Lava-Cement to replace Ferro-Cement?

[OpenD]

quote:

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Originally posted by dobanion

All the rebar and the difficulty of wrapping/bending/wiring it was what turned me off of monolithic domes previously. This is fantastic.
And, you can use the same airform over and over, when built "Ecoshell" style like above.

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Not to mention that reels of basalt roving are a lot easier to ship/transport/handle than 20' long sections of rebar. And the "spatter" technique of hand troweling makes it practical for an owner/builder to build an Ecoshell without needing a concrete pump.

A little "napkin calculation" shows the materials for a 20' diameter, 320 sq. ft. dome to be about $1,500. That's hard to beat.

The prime issue, of course, is the cost of the airform. That's gonna cost about $5,000 delivered in Hawai'i, plus you need 2 inflation fans and controls (for redundancy - inflation failure for even a short time can ruin the project.) plus the power to run them non-stop for a week or more.

And while it is true that the Ecoshell airforms
can be reused many times, as they have done in India, for the owner/builder wanting a single use, there are no good options. To me, this is the biggest weakness to the Monolithic approach. A rental option would solve this, but they don't seem interested.

So, I am exploring alternate approaches that would allow forming a thin-shell reinforced concrete structure over some other temporary support. I'd like to find a way to be able to build these off the grid, by hand, without the use of any power supply.

[Rob Tucker]

Concrete's primary structural attribute is compressive strength. It lacks tensile strength. So in most all uses of concrete tensile strength must come from somewhere. Generally the tensile strength comes from steel. Concrete in all it's manifestations is a well understood science from an engineering perspective. Just slapping cement on an air form is a recipe for disaster. Saying you want a concrete dome but are too lazy to do the reinforcing work is a good way to get killed. It could be added to that list of "1000 ways to die".


Thomas Edison did some really good experimenting with concrete using bamboo for reinforcement. But bamboo has never been accepted for that purpose largely because there are too many varieties, variables and no system for consistently determining the structural capacity. With rebar of any grade you can dependably calculate the load and tensile capacities.

Lava or cinder is commonly used to produce "light weight" concrete. It is lighter than stone as an aggregate. But lava is extremely fragile and provides minimal to no strength.

[OpenD]

Sorry Rob, you seem to have missed the point... this is about using oriented basalt FIBERs to supply tensile strength, not adding crushed lava to the mix. My humorous reference to it being lava- rather than ferro- may have thrown you.

If you view the video you will see them winding the basalt threads around the form to create a tensile network, adding the concrete matrix, and then after curing, testing the dome with a weight test that demonstrates the strength of the method.

[Seeb]

Rebar is the easy part you have all the time in the world,

I have actually been in one of the Edison style cast houses when it was being remodeled. They must of had a trainload of forms. but it was pretty impressive everything! was cast in place

[Rob Tucker]

I am familiar with fiber additives. They do have a function and purpose but the tensile properties come no where near steel. Getting that proposed system calc'd by an engineer and approved by the building department could be a real challenge.

The live load demonstration in the film is a very weak and unscientific demonstration. I think that they have an interesting little system which would be an improvement in many third world countries.... but there is no mention of shear testing... this guy is taking about third world countries where there are no standards to be met... and he is likely right that what he has is better than what gets done in Sudan, Haiti, etc. His demonstration has no penetrations of the shell except for a doorway. Start adding windows for light and air and everything changes. Start changing the diameter and span and everything changes.

I understand the attributes of the domes. Good attributes. I was a shop foreman for a dome manufacturer licensed by Bucky Fuller in the '70s. I know of a number of experimentals done similar to the video forty years ago.

I'm not enthused about lowering our standards down to third world metrics.

I'm not trying to be argumentative but the most dangerous structures on the planet, especially in earthquake zones, are unreinforced masonry. Basalt fiber appears to be a semi reinforced design.

