How Aerated Concrete 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.

The 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 ", 24 " 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, sheetrocked or just left exposed. Concrete Comparison

Spacers are the material used to separate the two panes of glass. Spacer can insulate by using materials that reduce the “conduction” from the outside pane of glass to the inside pane. Using metal systems where the metal does not touch the glass and is cushioned by a bed of sealant limits the conduction that can occur. Intercept Spacer is an example of this type of system.

FIGURE A - INTERCEPT Spacer

Some more dense materials that do not include any metal, like siliconized foam spacer, can further improve the inside pane’s temperature. Edgetech’s SuperSpacer is an example of a foam spacer.

FIGURE B - SuperSpacer Unit

Desiccant

Desiccant is a drying agent that is inside the spacer material to absorb all of the initial moisture inside the unit.

Sealant

The two panes of glass must be hermetically sealed together using a bonding agent like hot-melt butyl, silicone, polysulfide, etc. The sealant bonds the inside pane to the outside pane and creates the sealed airspace which creates the insulation effect. The dead air space further lowers the conduction effect.

Airspace

As stated above, the dead air improves the conduction effect. However, convection can occur, which is the air turning over inside the unit and raising or lowering the temperature of the inside pane based on the outside conditions. The convection effect is minimized by trying to maintain optimal spacer thicknesses based on the design of the unit. In general, a ½” airspace is proven to minimize the convection effect. To further improve the energy performance, the use of an inert gas like argon, or krypton, which is heavier than air, can greatly limit both the conduction and convection effects. To take it further, a “Triple Glazed” unit can combine three panes of glass and two airspaces for some of the best energy performance.

FIGURE C - Triple Glazed unit with SuperSpacer

Glass

Most of the insulated unit is glass. The glass that is selected is the only component that can have an impact on all three types of heat transfer. The use of tinted glass, like bronze or gray, can absorb energy and not allow it to pass on to the inside of the house. More prevalent is the low emissivity glass, or low-e.  

Low-E glass is designed to reflect radiant heat and can be used to reflect heat outside in cooling climates or reflect heat inside in heating climates. Low-e is also referred to as spectrally selective, which means it selectively allows only certain waves to penetrate through the pane of glass. By controlling the temperature of the outside pane of glass, it not only reduces radiant heat gain or loss, but also minimizes convection and conduction by helping to maintain the ambient temperature. The images above are thermal photographs of a foam spacer unit with clear glass on the left and a foam spacer unit with low-e glass on the right. The greens and blues show cooler temperatures, while the yellows and reds represent warmer temperatures, demonstrating the ability of low-e glass to control the heat.