Source: ARCHITECT Magazine
Publication date: March 1, 2008
By Bradford Mckee
They look dull and, in fact, if you've seen one concrete masonry unit— or concrete block or CMU—you may think you've seen the lot of them: Usually they're rough, gray oblong blocks formed from water, sand, crushed stone, and cement, with two big holes in them. Many, in fact, are more hole than concrete.
Yet concrete blocks are the potatoes of common architecture—sort of ugly and endlessly useful. They're laid and stacked in bonds like bricks from the lowest basements to the highest floors of a building, as foundations, inner and outer walls, mechanical core linings, and, not least, the main line of safety around fire stairs. Even without a fire, they protect us more than we appreciate. Architects and contractors rely on concrete blocks—8 billion of them produced in North America in 2007 alone—for their compressive muscle. Blocks can carry weight like other, more plastic incarnations of concrete, often with steel rebar and poured concrete inside the cavities. But, given their déclassé look, as often as not they're hidden like underwear behind brick veneers, ceramic tiles, modular panels, or exterior finishing systems. Or they're simply glazed or slapped with coats of paint.
Concrete block's value lies in its versatility—certainly not in portability. Because concrete is heavy, it is generally made close to where it is used.
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