Hello Pankaj,

As clinker nodules form they are initially quite porous structures. However as more liquid phase infiltrates the nodule and CaO dissolved in the liquid phase migrates toward areas of high silica. The creation of C2S and ultimately C3S (which both involve an increase in volume) cause the pores to become smaller and fewer, making the nodules therefore denser and harder.

 The harder the clinker is burned the denser the nodule becomes as liquid phase is drawn into the nodule by surface tension, filling the open pores.

The presence of open clinker pores and micro cracks in the clinker mineral crystals greatly assists grinding. If pores and cracks are absent, the clinker is harder to grind.

Hope this helps,

Ted.