Thank you Mr. Krapkat, your information is very helpful.
One last question, what test can i perform (eg. TGA, DTA etc) to confirm that yes the false set was as a result of a different form of gypsum?
Thanks.
Hello Stephen,
DTA will allow you to identify the presence of the different hydrate forms of Ca2SO4, and with TGA you are able to quantify the percentage of each of the different forms by using the weight loss at each dehydration stage. TGA is also faster and more precise than DTA.
A combination of DTA + TGA is the ideal scenario but TGA alone can be used to determine the proportion of each hydrate form in the cement (as well as carbonate content if required).
The links below may contain further useful information...
http://mitrask.com/blog/determination-of-gypsum-content
Regards,
Ted.
Dear Stephen !
Ted Krapkat give a full information. I'm only want give same simplifier methods.
TGA give information about masses of lost waters. Our students in order to determine the modified of gypsum measured loss on ignition. LOI in 400 oC give you content of crystalline hydrate water. LOI in 1000 oC give you summ of crystalline hydrate water and losses of CO2. If you know teoretical content of crystalline hydrate in modifier of gypsum, you may define this modification and calculate it quantity. Teoretical content of crystalline hydrate water in hemihydrate is 6.21 %, in dihydrate 20.93 %. Don't forget to multiply the gypsum content in cement-0.05.
Thank you all