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Cement class in BS EN 1992-1-1

Unless otherwise stated, the cement type in concrete is assumed not to affect the concrete’s 28 day design strength. However the strength development of concrete before and after 28 days is significantly affected by the type of cement. The concrete supplier should be able to provide indicative concrete strength data at various ages on request.

For design purposes, prior to a supplier being known, BS EN 1992-1-1, Eurocode 2: Design for concrete structures, sub-clause 31.2(6) gives an expression for the development of mean concrete strength at 20C at a particular age t in days for specimens cured in accordance with BS EN 12390, see below.

The coefficient s depends on the cement type;

• 0.20 for cement of strength classes; 42,5R, 52,5N and 52,5R, designated Class R
• 0.25 for cement of classes; 32.5R, 42,5N, designated Class N
• 0.38 for cement of class; 32,5N, designated Class S

Generally Class R should be assumed unless the cement contains additions as follows;

• 35 to 65% ground granulated blastfurnace slag, use Class N
• exceeds 65% ground granulated blastfurnace slag; use Class S
• 20 to 35% fly ash; use Class N
• exceeds 35% fly ash; use Class S

These classes are also used in BS EN 192-1-1 to estimate creep and shrinkage. Note that cement strength classes R, N and L are a descriptors used in EN 197 Cement to denote Rapid, Normal and Low early cement strength development.

Equations 3.1 and 3.2 from BS EN 1992-1-1

Acknowledgement: Concrete Society