Which one of the following compounds in cement is responsible for flash setting in the absence of gypsum?
- ATetracalcium Aluminoferrite
- BTricalcium silicate
- CDicalcium silicate
- DTricalcium AluminateCorrect
Solution
Concept
Compounds responsible for flash setting in cement
Formula
NONE
Step-by-step solution
1. Flash setting refers to the rapid hardening of cement paste upon addition of water. 2. In the absence of gypsum, rapid hydration of specific aluminate or silicate compounds occurs. Answer: D
Explanation
Tricalcium aluminate reacts rapidly with water and causes immediate stiffening or flash setting of cement paste. Gypsum is added during cement grinding to retard this initial reaction and control the setting time. Therefore, in the absence of gypsum, tricalcium aluminate causes flash setting, making option D correct.
Why the other options are wrong
A) Tetracalcium Aluminoferrite hydrates slowly and does not cause flash setting. C) Dicalcium silicate contributes to long-term strength rather than flash setting.
Shortcut
C3A (Tricalcium Aluminate) causes flash setting without gypsum: think C3A = Flash setting.
Common mistake
Confusing Tricalcium Aluminate with Tetracalcium Aluminoferrite or Tricalcium Silicate which are involved in hydration and strength development.
Correct answer: D) Tricalcium Aluminate