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Woodruff Block Optimizes Cement With Recycled Glass

Beyond enhancing campus social and cultural life, the new 56,000-sq.-ft. student center at Clarkson University showcases practical rewards of research

Beyond enhancing campus social and cultural life, the new 56,000-sq.-ft. student center at Clarkson University showcases practical rewards of research conducted at the school's Center for Advanced Materials Processing (CAMP). There, a project to develop the structure's uniquely ÎgreenÌ building blocks was spearheaded by Civil Engineering and Environmental Engineering Professor Narayanan Neithalath, an expert on cement-based materials and sustainable concrete. Substituting 20 percent of the most expensive and energy-intensive concrete ingredient Û portland cement Û with recycled industrial glass powder produced a mix for concrete block more economical, energy-efficient, and environmentally friendly than traditional units. Plus, CAMP researchers assert, the block is stronger and more durable than CMU molded from conventional mixes.

Sparking development of the ÎgreenÌ blocks was a surplus of fine glass powder generated by Potters Industries, an international manufacturer of engineered beads made entirely from recycled glass. Its Potsdam, N.Y., plant was producing 8,000 tons of excess fine powder annually in the course of fabricating tiny pieces for high-tech applications ranging from reflective highway lane paint to hypodermic needles. Potters sought an efficient use for the byproduct, which resembles grayish-white baby powder in texture and appearance.

An innovative solution was developed through research at CAMP funded by the New York State Department of Economic Development Environmental Investment Program and the New York State Foundation for Science, Technology and Innovation. Initiated by Neithalath in June 2006 and concluded in December 2008, the project entailed extensive field tests at Potsdam-based Woodruff Block. After investigators confirmed test units' performance, the producer fabricated 7,500 blocks for the student center using Neithalath's mix design.

Working with two undergraduate and two graduate students, Neithalath conducted his research on use of the byproduct powder as a mix ingredient just a short walk from the site of the student center now pioneering his ÎgreenÌ concrete in walls and an elevator shaft constructed with block that looks and feels like its traditional counterparts. Highly anticipated were the environmental benefits of replacing a portion of the portland cement in concrete with glass powder, since the limestone-based binder is an essential constituent in the world's most widely used man-made material. Some 12 billion metric tons of concrete are produced annually Û equivalent to a cubic meter for every person worldwide, CAMP reports Û for construction of roads, bridges, buildings, and infrastructure. Replacing portland cement with powdered glass promotes sustainability by limiting carbon dioxide emissions, reducing energy consumption, and preserving mineral resources. Moreover, recycling an industrial byproduct offers additional ÎgreenÌ benefits.

Less predictable than the environmental merits of sourcing the Potters byproduct were the performance advantages of replacing some of the cement. Neithalath determined that the substitution improves concrete's mechanical properties. While researchers previously have blended other types of crushed or powdered glass with cement in concrete mixes, analysis or testing had never specifically targeted the introduction of industrial-bead manufacturing byproduct.

Glass powder is effective in concrete primarily because it is rich in silica, which can react with other cement components, e.g., calcium hydroxide, to increase the material's strength through hydration that leads to hardening. Such secondary binding compounds also reduce porosity and improve long-term durability. Therefore, you can eliminate some of the expensive and energy-intensive portland cement without losing any of its important properties, affirms Neithalath. In fact, you make the concrete better.

However, he observes, proportioning is critical. Excessive amounts of glass can make concrete weaker, because it lacks sufficient calcium compounds to generate strength. Also, glass has lots of alkalis, which in excess might lead to chemical reactions that can compromise long-term performance.