-to engineer for 3D printed concrete in your area.

 

[KootK]

And if you pull it off, jerseyshore will be the go-to engineer for 3D printed concrete in your area.

That's my feeling on it as well. As we all know, a structural engineer without a specialty is mostly a commodity other than from a general, client service perspective. This could be your specialty if you pull it off. If the owner plans to do a lot of this stuff, have them get their own insurance and add you to that policy as a named insured so that you can have it as an exclusion on your own policy.

When weighing the risk proposition for this, there probably isn't much in it for you personally if you're an employee. If you bother with it, I'd keep the client handling close to your chest for when you go out on your own.

 

[Brad805]

I would consider the project, but only if the owner has some concrete background. This technology requires a much better understanding of pour rates and mixes.

What I find interesting is how owners are sold on this. The technology to pour the walls is fascinating, but building a wall for a home with concrete on both sides is a huge step backwards unless I am missing some part of the puzzle. It seems largely like a high tech method to make a URM wall. Why would I do that if I want to heat or cool my building efficiently?

 

[phamENG]

Brad - you're largely correct. That's one of the reasons most of this is happening in areas with arid climates. The look even fits well with local vernacular architecture.

There is a company doing them here in the mid-Atlantic. Sadly they don't show any details or footage of installing any sort of moisture control/insulation for the exterior walls. In one video it looked like somebody when around with a trowel and 'smooshed in' the bulges from each pass of the nozzle to make it fit in a bit better around here (lots of colonial style clay brick or clapboard siding).

 

[jerseyshore]

So I would be doing this on my own, for my company.

Like I said above, the owners want to purchase the 3D printers themselves and run it with help from the manufacturer. I would be EOR for the building with some guidance from the manufacturer and another engineer who did a project in Florida recently (or so I'm told).

From what they showed me, the walls print in a sort of lattice type fashion and I think the rebar would then fit into the voids and filled solid.

They would be using a Sika material that I'm told gets to 3000 psi pretty quickly, maxing out around 5 or 6ksi I think.

It's a pretty basic use for these walls. Just 10 ft tall ground floor walls with 2 stories of wood above. Low seismic, average wind, not retaining anything.

And the only reason I am interested in this is for the reasons stated above, I'd be one of the first engineers in the state to touch it and it's a relatively basic use.

 

[jerseyshore]

And just to add some context, the owner is a custom millwork/ fabricator/ carpenter etc. They use regular 3D printers for a lot of their work so they're very familiar with that side of things. That's the reason they want to invest that type of money into the printers.

 

[SWComposites]

What is their plan for QC of the printed material? Periodically print some test specimens?

In general for 3D printing, process control seems to a big issue that a lot of the material and printer suppliers want to avoid discussing.

 

[phamENG]

jerseyshore - that does change things a bit. If they're looking to get into the business cold, then by all means go along with them. But I'd be looking for other engineers who have gotten these through county/city building departments. Or maybe going straight to those departments and find out what they required and what was provided. Some of them are really excited to be part of it, and may be more willing to share some of that information. On the other hand, most of these outfits are tech firms first and guard their process like it's the next billion dollar idea (to be fair, it might be).

Once you do that one, if they decide to come south of New Jersey at all let me know - I wouldn't mind getting in on it!

 

[jerseyshore]

I have no idea about plan for QC. The only info I've seen is just a quick video and some photos the owner had from the manuf. In my proposal I said specifically that I need all the documentation before I start any work.

The good thing is that the owner understands this may be a challenge and if they have to just build it out of CMU that's no problem. But he wants to give it a shot to see if it's feasible. So I'm down for a little adventure.

 

[milkshakelake]

@Brad805 I didn't get the point of heating/cooling effectively. I'm not sure about concrete, but CMU is pretty good as insulation, though not just by itself. As far as I understand, CMU+insulation is better than wood/CFS+insulation.

 

[phamENG]

MSL - I'm going to be a bit pedantic: CMU, like brick, is actually horrible as insulation. What it is good at is providing thermal mass. Insulation restricts the movement of thermal energy, but a material with thermal mass absorbs it. If done properly, it can be used to passively heat a space in the winter.

For instance, one year I was able to grow tomatoes along the back brick wall of my house well into late November, several months after the ones in the garden froze to death. That back wall gets about 6-8 hours of direct sun, and the thermal mass stored that heat and kept a micro-climate just big enough to let those plants survive a mild frost or two.

So yes, CMU + insulation can be better in certain climates, but to get the benefits you have to design it properly as a passive energy element in the house.

 

[milkshakelake]

@phamENG That makes sense. Though in any case, wouldn't it still be better than any type of stud wall? I was speaking to an architect that told me stud walls are the worst type of wall in my climate (not super hot, not frigid, but sometimes freezing). For normal living, I think a good thermal mass would be an advantage in all cases. In cold climates, it holds the heat from inside. In warm climates, it traps the heat from the sun from entering. Insulation would be placed accordingly to restrict the transfer of heat from the CMU.

 

[Brad805]

Milkshake, take a Flir thermal camera out on a hot day and take some images of your CMU walls. You can find all the solids easily with one of those. It is a similar story in the winter. We have clients who have built ICF walls from ground to ceiling. They find significant reductions in heating or cooling costs by eliminating all of the thermal breaks. Does it pay off? At one time likely not. Now it can be quite close in some markets. Wood stud with finishes directly applied to the exterior sheathing are the same as your CMU.

 

[phamENG]

Not quite. In colder climates, it can be used to passively store radiant heat from the sun and discharge it into the space at night. But it's passive, and there other design elements that have to be in place.

In warmer climates, it doesn't stop the heat from entering - it just slows it down a bit. It stores up heat all day, and discharges it continuously. So any advantage you might have from a cooler night is mostly lost as your wall continues to discharge heat through the night. In those cases, it's best to insulate and prevent it from heating up in the first place and conditioning the air inside (since in a lot of hot climates you have to deal with hurricanes, and a block house has more important advantages there).

This is one of the reasons exterior insulation is being brought into the newer residential codes. I believe my area is going to have a requirement for "+R5 continuous" or something like that. So we still have the R19 requirement in the wall, but there has to be an additional layer of insulation outside the wall to cut off the thermal breaks from the studs.

 

[jerseyshore]

All I hear from architects and builders the last 3 months are how much a PITA the new energy code has made construction since it went into effect here. Lots of R6 Zip sheathing being used. Lotta spray foam. Bye bye 2x4 walls. Lucky for us it doesn't really change our jobs. Actually makes it easier since I don't have to fight for 2x6 walls or 2x10 ceiling joists/ roof rafters anymore.

But for this project, the walls will be exposed. The ground floor is going to be a drive-thru/ carport style when finished so no heat/cool issues to worry about here.