As one of our most relied upon construction materials, concrete makes a significant contribution to our overall carbon emissions. By slightly altering the quantities of materials used in cement, scientists from MIT have uncovered a new method of concrete mixing that could reduce these emissions by more than half.
To produce cement, calcium-rich materials such as limestone are burned, typically with clay, at temperatures as high as 1,500° C (2,732° F). The energy to heat up the mix combined with a resultant chemical reaction generates carbon dioxide, a process responsible for between 5 and 10% of total industrial greenhouse gas emissions.
The MIT team, led by senior research scientist Roland Pellenq, found that reducing the ratio of calcium to the silicate-rich clay substantially reduced the output of carbon dioxide. Typically, calcium to silica ratios can vary between 1.2 to 2.2, though 1.7 is seen as the standard. By compiling a database that compared the chemical makeup of the different ratios, the researchers determined that 1.5 ratio was in fact the optimal mix. According to the researchers, this slight change in calcium levels could reduce carbon emissions by as much as 60%.
With the altered ratio the mix also had a higher resistance to fractures. The researchers claimed this is due to the molecular structure transforming from a tightly ordered crystalline to a disordered glassy structure. Pellenq describes the mix of 1.5 to be the “magical ratio,” with twice the mechanical resistance to fractures of normal cement.
Analysis of the cement mix was undertaken at a molecular level, so conduct further research would be necessary to ensure it can apply to engineering-scale applications.
The research was published in the journal Nature Communications.
By Nick Lavars
Source: MIT
http://www.gizmag.com/mit-recipe-cement-mixing-carbon-emissions/34009
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