Bricks MCQ with answer and solution

Concept

In the cold water absorption test, dry bricks are fully immersed in clean water at 27 ± 2 °C for 24 hours.

Formula

Water absorption (%) = (W₂ - W₁) / W₁ × 100

Step-by-step solution

1. Dry the brick in an oven at 105-115 °C until its mass is constant. Cool it and weigh it (W₁). 2. Immerse the dry brick fully in clean water at 27 ± 2 °C for 24 hours. 3. Take it out, wipe off surface water with a damp cloth, and weigh it within 3 minutes (W₂). 4. Water absorption = (W₂ - W₁) / W₁ × 100. 5. The soaking time is 24 hours, so the answer is (B).

Explanation

IS 3495 (Part 2) gives a cold water immersion test. The dry brick is kept in water for 24 hours, then weighed again to find how much water it absorbed. Good bricks should absorb less than 20% (first class bricks less than 15%).

Why the other options are wrong

(A) 16 h, (C) 12 h and (D) 9 h are not the periods given in the code. The code also has a 5 hour boiling water test, which students often confuse with this one.

Shortcut

Cold water test = 24 hours; boiling water test = 5 hours.

Common mistake

Mixing up the 24 hour cold water soak with the 5 hour boiling test, or with the 24 hour soak used in the compressive strength test.