How to see through walls
Transparent concrete is encouraging architects to rethink how they design buildings
CONCRETE has been a high-tech material since Roman times, when it was discovered that adding volcanic ash to the mix allowed it to set under water. Similarly, the Romans knew that adding horsehair made concrete less liable to shrink while it hardened, and adding blood made it more frost-resistant. In modern times, researchers have added other materials to create concrete that is capable of conducting electricity. It heats up when a voltage is applied, making it possible to build runways and drives that clear themselves of snow. Bill Price of the University of Houston now has an ambitious plan to make concrete with an even more unusual property: he wants it to be transparent.
Dr Price first had the idea when he saw an architect's model of a concert hall made using translucent materials, so that the model's structure could be seen more easily. He started to wonder whether the actual concert hall could be built so that it resembled the translucent model. That meant finding a way to make concrete transparent.
That is not as crazy as it sounds. Technically, concrete is simply a mixture of three ingredients: big lumps of material called the coarse aggregate (such as gravel), smaller lumps called the fine aggregate (such as sand) and a binding agent, or cement, to glue it all together into a solid. So translucent concrete, in theory, should be fairly easy to make using bits of plastic or glass of various sizes, with some kind of transparent glue to act as a binding agent.
Since early this year, Dr Price has been experimenting with various recipes for translucent concrete, though he has yet to reveal his ingredients. Since concrete is often reinforced with steel rods, he has also looked at using transparent plastic rods for a similar purpose. Tests of his initial samples suggest that, structurally, translucent concrete is just as good as the traditional kind. But it would cost around five times as much.
Dr Price is also the first to admit that translucency is a far cry from transparency. His aim is to champion the idea in the hope that fully transparent concrete will eventually become possible. By discussing the notion of transparent concrete, he observes, he gets people thinking in new ways. "As soon as people encounter the term, even people who aren't architects or designers, they are full of desire, full of excitement," he says. He has visions of cities that glow from within, and buildings whose windows need not be flat, rectangular panes, but can be arbitrary regions of transparency within flowing, curving walls.
As if the goal of transparent concrete were not already lofty enough, Dr Price has also decided that it should be possible to mix, transport and pour transparent concrete using existing equipment and techniques. At the moment, his translucent concrete has to be pre-cast, rather than poured on site. He is also keen for transparent concrete to be an environmentally friendly material that can be recycled—though that, too, seems a tall order.
So far, Dr Price's work has spread among architects largely by word of mouth. Architectural practices have been requesting information, and asking when translucent or transparent concrete will be commercially available. That is probably some years off, although Dr Price recently held preliminary discussions with a major concrete manufacturer. Meanwhile, he continues to refine his translucent concrete, and is now seeking approval for limited use of the material in a private house in San Antonio, Texas. For the time being, the future of his innovative material remains opaque.
This article appeared in the Technology Quarterly section of the print edition under the headline "How to see through walls"