As the world becomes increasingly aware of the potentially devastating effects of climate change, nanotechnology may hold the key to reducing carbon dioxide emissions in the production of cement.
Carbon Dioxide in Cement Production
Cement is a fundamental building material used around the world. Approximately 2.35 billion tons are produced every year and this production accounts for 5 to 10 percent of the carbon dioxide emissions around the world. A simple 10% reduction in the amount of carbon dioxide produced would meet 20% of the Kyoto Protocol greenhouse gas reduction goal.
Cement is a major component in one of the oldest and the worlds most widely used construction material, concrete. Researchers from MIT with backing by cement manufacturers LaFarge are examining the nanostructure of concrete with an eye to reducing CO2 output.
The research work has shown that the key to the strength and durability of concrete comes from the organizational structure of nanoparticles.
How Cement is Made
Cement is made by crushing limestone and clay into a powder and then by heating to around 1500°C in a kiln. When the cement powder is mixed with water calcium-silicate-hydrate (C-S-H) is produced that acts as a glue to bind together the other components in concrete, sand and gravel. Most of the problematic CO2 is produced as part of the heating process.
With samples taken from all around the world, researchers used a nanoindentation technique to measure strength at the nano level. They found that all the samples showed a unique nanosignature for the C-S-H material regardless of the sample origin. This is known as the material’s genomic code and means that the strength of cement paste is not a function of specific minerals but relates to the way the nanoparticles are arranged.
"If everything depends on the organizational structure of the nanoparticles that make up concrete, rather than on the material itself, we can conceivably replace it with a material that has concrete's other characteristics--strength, durability, mass availability and low cost--but does not release so much CO2 into the atmosphere during manufacture." said Professor Franz-Josef Ulm from civil and environmental engineering at MIT.
Nanostructure of Concrete
Professor Ulm and Georgios Constantinides, a postdoctoral researcher in materials science and engineering found that at the nanostructure of cement is organised into a pyramid like shape, the most densely packed structure for spherical objects.
Now that the secret behind the strength of concrete has been revealed the next step involves turning to nanotechnology to nanoengineer a material for use in the cement paste. This replacement material will be required to have the same packing density but not require the high production temperatures needed to produce standard cement.
Depending upon global distribution of the new material it could reduce world carbon dioxide emissions by up to 10 percent. Additionally, depending upon the material used, the amount of carbon in the atmosphere could be reduced even further. Current research is investigating the replacement of calcium in cement with magnesium.
Magnesium In Cement
Magnesium incorporated into cement will also solve other environmental problems. Magnesium is an industrial waste product that requires managed disposal. A cement incorporating magnesium has already been developed in Australia. Marketed as Eco-cement, this material is a composite of the magnesium compound, magnesite, recycled industrial waste and ordinary cement.
As Eco-cement sets and hardens, it absorbs CO2 from the atmosphere and the magnesite converts it to carbonate. This process continues for roughly a year, before the power of the porous magnesite to convert CO2 is exhausted.