Testing Bricks for Water Absorption

Testing bricks for water absorption is crucial for determining their durability and suitability for construction. This guide will walk you through the methods of testing bricks, including the 24-hour immersion cold water test and the 5-hour boiling water test. We will also discuss the initial rate of absorption and its importance.

Testing Bricks for Water Absorption

Methods of Testing Bricks for Water Absorption

1. 24-hour Immersion Cold Water Test

This test measures the water absorption of bricks by immersing them in cold water for 24 hours.

Procedure:

• Dry bricks are kept in an oven at $110\pm 5^{\circ }C110\; \backslash pm\; 5^\backslash circ\; C$ until they attain a constant mass (W1). This is recorded as the dry weight.
• Bricks are immersed in water at $27\pm 2^{\circ }C27\; \backslash pm\; 2^\backslash circ\; C$ for 24 hours.

• Bricks are taken out of the water and wiped with a damp cloth. The weight (W2) is recorded.

Water Absorption Calculation:

$\text{Water absorption in \%}=\left(\frac{W2-W1}{W1}\right)\times 100\backslash text\{Water\; absorption\; in\; \backslash \%\}\; =\; \backslash left(\; \backslash frac\{W2\; -\; W1\}\{W1\}\; \backslash right)\; \backslash times\; 100$

Classification:

• 1st class brick: Water absorption ≤ 20%
• 2nd class brick: Water absorption ≤ 22%
• 3rd class brick: Water absorption ≤ 23%
• Common building brick: Water absorption ≤ 25%

Note: In some cases, 3rd class bricks with water absorption ≤ 25% are given.

2. 5-hour Boiling Water Test

This test involves immersing bricks in boiling water to measure water absorption.

Procedure:

1. The same dry weight (W1) is noted.
2. The specimen is immersed in water and heated to boiling in 1 hour. Boiling is continued for 5 hours.
3. The specimen is then cooled down to $27\pm 2^{\circ }C27\; \backslash pm\; 2^\backslash circ\; C$ by natural loss of heat within 16-19 hours.
4. Bricks are taken out of the water and wiped with a damp cloth. The weight (W3) is recorded.

Water Absorption Calculation:

$\text{Water absorption in \%}=\left(\frac{W3-W1}{W1}\right)\times 100\backslash text\{Water\; absorption\; in\; \backslash \%\}\; =\; \backslash left(\; \backslash frac\{W3\; -\; W1\}\{W1\}\; \backslash right)\; \backslash times\; 100$

Saturation Coefficient:

$\text{Saturation Coefficient}=\frac{\text{24-hour water absorption (W2)}}{\text{5-hour water absorption (W3)}}\backslash text\{Saturation\; Coefficient\}\; =\; \backslash frac\{\backslash text\{24-hour\; water\; absorption\; (W2)\}\}\{\backslash text\{5-hour\; water\; absorption\; (W3)\}\}$

Aim: To predict the durability of bricks.

Initial Rate of Absorption (IRA)

The initial rate of absorption measures how much water a brick draws in during the first minute after contact with water.

Key Points:

1. Suction has a direct bearing on the bond between bricks and mortar.
2. When a brick has high suction, a strong water-tight joint may not be achieved. High suction bricks should be wetted for 3 to 24 hours before laying to reduce suction and allow the bricks to surface dry.
3. Very low suction bricks should be covered and kept dry on the job site.

Notes:

• Generally, bricks are soaked in water before use in masonry work to ensure they don’t absorb water from cement.
• Average water absorption should not be more than 20% by weight for 1st class bricks and 15% by weight for high-duty bricks.
• For water absorption less than 5%, the danger of frost action is negligible.

Frequently Asked Questions (FAQs)

• Why is it important to test bricks for water absorption?
• Testing bricks for water absorption is crucial to determine their durability and suitability for construction. High water absorption can weaken the bond between bricks and mortar, leading to structural issues.

• What is the significance of the initial rate of absorption (IRA)?

• The initial rate of absorption (IRA) indicates how much water a brick absorbs in the first minute of contact with water. It affects the bond strength between bricks and mortar and helps in determining the necessary pre-wetting time for bricks.

• How is the water absorption percentage calculated in the 24-hour immersion cold water test?

• The water absorption percentage is calculated using the formula:

$\text{Water absorption in \%}=\left(\frac{W2-W1}{W1}\right)\times 100\backslash text\{Water\; absorption\; in\; \backslash \%\}\; =\; \backslash left(\; \backslash frac\{W2\; -\; W1\}\{W1\}\; \backslash right)\; \backslash times\; 100$

where W1 is the dry weight of the brick and W2 is the weight after 24 hours of immersion in water.

• What is the saturation coefficient, and why is it important?
• The saturation coefficient is the ratio of 24-hour water absorption to 5-hour boiling water absorption. It helps predict the durability of bricks by indicating their potential to withstand moisture without deteriorating.

• How can high water absorption in bricks be prevented?

• High water absorption can be prevented by ensuring proper firing of bricks during the manufacturing process, using quality materials, and pre-wetting bricks before laying them in masonry work.

Conclusion

Testing bricks for water absorption is a vital step in ensuring the quality and durability of construction materials. By understanding the methods and importance of these tests, builders can make informed decisions and improve the longevity of their structures.