There is more than one type of cement available in bags from builders’ merchants. In today’s market cement does not automatically mean Ordinary Portland Cement, now termed just Portland cement and designated by CEM I on the bag. BS EN 197-1 compliant CE marked CEM II composite cements may contain fly ash (V), limestone (L or LL) or ground granulated blastfurnace slag (S) in varying proportions.
This does not make the ´cement´ inferior to the traditional Portland cement. In fact in certain situations it improves the durability of a concrete, but the user should be aware that interchanging different ´cements´ may change the setting time, strength, water demand and colour of the batched concrete. This variance of properties may also occur for the same brand cement from differing manufacturing locations.
The bags should have the printed information indicating the cement product designation, strength class and the name or identifying mark of the factory where the cement was produced.
Examples of standard designation:
CEM I 42,5N indicating Portland cement
CEM II A-LL 32,5R indicating, Portland cement with 6 to 20% limestone
CEM II B-V 32,5R indicating Portland cement with 21 to 35% fly ash
Other noted properties may include the addition of an air entrainer to aid workability and mix cohesiveness and reduce the risk of long term freeze-thaw attack.