Roger Babb, president of Babb International of Ringgold, Ga, whose family has owned a lumber operation for 47 years, saw good reasons to start up a research and development facility for autoclaved aerated concrete (AAC) in 1998 and break ground for a full-scale plant last year.

In a strong economy, traditional building products such as lumber, gypsum board, and glass fiber insulation can't keep up with demand in some areas. Moreover, "it is our opinion that the U.S. market will go the way of the European markets," says Babb, noting their stronger reliance on masonry construction. "We don't know how long it will take, but some years down the road, we will not see wood as the dominant framing structure for homes and businesses."

Economic reality is one reason for the reintroduction of AAC in North America in the mid-1990s after the concept failed in the '60s and '70s. The benefits of AAC, developed more than 70 years ago and produced in more than 200 plants around the world, are other reasons the material is getting a second look from producers such as Babb.

AAC is a factory-produced precast concrete used for masonry building blocks and reinforced structural panels. AAC can be described as a rigid "concrete foam" since up to 80% of its volume consists of small air bubbles. The structure of the concrete gives the material exceptionally light weight, high thermal and fire resistance, and suitability for cutting with ordinary hand or power tools.

AAC can be used as walls, partitions, floor and roof decks, and other building components, or as an integrated system for structures up to seven stories high. It is substantially unaffected by shrinkage, moisture, decay, termites, and other common causes of building deterioration, and it is an environmentally "green" building material because it is easily recycled back into its own production.

AAC also appears to be a cost-competitive building material. The light weight and ease of cutting boosts construction productivity. AAC also simplifies construction by performing a wide range of functions, including structure, insulation, and enclosure, with just a single wythe, significantly reducing setup costs. Prefabrication of AAC panels shortens building erection time to allow earlier occupancy. AAC also offers indirect benefits: lighter weight means reduced foundation costs, better insulation reduces HVAC requirements, and increased fire resistance can cut insurance costs.

Current economic conditions appear favorable to AAC. Lumber prices have increased, forcing builders to consider alternatives. Building codes have been strengthened in regard to hurricanes, earthquakes, and fires. An aging Baby Boom generation and low inflation have made many investors and home builders more sensitive to the life-cycle economy of buildings. Finally, energy conservation and environmental concerns play an increasing role in design decisions.

For Babb, the way to get builders to accept a slightly higher cost is to market AAC as a value-added wood substitute. He notes that a house built with AAC uses less energy and has lower insurance rates, is safer, more solid, and durable.

"The insulation value and airtightness of the house deteriorates over time, but with AAC it remains constant," Babb says. "Cost is a minor issue." The cost of an AAC house vs. a stick-frame with a siding product such as vinyl siding will be slightly higher.

Another potential segment in which AAC has huge growth potential is schools.

AAC has also found early acceptance in motel, commercial, apartment, industrial, and residential construction. Nonstructural applications for AAC are also emerging. For example, thin veneers of AAC are being used as a replacement for failing exterior insulation and finish systems (EIFS). Taking advantage of suitability for carving, AAC is also being fabricated into moldings and trim pieces for the plastering trades.

Two trade associations have combined into the Autoclaved Aerated Concrete Products Association to promote use of the material and coordinate the development of industry standards. The material is already recognized under ASTM C 1386-98A, "Standard Specification for Precast Autoclaved Aerated Wall Units" and ACI 523.2R, "Guide for Precast Cellular Concrete Floor, Roof, and Wall Units" and has been approved by the model building codes. Masonry labor organizations have endorsed the material, seeing it as a way to boost productivity and keep their members competitive.

While most producers are actively recruiting and training contractors to install AAC, Angelo Coduto, manager of Corporate Development at ACCO, says his firm has embraced a design-build strategy. "We sell a total package including the AAC structure, erection, and finishes, complete with a 7-year system warranty," he says. "By offering our customers a single-source responsibility, we have been able to overcome their concerns about using a new material."

Led by companies such as ACCO, AAC has established a foothold in North America and appears set to break out into the construction mainstream. Babb sees enough potential in AAC to eventually replace the framing material the company offers.

The best strategy may be for domestic producers to combine the best of the old products with that of the new. Who would be better suited than a concrete producer to introduce AAC into the local market? With their existing material-handling capabilities, basic understanding of cement technology, sales and distribution channels, and access to an established client base, producers already have much of the infrastructure for an AAC business in place.

The real victory will be for the U.S. building industry, which will gain, with AAC, a valuable new product in its arsenal of building materials.

The article also includes a description of the AAC production process, contributed by Michael Grutzeck.