MIT
develops better, greener, concrete
David L. Chandler, MIT
Concrete is the world's most-used construction material, and a
leading contributor to global warming, producing as much as one-tenth of
industry-generated greenhouse-gas emissions.
Now a new study suggests a way in
which those emissions could be reduced by more than half - and the result would
be a stronger, more durable material.
The findings come from the most detailed molecular analysis yet of
the complex structure of concrete, which is a mixture of sand, gravel, water,
and cement.
Cement is made by cooking calcium-rich material, usually limestone,
with silica-rich material - typically clay - at temperatures of 1,500 degrees
Celsius, yielding a hard mass called "clinker."
The new analysis suggests that reducing the ratio of calcium to
silicate would not only cut those emissions, but would actually produce better,
stronger concrete.
These findings are described in the journal Nature
Communications by MIT senior research scientist Roland Pellenq; professors
Krystyn Van Vliet, Franz-Josef Ulm, Sidney Yip, and Markus Buehler; and eight
co-authors at MIT and at CNRS in Marseille, France.
"Cement is the most-used material on the planet,"
Pellenq says, noting that its present usage is estimated to be three times that
of steel. "There's no other solution to sheltering mankind in a durable
way - turning liquid into stone in 10 hours, easily, at room temperature.
That's the magic of cement."
In conventional cements, Pellenq explains, the calcium-to-silica
ratio ranges anywhere from about 1.2 to 2.2, with 1.7 accepted as the standard.
But the resulting molecular structures have never been compared in detail.
Pellenq and his colleagues built a database of all these chemical formulations,
finding that the optimum mixture was not the one typically used today, but
rather a ratio of about 1.5.
Read more at MIT news.
