A small modification to the contents of cement mix could lower the carbon emissions of the construction sector and result in stronger, more durable concrete.
The world’s most commonly used construction material is concrete. Unfortunately, concrete is also a leading contributor to global warming, producing as much as one-tenth of the greenhousegas emissions generated by the construction sector.
Concrete is made of a mixture of sand, gravel, water and cement. Cement is made by cooking calcium-rich material, like limestone, with a silica-rich material, like clay. The calcium silica mix is heated to temperatures of 1,500 degrees Celsius to yield a hard mass called clinker which is then ground up into a powder. It is the decarbonation of the limestone and the heating of the cement which is responsible for most of the material’s greenhouse gas output.
Researchers from the Massachusetts Institute of Technology are suggesting that, reducing the ration of calcium to silicate in cement would reduce its emissions and also produce better, stronger concrete.
The normal calcium-to-silica ration of concrete ranges from about 1.2 to 2.2, with 1.7 accepted as standard. However, the research team conducted a detailed molecular analysis of the structure of concrete and found that the optimum mixture was a ratio of about 1.5.
As the ratio of calcium-to-silica varies, the molecular structure of the hardened material progresses from a tightly ordered crystalline structure to a disordered glassy structure. According to M.I.T. senior research scientist Roland Pellenq, the ratio of 1.5 parts calcium for every one part silica was found to be the “magic ratio” at which point the material can achieve two times the resistance of normal cement in mechanical resistance to fracture.
Since emissions related to concrete production are such a big part of the industry’s greenhouse gas emissions, any reduction in calcium content can have a positive impact. According to Mr. Pellenq, the reduction in carbon emissions from using the magic ratio could be as much as 60 percent.
The work is the culmination of five years of research by a collaborative team from M.I.T. and CNRS, where Mr. Pellenq is research director. – EcoSeed Staff
Ubicación: http://ecoseed.org
Autor: Ecoseed.org
Procedencia: Estados Unidos
Fecha de Publicación: 2014/09/29