Extreme Weather Concreting MCQ with answer and solution

Concept

Retarders in hot weather concreting

Formula

NONE

Step-by-step solution

1. Hot weather concreting accelerates cement hydration and moisture evaporation, causing rapid slump loss and premature stiffening. 2. Rapid setting creates cold joints, prevents thorough consolidation, and increases thermal cracking risks. 3. Retarding admixtures delay the chemical hydration of aluminate and silicate phases, extending setting time. 4. Therefore, a retarding admixture is selected to preserve workability in hot weather. Answer: B

Explanation

Concreting in elevated ambient temperatures accelerates cement hydration, which leads to rapid slump loss, flash setting, and thermal cracking. Retarding admixtures delay early hydration reactions of tricalcium aluminate and alite, extending setting time and preserving workability. This ensures proper placement, consolidation, and prevention of cold joints.

Why the other options are wrong

A) Accelerators hasten setting and early strength, which would lead to flash setting in hot conditions. C) Air-entraining agents improve freeze-thaw durability, not setting delay in high temperatures. D) Water-repellent admixtures reduce dampness penetration in hardened plaster.

Shortcut

Hot weather = Retarder (delays setting); Cold weather = Accelerator (speeds setting).

Common mistake

Choosing an accelerator, which would speed up hydration and worsen flash setting in hot weather.