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Sixteen-year-old Jennie Cho wanted to win one of the prestigious scholarships in the Westinghouse Science Talent Search and knew she had to do something bright and original. She thought about a biology project, but then heard that Columbia University might let her try something different: making strong concrete out of fragile glass.
Jennie and 16 other students have been spending weeks researching glascrete, a construction material like concrete that replaces some of the aggregate with waste glass culled from city recycling bins. Christian Meyer, professor of civil engineering and engineering mechanics at Columbia, is developing the new material.
"My physics teacher pointed out this opportunity, and I decided to go after it," said Cho, a resident of Jackson Heights, N.Y., who is beginning her senior year at Stuyvesant High in lower Manhattan. She is a member of Professor Meyer's Summer Institute at Columbia's Morningside Heights campus and will continue her work on glascrete through the fall.
The students have taken day trips to New York landmarks (JFK Airport, Williamsburg Bridge, the World Trade Center, Water Tunnel No. 3) that illustrate the marvels of civil engineering, heard prominent engineers discuss both the city's decaying infrastructure and career opportunities in engineering, and spent hours in the lab mixing cement, aggregate, glass and water in many different proportions.
Glascrete holds promise to find a use for the hundred-thousand or so tons of glass the city generates every year, almost all of which it must pay to have carted away. A minute amount is ground up into glasphalt for use as a paving material.
Professor Meyer has found that green glass, unlike clear or amber glass, strengthens and stabilizes concrete by minimizing a chemical reaction that takes place between the alkali in cement and the silica in certain aggregates. The reaction, which occurs over months and years, causes the concrete to expand and eventually to deteriorate.
Green glass contains trace amounts of chromium oxide, but Professor Meyer and a research associate, Stephen Baxter, have found that adding the chemical directly to a concrete mix doesn't suppress the reaction. The chromium oxide must be in the glass.
Enter Jennie Cho, who is melting clear glass and adding different amounts of chromium oxide to find the optimum mix. "We're not sure why adding green glass suppresses the alkali-silica reaction," she said in the lab recently. "We do hope to find the answer to why green glass works the best."
The other students, too, have been plumbing the mysteries of how to make a stable, high-quality concrete. Most of the students are from two Manhattan schools, Stuyvesant and Marta Valle High, both on the Lower East Side. All reside in Manhattan, Brooklyn or Queens. Stuyvesant students, many of whom are submitting glascrete projects to the Westinghouse contest, have been paired off with students from Marta Valle and other high schools, so those students, some from disadvantaged neighborhoods, can learn from their lab partners. The Westinghouse projects are due in early December.
John Jen of Bayside, N.Y., a Stuyvesant student, and Jennifer Gaona of Washington Heights, from Louis Brandeis High, filled a sieving machine with aggregate, let it run and then removed nine trays with nine different gradations of sand. They and other students replaced some of the aggregate with ground waste glass of the same size, then used their specially-mixed glass-and-sand aggregate to make concrete cylinders that Professor Meyer's staff tested for strength. "If this helps solve New York City's garbage problem, it's worth it," John confided.
Professor Meyer noted with pride that the high-school students are doing real research in a real lab, not make-work. "We need answers to all the questions the students are researching," he said. One of last year's students, Chun hua Zheng, was a semifinalist in the 1995 Westinghouse competition.
The Summer Institute is sponsored by the American Society of Civil Engineers and its New York section; Sigma Xi, the Scientific Research Society; and the Carleton Materials Laboratory at Columbia.