Clinker Formation and Phases Questions and Answers

Answer: C

Correct answer: insufficient liquid phase to nodulise the material

About a quarter of the charge melts in the burning zone, and it is that liquid which draws the particles together into nodules. Too little of it - from a low alumina or iron content, or from underburning - leaves the material as dust, which is difficult to handle, cools too fast and carries free lime.

Answer: D

These oxides form the low-melting compounds that provide the melt in which the silicates crystallise. This is why the alumina modulus is one of the parameters controlled in raw mix design. Too little melt gives dusty clinker and too much gives rings and coating.

Answer: A

Correct answer: crystal size and distribution of the phases present

A polished and etched section under the microscope shows the alite and belite crystals, their sizes and shapes, the interstitial material between them and any free lime. Those features record how the clinker was burnt and cooled, so microscopy is used as a diagnostic on the kiln as much as a description of the product.

Answer: B

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. Large alite crystals mean a long time at high temperature; rounded belite with lamellar structure means slow cooling; a fine interstitial matrix means rapid cooling. Each feature is a record of a condition the material passed through, so the section can be read as a history of the burn.

Answer: C

Crystals grow with time and temperature, so their size is a direct record of the burning conditions. Very large crystals accompany the hard, difficult-to-grind clinker produced by overburning. Grinding energy at the cement mill rises accordingly.

Answer: D

Slow cooling gives the belite time to react with the surrounding melt and develop the characteristic fringe. Rapid quenching freezes the crystals with sharp boundaries instead. The rim is therefore a direct record of how the cooler performed.

Answer: A

Decomposed alite, fringed belite and large aluminate crystals all record it in the microstructure. This makes microscopy a useful diagnostic when strength results come in lower than expected. The clinker itself carries the evidence long after the event.

Answer: B

Correct answer: aluminate and ferrite phases

The two silicates crystallise out of the melt, and what remains solidifies between them as tricalcium aluminate and the ferrite phase. These are the fastest reacting components of cement - the aluminate would flash-set without gypsum - and they largely determine the early behaviour of the paste.

Answer: C

The first two are correct. The third is wrong, since free lime is unreacted material rather than a designed phase, and its presence indicates that the burning was incomplete. Free lime is measured as a control figure rather than designed for.

Answer: D

Adding 60 and 15 gives 75 per cent. The silicates dominate a Portland clinker and between them supply almost all of its strength, with the interstitial phases contributing comparatively little. Alite alone typically accounts for over half of a Portland clinker.