A FREE DIRTY CONCRETE TEXTURE from my website goodtextures.com [link]
This is one of many textures (8000+ and growing) from my fairly new website.
All textures are FREE to use/download, and can be used either for private or commercial use.
There are however some Terms and Conditions which can be found on my website.
The average texture resolution including this one is 6mp (3008x2000)
Hope you like them and enjoy.