Testing of Cement Questions and Answers

Answer: C

The first two are correct. The third overstates what the test does, since a mortar of fixed proportions cannot predict the strength of a concrete whose mix design has not yet been chosen. The class is an input to mix design rather than its output.

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.

Answer: A

Compositing evens out short-term variation so the result describes the material actually supplied. A grab sample would describe only whatever happened to be at that spot at that moment. Compositing is written into every sampling standard for this reason.

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 the justification. Cement production varies continuously with feed, fuel and mill conditions, so a single grab sample tests one instant rather than the consignment. Combining increments taken through the loading gives a composite whose result represents what the customer actually receives, which is what a compliance test has to do.

Answer: C

If a structure gives trouble, the retained sample allows the cement actually delivered to be tested again. Without it the argument would rest on records alone with nothing to examine. Retained samples are usually kept for several months at least.

Answer: D

Correct answer: True

A standard specifies the method as tightly as the limit, because a requirement is meaningless without a defined way of testing it - the apparatus, the specimen, the curing, the loading rate and the tolerances all affect the number obtained. That is why a result is reported against the standard it was measured to, and why figures from different standards are not directly comparable.

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.

Answer: B

Flash set involves genuine hydration of the aluminate phase and cannot be reversed by mixing. Only false set, which is a physical stiffening from recrystallised gypsum, responds to further working. The remedy for one is useless against the other.

Answer: C

Correct answer: 3.15

Portland cement has a specific gravity of about 3.15, and the figure is used constantly in mix design to convert masses into the absolute volumes that must sum to a cubic metre. It is a property of the solid particles, quite distinct from the bulk density of about 1440 kg per cubic metre, which includes the air between them.

Answer: D

Dividing 315 kilograms by a density of 3.15 kilograms per litre gives 100 litres. This conversion is needed constantly in mix design, where quantities are batched by mass but volumes must balance. Yield calculations depend on getting this conversion right.