Concrete gives off greenhouse gases?

I had no idea it's responsible for 5% of the world's total carbon dioxide emissions:

Scientists studying the nanostructure of concrete said a change in the process used to create the widely-used material could significantly reduce carbon dioxide emissions worldwide.

Tests conducted by a team of engineers from the Massachusetts Institute of Technology discovered the secret to cement's strength lay not in its ingredients, but in how its smallest particles 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 Franz-Josef Ulm, a professor of civil and environmental engineering at MIT.