form of MgO in clinker, relation to Bogue relations

MgO enters into solid solution in all the cement clinker minerals to different degrees. In these solid solutions it essentially substitutes for CaO. The convention is that up to 2% MgO can be accommodated in solid solution in the clinker minerals. Beyond 2% there is the likelihood that free MgO will be present and then there is the possibility of long-term durability problems due to expansion when the cement is used in concrete.

Dr Michael Clark

Thanks Michael,

Would it mean that in the Bogue formula CaO has to be replaced by (CaO+56*MgO/40) with an ad-hoc correction on the weight of each phase?

Also, can we assume that MgO is uniformly distributed in the four phases, in proportion of the CaO in these phases?

Of course we know that the Bogue formulas are the result of a mass balance assuming a 4 elements ==> 4 components mapping. We know also that this assumption is generally not true physically.

But, generally speaking, would you prefer to stick to the basic version of the Bogue formula, or do you think it makes some sense to correct them for various effects like MgO, SO3, free lime, ... ? In other words, is there some useful physics in these corrections, or is reality simply more subtile?

Thanks again

Yes, up to a maximum of 2% MgO in clinker. The MgO does not partition equally between the clinker mineral phases. There is the greatest solid solubility in the C4AF phase, with the lowest in the C2S phase. The 2% overall limit is a compromise value taking these differing solid solubilities into account.