Definition:

Concrete durability has been defined by the American Concrete Institute as its resistance to weathering action, chemical attack, abrasion and other degradation processes.

Important degradation mechanisms in concrete structures include the following:

1. Freeze-thaw damage (physical effects, weathering).
2. Alkali-aggregate reactions (chemical effects).
3. Sulfate attack (chemical effects).
4. Microbiological induced attack (chemical effects).
5. Corrosion of reinforcing steel embedded in concrete (chemical effects).
   a) carbonation of concrete
   b) chloride induced
6. Abrasion (physical effects).
7. Mechanical loads (physical effects).

In practice, several degradation mechanisms can act simultaneously with possible synergistic effects. The schematic diagram below illustrates how different degradation mechanisms can act on concrete exposed to sea water.

click on image to enlarge
Adapted from V.M. Malhorta: "Durability of Concrete", Chapter 26,
Uhlig's Corrosion Handbook Second Edition, R.W. Revie Ed., Wiley, 2000.
Original Reference: P.K. Mehta and P.J.M. Monteiro: "Concrete: Structures,
Properties and Materials", 2nd Edn., Prentice Hall. 

Basic concrete terminology