Casting New Light on Concrete

Industry Evolutions Include Reycled Materials and Translucent Concrete

By Elaine Schmidt

Concrete just is not what it used to be. From eco-friendly slag cement, to translucent concrete and durable two-lift concrete, innovations in the industry are causing designers, engineers, fabricators and builders to take a new look at concrete.

Tom Hale, vice president of sales for Wausau Tile Inc., Wausau, Wis., stands amid security planters made of concrete that incorporates slag, a waste product from steelmaking. (Photo courtesy of Wausau Tile Inc.)

Gray Is the New Green In what is called a win-win green approach to cement production, Wausau Tile, Inc., of Wausau, Wis., is using slag cement for some applications and recycled glass aggregate for others, creating enhanced construction products in the process.

The company recently supplied 228 concrete planters, all made with slag concrete, to the U.S. State Department. They were used as attractive, unobtrusive security barricades capable of stopping a truck, and they had to be in place in time for the January presidential inauguration.

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Slag—a waste product of the blast furnaces used in integrated steel mills—can be ground into a sand-like consistency. Like portland cement, slag cement forms an adhesive substance when combined with water and sets into a hard, durable building material.

According to Tom Hale, vice president of sales for Wausau Tile, “Slag is less expensive [than portland cement] because it’s a by-product the mills are trying to get rid of. It gives more flexural strength to the concrete [than portland] because of the steel content.” He adds that as a recycled product, it helps companies achieve LEED certification.

“We use up to 10 percent slag in our decorative products,” he says, explaining that a higher percentage can produce color variations in the final product. In applications in which such variations are not an issue, the company uses up to 50 percent slag.

Hale says Wausau Tile, which provides concrete products to customers around the world, also uses recycled glass aggregate for decorative purposes. One particularly visible project was planters for the main street of Burbank, Calif., where recycled blue glass in the aggregate created planters that sparkle blue in the sunlight.

An Enlightening Material Imagine seeing through a concrete wall clearly enough to make out the shadow of a person standing on the opposite side. Although it sounds like a superhero power, it is actually one of the selling features of a new type of material called translucent concrete.

Workers at Wausau Tile fill a planter form with slag concrete. (Photo courtesy of Wausau Tile Inc.)

Mixing traditional concrete with certain polymers or with fiber optic threads allows light to pass through what otherwise looks like solid concrete.

Steve Kosmatka, vice president of research and technical services for the Skokie, Ill.-based Portland Cement Association, sees two principal uses for translucent concrete.

“This is aimed at architects wanting to do something more interesting in a project or for someone looking for security – where someone needs to know if there’s a person on the other side of a wall, for instance.”

He explained that light, even sunlight, on one side of a translucent concrete wall allows a person on the opposite, darker, side of the wall to see a clear shadow of what’s on the lighter side. Anyone looking at the wall from the lit side sees just a normal concrete wall.

Although translucent products, with brand names like Luccon (Germany) and LitraCon (Hungary), are being used in many parts of the world, they are just beginning to appear in the U.S. on a few projects. The largest use of light-transmitting concrete blocks in the U.S. to date is the Iberville Parish Veterans Memorial in Baton Rouge, La.

Kosmatka explains that translucent concrete is not just for show. It also retains the strength of traditional concrete, giving it tremendous architectural potential.

Looking to the Past to Face the Future Another good example of gray going green can be found in the reappearance of two-lift concrete in paving applications.

Two-lift concrete, which has a track record of great durability in roadway applications such as Chicago’s 40-year-old Edens Expressway, employs two wet-on-wet layers of concrete instead of the usual single layer of paving. A thick bottom layer using coarse, lower-quality material (often recycled aggregate) is topped with a thinner layer made with higher quality aggregate.

According to Peter Taylor, associate director of the National Concrete Paving Technology Center in Ames, Iowa, two-lift paving addresses two major current paving needs: eco-friendliness and durability.

Where an existing roadway is being replaced with two-lift concrete, pavement from the existing road can be recycled and reused on site. The dollar savings over hauling off old concrete and the environmental benefits of keeping that material out of landfills add up quickly.

He adds that the use of recycled materials is growing in importance for another reason as well.

“We are using up all the good aggregate materials,” he says. Using recycled materials in the bottom layer of a roadway slows the consumption of a dwindling resource.

Using Chicago’s Edens Expressway, which has required only top-layer maintenance since it was constructed, as an example, Taylor says, “If you get this right it lasts forever.”