This specification covers coal fly ash 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 fly ash and raw or calcined natural pozzolans may be desired or where both objectives are to be achieved. Note 1??Finely divided materials may tend to reduce the entrained air content of concrete. Hence@ if a fly 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. The values stated in SI units are to be regarded as the standard.