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Lightweight concrete hits the wall in search of acceptance

Ian Harvey
Lightweight concrete hits the wall in search of acceptance

Cellular Lightweight Concrete has been long used for slabs and road construction, but getting the industry to look at it as a building block for structural walls has been a challenge.

CLC, and its cousin Aerated Autoclaved Concrete block (AAC), reduce masonry partition wall weight and allow fast construction. The latter is expensive because of the steaming process required to cure it. Proponents of CLC argue their formula is cheaper than AAC and has many benefits which more than compensate for the slightly higher cost over traditional blocks and precise material requirements.

When it comes to roads and pavement, however, CLC has made inroads. For example, a couple of years ago, CLC was used on a 120-metre-long portion of Dixie Road in Caledon, Ont. Calgary-based Cematrix Cellular Concrete Solutions, one of the major developers of CLC, sprayed the material insitu. It was also used for an Ontario bridge abutment where the footings had started to slip as the soil around it slumped.

Allan Hunt, whose company CellConInc in Cambridge, Ont. has been researching and developing a formula for CLC with hopes of producing blocks on a commercial basis and finding a market, is hoping to break through. He said roads are an area with good growth potential for CLC, noting it’s been used on a project in western Canada where it was floated over muskeg to provide a base impervious to frost using closed cells and then finished off with a paving surface.

Still, he said, while CLC is making progress for paving, it’s is slow getting interest in North America as a building block.

"We’ve been building in the Bahamas with it and it’s big in Asia," said Hunt.

"We’re working with a local Mennonite company here in Cambridge to develop blocks."

He said the mix goal is 800 kilograms per cubic metre, about a third of conventional concrete. The blocks will be made in two basic sizes, 10 inches by eight inches and 20 by 8 inches. The smaller blocks will be about 30 pounds and the large blocks 40 pounds, each 10 pounds lighter than a conventional cinder block.

CLC has been around since the 1920s and is concrete made with a foaming agent to create bubbles of air inside which are trapped when it cures. It can be poured for road beds or into moulds at a factory and then shipped to sites. The blocks are stacked and secured with a thin-set mortar.

They are lightweight, durable, have good heat gain and heat loss properties and resist mold which is especially important in high countries with high humidity. They are popular also in cold climates such as Eastern Europe and Russia because of their built-insulating qualities and because they are airtight when finished inside and out.

The weight advantage also means it’s easier and safer for masonry workers to lift them into place, and they fit together quickly because they’re made with a self-aligning tongue and groove system. Also, they have a remarkably higher insulating factor than cinderblock and are easier to deal with than ICF (insulating concrete forms) and have a higher R factor which also gives it good acoustic-dampening characteristics.

ICF cost about $12 to $14 a square foot and ours which doesn’t have styrene in it comes in at about $10 to $11 a square foot, but there are concerns about ICF because in a fire it produces toxic smoke and that’s an issue during the construction phase if someone drops a cigarette into the forms or around the inventory," said Hunt.

He said CLC is a much better and practical alternative to AAC blocks because the autoclave set up is extremely expensive and that cost is passed down to customers.

"It just uses too much fuel and they tried years ago to bring it into Canada from the U.S. but never could," said Hunt.

The CLC formula he is working on is a variant of several different mixes in the marketplace now.

Rishi Gupta, assistant professor at the University of Victoria’s engineering faculty says industry resistance is one of the biggest hurdles CLC faces in wider applications despite its sustainable properties. The other is getting the strength higher enough without increasing weight too much. He said it takes more attention to detail in the mix to get the aeration quotient right.

"It is not just the volume, which ranges anywhere from 15 to 40 per cent in typical mixes, but the distribution of the air bubbles," he said.

"Anytime more air is incorporated in a cement-based material, the strength goes down.  The air matrix also allows for moisture to travel through which reduces the life of the material.  The only caveat to this is the need to have a minimum amount of air content in concrete for freeze-thaw resistance. This is typically between three and seven per cent."

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