Hello Dharmesh,
I agree with 123red. The number, distribution and size of belite (C2S) clusters have a significant effect on clinker grindability. This is because C2S is the least brittle clinker mineral and therefore the most diffiicult to grind. Microscopic examination
of the two clinkers should be able to measure the C2S cluster distribution and determine if an abnormal condition exists. A crystal count would also quantify the actual amounts of C3S and C3S present in the two clinkers. It may well be that clinker #1 actually
has more C2S than clinker #2, even though the Bogue calculation says the opposite. The size of individual crystals has an impact on grindability as well. Clinker nodules made up of larger, well formed crystals are harder to grind than those composed of smaller
crystal sizes.
There are also other factors that can effect grindability. One of these is clinker density, or degree of porosity. Hard burned clinkers (lower free lime) are more dense than clinkers with higher free lime contents. ie they have a lower porosity. This generally
makes harder burned clinker harder to grind. This may be one reason why the clinker with a lower free lime is harder to grind in your case. (even though the litre weight is marginally lower)
Another factor is degree of cooling. If clinker is not cooled fast enough, C3A crystallises out of the liquid phase in long, large crystals, which strengthen the clinker nodules internally and make them difficult to grind. This can also be easily seen under
the microscope.
I would therefore suggest that you arrange for a comprehensive mineralogical analysis of both clinkers.
The following links may also be helpful;-
http://www.cemnet.com/Forum/thread/108976/impact-of-free-lime-on-grinding-efficiency.html
http://www.cemnet.com/Forum/thread/109059/clinker-hanrdess.html
Regards,
Ted.
