Green cement: Concrete solutions

Cement manufacturing is a major source of greenhouse gases. But cutting emissions means mastering one of the most complex materials known.

Ivan Amato
20 February 2013

If this year’s expected global output of cement were somehow poured across Manhattan island, the 3.4-billion-tonne mass would solidify into a monolith about 14 metres high. If the monolith were created next year, it would probably be even bigger, given the construction boom now under way in developing nations such as China and India. Cement is a crucial raw material for civilization, holding together artefacts ranging from the 2,000-year-old Pantheon in Rome to modern skyscrapers and highways.

Unfortunately for Earth’s climate, however, the most widely used form of that material today — ‘portland’ cement — is made by roasting limestone and clay in giant kilns in a process that sends nearly a tonne of carbon dioxide skywards for every tonne of final product. The manufacture of portland cement accounts for roughly 5% of all human-generated greenhouse-gas emissions.

Worse, for researchers looking for ways to reduce emissions, cement is not just a commonplace, high-volume commodity; it is also one of the most complex substances known in materials science. From its structure and composition to the reactions that ensue when it is mixed with water and poured into a mould to set, “we still have some of the most basic questions about cement unanswered”, says Hamlin Jennings, director of the Concrete Sustainability Hub (CSHub) at the Massachusetts Institute of Technology in Cambridge.

“The details of what is happening once water touches cement powder are a matter of lively debate,” adds Kenneth Snyder, a cement expert at the US National Institute of Standards and Technology in Gaithersburg, Maryland. “There are almost religious wars over this.”

Nonetheless, the prospect of carbon taxes and cap-and-trade markets has led industry groups around the world to adopt green or sustainable cement initiatives. Their approaches range from supporting basic research to pushing to reform international building codes, and, if successful, could eventually cut the cement industry’s carbon dioxide footprint by half.

The CSHub is one of the field’s largest academic-research centres. Founded in 2009 with funds from industry sponsors totalling US$10 million over five years, the CSHub now comprises about a dozen principal investigators seeking to understand cement — from its function in various structures to its quantum-mechanical properties. It is a struggle, says Jennings, for reasons that become apparent when one considers what happens on the molecular scale when cement is made.

Read more: Green cement: Concrete solutions : Nature News & Comment.

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