Hello Maw,

Sorry I didn't reply earlier but I only just noticed your question.

If cement containing high free CaO and/or MgO is ground finer, the particles of  free lime and MgO are reduced in size and will then hydrate faster. If the cement is ground fine enough, the Free CaO and MgO will have already fully hydrated before the cement paste starts to stiffen.

It is only when larger particles of Free CaO and MgO continue to hydrate after the cement paste has set that destructive expansion occurs.

Regards,

Ted.

Thanks a lot Mr.Ted