This is a very complicated question and will be the subject of the Tech Forum in the October issue of ICR. In the normal case C11A7.CaF2 is not formed and the fluoride ions are taken into solid solution in the C3S along with aluminium ions. In this case the setting time is increased. However, if C11A7.CaF2 is formed then the setting time will be reduced as this mineral is fast setting (hence it being the main component of Jet cement. The key question is why is C11A7.CaF2 being formed in this case? That must be related to unusual kiln burning conditions.

Respected Dr.Michael Clark,

What will be the effect of high free lime in setting time and why? In the above said cement-1, we found higher free lime in comparision to Cement-2.

Dr. clark 

 to summarize , 

in normal operations with addition of CaF2 as mineralizer the setting time increased as you mentioned before due to the mechanism of Al ion replacement  ( and this is the normal case )

 and in unusual kiln burning conditions ,C11A7.CaF2 phase formed which lead to decreasing the stting time due to high reactivity of this phase 

my question is

1- what are the unusual kiln burning condition ?

2- what is the tech forum of ICR ( could u please specify to be able to follow up this issue )   

Dear Raj. 

Free lime of course accelerates setting of cement, you can see it in Vicat Initial Seting Time equation correlation:

VIST (min) = 216 - 44 x (% free lime) - 0.125 x (m2/kg) - 2.22 (C3A).

As you can see free-lime content has great affect on initial setting time, the cause of that is small crystal (like underburned) sructure of clinker, that is very active.

Raj, can you also write about alkalis quantity in cement-1 ?