Here is one patented in 2009...

Here is one patented in 2009 http://www.freepatentsonline.com/y2009/0229494.html
the present invention provides a nanocomposite cementitious material that exhibits increased Young's modulus as compared to the same cementitious material without carbon nanotubes. For example, the nanocomposite cementitious material exhibits an increase of the Young's modulus of at least 15% and up to about 55% as compared to the same cementitious material without carbon nanotubes. Similarly, the present invention provides a nanocomposite cementitious material that exhibits increased flexural strength as compared to the same cementitious material without carbon nanotubes. For example, the nanocomposite cementitious material exhibits an increase in flexural strength of at least of 8% and up to about 40% as compared to the same cementitious material without carbon nanotubes.
Another one filed in 2011 http://www.freepatentsonline.com/8426501.html