Cement Shelf life

  Hello Sundar,

  The answer to both questions is;- it depends on the conditions of humidity and temperature under which the cement has been stored. eg;-

  If the container in which the cement has been stored is airtight and has been stored in an environment where the temperature and humidity have been carefully controlled, (eg air-conditioned  or dehumidified room),  then  the cement may remain fully reactive for up to 12 months, as long as the container has not been opened. However, this is the best-case scenario and, in practice, cement is rarely stored in this way, except for bulk laboratory reference cements.

  Bagged cement is not airtight and even if unopened should be used within a few months. Although again, the shelf life of individual bags depends on the conditions under which they have been stored. At best, correctly-stored, unopened bags might have a shelf life of up to six months.

  As long as the cement is less than six months old, has no lumps and is a completely free-flowing powder, it should be okay to use for non-structural purposes. All structural jobs (ie. jobs that require maximum strength) should always use fresh cement.

  Regards,

  Ted.

Dear All,

As per indian standards, cement with retention of more than 6 months, can only be used only after retesting for its conformance.

Ted, an, thus, expired cement best be recycled by mixing with raw material to rejuvenate it again as clinker.Isn't it?

Regards,

Gulam Dastgir

Dastgir:

Ted, an, thus, expired cement best be recycled by mixing with raw material to rejuvenate it again as clinker.Isn't it?

Hello Gulam,

Yes, that is one way, however it depends on the age and condition of the cement to be recycled.

If cement is badly hydrated (ie. solid mass or large lumps with little or no free-flowing power) then blending with the raw materials is really the only way to recycle it.

But, if a significant proportion of free-flowing powder remains, and can be economically sparated from the lumps, then this can be blended back through the cement mill at a rate low enough to prevent quality impacts on the fresh cement. (ie all quality specifications are preserved)

If the first option is used, care should be taken not to upset the ALK/SO3 balance too much, due to the extra SO3 contribution from the recycled cement. ie ALK/SO3 should be not be allowed to fall below 0.9

In addition,  too much gypsum in the raw materials can also lead to sulphate spurrite (4CaO.2SiO2.CaSO4) build-ups in the middle to lower parts of the preheater where meal temperatures are between 700 and 910 deg. C

Regards,

Ted.