AAC, or Autoclave Aerated Concrete, was something I just became aware of. I watched a show late last night on Discovery channel about this unusual (to me) type of concrete. It weighes 1/5 what conventional concrete weighs. The take sand, if I remember correctly, grind it extra-fine, mix with water for a really smooth slurry, add Alumina, mix and pour into a mold with suspended rebar and place into the first oven at about 120ºF for an hour, or so. Then, that take it out of the mold, trim the pudding-consistent result with piano-wire thin cutting wires and put it into an Autoclave oven at 300-350ºF for 3-4 hours and it bakes like bread–it actually rises.
Evidentally its a product that has been in use in Europe for years. It has a thermal value of R-20 for an 8″ thick slab and remains structurally stiff (can be used for floors and ceilings) for load-bearing uses. I watched on person use an ordinary hand saw cutting it as well as a hole-saw.
The show suggested that the reason why it hasn’t been adopted in North America (or rather the United States) is the expensive factory setup costs, and this must be the Autoclave ovens. Still, there is one factory down in Florida (outside of Orlando, they said). I wonder how this could be used in precast, rapid-erection hahahahaha residential construction like SIPs offer.
I have no idea what the costs are and how it would compare to SIPs for shell construction.
Replies
The first question that comes to mind is how they control that 'rising' factor you mentioned. Are the resultant panels/units/whatever conceived of as cast to finished working size, or are they meant to be trimmed/shaped on site like a piece of dimensional lumber?
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Azek starts out as a thin strip and rises just like that foamy insulation stuff.
I don't how they control it but they do. It is not shaped for thickness, only width.It's Never Too Late To Become
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Okay, you've got me on this one. I've been hearing the name Azek bandied about but don't know anything about it. Is that a trade name for ærated autoclaved concrete? (Hope that's not the dumbest question I've asked this month, LOL....)
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
http://www.azek.com/
PVC (?) trim boards.
It's the nuts around here. 18' lenghts, you can leave it unpainted.
There was an intereesting thread here last year sometime. Apparently there are minor (!!) problems with expansion and contraction esp. in long runs and depending on the temps when installed and overall temp range on site.
EricIt's Never Too Late To Become
What You Might Have Been
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Maybe tht comparison of the two was a bad analogy.
I DON"T want to go there again!It's Never Too Late To Become
What You Might Have Been
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PVC (?) trim boards.
Okay, so it was one of my dumber questions, LOL. (But the fact it is one more plastic product supposedly going to replace wood would explain why I've been happily ignoring it....)
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
This stuff has been around since the 1920s. Used in Europe, mostly Germany and Scandinavian countries, but it never caught fire in the US. I'm not sure why. Perhaps it has to do with it having low volumetric economy, it can't be compacted or folded, during shipping.
Homebuilders in the US are also world-class stick-in-the-muds, very resistant to change and innovation. In a lot of places two-stud corners and leaving out the jack studs under the windows is still considered controversial and risky. Other than joist hangers, steel reinforcements and minor material changes houses are very like those built sixty years ago. I commonly climb into and under houses seventy plus years old and I see little real and substantial change.
SIPs and ICFs are relatively new but both are adaptations that were being used fifty years ago. Remember the flood of stressed skin panel construction during the 60s. Don't see them much any more. SIPs are an adaptation of the basic design substituting foam for the support grid or stiff fiberglass insulation.
SIPs have been around for over a decade but most residential construction still use frame construction designs going back to the 1900s. AAC is clearly a useful product. In some ways better than SIPs. SIPs are subject to anything that compromises the OSB skins, moisture, insects, rot, fire. ACC is largely immune to all of these.
I think ACC is superior to most ICFs also. IMHO Styrofoam, even the glorified borate loaded versions, isn't an effective and long-lasting building material. Substitute ACC for the same foundations, think cored ACC blocks, and your on to something.
Of course all of this going for the material still hasn't made it widely available or used. Most people still have to ship in the product from long distances. Some all the way from Europe.
Digging around for suppliers I found one in Apopca Florida:
http://www.accoaac.com/ACCO_frames.html
Close enough to me to make it reasonable to ship and use but their product on hand is short, their 'employment opportunity' page says there are no openings, they are offering an 'inventory sale', and the plant is up for sale, if your willing to swing something north of $19,000,000.
I don't think you need to be psychic to figure out they are down for the count if not out completely. What happened and why remains unknown. Such failures may have nothing to do with the product. Lots of businesses fail due to bad management or poor timing during an economic cycle. ACC is a great product IMHO but the outlook in Florida doesn't look bright for anything in the near term.
A shame in my opinion.
