Stumbled on a cool innovation today called "Hycrete".
Concrete is typically sealed with a petroleum-based coating to protect it against the elements. This coating renders the concrete unrecyclable, however, because it changes the chemical composition significantly enough that it can't be broken back down into its base elements.
Hycrete is a monomolecular sealant that claims to offer the same waterproofing abilities as traditional sealants, but in such a way that the concrete doesn't have to be landfilled at the end of its life. Instead, it can be crunched up, fired, and used again.
Pretty simple, straightforward way to make concrete a little more green..
http://www.hycrete.com/site/content/why.html 
