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WASHINGTON - It used to be only Superman who could see through concrete walls, but an exhibit at the National Building Museum shows mere mortals can do it too.
Called "Liquid Stone," the show features variations of translucent concrete, a newfangled version of the old construction standby that offers a combination of aesthetics and practicality.
One display is a wall of translucent concrete blocks. When someone stands in front of it and light is shone from behind, the person's shadow can be seen clearly on the other side.
"I think it's beautiful in itself, so it might be attractive in a restaurant or a hotel," said G. Martin Moeller Jr., the museum's senior vice president. "But it might also be used in an indoor fire escape where you wanted light to come through in case of a power failure. It could become a lifesaver."
The translucent blocks are made by mixing glass fibers into the combination of crushed stone, cement and water, varying a process that has been used for centuries to produce a versatile building material. The process was devised by Hungarian architect Aron Losonczi in 2001.
"The idea came from a work of art I saw in Budapest," he said. "It was made of glass and ordinary concrete, and the idea of combining the two struck me. Then I went to Stockholm to do postgraduate work in architecture and it developed there."
One of the first demonstrations was a sidewalk in Stockholm made of thin sheets of translucent concrete. It looks like an ordinary sidewalk by day but is illuminated at night by lights under it.
An Aachen, Germany, company called LiTraCon for "light transmitting concrete," makes translucent blocks and plans to have them on the market this year. Marketing chief Andreas Bittis said they have mainly been used in demonstration projects, such as the Stockholm sidewalk.
Bittis has many ideas for practical uses.
"Think of illuminating subway stations with daylight," he suggested. Or using the concrete for speed bumps and lighting them from below to make them more visible at night.
Translucent concrete is strong enough for the uses for traditional concrete, and chemical additives can greatly increase the strength. Moeller pointed out, however, that until demand increases, experimentation continues and production costs fall, the price of any new product will be significantly higher than similar older products.
Will Wittig, who teaches architecture at the University of Detroit Mercy, has developed concrete panels shown in the exhibit that in some places are only a tenth of an inch thick. He said he has ideas about an all-concrete building, part of which would consist of ordinary opaque concrete and the translucent kind.
Inventor Thomas Edison had the idea of an all-concrete house almost a century ago. Though he worked on it for years and spent a lot of money, the idea never caught on.