Consider this: concrete is the most widely used construction material on the planet and its production accounts for roughly 5% of global greenhouse gas emissions. Recently, a fascinating new study from MIT reports that these carbon emissions could be cut in half while creating a stronger and longer-lasting concrete. The findings come from the most detailed examination of the molecular structure of concrete to date and the study has yielded promising results.
Concrete is composed of sand, gravel, water, and cement, the latter being the primary focus in the MIT study, which concentrates on the production of cement. Cement is produced by cooking calcium-rich material, usually limestone, with silica-rich materials like clay at temperatures around 1,500 degrees Celsius. This produces a hard mass, which is ground up into a powder. During this process, the heating of cement and the de-carbonation of limestone are responsible for the majority of carbon emissions.
The study’s analysis suggests that reducing the ratio of calcium to silicate would both reduce carbon emissions and create stronger concrete. These findings were published in the journal Nature Communications by MIT senior research scientist Roland Pellenq as well as professors Krystyn Van Vliet, Franz-Josef Ulm, Sidney Yip, Markus Buehler, and eight additional co-authors at MIT and The French National Centre for Scientific Research (CNRS) in Marseille, France.
Pellenq explains that in conventional cements, the calcium-silica ration ranges from 1.2–2.2 parts calcium per 1 part of silicate, with a commonly accepted standard of 1.7. However, the resulting mixture had never been examined in detail at a molecular level. Pellenq and his colleagues studied all of the chemical formulations within the 1.2–2.2 range and found that a ratio of roughly 1.5 is a more ideal standard. Pellenq says that at this ratio, the material can achieve “two times the resistance of normal cement, in mechanical resistance to fracture, with some molecular-scale design.” This is a significant improvement in terms of performance, considering the relatively small change in recipe.
Pellenq estimates that, if widely implemented, the decrease in carbon emissions from the production of cement could amount to as much as 60 percent. However, the analysis so far has remained at the molecular level and still needs to be field-tested on a larger scale.