State whether the following is true or false.
Grinding cement ever finer improves it without limit.
Answer: C
Beyond a point the extra energy is not repaid, the water demand rises and the cement becomes prone to pre-hydration in storage. Fineness is optimised rather than maximised. Every property has an optimum rather than a direction of improvement.
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Consider the following statements about cement types.
1. Low heat cement has a reduced C3S and C3A content.
2. Sulphate resisting cement has a low C3A content.
3. Rapid hardening cement has a lower C3S content than ordinary cement.
Answer: D
The first two are correct. The third is the reverse of the truth, since rapid hardening cement has a higher C3S content and is ground finer to gain strength quickly. Its whole design is aimed at early rather than ultimate strength.
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The principal reason cement is stored in dry conditions is that
Answer: A
Even atmospheric moisture starts the reaction, forming lumps and reducing the strength the cement can later develop. Bags stored badly lose strength measurably within a few months. Lumps that cannot be crushed between the fingers indicate real damage.
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State whether the following is true or false.
Cement has an indefinite shelf life if kept in its bag.
Answer: B
It absorbs moisture from the air over time and loses strength, which is why standards recommend using it within a few months. Warehouses rotate stock for exactly this reason. Older bags are used first as a matter of routine practice.
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Portland cement is so named because
Answer: C
Joseph Aspdin chose the name for its resemblance to a well-regarded building stone from the Isle of Portland. It was a commercial description rather than a statement of origin. The name has outlived the comparison that prompted it by two centuries.
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