Autoclaved aerated concrete, Aerated Cellular Concrete, Autoclaved Lightweight Concrete. This precast, porous, foam concrete building material goes by many different names.
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Chapters
0:00 Introduction
0:17 How its made
1:25 Type of blocks
1:56 Insulation
3:06 Strength
3:47 Fire resistance
4:47 Sound insulation
5:19 Water resistance
6:08 Earthquake resistance
6:32 Ease of use
7:00 Environmentally friendly

Its main ingredients are
Cement which is a mixture of silicates and oxides
Lime which is calcium oxide and/ or calcium hydroxide
Gypsum anhydrite which is anhydrous calcium sulfate CaSO4
Finely ground sand or silicon dioxide SiO2 or fly ash
Aluminum powder
Water

Calcium oxide reacts with water in an exothermic reaction to form Calcium hydroxide and 65.2 kj/mol. Calcium hydroxide reacts with aluminum powder and water to generate hydrogen gas and cause the mixture to expand like bread dough. Finally, silicon reacts with calcium hydroxide to form tobermorite or hydrated calcium silicate C5S6H5.

AAC products are cured under heat and pressure in an autoclave. Steam is fed into the autoclave at a high pressure of 800kPa and a temperature of 180C or 350F. Steam curing allows the concrete block to retain its porous form and harden in just 812 hours, unlike normal air curing that can shrink materials and take longer.

AAC has millions of small air pores. In fact, it’s 80% air. It is 5 times lighter than traditional concrete. AAC doesn’t compress, decay or lose its shape over time. It has excellent dimensional stability despite its porous nature. Air is a poor conductor, so the closed cellular structure and high thermal mass of AAC makes it an excellent insulator.

Because it is so lightweight, its strength is 1/6 to 1/3 that of traditional concrete blocks and it has a lower thermal mass. It is still strong enough to be used on floors, roofs and walls. AAC is also quite brittle and requires special care during handling and transporting to avoid breakage.

AAC has an excellent fire rating, as expected from a cementitious product. It can withstand fire exposure up to 4 hours, without charring or losing its structural integrity. They do not emit toxic fumes even under intense heat.

To measure the spread of heat, I bought this FLIR one thermal imaging device on Amazon. I’ll link it in the description below. It plugs into your iphone or android and allows you to measure the temperature of surrounding surfaces. Even when the hottest part of the block was over 150 degrees Fahrenheit, the area around it was cool to touch.

Since aerated concrete has a porous structure and high surface mass, it is a great acoustic insulation and soundproofing material. It has an stc rating of 40 for 4 inch thickness and 45 for 8 inch thickness.

When aerated concrete comes in contact with water, the tiny pores are immediately filled and the surface is discolored. Since it is vapor open, it dries out pretty quickly and water doesn’t pass through the brick reducing the possibility of condensation inside the wall. It’s inorganic and not a food source which makes it termite, mildew and moldresistant.

Due to mass production in controlled factory environments, all the blocks are of uniform quality and identical size. This speeds up assembly on job sites and reduces waste. Routing electrical and plumbing lines is relatively easy. It can also be easily cut, drilled or grooved with manual or power tools.

One of the drawbacks is the learning curve associated with using AAC. Masons who are used to traditional concrete have pushed back on switching to AAC. Also while you can screw and nail into aac blocks, the attachment is not as strong. Screws can strip out, nails can twist., so it is recommended to use plastic anchors. Hebel has designed special, largeheaded, square shank cut nails with better holding power. Aerated concrete is considered to be environmentallyfriendly even though the autoclaving process requires significant amounts of energy and water. It is recyclable, nontoxic, longlasting and has lowerembodied carbon levels compared to traditional concrete.

SOURCES:
   • CSR Hebel  Autoclaved Aerated Concre...  
   • What is Autoclaved Aerated Concrete (...  
   • How Hebel is made  manufacturing pro...  

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#lightweightconcrete #concrete #fireproof #aerated #autoclaved