16,000 years from now, what will the remains of 21st century human civilization look like? If a new high-density, long-lasting type of concrete gains popularity as a building material, they may hold up surprisingly well. Civil engineers at MIT are developing a type of concrete that will enable lighter, stronger structures with the potential to last millennia into the future.

Concrete is the world’s most widely used material, and the production of its primary material, cement, accounts for 5 to 10 percent of the world’s total carbon dioxide emissions, making it a primary contributor to global warming. This new innovation could conceivably cut carbon dioxide emissions enough to accomplish one-fifth of the Kyoto Protocol.

The trick behind making concrete so durable lies in the organization of its nanoparticles. MIT Professor Franz-Josef Ulm and post-doc Georgios Constantinides found that at the nano level, cement particles organize naturally into the most densely packed structure possible for spherical objects – similar to a pyramid-shaped pile of oranges.

The MIT team used a nano-sized needle and an atomic force microscope to see the nanostructure and judge the strength of various cement pastes made from different types of minerals from around the world.

"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 Ulm.