Concrete has been used since the times of the Ancient Egyptians and Ancient Chinese. It is now a vital part of construction worldwide. Below is a list of masonry industry associations that provide technical information on their websites.
For concrete related articles on archtoolbox.com, visit the Concrete page.
American Concrete Institute
Concrete Reinforcing Steel Institute
The Concrete Reinforcing Steel Institute has a store that contains a number of free technical guides. The Reinforced Concrete Explorer serves as an inspirational vault of concrete (free, but registration is required).