ABSTRACT
Failure of concrete in a structure in a period less than its de sign life may be caused by external factors i.e. the environ ment to which it has been exposed or by a variety of internal causes. External factors may be physical or chemical in na ture, such as weathering, extremes of temperature, abrasion, and exposure to aggressive chemicals. Internal causes may lie in the choice of materials or in inappropriate combinations of materials. Of all the causes of lack of durability in concrete, the most important is excessive permeability. Permeable con crete is vulnerable to attack by almost all classes of aggres sive agents. To be durable, portland-cement concrete must be relatively impervious.
