(i) The design service life of each structures is different and depends on various factors such as
structural characteristics
Size
importance of the structure
location
cost of the structure
etc.
(ii) Durability of concrete structures must be considered together with their strength.
(iii) The deterioration causes reduction with time of the mechanical properties of the materials.
(iv) Various chemical, physical, mechanical, and biological processes can cause time-dependent deterioration of the materials.