Insoluble residue in a cement analysis is a measure of
Answer: A
Portland clinker dissolves almost completely, so a high residue points to siliceous material having been added. The test is a check on composition rather than on any performance property. It answers a question about honesty rather than about behaviour.
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Consider the following statements about cement testing.
1. Standard consistency is determined before setting time.
2. The Le Chatelier test measures soundness.
3. Loss on ignition measures the fineness of the cement.
Answer: B
The first two are correct. The third confuses two quite separate tests, since loss on ignition indicates pre-hydration and carbonation while fineness is measured by air permeability or sieving. Each test has its own apparatus and answers its own question.
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State whether the following is true or false.
A cement can meet every chemical requirement of a standard and still fail it.
Answer: C
Correct answer: True
Standards impose physical requirements as well as chemical ones, so a cement of impeccable composition can still fail on setting time, soundness, fineness or strength. Soundness is the clearest case: it is caused by free lime or magnesia hydrating slowly, and the chemical limits alone will not always catch it, which is why the Le Chatelier and autoclave tests exist.
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Testing of cement at a works is normally carried out
Answer: D
Correct answer: continuously on production samples as well as on dispatch
A works tests continuously, on samples taken through the process and again at dispatch, because production is continuous and a single sample would represent only one moment of it. The regime also serves control rather than just compliance - the results feed back into the kiln and mill settings, so the testing is part of making the cement, not merely of certifying it.
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A cement strength class such as 43 or 53 in Indian practice refers to
Answer: A
Correct answer: the minimum 28-day compressive strength in megapascals
A 43 grade cement must reach at least 43 MPa on standard mortar cubes at 28 days, and a 53 grade at least 53. The figure is a floor rather than a typical value, and it is a mortar strength under standard conditions - not the strength of any concrete made with it, which depends on the mix as much as on the cement.
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A 53 grade cement is tested and gives 51 megapascals at 28 days. What follows?
Answer: B
The grade states a minimum, so anything below it fails regardless of how close it comes. Producers therefore aim well above the nominal figure to allow for normal variation between batches. The margin is calculated from the observed scatter of results.
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Assertion (A): A cement producer aims for a mean strength well above the grade minimum.
Reason (R): Test results vary from batch to batch, and the minimum must be met by nearly all of them.
Answer: C
Both are true and the reason gives the statistics: if the mean sat on the limit then roughly half the batches would fail, so the target is set some way above according to the observed variability. A more consistent process can run closer to the limit safely.
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State whether the following is true or false.
Aiming exactly at the specified minimum strength is sound practice for a cement works.
Answer: D
Half the production would then fall below it, since results scatter about the mean. The target is set above the minimum by a margin determined by the standard deviation of the process. Reducing variability is as valuable as raising the mean.
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A cement has a mean strength of 50 megapascals with a standard deviation of 3. Roughly what proportion of results would fall below 44 megapascals?
Answer: A
Correct answer: about 2.5 per cent
44 MPa lies two standard deviations below the mean: \[ z = \frac{44-50}{3} = -2. \] For a normal distribution about 2.3 per cent of results fall below \( -2\sigma \), so roughly 2.5 per cent. The 16 per cent offered is the proportion below one standard deviation, which is what results from dividing by 6 instead of 3.
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Chemical analysis of cement for its oxide composition is most often carried out by
Answer: B
The same technique used for raw mix control serves for the finished product, giving a full analysis within minutes. Wet chemical methods remain the reference but are far too slow for routine use. Speed is what makes control rather than mere verification possible.
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