Cement MCQ with answer and solution

Concept

In PPC, part of the clinker is replaced by a pozzolana such as fly ash, so it gives less heat of hydration than OPC.

Step-by-step solution

1. PPC = OPC clinker + gypsum + pozzolana (fly ash or calcined clay). 2. The pozzolana reacts slowly with the Ca(OH)₂ released during hydration and forms extra C-S-H gel. 3. Because of this slow reaction, PPC gains strength slowly but has higher long-term strength if moisture is available. So (A) is correct. 4. Fly ash is a common pozzolana used to make PPC. So (B) is correct. 5. PPC has less free lime and lower permeability, so it resists sulphate and seawater attack better. This makes it good for marine and hydraulic structures. So (C) is correct. 6. PPC has less clinker, so it produces LESS heat of hydration than OPC. Statement (D) is wrong. 7. So the answer is (D).

Explanation

PPC has less clinker than OPC, so it releases less heat of hydration. This is why PPC is used in mass concrete such as dams. Statement D says the opposite, so it is the incorrect statement.

Why the other options are wrong

A: Correct statement. The slow pozzolanic reaction raises strength in the long term. B: Correct statement. Fly ash is a standard pozzolana for PPC. C: Correct statement. PPC is dense and chemically resistant, so it suits marine and hydraulic works.

Shortcut

PPC means low heat, slow early strength, high later strength and good durability.

Common mistake

Thinking that the extra pozzolanic reaction adds more heat. In fact the total heat is lower.