Gypsum is used as an admixture in cement grouts for
- AAccelerating the setting time
- BRetarding the setting timeCorrect
- CIncreasing the plasticity
- DReducing the grout shrinkage
Solution
Concept
Gypsum as a Retarder in Cement
Formula
No formula
Step-by-step solution
- Gypsum reacts with tricalcium aluminate (C3A) in cement during hydration - This slows down the chemical reaction and prevents flash setting - Therefore, gypsum is added as an admixture to retard setting time
Explanation
Gypsum slows down the chemical reaction between water and cement when they are mixed. By doing this, it delays the initial setting of the cement, allowing workers enough time to mix, handle, and place the grout properly before it hardens.
Shortcut
Remember: "Gypsum Gives time" — G for Gypsum, G for Gives time (Retards setting).
Common mistake
Students often confuse retarders with accelerators, mistakenly choosing option A (Accelerating the setting time) because they confuse delaying the initial setting process with speeding up strength gain.
Correct answer: B) Retarding the setting time