Cement Grinding and Additives Questions and Answers

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. The water is dosed so that it flashes to steam within the mill, and the latent heat it absorbs in doing so removes a great deal of heat. None survives to hydrate the cement, so the product is unaffected - the control of the dose is what makes the practice safe.

Answer: B

The first two describe the two mechanisms correctly. The third is wrong, since most additions lower early strength while improving later strength or durability, which is the usual trade. Early strength is given up in return for durability or lower emissions.

Answer: C

Since most of the emission is associated with clinker, replacing part of it with a material that is already a by-product cuts the total proportionately. It remains the most widely applied measure available to the industry.

Answer: D

Correct answer: False

Blended cements are very old. The Romans used volcanic ash with lime, and slag cements have been made industrially since the nineteenth century. What is recent is the scale of their use, driven by the cost of clinker and by the carbon dioxide released in making it.

Answer: A

Correct answer: reacts slowly and benefits from a greater surface area

Slag is latent hydraulic and reacts far more slowly than clinker, so it is ground finer to give the reaction more surface to work on. Note that it is also harder than clinker, not softer - which is why intergrinding leaves it too coarse and separate grinding is the better route.

Answer: B

Correct answer: 7.5 tonnes

\[ 0.25 \times 30 = 7.5\ \mathrm{tonnes}. \] The rest is 21 tonnes of clinker and 1.5 of gypsum. Both of those figures appear among the distractors, so the arithmetic is straightforward and the reading of the question is what settles it.

Answer: C

Correct answer: True

Mills are routinely switched between products, and many plants run campaigns of one cement type and then another through the same mill. What the change requires is a cleanout to avoid cross-contamination, and a period of production that is checked before it is accepted into the right silo.

Answer: D

Cement can leave a mill well above a hundred degrees, which stresses silo aeration equipment and risks further dehydration of the gypsum. A cooler on the mill discharge is the usual answer. Cooling also protects the bagging plant and the conveyors.

Answer: A

Correct answer: False

Cement leaves a mill hot - often 100 degrees or more - because nearly all the grinding energy becomes heat. It is cooled to some extent before dispatch, but it is commonly loaded at 60 to 80 degrees rather than at ambient, which is why silo residence time and cooler capacity matter.

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. Hot cement raises the temperature of the fresh concrete, and hydration accelerates with temperature, so slump is lost faster and the time available for placing and finishing is shortened. In hot weather that can be decisive, which is why a maximum delivery temperature appears in the specification.