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- Total number of questions : 20
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Cement Technology [ Question No: 1 To 20 ] :
State whether the following is true or false.
Restored quarries can have significant value for nature conservation.
State whether the following is true or false.
Switching a cement kiln entirely to renewable electricity would eliminate its carbon dioxide emissions.
Assertion (A): One-part geopolymer systems are of considerable practical interest.
Reason (R): Supplying the activator as a dry powder removes the need to handle caustic solutions on site.
Assertion (A): Calcium sulphoaluminate cement is not simply a drop-in replacement for Portland cement despite its lower emissions.
Reason (R): It depends on bauxite or other aluminous materials that are far less abundant than limestone.
A false set is distinguished from a flash set in the laboratory by
State whether the following is true or false.
Cement testing measures the cement rather than the concrete.
Heat of hydration is measured by
State whether the following is true or false.
Restraint is necessary for shrinkage to cause cracking.
If a concrete element shrinks by 500 microstrain and is 10 metres long, how much would it shorten if entirely unrestrained?
Assertion (A): Entrained air improves durability while slightly reducing strength.
Reason (R): The bubbles relieve freezing pressure but also add voids to the paste.
The theoretical water needed for complete hydration of cement is roughly
A cement is 70 per cent clinker, 25 per cent slag and 5 per cent gypsum. How much slag is in a 30-tonne tanker load?
State whether the following is true or false.
Hot clinker entering the cement mill is a problem as well as a lost opportunity.
The residence time of material in a modern precalciner kiln is roughly
Assertion (A): False air entering through worn kiln seals increases fuel consumption.
Reason (R): The leaked air must be heated to kiln temperature without contributing to combustion.
Alternative fuels used in cement kilns include
State whether the following is true or false.
A vertical roller mill can grind and dry the material in the same machine.
A works replaces 5 per cent of its 3,000 tonnes of daily raw meal with an alternative material. How much quarried stone does it save in a 300-day year?
Selective quarrying means
Assertion (A): Sulphate resisting cement contains little tricalcium aluminate.
Reason (R): Sulphates attack concrete chiefly by reacting with the aluminate phase.
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20
Cement Technology [ Question No: 1 To 20 ] :
State whether the following is true or false.
Restored quarries can have significant value for nature conservation.
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: True
A worked-out quarry leaves cliffs, ledges, bare ground and water bodies - habitats that are scarce in a farmed landscape and that support species which need them. Restoration schemes are now designed for that rather than merely for landscaping, and some former quarries are designated nature reserves.
State whether the following is true or false.
Switching a cement kiln entirely to renewable electricity would eliminate its carbon dioxide emissions.
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: False
Roughly 60 per cent of the emissions come from calcining the limestone, and that carbon dioxide is released by the chemistry of the rock whatever heats the kiln. Renewable electricity would address the smaller fuel share only, and even that indirectly, since the kiln burns fuel rather than running on electricity.
Assertion (A): One-part geopolymer systems are of considerable practical interest.
Reason (R): Supplying the activator as a dry powder removes the need to handle caustic solutions on site.
Your Answer : (Not Answered)
Correct Answer : D
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. A one-part system supplies the activator as a dry solid blended with the precursor, so the material is mixed with water like ordinary cement. That removes the caustic liquid from the site entirely, which is the obstacle a two-part system presents.
Assertion (A): Calcium sulphoaluminate cement is not simply a drop-in replacement for Portland cement despite its lower emissions.
Reason (R): It depends on bauxite or other aluminous materials that are far less abundant than limestone.
Your Answer : (Not Answered)
Correct 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. Calcium sulphoaluminate cement emits substantially less carbon dioxide, but it needs an aluminous raw material, and bauxite is neither as abundant nor as widely distributed as limestone. The constraint is on raw material supply rather than on the chemistry, and it caps how far the cement can be adopted.
A false set is distinguished from a flash set in the laboratory by
Your Answer : (Not Answered)
Correct Answer : A
False set is caused by recrystallised gypsum and yields to further mixing, whereas a flash set from aluminate hydration does not. The distinction matters because one is a nuisance and the other makes the cement unusable.
State whether the following is true or false.
Cement testing measures the cement rather than the concrete.
Your Answer : (Not Answered)
Correct Answer : D
Every variable except the cement is fixed by the standard so that results are comparable between samples and laboratories. Predicting the concrete requires a trial mix using the actual materials. Only the real aggregates and water can answer that question.
Heat of hydration is measured by
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: dissolving hydrated and unhydrated samples in acid and comparing
This is the heat of solution method. The heat released when unhydrated cement dissolves in acid, less the heat released when a hydrated sample of the same cement dissolves, is the heat the hydration itself gave out. It measures the total heat rather than the rate; isothermal conduction calorimetry is the alternative where the rate over the first days is what matters.
State whether the following is true or false.
