Clinker Formation and Phases Questions and Answers

Answer: A

Correct answer: alite

Alite is impure tricalcium silicate and is the principal phase of Portland clinker, typically half to two thirds of it. It is what gives early strength, hydrating rapidly and evolving considerable heat. Belite is the corresponding name for dicalcium silicate, which hydrates slowly and contributes later strength.

Answer: B

It hydrates far more slowly than alite and supplies the strength gained after the first few weeks. Its proportion is raised deliberately in low heat cements where early strength matters less than heat evolution. Belite grinds harder than alite, which is one cost of raising its proportion.

Answer: C

Correct answer: drying, calcination, solid-state reaction, clinkering

The sequence follows the rising temperature along the kiln: water is driven off first, then the carbonate decomposes from about 800 degrees, then lime and silica begin to combine in the solid state to form belite, and finally at about 1,450 degrees a liquid phase appears and alite forms in it.

Answer: D

Correct answer: about 650 degrees

\[ 1450 - 800 = 650\ \mathrm{degrees}. \] The interval matters because it is the range over which the meal must be carried after calcining, and moving the calcination out of the kiln into a precalciner leaves the kiln only this last stretch to accomplish.

Answer: A

Either the meal was too coarse, the mix too high in lime, or the burning too short or too cool. It is measured routinely because it is the most direct indicator of how well the kiln is doing its work. A rising figure is usually the first sign that burning has slipped.

Answer: B

Both are true and the reason gives the purpose: the figure moves before the strength results do, so it lets the operator correct the kiln long before a batch of substandard cement has been made. Strength tests confirm the outcome only weeks afterwards.

Answer: C

It can equally mean the kiln has been overburnt, wasting fuel and producing hard clinker that grinds poorly. Free lime is controlled within a band rather than driven as low as it will go. Around one per cent is a common target for a well-run kiln.

Answer: D

Excess temperature enlarges the crystals and consolidates the clinker, so more electricity is needed at the cement mill. The fuel and the electricity are both wasted for no gain in quality. Overburnt clinker often shows large alite crystals under the microscope.

Answer: A

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. Underburning leaves free lime and unreacted belite; overburning grows large well-formed crystals which are hard to grind and which hydrate more slowly. The optimum is a burning zone hot enough to combine the lime and no hotter, which is why free lime is monitored continuously as the control variable.

Answer: B

The partial melt binds the particles into nodules of a convenient size for handling and grinding. Dusty clinker and very large lumps both signal that something in the burning is wrong. Nodule size is judged by eye at the cooler as a routine check.