Cement Grinding and Additives Questions and Answers

Answer: C

Correct answer: True

The stiffness comes from a fragile network of secondary gypsum crystals, not from the cement setting, so continued mixing breaks it down and the paste becomes workable again with no water added. That is exactly what distinguishes false set from flash set, which is genuine and irreversible.

Answer: D

Water sprays or ventilation hold the temperature below the point at which gypsum loses its water. This is one of the few places in the plant where cooling rather than heating is the concern. Grinding energy nearly all appears in the end as heat.

Answer: A

The finer the powder the stronger the tendency of particles to stick together and coat the media, so the penalty for not dispersing them grows with fineness. This is why almost every cement mill doses an aid while many raw mills do not.

Answer: B

The increase of 15 tonnes on a base of 100 is 15 per cent. Gains of this order are typical and are weighed against the cost of the additive per tonne of cement produced. The dose is typically a fraction of a kilogram per tonne.

Answer: C

Certain compounds influence the early hydration reactions as well as dispersing the particles, so strength rises beyond what the extra fineness alone would give. The distinction from a plain grinding aid is one of effect rather than of dosing.

Answer: D

Correct answer: False

A grinding aid acts in the mill, reducing agglomeration and raising throughput. A quality improver acts in the finished cement, usually to raise strength or improve flow at a given clinker content. Many commercial products do both, but the two functions are distinct and are specified separately.

Answer: A

It performs exactly the duty described for raw grinding, returning coarse material to the mill and passing fine product forward. The other three names belong to the pyroprocessing side of the plant. The same classification principle serves both grinding circuits.

Answer: B

Correct answer: improves particle packing and reduces clinker use

Finely ground limestone fills the spaces between the larger cement grains, giving a denser packing and a lower water demand at the same workability. It also nucleates hydration and reacts a little with the aluminate. The result is that a proportion of the clinker - typically up to 15 per cent - can be replaced with little loss of performance.

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. The limestone is not merely inert filler: its fine particles improve the packing and provide nucleation sites, and it reacts with the aluminate phase to form carboaluminates. Together those effects offset much of the dilution, which is why the substitution is permitted by standards rather than merely tolerated.

Answer: D

Subtracting 5 and 15 from a hundred leaves 80 per cent clinker. Standards define the permitted ranges for each constituent, and a cement is designated according to where its composition falls. Composition limits are set by standard rather than by the maker.