Printed House (Concrete) failed in-situ strength tests 2

[JAE]

A printed house in Iowa was being built in Iowa and the test cylinders apparently came in at >5,000 psi compressive strength.

However, upon testing the concrete in place it wasn't that strong so they decided to tear it down and start over....an engineering failure of sorts.

https://hackaday.com/2023/11/29/iowa-demolishes-its-first-3d-printed-house/

I don't know anything more about this house other than what's in the link but my first thought was that this "printing" of concrete relied on repeated placement of concrete in the open air.

Did they not cure the concrete properly (i.e. test cylinders don't match in place strength)??
Normally concrete wass are formed and the forms act as a form of curing. This is simply stacked passes of concrete exposed to much more evaporation.
I could only guess that the curing may have been immediate spray curing applications as the wall was sequentially placed. Seems awkward.

That's what appears to be the case to me.

 

[phamENG]

hokie - I agree. That's why I'm saying the fix may be to add it in. If they're doing nothing for crack control at present, there may be alternatives that fit more with the 3D printing setup, but if they've already tried those they may need to go back to 'tried and true' method for CMU (since it's essentially just a bunch of mortar joints).

All in all, none of these issues seem drastically different than issues experienced in regular concrete or masonry construction, especially residential where reinforcing is somewhat optional (looking at you, ACI 332). Curing is done wrong, strength doesn't come up to where you expect it. They're not that common, but they do happen. We just don't normally hear about them on smaller and residential jobs because nobody bothers to check. Kudos to these guys for testing their product and verifying that it would do what they expected, and for doing the right thing when it didn't.

I think this technology has a future, but it needs to go through some growing pains to get the kinks worked out.

 

[spsalso]

" Kudos to these guys for testing their product and verifying that it would do what they expected, and for doing the right thing when it didn't."

They were paid $328,000 for that testing. As to verifying that it would do what they expected, that implies they expected the cracking--probably should have included that fact in their proposal.

The "right thing" appears to be patching the cracks. Perhaps with structural spackle?



spsalso

 

[phamENG]

Well, it is normal to pay somebody for their services. Testing labs don't run on kind words, after all. As for who got paid, I'm not aware of the particulars, but the generally accepted practice is that the owner hires the inspector and testing lab - the contractor is not able to profit from inspections through markups and it removes (or at least limits) the potential conflict of interest that results from the wolf paying the sheep dog that guards the sheep. This is still considered a novel construction technique, so there may have been an alternative arrangement. I curious where you got that number? Reports that I've found indicate that the houses will list for $300k or less, and the subcontractor responsible has agreed to absorb the cost of the failed house and won't be increasing their bid for the other houses. So the $328k for testing on a single house doesn't add up unless it's part of a proof of concept cost they're putting together for potential investors to expand after this project.

Testing is done (or is supposed to be done) on all concrete construction projects of consequence that are under the jurisdiction of a building official in the US. They're called special inspections. It's because we know that things don't always work out. Contractors make mistakes in the field, concrete suppliers use the wrong material, the truck sits a little too long in traffic and they use the concrete anyway, etc. Concrete cracks - it's a simple fact that everyone who's been in the industry for more than a day or two should be fully aware of. Houses are another story - testing isn't usually required at all. The Engineer or Record (if there is one) or the Building Official can decide that they need to be done, but it's rare. I'm not surprised it was done on this, but I wouldn't have been surprised if they hadn't, either.

The right thing is tearing it down when they determined the material wasn't behaving the way they anticipated. Half-assed patch jobs on potentially critical structural deficiencies aren't the right thing to do.

 

[spsalso]

"Well, it is normal to pay somebody for their services. Testing labs don't run on kind words, after all."

"This is still considered a novel construction technique..."

I guess it depends on the contract. If the purchaser knew that the building would use a "novel construction technique", and still agreed to pay for the job, as delivered by the builder, then of course it's pretty much work for hire. Or, as you call it: "...pay somebody for their services."

On the other hand, if the purchaser was not made aware of the fact that this construction method was new and relatively untested, then it appears that the "testing" was done for the benefit of the builder at the expense of the customer.



"I curious where you got that number?"

From the first link provided by Tomfh (above):

"Cr Dickerson said it cost the council nearly half a million dollars to build three toilets in the CBD during 2020.

The new 3D printed construction would be $178,000 cheaper, and would include more than double the amount of toilets plus an additional three urinals."


$500,000 - $178,000 = $322,000 (sorry about the error of $6000)



"The right thing is tearing it down when they determined the material wasn't behaving the way they anticipated. Half-assed patch jobs on potentially critical structural deficiencies aren't the right thing to do."

Totally agree. At the builders' expense. Plus they need to refund all the "testing" money, so that the building can still be built.



spsalso

 

[phamENG]

Ah. I was still talking about the house in the OP. I have no idea what the norms are in Australia for testing.