Concrete is the most widely used material in the world but, as a March 2008 Chemistry World article points out, “it has a carbon footprint to match.”
Manufacturing cement, which binds concrete together, is an energy-intensive process that requires massive amounts of heat. About 4.7 million BTUs of energy is needed to produce one ton of cement.
That’s roughly the same as burning 400 pounds of coal. Put another way, for every ton of cement that’s produced, another ton of carbon dioxide is released into the atmosphere. Today, about 5 percent of global CO2 emissions can be traced to concrete.
That’s what makes a recent MIT discovery so exciting for the carbon reduction movement.
Recently, a team of MIT scientists concluded half a decades’ worth of molecular analysis on the structure of concrete. By comparing the ratios of calcium to silica in cement mixtures, they concluded that the optimum mixture was 1.5 – surprising, when considering that 1.7 is the industry standard, with the range varying between 1.2 and 2.2.
But 1.5 is the “magical ratio,” according to senior research scientist Roland Pellenq. That ratio maintains an ordered, crystalline structure in the molecules, endowing the cement with “two times the resistance of normal cement, in mechanical resistance to fracture.”
The 1.5 ratio requires less calcium in the mix, reducing the overall energy demand. “Any reduction in calcium content in the cement mix will have an impact on the CO2,” says Pellenq, adding that it could potentially reduce carbon emissions by 60 percent.
The study was conducted jointly by MIT and the French National Center for Scientific Research at MIT’s Multi-Scale Materials Science for Energy and Environment, and published in the journal Nature Communications.
Pellenq says the next stage of their study will test whether the greener concrete’s “nanoscale properties translate to the mesoscale” by actually using it in construction.