Question

Cement is made hard by -

• A. Dehydration
• B. Hydration and dissociation of water
• C. Dissociation of water
• D. Polymerisation

Answer 1

The correct option is B

Hydration and dissociation of water

Explanation of correct answer.

(C) - Hydration and dissociation of water

• The cement hardens when it comes into contact with water.
• This hardening is a process of crystallization. Crystals form (after a certain length of time which is known as the initial set time) and interlock with each other.
• Concrete is completely fluid before the cement sets, then progressively hardens. The cement and water mixture that has crystallized in this way encloses the aggregate particles and produces a dense material. The concrete continues to harden over several months.
• Hardening is not a drying process and can very well take place in water.
• Heat speeds up the setting and hardening of cement, and cold slows it down and can even completely stop the processes.
• The hardening of cement can take place even underwater and if the water is hot it will accelerate the process. Hardening of cement even takes place if we left the cement in the open air for some time.

The explanation for the incorrect options

(A) - Dehydration

• Dehydration is the removal of water molecules.
• Hardening is not a drying process and can very well take place in water.

(C) - Dissociation of water

• Hardening is not a drying process and can very well take place in water.
• It involves both hydration and dissociation of water.

(D) - Polymerization

Polymerization is the process through which a large number of monomer molecules react together to form a polymer.

The polymer phase in the concrete will help reduce the porosity and microcracks that are formed in the cement matrix.

Hence Cement is made hard by hydration and dissociation of water

Therefore, option (B) is the correct answer.