ASTM classifies cement into Type I, Type II, Type III, Type IV, Type V and other sub-types like Type IP, Type IA, Type IIA, Type IIIA.
ASTM classification of cement is described here extensively.
Type I Cement
This type of cement is for OPC. Where special properties specified in Type II, III, IV and V are not required, this type is used to designate the cement class.
Type II Cement
Where there is moderate sulfate action and some amount of heat of hydration is required, these types of cement falls in this category.
Type III Cement
These types of cement have high early strength. (Rapid Hardening Cement)
Type IV Cement
Where high sulfate resistance is required, this type of cement is used.
Type IP Cement
This type of cement is a perfect uniform blend of OPC and pozzolanic material.
Type IA, IIA and IIIA Cement
These types of cement have air-entraining admixtures inter-ground with cement.
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ASTM stands for American Society of Testing and Materials.
OPC is the acronym for Ordinary Portland Cement.
PPC is short form of Portland Pozzolana Cement.