local sustainable bldg materials and methods?

[Ccat]

See my attachment. I pondered doing something like that, but with lava rocks. So the bulk of the wall is still lava, free material, and it looks cool, but backed with steel reinforced concrete.

I have a 6ft tall circular outdoor shower made of stacked lava rocks, but I wouldn't trust it to last during a 7.0+ quake. It took a 5.8 ok.

Wow!  thats beautiful.  Is that in hawaii?  How much time did it take?

Ccat

[dobanion]

Nope, just found it when scrolling through dozens of photos on a google search for "rock wall construction." It was the best example of what I had in my minds eye, were I to do something with the pile of rocks I too have on my lots.

I also consider doing the above but changing it to a round structure (my dome obsession again), and capping it with a yurt style roof. No reason you couldn't thatch a roof like that either.

[MarkP]

Due to ADD and autism, I tend to be "free thinker" and I spend a lot of time reinventing the wheel. This is mostly a negative.

With regards to this picture and variations like it (looking at you, slip-form stone masonry) I think that the strength comes from the steel reinforced concrete. The rocks are decorative and because of their mass they make it that more steel and concrete is required so the wall is strong enough to not fall down in an earthquake. Furthermore the kind of stone masonry that does best in an earthquake is ashlar masonry where the stones are cut so they have horizontal surfaces that overlap. Such stones do not try to wedge between the stones in the lower courses as gravity pulls them down, and the tensile strength of the stone comes into play. If you had a good foundation and were careful you could stack concrete blocks really high but you could not do so with bowling balls. The stones in the picture remind me of bowling balls.

I could be wrong but I think in many cases where a stone wall is combined with reinforced concrete, adding the stone results in more concrete being used not less and makes the wall more susceptible to earthquake damage. The wonderful examples from the past seem to be due to workmanship so good that the stones, when displaced, would just as soon fall back into place as fall apart.

I think that remarkable things were done in the past and could theoretically be done again. One variation of the masonry of the past is called Cyclopean masonry. The term comes from the belief of classical Greeks that only the mythical Cyclopes had the strength to move the enormous boulders that made up the walls of Mycenae and Tiryns. So if the building department balks at the idea of building with unreinforced lava rock just tell them "No worries. We know a guy".

[Ccat]

Domegaias aircrete domes?  yep, an artists delight!  

But, I have heard there are problems with cracks that form, after construction.  Is that a structural thing with domes, or is that due to the basic nature of aircrete?


Ccat

[dobanion]

I contend it’s aircrete, and more specifically, the lack of tensile reinforcement that leads to cracking. It all comes down to the concepts of compression and tension. Domes, all domes, have areas that are under compression (mostly), and tension (usually halfway up). Concrete has lots of compressive strength, aircrete less so, but still enough not to pulverize under it's own weight, but neither of them have much in the way of tensile strength. If you don't have any tensile reinforcement, it's going to crack in the areas under tension. So, yeah, it's part of domes in general, but easily solved by incorporating reinforcement. But aircrete constrution using blocks makes that nearly impossible to incorporate in the aircrete itself. Reinforce the blocks, and the cracks will just move to the joints between the blocks.

I saw Domegaia recently made a arched structure, like a quonset, out of aircrete, and coincidentally made the shape that of a inverted cantenary, like the St Louis Arch. Very good reason for this. That shape has almost zero tensile forces, it exists in perfect compression along the entire shell.

Were I to build anything with aircrete, I’d cover it with some basalt or fiberglass mesh and apply some mortar. By then it would have just been easier IMO to build a dome with rebar in it to begin with.

I think on this often, and it's really hard to beat the utility and especially the speed and ease of construction of a concrete dome built using conventional redi-mix delivered concrete, concrete pump, and shotcrete application. Yes, you need a lot of equipment to do it this way, but you can get the whole job of concrete application done in an hour.