It may be that there is a fiber that mixed in the right calculated mixture could produce a load bearing dome structure that would be safe in some conditions. But guessing doesn't get you there. I do know that research is ongoing for steel fiber mixes and those results are mixed.. Most non steel fiber mixes are used to minimize cracking, not provide tensile, and are in fact used in addition to steel reinforcement.

Concrete is great stuff. My own home is reinforced concrete. Concrete has been around since Roman times and it a very well documented science. There's often proposals on how to save a nickel and if saving a nickel is more important than structural safety than all I can say is I am very glad our society requires building permits.

I don't really see the advantage to eliminating steel. Grade 40 rebar is really cheap. It is also generally 100% recycled material. So I am I guess merely cautioning about cutting corners in the name of expediency.

Best wishes.

[Peter Epperson]

I used to buy steel fibers from a company called Ribtec. Their offices were inside a 150' diameter dome that was reinforced entirely with steel fibers that were shot onto an airform. Their manufacturing facility was a series of barrel vaults reinforced the same way. There was a cable around the perimeter of the dome to provide hoop strength but the entire field of the dome was fiber reinforced. A dome, or vault, is different from most other structures in that almost all of the load is in compression. You should be able to get by with very little reinforcement.

There are other synthetic fibers out there that will give you long term reinforcement and by weight are stronger than steel. I've tried a few of them and all seem to have their place. The fibers that get delivered by local ready-mix trucks are polypropylene and they only give reinforcement for a few days after pouring. They are designed to help prevent shrinkage cracks while curing.

Steel fibers are nice because they distribute the load like ferrocement does. There is a guy in Scandinavia that builds boats using only steel fibers shot onto a form. They make stainless steel fibers also. Less strength but no corrosion. A rebar boat will crack to pieces. The Navy tried it. Their ferrocement boat on the other hand was a winner.

[Rob Tucker]

The steel fibers I've seen, that can be pumped or shot, are like little tiny barbells. Very small deformed bars. It would be nice if the steel component or a good tensile composite component could be pumped with the mix. I've been watching and waiting for twenty years. Doesn't seem quite on the horizon of commercial availability yet. Be nice when it is though.

I worked some with Navy engineering on some high grade composites too. Performed beautifully but were, at the time, 20x the price. All this experimentation is good stuff. I don't like to be experimented on though and I don't experiment on my clients.

[Jay Bondesen]

http://www.ecotopia.com/baggins.end/photos/nelson/

I can't help but add this link to some photos of a dome I worked on in 1971. It relates to a few things in this thread but just not the basalt part.
It's a dome made of PVC pipe shapes erected on a post & pier supported floor. We stretched burlap over the framework and sprayed on polyurethane. We then sanded the entire exterior surface and applied fiberglass with a chopper-gun. In one photo you can see the inflatable we put up over the whole jobsite to keep us out of the rain in the Santa Cruz mountains. We went on to build several small fiberglass domes on campus at UC Davis. They were supposed to be used as student housing for the time the students that helped build them were at school there and then removed as it was a class project. They still stand, after 38 years, and are in use by current students but I understand that this will be the last year for them. They suffer from numerous things but probably fewer problems than you would expect from a class project accomplished by a couple dozen college kids along with 3-4 tradesmen.
A search for Davis Domes will find pictures of them.

Jay

[allensylves]

Hey Jay, What kind of a hippy-dippy thread is this turning into - LOL? I was at grad school at UCD while you were bulding the hobbit village. I passed nearby since I was in Briggs Hall and the Bee Lab out by the airport but never actually knew anyone that stayed there. It is a surprise that they have survived this long. With the budget crisis in Cal, they might still survive??

Allen
Baton Rouge, LA & HPP

[Jay Bondesen]

Hi Allen, I know I got a bit distracted from the eco-shell but the dome talk just got me going. I was about 20-21 at the time and was the one spraying the foam inside the domes. The kids that built those things created and lived a kind of cult that has survived all these years. That experience is what led to move to Colorado a few years later where I ran into David South who later started Monolithic... Just a few degrees of seperation.
They might still survive but it will take some funding for repairs. There is a movement underway to try and make that happen.

Jay