Materials: Recycling Holds Promise

Research is under way to help turn waste-stream raw materials into building products with unique characteristics that can solve some tricky construction problems. If successful, the projects may lower construction and project life-cycle costs. Two materials involved are alpha hemi hydrate gypsum and glascrete. But other researchers claim that government and testing agencies may be obstacles to wider use of recycled materials.

"Our goal is not to create substitute materials, but to create new materials to fill needs not currently met or unsatisfactorily so," says Hank Schlieper, president of NuSource Materials Technologies, Piscataway, N.J. The firm is a subsidiary of ENSR, an environmental design firm based in Acton, Mass. It was formed in January partly to take advantage of proprietary gypsum technology developed by other shareholders in Germany. NuSource also is exploring uses for other mineral-rich waste from the metals, paper and mining industries.

The technology focuses on adding value and function to gypsum produced as a byproduct of flue-gas desulfurization at coal-fired powerplants. "It is purer than natural gypsum," says Schlieper. After processing into its alpha hemi hydrate form, the material can be used in a variety of construction and industrial products.

The recycled product has the strength of concrete at about 4,000 psi, says Schlieper. It can be fiber reinforced with waste paper or "foamed" to produce lesser-strength (450 psi) lightweight (about a third of masonry) building blocks with excellent fire resistance. Applications include floor leveling systems, non-load bearing partitions, fire protection, interior ornamentation and other masonry or concrete applications.

In floor-leveling, flatness deviation is about 5mm over a 20,000-sq-ft floor when applied on a concrete base, says NuSource Vice President Rudi Kwasny-Echterhagen. The material only needs to be raked out to remove air.

NuSource is working with the New Jersey Institute of Technology, Newark, to research applications, costs and code applicability and acceptance. It hopes to produce a premium-priced product that can reduce construction costs because its characteristics. For instance, the lightweight foamed blocks could reduce handling and labor costs. "We will cost out various systems and determine where the greatest cost effectiveness will be," says Ezra D. Ehrenkrantz, executive director of NJIT's Center for Architecture and Building Science Research.

Alpha hemi hydrate gypsum is not a new material, but traditional means of production are costly, which has limited use, claims NuSource. The firm's process will allow the material to be competitive with portland cement. "It must be sold at a competitive price," says Schlieper.

"What is particularly interesting here is changing the mindset," says Ehrenkrantz. "It would be like if you went to a planet where there was no wood and you gave someone a piece of wood. What would they do with it?"

Students and faculty at New York City-based Columbia University have much the same objective in their quest to find a use for the roughly 100,000 tons of glass that city residents discard each year. They hope to develop stronger, longer-lasting concrete by adding certain types of glass.

The research is sponsored by the American Society of Civil Engineers; Sigma Xi, the Scientific Research Society; and the Carleton Materials Laboratory at Columbia. The researchers discovered that green glass "strengthens and stabilizes concrete by minimizing a chemical reaction that takes place between the alkali in cement and the silica in certain aggregates," says a Columbia spokesman. The reaction causes concrete to expand and deteriorate.

The glass being considered contains trace amounts of chromium oxide, but the researchers have found that adding it directly to the concrete mix does not suppress the reaction. Students are melting clear glass and adding various amounts of chromium oxide to find the optimum mix.

Construction materials containing recycled materials are having a tough time finding their way into industry applications because their use is discouraged by government building codes and construction standard setters, according to research by the Los Angeles-based Reason Foundation. "Governments often don't rely on measures of performance," but rather tend to specify materials and methods based on past practices, concludes Alexander Volokh, a Reason Foundation analyst.

Volokh says the same government rigidity backfired in the case of the federal mandate that requires states to use crumb rubber in asphalt pavement. "Scrap tire rubber was originally used in asphalt to enhance asphalt's properties, not to alleviate real or perceived waste disposal problems," says Volokh. "The rubber mandate was designed with tire disposal in mind, and the percentages . . . were more ambitious than the state of practical technology."