I was involved with a project building a house out of AAC block - Hebel block to be specific. It was about 5 years ago, so I may be a little foggy on the details. We had a regular footer guy pour concrete, then added a few rows of block to get just above grade. Then started with the AAC block. You lay the first course in regular mortar, with head joints of thinset. Then, successive blocks/courses were laid with thinset in both the head and bed joints. The problem was that the blocks were not exactly uniform, so you had to watch it or you would get off. They advertised it as easier to lay than regular block, but I'm not so sure. With regular block, you can make up errors with the mortar. The thinset really doesn't work so good for this. Also, I found that block that was laid a week ago, atached by 1 bed joint and 1 head joint could actually be ripped from the top of the wall by hand... pretty disconcerting... I guess the idea is that once you get them all in there, they kind of bond together to make a strong unit. You worked with it pretty similar to CMU block: corner plumb boards - strings and line blocks, trowels and a special notched trowel for spreading the thinset on the block. If you dropped a block it could break like a cinder block, although maybe not that easily...
The supplier lent (rented?) us a big bandsaw which made cutting it much easier. Yea, you can cut it with a hand saw, but how many hand saws do you actually see on the job site these days? Per manufacturer's instructions, we ran rebar up the corners and on each side of a window/door opening. This necessitated drilling ~2" holes through the block. This woulda been OK except that we went through several $100 drill bits... Working with the stuff is a little like fiber cement except that is not that dusty... Really cuts more like wood but it is the constancy (in appearance) of polyisocyanurate foam. Can't really remember but I think each block was about 8"x8"x20" and weighed maybe 12 lbs. The masons like the weight factor but complained a lot about other stuff - maybe mainly just because it was a new material and it was somewhat slow going.
So anyway, you pour the drilled rebar holes full of grout - which we mixed on site in an electric mixer.
We poured lentils over the window and door openings and had a bond beam that went around the entire top perimeter of the walls. This was filled with grout (or was it concrete?) and J bolts were set in to hold down a PT top plate that the roof trusses were nailed to
OK - eventually we got to the rough-in stage. The idea was that the ACC could easily be cut out with a power saw or router to make raceways to run the necessaries. Electrical and plumbing subs ran from the stuff. It was about then that I left the project... I saw some of those people maybe a year later and I was told that it took a year to finish the house (~1200 sq ft...) Anyway, that was just my experience.
I did a search and found this:
http://www.taunton.com/finehomebuilding/pages/h00002.asp
Hey Matt, was that house in Durham? I did some stuff with Cameron when he built cabinets...interesting bill of goods he was pushing, even then. "what's in a name?" d'oh!
AAC (and not ACC) is concrete with less material density. I found this links that may help (first made in 1914!) via a Google search:
http://www.toolbase.org/techinv/techDetails.aspx?technologyID=147
http://www.curranaac.com/
I get the feeling that Fine Homebuilding's elite builders are not too experienced with this stuff.
It was in Wake Forest.
Did you change your screen name from BBS to the illustrious BiteMe?
Taahhh Daaahhh! "what's in a name?" d'oh!
Matt, you said something about AAC block? Are you talking 'block' like CB? How big were these blocks? I ask, because the show I watched said the mass was one-fifth (1/5) normal concrete. To me, this seems like an opportunity to make blocks bigger and decrease the time of construction. Have a link for the product you worked with?
I think I answered the size Q. Re a web site, try http://www.hebel.com/html/com/en/index.php and navigate to the Hebel building systems.
The Japanese are the world's largest producers and consumers of this stuff, although they call it ALC (I think it's the same) or else hebels.
40% or Japanese buildings utilize it somewhere.
Usually, when used in a building shell, the 3 inch thick hebel panels are bolted onto a light or heavy gauge steel frame. Then caulked and painted and you have a very good if ugly utility building. The Japanese regs do not allow hebels to be used by themselves structurally as in laid-up blocks, for seismic reasons, I suppose.
Nichiha and others make a vast array of siding planks with decorative effects. I think the decorative element is a ceramic coating. When so coated, you have a pretty much an ideal siding. Low maintenance, waterproof, insulated, soundproof, projectile resistant--and qualifies for a special discount on fire insurance. Only thing I don't like is it's kinda ugly to my eye. This siding is from around an inch to three inches thick.
They also use this stuff in horizontal applications. For instance, it's very good when used outdoors for a concrete deck or balcony.
Used indoors, it's sometimes deployed as soundproofing for second floor. Achilles chemical makes an inch thick panel that goes on over your subflooring and below your finish flooring to provide good soundproofing. Others also make SIP-like subfloor panels involving sandwich of plywood on the outside and concrete on the inside for soundproofing. Some high end houses have three inch thick hebels fastened under the subfloor via ledgers, again for soundproofing.