Restraint is necessary for shrinkage to cause cracking.
Your Answer : (Not Answered)
Correct Answer : B
Unrestrained concrete simply becomes slightly smaller without any stress developing. It is the combination of shrinkage and restraint, whether from foundations, reinforcement or adjoining members, that produces the tension.
If a concrete element shrinks by 500 microstrain and is 10 metres long, how much would it shorten if entirely unrestrained?
Your Answer : (Not Answered)
Correct Answer : D
Five hundred microstrain is 0.0005, and multiplying by 10 metres gives 5 millimetres. Restraint converts most of that movement into tensile stress instead, which is what causes the cracking. Reinforcement distributes that cracking into many fine cracks.
Assertion (A): Entrained air improves durability while slightly reducing strength.
Reason (R): The bubbles relieve freezing pressure but also add voids to the paste.
Your Answer : (Not Answered)
Correct Answer : A
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason states both effects of the same bubbles. The voids relieve freezing pressure, which is the point, and they also reduce the solid volume of the paste, costing roughly five per cent of compressive strength for each one per cent of air. In an exposed structure that is a trade well worth making, since a concrete destroyed by frost has no strength at all.
The theoretical water needed for complete hydration of cement is roughly
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: a quarter of the mass of the cement
About 0.23 to 0.25 of the cement mass is chemically combined in complete hydration. In practice a somewhat higher ratio is needed - around 0.38 - because the gel pores must also be filled for hydration to proceed, and higher still for workability without admixtures. Everything above that requirement becomes capillary porosity, which is why the water-cement ratio governs strength so directly.
A cement is 70 per cent clinker, 25 per cent slag and 5 per cent gypsum. How much slag is in a 30-tonne tanker load?
Your Answer : (Not Answered)
Correct 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.
State whether the following is true or false.
Hot clinker entering the cement mill is a problem as well as a lost opportunity.
Your Answer : (Not Answered)
Correct Answer : B
Excessive mill temperature dehydrates the gypsum and can cause false set in the finished cement. Cooler performance therefore affects the grinding plant as well as the heat balance of the kiln. A fault at one end of the plant shows up at the other.
The residence time of material in a modern precalciner kiln is roughly
Your Answer : (Not Answered)
Correct Answer : B
The shell is short and the material moves through it fairly quickly once calcination has been done in the tower. Gas passes through the whole system in a matter of seconds. The contrast between the two residence times is very large indeed.
Assertion (A): False air entering through worn kiln seals increases fuel consumption.
Reason (R): The leaked air must be heated to kiln temperature without contributing to combustion.
Your Answer : (Not Answered)
Correct Answer : D
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. Air leaking in through a worn seal is heated to whatever temperature it reaches before leaving with the exhaust, and it takes that heat with it. It contributes nothing to combustion, since it enters downstream of the flame, so the fuel that heated it is simply lost.
Alternative fuels used in cement kilns include
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: waste tyres, solvents and processed municipal waste
A cement kiln burns these well because the gas residence time is long, the temperature is very high, and the alkaline charge neutralises acid gases. The ash is incorporated into the clinker rather than left over, which is why the kiln is used for wastes that would otherwise need dedicated incineration.
State whether the following is true or false.
A vertical roller mill can grind and dry the material in the same machine.
Your Answer : (Not Answered)
Correct Answer : B
Correct answer: True
A vertical roller mill grinds between rollers and a rotating table while hot gas passes up through it, carrying the moisture away and sweeping the ground material to the integral separator above. Grinding, drying and classification therefore happen in one machine, which is a large part of why the type has displaced the ball mill for raw grinding.
A works replaces 5 per cent of its 3,000 tonnes of daily raw meal with an alternative material. How much quarried stone does it save in a 300-day year?
Your Answer : (Not Answered)
Correct Answer : C
Five per cent of 3,000 tonnes is 150 tonnes a day, and over 300 days that is 45,000 tonnes. A seemingly small substitution rate translates into a very substantial saving across a year. Substitution rates are quoted per tonne but judged on the annual total.
Selective quarrying means
Your Answer : (Not Answered)
Correct Answer : A
Where a deposit varies, benches of differing composition can be worked in proportion to give a consistent blend. It is a cheaper way of controlling chemistry than buying corrective materials, and it extends the useful life of a variable deposit.
Assertion (A): Sulphate resisting cement contains little tricalcium aluminate.
Reason (R): Sulphates attack concrete chiefly by reacting with the aluminate phase.
Your Answer : (Not Answered)
Correct 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 cause. Sulphate entering the paste reacts with the calcium aluminate hydrates to form ettringite, which occupies a much larger volume and disrupts the concrete from within. Limiting the tricalcium aluminate content - typically to five per cent or less - removes most of what the sulphate can attack, which is precisely how the cement is specified.
Marks
Total number of questions : 20
Number of answered questions : 0
Number of unanswered questions : 20