Let It Shine

Ductal and Agilia may be high-tech, but they’re destined for concrete’s primary role as a structural material. Will Wittig, who teaches architecture at the University of Detroit Mercy in Michigan, wanted to take this “heavy and monolithic” construction material and turn it into something “more ethereal.” So, he set out to make concrete translucent.

Says Wittig: “I wanted to challenge our assumptions about what concrete is or what it can do.”

In pursuit of that goal, Wittig mixed white silica sand and white Portland cement, varying the ratios to get a paste that cures in thinner preparations than standard concrete mixes do. He added short strands of fiberglass to reinforce the material.

Next, Wittig built a table topped with a Plexiglas square mold into which he poured his concrete mixture. He made a number of prototypes, always pushing for panels that were thinner, but not so thin that they would break. The final concrete panels were thin as a coin at the centers and close to a centimeter thick at the edges.

The panels were originally meant as a shell for a one-room garden house that Wittig had designed several years ago. “My hope was that [the panels] would be translucent enough so that on a sunny day, you could sit inside and have enough light to read a book,” says Wittig.

His thinnest sheets of the new concrete transmit about 1 percent of sunlight. That would be in the ballpark of providing sufficient light to create a glow inside the structure, says Wittig. However, he never built the building—lab tests showed that the panels were too fragile to withstand wind and rain.

OPTICAL TRICKS.

A translucent concrete material contains glass optical fibers that transmit light through the entire length of the block. It can bring sunlight through a wall.

LiTraCon

Instead of making concrete itself translucent, a small company in Germany is taking a different tack: incorporating transparent materials into the concrete. LiTraCon, based in Aachen, has developed a concrete that contains glass optical fibers the thickness of a hair. They transmit light from one side of the material to the other. Hungarian architect Áron Losonczi—who, like Wittig, experiments with construction materials—invented the translucent concrete.

To ensure that the ends of each fiber make contact with the surfaces on both sides of the material, blocks of concrete are built in stages. First, a thin layer of concrete is poured into a long, narrow mold. Then, a layer of optical fibers is laid along the length of the mold. After several repetitions, the resulting long beam can be cut into short, rectangular building blocks riddled with the thin light pipes, says LiTraCon’s Andreas Bittis.

The fiber diameters range from 2 microns to 2 millimeters. By using fibers of different diameters, LiTraCon designers can achieve different illumination effects. Varying the size of the blocks, however, doesn’t change the effect. So far, LiTraCon has made continuous concrete beams up to 20 meters long, and the fibers transmit light the entire length.

With these blocks, architects can design and build a large variety of structures, ranging from translucent concrete walls to floors lit from below. LiTraCon has already received a number of requests from architects interested in the material, says Bittis. One firm in New York has proposed using the new concrete in its design of a police college in Kuwait City. Because concrete is an excellent insulating material, the building would protect against the desert heat while letting through some sunshine.

To Be Continued…