If (W1) is the weight of a dry brick and (W2) is the weight after immersion in water for 24 hours, then the percentage of brick water absorption is calculated as:
Correct Answer:
D. $$ \frac{W_2 - W_1}{W_1} \times 100 $$
💧 Understanding the Water Absorption Calculation
The water absorption test measures a brick's porosity, which is a key indicator of its quality and durability. The goal is to find out how much water the brick absorbs and express this as a percentage of its original dry weight. A lower percentage generally indicates a denser, stronger, and more durable brick.
🔬 Detailed Analysis of the Formulas
D. $$ \frac{W_2 - W_1}{W_1} \times 100 $$
This is the correct answer. This formula correctly calculates the percentage absorption.
- (W₂ - W₁): This part of the formula calculates the weight of the water absorbed by the brick (Saturated Weight - Dry Weight).
- / W₁: The weight of the absorbed water is then divided by the original dry weight of the brick to find the absorption ratio. The dry weight is used as the baseline for comparison.
- x 100: This converts the ratio into a percentage.
A, B, and C
These formulas are incorrect because they do not represent the percentage increase in weight relative to the original dry weight.
- Option A is a simple ratio of dry to wet weight.
- Option B incorrectly uses the wet weight (W₂) as the denominator and has the subtraction reversed.
- Option C calculates the ratio of wet to dry weight, not the percentage of water absorbed.
📊 Summary: Formula Components
| Variable | Description | Role in Formula |
|---|---|---|
| W₁ | Weight of the oven-dried brick. | The original, baseline weight. Used as the denominator. |
| W₂ | Weight of the brick after soaking in water for 24 hours. | The final, saturated weight. |
| (W₂ - W₁) | Weight of water absorbed. | The increase in weight. Used as the numerator. |
💡 Study Tips
- Think "Change over Original": Most percentage calculations in engineering follow this logic. The "change" is the water absorbed (W₂ - W₁), and the "original" is the dry brick's weight (W₁).
- Dry Weight is Key: The calculation must be based on the dry weight (W₁), as it's the constant starting point. Using the wet weight (W₂) as the base would give an incorrect result.
- Logical Check: The final weight (W₂) must be greater than the initial weight (W₁), so the numerator (W₂ - W₁) should always be a positive number.