Recently we started production of SRC with 97.5 LSF, 2.35 SM, and 0.75 AM raw meal composition. After that free lime become normal (i.e 1.1 - 1.20). Do you think that with OPC we were operating with high alumina modulus? (Continuation question)

I don't think the high free CaO was associated with the alumina modulus itself. However, the mix of raw materials must have changed in the switch to SRC production. Which raw materials have reduced significantly? Whichever one is the most likely culprit. We can rule out the coal as presumably this remains the same blend as when OPC was produced.

Please advise the chemical and physical properties of:
1. Oil well cement
2. Sulphate resistant cement
3. Slag cement
4. Fly ash cement
Can sulphate resistant cement be replaced with any of the other three cements mentioned above?

1. Oil well cement comes in different grades (API Grades A to J inclusive).They are designed to be slow setting and therefore have very low C₃A contents and are coarsely ground. Some grades also contain added retarders. As they have low C₃A content they are sulphate resisting and could be substituted for SR cement, however the setting time would be long.
2. Sulphate Resisting cement has a limit of four per cent on the C₃A content to prevent attack by sulphates on the hydrated C₃A.
3. Slag cement has up to 65 per cent granulated blast furnace slag added to the cement clinker and gypsum. The slag content undergoes the pozzolanic reaction and this enhances the impermeability and durability of concrete made from the cement. This makes the concrete resistant to sulphate attack and these cements can be substituted for SR cements.
4. Fly ash cement contains up to 35 per cent fly ash added to the cement clinker and gypsum. The fly ash undergoes the pozzolanic reaction and this enhances the impermeability and durability of concrete made from the cement. This makes the concrete resistant to sulphate attack and these cements can be substituted for SR cements.