Which compound is added to cement to increase its setting time?
Which compound is added to cement to increase its setting time?
Gypsum
Lime stone
Clay
Calcium carbonate
The Correct Option is A
Solution and Explanation
Gypsum (CaSO4·2H2O)
Explanation:
- When cement is mixed with water, the setting process begins due to hydration reactions of the compounds present in cement, especially tricalcium aluminate (C3A).
- These reactions occur rapidly, leading to a very quick setting of cement, which can make it difficult to work with during construction.
- Gypsum, which is chemically calcium sulfate dihydrate (CaSO4·2H2O), is added to cement to regulate the setting time.
- Gypsum slows down the hydration of tricalcium aluminate (C3A) by forming a coating around the particles, giving more time for mixing, transportation, and placing of the cement.
Conclusion:
Gypsum is added to cement to increase its setting time and make it workable during construction.
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Concepts Used:
Surface Chemistry
The study of the chemical phenomena that occur at the interface of two surfaces which can be solid-liquid, solid-gas, solid-vacuum, liquid-gas, etc.
Read Also: Surface Chemistry
Applications of surface chemistry are:
Adsorption:
The process of attraction and aggregation of the molecules of a substance on the surface of a solid is known as adsorption. For Example, N2 adsorbs on the surface of activated charcoal
Two types of adsorption are:-
- Chemisorption: It is also known as Chemical Adsorption.
- Physisorption: It is also known as Physical Adsorption.
Corrosion:
The process through which the refined metals convert themselves into more stable compounds is known as corrosion.
Crystallisation:
The type of technique used in order to purify the substances to separate Solids from liquids is known as crystallisation.
Heterogeneous Catalysis:
The process wherein a catalyst is used in order to increase the rate of a chemical reaction is known as catalysis. The catalyst does not undergo any transformation and can be recovered in a chemically unchanged state.
There are two types of catalysis:-
- When the catalyst involved and the reacting substances are same states of matter or in the same phase, it is known as Homogeneous Catalysis.
- When the catalyst involved and the reacting substances are in different states of matter or different phases, it is known as Heterogeneous Catalysis.