[Ccat]

I contend it’s aircrete, and more specifically, the lack of tensile reinforcement that leads to cracking. It all comes down to the concepts of compression and tension. Domes, all domes, have areas that are under compression (mostly), and tension (usually halfway up). Concrete has lots of compressive strength, aircrete less so, but still enough not to pulverize under it's own weight, but neither of them have much in the way of tensile strength. If you don't have any tensile reinforcement, it's going to crack in the areas under tension. So, yeah, it's part of domes in general, but easily solved by incorporating reinforcement. But aircrete constrution using blocks makes that nearly impossible to incorporate in the aircrete itself. Reinforce the blocks, and the cracks will just move to the joints between the blocks.

I saw Domegaia recently made a arched structure, like a quonset, out of aircrete, and coincidentally made the shape that of a inverted cantenary, like the St Louis Arch. Very good reason for this. That shape has almost zero tensile forces, it exists in perfect compression along the entire shell.

Were I to build anything with aircrete, I’d cover it with some basalt or fiberglass mesh and apply some mortar. By then it would have just been easier IMO to build a dome with rebar in it to begin with.

I think on this often, and it's really hard to beat the utility and especially the speed and ease of construction of a concrete dome built using conventional redi-mix delivered concrete, concrete pump, and shotcrete application. Yes, you need a lot of equipment to do it this way, but you can get the whole job of concrete application done in an hour.

What do you think about adding fiber to the mix?  Does that really solve the cracking problem?

Ccat

[Punatang]

What a great thread.  Thank you all, I've been turned onto Domegaia and Rastra and other great ideas and I have a question. Is there any reason that aircrete blocks could not be formed with cavities similar to the Rastra blocks and utilized in the same manner as Rastra?

[punikahakaiferret]

There is currently an episode on YouTube on the "Exploring Alternatives" channel featuring Joel from Domegaia and it goes thru the process explaining and demostrating how their aircrete is made, with fiberglass both inside and out, with aircrete blocks sandwiched between.

But if anyone has gone to Domegaia's website they've probably seen this. Just wanted to share.

Love this thread!

[dobanion]

Sure, no reason you couldn't mold aircrete into blocks, and those blocks could be the same basic shape as Rastra, ie leaving those round channels for rebar and full strength concrete.

I need to go see this video with inside/out fiberglass on aircrete. I'll assume they used some sort of mesh?

Theoretically, you wouldn't need to do both sides. The tension forces on a dome are the highest at the outside surface. Same reason a conventional monolithic dome is built with the rebar not in the center of the shell, but rather as close to the outside surface as possible. So, I'd suggest a aircrete dome could be wrapped in reinforcement, then a thin topping of conventional mortar would do the job.

Does have me thinking a bit. Me being the dome guy I am, and owning an airform, I always figured whatever I did had to be spray applied. Aircrete is generally regarded as being so fluid before setting, that the only way to make it useable was to pour into forms, making bricks of various sizes. But, I have access to some interesting thickening compounds which could made aircrete "stand up" in such a way as to be applicable to a airform. Calls for an experiment.

[Punatang]

Calls for an experiment.

Somewhere in this rabbit hole you guys have lured me into, I watched a video of a guy who poured a circular footing 14' ish and then plopped a tyvec air-form on top of the foundation, draped fiberglass mesh, sprayed a layer of "latex concrete" over the whole thing, let it cure, then laid chicken wire over the whole thing and sprayed another layer of concrete. Reinforced 14' dome for like 5k (probably mainland prices so 10k here) and it took a few days. He claimed this would be "up to code" and could be permitted in most locales. With your equipment you probably are half way there already.

EDIT* found the vid: https://www.youtube.com/watch?v=DVk6xNFduH4&ab_channel=AircreteHarry

EDIT#2 in this vid he shows a double wall shell made of stucco into which he pours aircrete. https://www.youtube.com/watch?v=-90FPThl0ak&ab_channel=AircreteHarry

Haven't seen anyone spraying thickened aircrete yet. Maybe you can make an Aircrete Dobanion video! What do you think would thicken it enough to make it work on an airform?

And thanks for the response on the aircrete/Rastra idea. Seems a bit more local/green/economical that way.