The consistency of standard paste, used as the basis for several tests, is the water content at which
Answer: A
Establishing this reference water content first means that setting time and soundness are compared on pastes of equivalent stiffness. Without it the results would depend as much on how much water was added as on the cement itself.
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Assertion (A): Standard consistency is determined before the setting time test is carried out.
Reason (R): Setting time depends on the water content, so a reference stiffness must be fixed first.
Answer: B
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason is why the order is fixed. A wetter paste sets later and a drier one sooner, so a setting time is meaningless unless the water content is standardised first. Standard consistency - the water percentage at which the Vicat plunger penetrates to a specified depth - establishes that reference, and the setting time and soundness tests are then run at a fixed fraction of it.
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Initial setting time is measured as the interval from adding water until
Answer: C
It marks the point at which the paste is no longer usefully workable, so it sets a practical limit on how long concrete can be transported and placed. Final set is measured later with a different attachment. Both figures are quoted because each has a different practical meaning.
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Final setting time is distinguished from initial setting time by
Answer: D
The attachment leaves a mark only while the paste is still soft, so its failure to mark the surface defines final set. The same specimen and the same apparatus serve for both measurements. Only the attachment on the needle is exchanged between the two readings.
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A cement standard requires an initial set of not less than 30 minutes and a final set of not more than 600 minutes. A sample sets initially at 45 minutes and finally at 11 hours. Does it comply?
Answer: A
Forty-five minutes exceeds the minimum of thirty and eleven hours is 660 minutes, which is above the 600 permitted, so it does not comply after all. Converting hours to minutes before comparing is the step that decides it.
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State whether the following is true or false.
A cement that sets very quickly is always defective.
Answer: B
Quick setting cements are made deliberately for particular purposes such as underwater work and grouting. What is defective is a cement that sets faster than its own specification allows. Compliance is judged against the declared type rather than against habit.
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The Le Chatelier test measures
Answer: C
A split brass mould with indicator arms is boiled, and the separation of the arms records expansion caused by free lime. Excessive expansion means the cement will disrupt itself after hardening. The mould is boiled precisely to accelerate a reaction that is otherwise slow.
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The autoclave test differs from the Le Chatelier test in that it also detects expansion due to
Answer: D
The higher temperature and pressure hydrate periclase, which the boiling water test does not reach. This is why standards that limit magnesia generally specify the autoclave method. The two tests answer different questions about the same property.
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Assertion (A): A cement may pass the Le Chatelier test and still be unsound.
Reason (R): Boiling water does not hydrate magnesia, which the autoclave test does reach.
Answer: A
Both are true and the reason gives the gap in the simpler test: free lime is detected but periclase is not, so a cement high in magnesia can pass and yet expand in service years later. Where magnesia is a concern the autoclave test is the one specified.
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Compressive strength of cement is determined on
Answer: B
Using a standard sand and a fixed proportion removes the variability that aggregate would introduce, so the test measures the cement rather than the concrete. It is a comparative test rather than a prediction of structural strength.
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