Dear all, We are recently using mineral gypsum (Oman origin) in place of phospho gypsum (by product of fertilizer plants)particularity in PPC (FAB). Usage of Mineral gypsum is helping us to improve early strength (One day) by 40%, which facilitating us to increase the fly ash content up to 35% which is upper limit in India as per BIS. But seven days onwards compressive strengths are falling down by around 5%. Requesting experts what could be reason for falling ultimate strengths comparatively. Regards, BLM
Ted Krapkat
Hello BLM,
By increasing the flyash addition you may be reducing later strengths, which rely largely on the C3S and C2S content. Higher flyash addition proportionately reduces the amount of C3S + C2S in the cement.
Regards,
Ted.
Silastman
Phosphogypsum contains phosphate ion, which slows down the cement hydration. With the mineral gypsum cement hardens more quickly, so in early terms of hardening you have higher strength, but the final strength of cement with phosphogypsum higher than with mineral gypsum. Increasing of early strength is not a prerequisite for the use of fly ash .
chari
Ted and satisman are very right.
The acidity of phospogypsum reduces the early hydration of clinker particles reducing the initial strength.which is not the case with mineral gypsum. But if the %age of clinker is reduced than ultimate strength (7d and 28d) is reduced as per the decrese in clinker%.