This specification covers coal ash resulting from the combustion of coal and raw or calcined natural pozzolan for use in concrete where cementitious or pozzolanic action, or both, is desired or where other properties normally attributed to finely divided coal ash and raw or calcined natural pozzolans may be desired or where both objectives are to be achieved. Note – Finely divided materials may tend to reduce the entrained air content of concrete. Hence, if a coal ash or natural pozzolan is added to any concrete for which entrainment of air is specified, provision should be made to ensure that the specified air content is maintained by air content tests and by use of additional air-entraining admixture or use of an air-entraining admixture in combination with air-entraining hydraulic cement.