Cement Types and Properties Questions and Answers

Answer: B

Tricalcium silicate (C3S, about 40 to 50 percent) and dicalcium silicate (C2S, about 25 to 30 percent) together make up the greatest part, around 70 to 75 percent, of ordinary Portland cement. They are responsible for its strength. Tricalcium aluminate (C3A) is about 8 to 12 percent and tetracalcium aluminoferrite (C4AF) is about 8 to 12 percent, so any combination that includes one of those two is smaller. Hence the C3S and C2S pair has the largest share.

Answer: C

The correct matching is 1-C, 2-D, 3-A, 4-B. Portland slag cement has good resistance to chemical attack, so it protects reinforcement from corrosion (1-C). Low heat Portland cement gives off less heat of hydration and is used in massive water-retaining structures such as dams (2-D). Rapid hardening cement gains strength quickly, which makes it suitable for cold weather concreting (3-A). Super sulphated cement resists sulphates and sea water, so it suits offshore structures (4-B). The other codes swap these pairs.

Answer: B

Le Chatelier's apparatus finds the Soundness of cement.

Unsound cement expands after setting because of free lime or magnesia. In the test, a split brass mould with indicator arms is filled with cement paste, cured, then boiled; the separation of the indicator points measures the expansion, which IS 269 limits to 10 mm for ordinary Portland cement.

Setting times are found with the Vicat apparatus, workability is a property of concrete (slump test), and compressive strength is found by crushing mortar cubes.

Answer: B

Rapid Hardening Portland Cement conforms to IS 8041: 1990.

IS 8041 covers rapid hardening Portland cement, which is ground finer and has more tricalcium silicate than OPC, so it gains early strength quickly, roughly its 7-day OPC strength in 3 days. It is used where formwork must be removed early or for repair work.

IS 455 is Portland slag cement, IS 12600 is low heat Portland cement, and IS 12330 is sulphate resisting Portland cement.

Answer: C

Initial setting is mainly due to tri-calcium aluminate (C₃A).

C₃A reacts with water almost at once and with great heat, and it is this reaction that stiffens the paste first. Left unchecked it causes flash set, which is why gypsum is ground into cement: it slows the C₃A reaction enough to leave time for placing.

Tri-calcium silicate (C₃S) hydrates next and gives the early strength of the first weeks. Di-calcium silicate (C₂S) hydrates slowly and gives later strength. The tetra-calcium compound (C₄AF, an aluminoferrite) contributes little to setting or strength.

Answer: C

The key's answer is 5 mm.

In the Le Chatelier soundness test, the gap between the indicator points is read before and after boiling the cement specimen, and the difference is the expansion. The Indian cement standards allow at most 10 mm of expansion, a value not among the options.

5 mm is the stricter limit the same standards apply when a cement fails the first test and is retested after aeration (spread out and exposed to air for seven days). The key takes that limit. 15 mm is above any limit in the standards, and 4 mm and 9.5 mm are not specified values.

Answer: C

The cube size is 70.6 mm.

Cement mortar cubes for the compressive strength test (IS 4031 Part 6) are 70.6 mm on a side, which gives a face area of 70.6 × 70.6, about 5,000 mm² (50 cm²), a convenient area for converting the load to a stress.

150 mm and 100 mm are the standard concrete cube sizes, not cement mortar cubes, and 50 mm cubes are used in some other national standards, not in IS 4031.