Strength Classes Of Cement

The standard strength classes of cement are based on the 28-day compressive strength of mortar prisms, made and tested to the requirements of BS EN 196-1: 2005. The test uses specimens which are 40 X 40 X 160 mm, cast from a mix of 3 parts of CEN (European Committee for Standardisation) standard sand, 1 part of cement and 0.5 part of water. The sample is vibrated and cured for the appropriate time, then broken into halves and compression tested across the 40 mm face. Three specimens are used to determine a mean value from the six pieces.

Each cement strength class (32.5,42.5 and 52.5) has sub-classes associated with the high early (R) and the ordinary (N) development of early strength (Table 3.5). The strength classes and sub-classes give production standards for cements, but do not specify how a particular mix of cement, aggregate and admixtures will perform as a concrete; this needs to be determined by separate testing.

The most commonly used cement within the UK (formerly ordinary Portland cement or OPC) is currently designated to the standard BS EN 197-1:2000 as:

type of strength ordinary early cement class strength development

High early strength Portland cement is designated: CEM I 42.5 R CEM I 42.5R

type of strength high early cement class strength development

Low early strength low heat blastfurnace cement with a granulated blastfurnace slag content between 81 and 95% and a strength class of 32.5 is designated:

type of strength low early cement class strength development & low heat

Portland limestone cement with between 6 and 20% limestone of 0.5% total organic content, a strength class of 32.5 and normal early strength is designated:

type sub- strength ordinary of cement type, class early /proportion lime- strength of cement stone development clinker

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