How is Durability of concrete defined?
Durable concrete can be defined as one that is designed, constructed and maintained to perform satisfactory in the environment for the specified life of the structure without undue maintenance. The principal causes of deterioration of concrete have been identified as carbonation, corrosion of reinforcement, sulphate attack and alkali- aggregate reaction. The main factor's influencing the durability of concrete is its impermeability to the ingress of oxygen, water, carbon dioxide, chlorides, sulphates, etc. Various factors influencing durability are:
-cover to the embedded steel
-type and quality of constituent materials
-cement content and water- cement ratio
- workmanship to obtain full compaction and efficient curing
-shape and size of members.
IS 456-2000 classifies the general enviornment in which the concrete will be exposed into five levels of severity - mild, moderate, severe, very severe, and extreme, Table3.