You can calculate this based on the chemical analysis available for both the activators and the alumonisilicate precursor your're using.
For example, if you're activating slag with sodium silicate and sodium hydroxide, your SiO2 to Na2O ratio will be the ratio of the total SiO2 in the sodium silicate, soidum hydroxide, and slag divided by the total Na2O from also the activators and slag
Dear Ashwin, please refer to report published by D. Hardjito and B. V. Rangan. They have provided he detailed calculation in the Appendix of the report. I hope that helps. Regards.
You may refer to the paper for computing the molar ratios of alkaline activators:
Nasir, M., Johari, M. A. M., Yusuf, M. O., Maslehuddin, M., & Al-Harthi, M. A. (2020). Effect of alkaline activators on the fresh properties and strength of silico-manganese fume-slag activated mortar. Advances in concrete construction, 10(5), 403-416.
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