Question

1. a) What is the aim of intergrinding some gypsum rock with clinker during the production of portland cement? b) What are the effects of adding insufficient amount of gypsum and too much gypsum on the cement?

Answer 1

Gypsum is added to the clinker at an optimum level to control the setting characteristic of the cement. Its main function is to slow down the hydration process of cemnet once it is mixed with water. Gypsum is introduced to control initail rate of reaction. Blended cement clinker are produce by intergring cement clinker with materials like Limestone ash, fly ash etc.

Gypsum is added to control the setting of cement if not added cement will set immedately after mixing of water leaving no time for conrete placing .To get workable time an optimum amount of gypsum is added.

If you add high amount of gypsum. Gypsum itself will act as binder, causing the sensation of setting.Further it will produce excessive amount of ettringte. which is consdired bad as it is highle expansive casuing cracks.

For oridnary portland cement 3% to 4% of Gypsum is used and fro Fast setting cement 2.5% gypsum is used.