Retrieved from Īctually its perfectly rated, and you misinterpreted your own facts.įirst, all concrete is porous, no matter the percentage of cement used. Autoclaved Aerated Concrete (AAC): Will the U.S. If you've used it, how did it perform? If not, what would it take for you to try it out? We'd like to hear some empirical evidence from the field.Īre you using AAC on any of your projects? Unfortunately, much of the information we have on AAC performance in the U.S. Even then, its performance may still be outmatched by that of insulated concrete forms, depending on the needs of the client. That said, AAC does appear to have significant advantages for applications where conventional concrete would normally be the best material-like in the American Southwest and in other climates where thermal mass can increase the "effective" or "mass-enhanced" R-value of the wall. Unlike conventional concrete, AAC can't be used as a finish it is more porous and needs cladding or stucco on the outside so it won't absorb moisture.ĪAC is popular for residential construction but not suitable for high-rise buildings without structural reinforcement.But it seems to be popular for single-family homes as well as schools. Unless rebar is added-which adds to the weight and amount of material in the blocks-AAC can only be used for low- and mid-rise construction.(The European climate, where AAC is popular, is milder.) and Canadian climates without additional insulation. Thermal properties are better than those of conventional concrete, but they aren't good enough to make AAC a viable wall material (relative to BuildingGreen-recommended R-values) in most U.S.Since right now your AAC is most likely coming from Mexico, the advantages offered by lighter weight will diminish significantly as the mileage increases.(Taylor's looking forward to two new plants coming online in the States in the next couple years.) These often need to be sawed, adding labor and fuss to a building system that's supposed to be simple. According to Derek Taylor, owner of AAC distributor SafeCrete, the only manufacturer in North America right now is a German company whose block dimensions don't work for U.S. The barriers for builders don't stop with the mortar.We would like to add a few drawbacks that we've found: AAC requires a learning curve for builders, because the mortar application is more precise.(that was in 2006, and now there are almost none, since Xella has moved its Hebel operation to Mexico) this means higher costs, which is a huge barrier for adoption. There are few manufacturers in the U.S.In a report written for UC–Davis (PDF), Stefan Schnitzler finds few disadvantages to AAC. AAC also has excellent soundproofing properties.It's a better insulator, with a steady-state R-value just a hair above R-1 as opposed to something more like R-0.2 (neither of these factors in thermal mass, which we'll get to later).It's lighter, which cuts down on transportation costs and fuel use.Despite the energy-intensive autoclaving process, manufacturers say it takes about 50% less energy to make, because of the lower portland cement content by volume (we're haven't found anyone to challenge those claims, but are still looking for data).It uses less material-important for concrete, since portland cement is one of the most energy- and carbon-intensive building materials. It's still not wood, but in North America (unlike in Sweden at the time and in most of Europe now), wood is still plentiful and cheap.Ĭompared with conventional concrete, AAC still has advantages, though: The main advantage of AAC when it was first developed in Sweden in the early 20th century was simple: it wasn't wood. They are porous and light, like muffins, but not hollow. Like conventional concrete masonry units, AAC is sold in a variety of block shapes and sizes, but unlike conventional units, most don't have cores. SUPPORT INDEPENDENT SUSTAINABILITY REPORTINGīuildingGreen relies on our premium members, not on advertisers. The resulting blocks are so full of bubbles that a block of the same size has about one-fifth the material required by regular concrete. The concrete is poured into molds, left to rise, and then "baked" in an autoclave, which uses steam and pressure to complete the chemical reactions and speed up the curing process significantly-completing in hours rather than weeks. (Your muffins are full of carbon dioxide bubbles, but AAC is full of hydrogen bubbles.) AAC is similar to other concrete types, except that it contains no aggregate sand or fly ash is included, with aluminum powder added to react with one of these ingredients and "leaven" the concrete, creating tiny bubbles just like baking soda does when it reacts with the buttermilk in your muffin batter.
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