View full sizeFrank Lloyd Wright's design for an inexpensive house made of concrete, originally published in Ladies Home Journal in April 1907.Concrete is one of the most popular building materials, but its dirty little secret is its contribution to global warming. Its key ingredient is cement, and cement's key ingredient is limestone, which is mainly calcium carbonate, according to "Building a Better World With Green Cement" in December's Smithsonian magazine, which reports:
The recipe for making cement calls for heating the limestone, which requires fossil fuels. And when heated, limestone sends carbon dioxide gas wafting into the atmosphere, where it traps heat, contributing to global warming. Cement production is responsible for 5 percent of the world's human-produced carbon dioxide emissions; in the United States, only fossil fuel consumption (for transportation, electricity, chemical manufacturing and other uses) and the iron and steel industry release more of the greenhouse gas.
A number of companies are working to develop green cement, substituting other substances for the limestone. One obstacle, as the story makes clear, is that concrete in its current form is tried and true. Its strength and durability over time are proven.
Another is that cement and concrete are surprisingly little understood:
"We have never actually known the exact chemistry of how this stuff gets hard," said Hamlin Jennings, an expert on cement chemistry and head of MIT's Concrete Sustainability Hub, one of several academic initiatives to forge "green" cement. "I don't think there is any building material used in the world today that is more poorly understood than Portland cement."
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