Deleterious substances can be classified into the following three categories.
(1) Impurities which interfere with the process of hydration of cement.
(2) Coating on aggregate which prevents the development of good bond between aggregate and cement paste.
(3) Unsound or weak particles.
Deleterious substance may be organic compounds e.g. clay, silt and crusher dust etc.
The sum of % of all deleterious material shall not exceed five.
Deleterious substances effect the process of hydration, prevention of effective bond between the aggregate and matrix, These impurities some times reduce the durability and strength of concrete.
