Energy Source Builder

ACC Blocks Cut Labor Costs and Save Energy

Autoclaved Cellular Concrete house

Fred Etheridge doesn't always get shipments of building materials from England. However, in early August he watched three trucks deliver their cargos of autoclaved cellular concrete (ACC) blocks to his job site in Canal Fulton, Ohio. The blocks were manufactured in London, England, and imported by Ohio Edison/Penn Power for Schalmo Homes. Etheridge is Director of Land Development with Schalmo.

Because this is Schalmo's first ACC project, the blocks will be used only on the basement walls and around the master bedroom (for sound absorption). For Etheridge, energy efficiency and labor savings are the most immediate benefits of building with ACC.

"The blocks are light and easy to handle," says Etheridge, "though we've had to get used to the metric sizes."

Normally, a basement takes 12 courses of block. With ACC blocks, only 10 were needed, which saves a significant amount of labor. All the blocks are 24 inches wide and 10 inches high. Blocks for the basement are about 10 inches deep. Narrower blocks can be used for above grade walls and interior partitions.

A demonstration house built in Moon Township, Pennsylvania showed that material costs are slightly higher, but labor costs were 50 percent lower. The total cost for ACC block walls in that project was 10 percent lower than it would have been using conventional materials.

Promising Alternative

ACC blocks are a promising alternative to standard concrete blocks and wood framing. Initially patented in the United States in 1914, ACC was successfully commercialized in Europe. However, it has been dormant in the U.S. The Schalmo/Ohio Edison demonstration is intended to introduce the material to the American building industry. The timing appears to be good, because many builders are considering alternatives to traditional wood-frame construction.

ACC offers several advantages:.

  • Lightweight: 75 percent lighter than normal concrete
  • Easy to Work: Can be drilled, sawed, chiseled and nailed with conventional woodworking tools
  • Cost-effective: Reduces construction time and labor
  • Energy-saving: ACC blocks alone provide insulating value up to R-1.5 per inch compared with R-0.1 to 0.2 per inch for hollow concrete blocks and R-1.25 per inch for wood.
  • Strong and Stable: Autoclaving gives blocks strength, dimensional stability and durability
  • Durable: Resists decay and insects
  • Fire Resistant: Does not burn or emit environmentally damaging gases
  • Sound Absorptive: Provides highly effective sound barrier

Educating the Industry

Like any new building material, ACC blocks must pass muster with local building inspectors. The Building Officials Council of America (BOCA) has not completed its review of the ACC blocks. So, local officials reviewed engineering reports and other information before granting building permits to Schalmo. Among their concerns were thermal efficiency (R-value), fire rating and sound absorption. Structural issues received special scrutiny. How would the blocks hold up to lateral soil loads in below-grade applications? How would they withstand point loads under beams, lintels and headers? What type of reinforcement might be necessary? How can the wall be dampproofed?

After reviewing technical documents and visiting the Moon Township ACC house, the code official granted building permits.

At this stage of development, just about everyone involved needs education. Etheridge also took the mason and electrician to visit the Moon Township house. "You have to convince the code officials and the subcontractors," says Etheridge. "Then you have to educate the buying public."

Environmental Benefits

In addition to the advantages as a building material, ACC has an important environmental benefit.

Electric utilities in the U.S. produce millions of tons of fly ash each year at their generating plants. Some of the fly ash finds its way into highway construction, roofing shingles and industrial abrasives. ACC would be a way to recycle more fly ash and keep it out of landfills.

Utilities across the country are keeping tabs on additional uses for fly ash concrete and they're paying particular attention to the ACC demonstration projects in the East.

The homes pictured on the front page were demonstration projects built in Pennsylvania and Ohio in 1994. Sponsored by the builders and the Electric Power Research Institute (EPRI), these were the first homes in the United States built with fly ash ACC blocks. Ohio Edison/Penn Power along with several utilities and EPRI also sponsored a mobile ACC block manufacturing facility to support the demonstration projects. Blocks made by that plant were used for testing currently underway for national building code approvals.

Once code approval is granted, ACC blocks will offer a more energy-efficient and environmentally-friendly material for home builders.

How ACC Is Made

ACC is made by mixing fly ash with Portland cement, lime, aluminum powder and water. Chemical reactions in the mixture create millions of tiny bubbles. The resulting lightweight material can be cast or cut to any size or shape. The blocks are then cured 10 to 12 hours in a pressurized steam chamber. This processcalled autoclavingproduces a second chemical reaction that makes the material rigid, strong and durable.

You can find sources of ACC blocks in the Oikos Product Directory.

This article appeared in Energy Source Builder #41 October 1995
©Copyright 1995 Iris Communications, Inc.

Autoclaved Cellular Concrete

Masons lay ACC blocks for a demonstration house.