AAC stops 2,000-degree flame, but not in CA

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I was just linked to this article, and found it both facinationg and disturbing:Material stops 2,000-degree flame, but not in California.

To summarize, there's a material called Autoclaved Aerated Concrete (AAC) that has been shown to resist flames of up to 2,000-degrees for 4 hours, has wonderful insulation properties for both sound and heat, is lighter than regular concrete, just as strong, 100% non-toxic in it's creation (if you don't look into the source of the aluminum too closely), 100% recyclable, and can be cut and shaped with hand tools. It's been used in construction in Europe for 70 years, is approved and used in 49 states in the US, and has met every building code test so far... except in California, where the building code people refuse to accept the seismic testing data that all other 49 states accepted. Many claim political shenanigans as AAC is trying to break into a business traditionally owned by Wood (big business in CA) and Steel (another big business in CA).

More reading shows that the regulations that AAC supposedly doesn't meet are relatively new (a 2003 house in CA was built with AAC before restrictions) and, though published by an international body and generally accepted, were intended to be used with a companion piece providing different standards for residential zones (AAC's primary aim in CA), which CA never adopted.

The material sounds awesome, but the coding stuff sounds iffy to me.

 

Ultimately, AAC is concrete. It has the same brittle properties as concrete and cannot pass the rigorous seismic standards California requires -- which are far beyond the requirements anywhere else in the world. But then again, California routinely survives earthquakes of magnitudes which would destroy other communities.

Years ago, the builders in California realized that brick (no matter how it is made or what it is called) does not fare well in an earthquake. Wood has the ability to bend and sway with the moving terrain and wood structures (as well as steel structures) hold up much better in an earthquake than brick, concrete, and even AAC.

It is not that the building codes in California do not accept the testing that has been done, it is that the testing does not meet the requirements of California building codes -- there's a big difference.

By the way, it's not 100% recyclable, it's not just as strong as normal concrete, and it does not have "wonderful insulating properites" (it has an R value of 1 per inch thickness). AAC is not a wonder material -- it performs about the same as solid masonry blocks that have been used in the US for the past century. Its chief advantage is it can be cut and shaped.

I liked this quote:

He ignores that AAC is specifically addressed in Chapter 21 of IBC 2006:

AAC masonry is not permitted in the seismic-force-resisting system of structures classified as Seismic Design Category B, C, D, E, or F.

Which pretty much covers all of California. I have never heard of a "companion housing code" for IBC -- the IBC code is a stand alone code. If there is a "companion housing code for AAC" it was written by the AAC people to try to drum up more business.

 

Nitpick: you forgot Japan

 

Dammit, google image search lied to me. Nothing to see here.

 

Ziad -- we sell in Japan. The seismic requirements for California are tougher than Japan. Although I would place Japan in the top 10% (behind almost the entire west coast of the US and Nevada -- along with Florida, due to the cyclic wind forces from a hurricane).

 

Ok, I'm just pulling information from the article I linked, so I'm open to correction, but how does Italy stack up to CA for earthquakes? They're pretty famous for them (though I don't know the magnitudes they see). Also, there are other ways to protect a building from an earthquake than to make it flexible itself. I remember seeing something on a bank in CA that's withstood the worst earthquakes CA has seen in recorded history, not because it's materials are flexible, but because the foundation uses layers of sand and gravel, which apparently absorb the shockwaves wonderfully. They essentially vibrationally issolated the whole building.

 

Actually T2Bruno, AAC does very well as far as earthquakes go, safecrete
has a couple of pictures of AAC buildings in Kobe, japan after the earthquake in 1995(it was a 6.8, IIRC)
The biggest advantages of AAC(& also flexcrete) is the light weight, ease of use, ability to cut & shape it on-site with common hand tools.

Yes it does have downsides, a low structural compression strength of only ~ 1,200 PSI(most standard concrete is ~7,500-15,000 PSI) but it has a much higher tensile strength to compression strength ratio than standard concrete.

Also, not a lot of inspectors have ever dealt with it & are subsequently very leery of it, so be prepared to have all of your supporting documentation on hand.

Some reactive powder cocncretes can have a compressive strength as high as 116,000 PSI & a few blocks made with an aggregate of steel fibers & quartz have been measured at 160,000 PSI !

It is still a better insulator & water barrier than wood. If you want even more insulation protection go with an ICF(Insulated Concrete Form) these typically have a R value of ~4 per inch of concrete in the form(which can be from 4" to 24", but the average is 6"-8")

I think we will eventually see it in california, maybe within a few years. Especially if obama gets his national standards passed, there wont be any way for california to have stricter regs than the other states. Thats good and bad. Right now each state adopts the IBC & adds whatever changes they feel are needed for their state.

 

The tensile to compressive ratio is misleading -- it has the same tensile as normal concrete, but a much lower compressive. Instead of a positive canceling a negative, you have a negative and a wash (still negative in my book).

The results of Kobe are also misleading -- those houses should be compared to concrete construction which followed the same building codes. I think you'll find very little difference between houses build to comparable standards.

The ability to withstand one earthquake is not really an issue -- the ability to withstand multiple 6.0+ earthquakes is to the State of California. Building materials are required to survive multiple quakes, my company built a test platform capable of duplicating a 7.0 in order to ensure our products will meet California requirements (and actually exceed the requirements). We've found very few concrete based materials that can handle the testing we do -- except Hardie board over wood or steel. Blocks just don't survive the test program.

The R-value of wood is ~0.85 per inch, not much different than AAC -- except you can put fiberglass in between the wood joists and greatly improve insulation of a wall.

 

It's still much better than standard stick built in so many areas.
Water permeability, impervious to termites, fire proof, sound insulation(min STC of ~ 36), a pretty green product, & did i mention light weight(35lbs per cubic ft compared to standard concrete at 130lbs per cubic ft)?

I'll take the insulation of a ICF over any amount of wood & fiberglass insulation any day.

Think about it this way, a thin coffee cup of styrofoam doesn't let the heat through & when filled with an iced drink doesn't sweat.
Know imagine 2"-4" of this on each side of your concrete wall. It reduces noise, heat transfer, HVAC costs by 30%-70% & numerous other benefits.

I just think california is being a wee bit overboard.

 

I've been on the 27th floor of a downtown Los Angeles high rise when a 6.8 hit about a hundred miles away. Looking out the window, I could see the horizon rocking back and forth.

I lived in a cinderblock duplex in San Pedro when a 5.0 hit the area and watched cracks form in the walls around me.

I think the California regulations are right for California.

 

Better to have and not need than complete a platitude. Er. Or something.

 

T2Bruno, comparing a cinderblock construction to an AAc or ICF house is like comparing a leanto to a standard wood frame built house.

As i haven't had to mess with the cali standards, we will have to accept your greater knowledge of them as it applies to the siesmic regs.

 

Not really martaug. The basics of the construction are the same as are the properties of the materials. The look of the construction is much different I'll grant you (as are the insulative properties) -- but the strength is comparable.