What Is and When to Use Autoclaved Aerated Concrete (AAC)

Aerated Concrete is a type of precast concretecomposed of all natural raw materials producing great benefits and better energy efficient performance. As early as 1914, the Swedes discovered a mixture of cement, lime, water and sand, just like regular concrete but adding aluminum powder. This last material gives the Autoclaved Aerated Precast Concrete expansion properties.

Aerated Concrete: How It Is Manufactured?

Aerated Concrete is a lightweight pre-cast concrete that contains air bubbles throughout the material to generate the low-density lightweight material in an autoclave oven.

It is so manageable that can be cut with a saw blade and can be drilled easily. Because of its characteristics, the concrete must be tested for compressive strengths, moisture content, bulk density test, and shrinkage test. The concrete can be used on walls, floor, roof panels, blocks, and lintels.

Properties of Aerated Concrete

Aerated concrete blocks are solid lightweight blocks joined together with an adhesive and reinforced with steel for additional strength. AAC has incredibly high insulation values and provides an excellent soundproofing barrier and for such reason, they are used in above-grade construction. The precast autoclaved aerated concrete wall units are large-size solid rectangular prisms, which are to be laid using thin-bed mortar. Installed units shall be protected against direct exposure to moisture using a coating material.

Aerated Concrete Benefits and Applications

Some of the benefits that you will get when using autoclaved aerated concrete are:

• Excellent thermal protection, approximately 1.25 per inch. The thermal conductivity of AAC is 6 to 7.5% that of conventional concrete, making it energy-efficient.
• AAC will have lower energy costs because it has a greater thermal resistance.
• Excellent soundproofing material and acoustic insulation.
• Aerated concrete provides fire and termite resistance.
• AAC is manufactured in a variety of form and sizes.
• AAC blocks store and release energy over time.
• The aerated concrete is recyclable.
• Route chases can be cut to install electrical and plumbing rough-in.
• Extremely lightweight precast blocks stacked like conventional CMU.
• Shipping and handling more economical than regular concrete or CMU.
• Panels are available in thicknesses of between 8 inches to 12 inches, 24-inches in width, and lengths up to 20 feet.
• Blocks come 24”, 32”, and 48” inches long, between four to 16 inches thick, and eight inches high.

Autoclaved Aerated Concrete Drawbacks

Aerated concrete as any other material has also some disadvantages:

• Consistency in quality and color may be difficult to obtain.
• Unfinished exterior walls should be covered with an exterior cladding to protect them from wear and tear.
• If installed in high humidity environments, interior finishes with low vapor permeability and exterior finishes with a high permeability are recommended.

Aerated Concrete Material Cost

Autoclaved aerated concrete walls installed as CMU can cost approximately $3.50 in 8” x 8” x 24”, depending on the complexity of the project. Labor cost might be lower because it is easier to install and easier to handle.

These costs might change from zone to zone depending on the labor costs and building code requirements.

Building Codes Acceptance of Aerated Concrete

Aerated concrete has been accepted by many building codes and international standards such as:

• ASTM C1386 (Precast Autoclaved Aerated Concrete Wall Construction Units)
• ASTM C 1452 (Standard Specification for Reinforced Autoclaved Aerated Concrete Elements)
• ACI 523.5R, which is a guide for using autoclaved aerated concrete panels

How to Install Aerated Concrete 

Aerated concrete can be easily installed with a thin-set mortar and can be easily finished by paint, plaster, cladding, or siding materials. Autoclaved aerated concrete can be finished on interior surfaces by plastering, tiles, painted, sheet rocked or just left exposed.

Concrete Comparison

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