All About Autoclaved Aerated Concrete (AAC)

Aerated concrete
••• Lightweight concrete. Photo breccaconstruction.com

Autoclaved aerated  (AAC) is a type of precast concrete composed of natural raw materials. It was first developed in Sweden in the 1920s, where an architect combined the conventional concrete mixture of cement, lime, water, and sand with a small amount of aluminum powder. AAC concrete typically is made into blocks, or masonry units, and is used to build mortared walls similar to standard concrete block construction.

 

How Aerated Concrete Is Manufactured

Autoclaved aerated concrete contains air bubbles throughout the material that generate a low-density lightweight material when it is fired in an autoclave oven. It is highly workable and can be cut and drilled with conventional woodworking tools, such as band saws and ordinary power drills. Because it is lightweight and relatively low-density, the concrete must be tested for compressive strengths, moisture content, bulk density, and shrinkage. The concrete can be used on walls, floor, roof panels, blocks, and lintels.

Properties of Aerated Concrete

AAC blocks are solid blocks that are stacked and bonded with mortar and can be reinforced with steel or other structural members for additional strength. AAC offers only moderate insulation values of about R-10 for an 8-inch-thick wall and R-12.5 for a 10-inch-thick wall. However, AAC structures can be very airtight to reduce energy losses due to air leaks.

The thermal mass of AAC slows temperature swings to reduce the need for heating and cooling as outdoor temperatures change. AAC also creates an excellent soundproofing barrier. AAC structures can be finished with paint, stucco, and most standard siding materials. Interior surfaces can be finished with drywall, plaster, tile, or paint, or can be left exposed.

Concrete Comparison

PropertiesAerated ConcreteTraditional Concrete
Density (PCF)25–5080–150
Compressive Strength (PSI)360–10901000–10000
Fire Rating (hrs)≤ 8≤ 6
Thermal Conductivity (Btuin/ft2-hr-F)0.75–1.206.0–10

Aerated Concrete Benefits and Applications

Some of the benefits of using autoclaved aerated concrete include:

  •  of approximately 1.25 per inch.
  • Excellent soundproofing material and acoustic insulation.
  • Highly fire- and termite-resistant.
  • Manufactured in a variety of forms and sizes.
  • Offers thermal mass that stores and releases energy over time.
  • Recyclable material.
  • Chases and holes for electrical and plumbing lines are easy to cut.
  • Shipping and handling more economical than poured concrete or concrete block.
  • Panels are available in thicknesses of between 8 inches to 12 inches and 24 inches in width, and lengths up to 20 feet.
  • Blocks come in lengths of 24, 32, and 48 inches, and thicknesses of 4 to 16 inches thick; height is 8 inches.

Aerated Concrete Drawbacks

Like all building materials, AAC has some disadvantages:

  • Some inconsistency in quality and color.
  • Unfinished exterior walls require  to protect them from weather.
  • If installed in high humidity environments, interior finishes with low vapor permeability and exterior finishes with a high permeability are recommended.
  • Low R-value compared to energy-efficient insulated wall construction.
  • Cost is higher than a conventional concrete block and wood-frame construction.

Aerated Concrete Block Prices

Basic AAC block in the standard size of 8 x 8 x 24 inches costs about $2.20 to $2.50 per square foot as of July 2018. This is more than the standard concrete block cost of about $2.00 per square foot. However, labor costs for AAC might be lower because it is easier to install and handle. These costs will also vary from region to region and are affected by local labor rates and building code requirements.