Cement has long been a construction industry staple, and it is by far the most widely used construction material in the world. Unfortunately, cement is also one of the most environment-damaging materials in the world, producing 1/10th of the construction industry’s greenhouse gas emissions. But recently, researchers at the Massachusetts Institute of Technology have found ways to cut those emissions in half, making a stronger, more durable cement.
Typical cement is made my cooking calcium-based and silica-rich materials such as limestone and clay at temperatures of 1,500 degrees celsius to create “clinker,” a hard mass that is then ground into powder. The heating of the cement causes a decarbonation of the limestone, and this decarbonation process causes the output of greenhouse gas.
New materials analysis done by the MIT labs has revealed that a different ration of calcium-to-silica not only cuts those emissions in half, but also creates stronger cement. These findings, made by MIT senior research scientist Roland Pellenq, et al. were recently published in the Nature Communications journal and presented at this year’s CNRS conference in Marseille, France.
Pellenq explains that the standard calcium-to-silica ratio is 1.7, but can range anywhere from 1.2 to 2.2. The molecular structures of these ratios have gone untested until Pellenq and his colleagues built a database of all the different ratios and formulations and then compared them. The discovered that as the ratio varies, the molecular structure progresses from a tight, orderly crystalline lattice to a randomly distributed glassy matrix.
They then found that “a magical ratio” of 1.5 achieves “two times the resistance of normal cement, in mechanical resistance to fracture, with some molecular-scale design.” As the material becomes more glassy, the mechanical strength improves, and “no residual stresses in the material, so it would be more fracture-resistant.” A decrease in the amount of limestone translates to a lowering of carbon emissions from the cement-making process. This 1.5 ratio is the most ideal for cutting down on carbon emissions while strengthening the cement.
Having estimated the usage of cement to be three times that of steel, Pellenq says that “Cement is the most-used material on the planet,” adding that “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.”