Clinker Formation and Phases Questions and Answers

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Clinker arriving hot raises the mill temperature, and above about 110 degrees the gypsum loses its water and becomes hemihydrate. That rehydrates rapidly on mixing and stiffens the paste within minutes - a false set traceable directly to the cooler.

Answer: D

Removing the iron is how white cement is produced, which confirms that it is the source of the colour. Carbon is fully burnt in a properly run kiln and contributes nothing to the appearance. Colour is therefore a chemical rather than a combustion matter.

Answer: A

The first two are correct. The third contradicts both microscopy and practice, since the cooling rate determines whether alite survives and how the interstitial material crystallises. The cooler is part of the process rather than mere handling.

Answer: B

Correct answer: brown in colour and of lower strength

Insufficient oxygen reduces some of the ferric iron to ferrous, which changes the colour from grey to brown and disrupts the ferrite phase. Alite formation is impaired and the strength falls. The colour is therefore a visible indication of a combustion problem, and it is one of the things a clinker microscopist looks for.

Answer: C

The colour comes from iron in a lower oxidation state and is usually accompanied by lower strength. It is one of the visual checks an experienced operator makes at the cooler discharge. A change in colour prompts an immediate check of the kiln oxygen.

Answer: D

The difference between 1.5 and 1.0 is half a percentage point. Expressing the change in percentage points rather than as a percentage of the original figure avoids a familiar ambiguity. Percentage points and per cent of a value are different quantities.

Answer: A

Fineness governs how quickly the phases can react, so a coarse grind wastes the potential the kiln has created. The other three describe a clinker that is behaving exactly as it should. Kiln and mill both have to do their part for the cement to perform.