What should be the water absorption of second class bricks when compared to its dry weight when immersed in cold water for 24 hours?
16 - 20 percent
Water Absorption in Second Class Bricks
Water absorption is a crucial property of bricks that indicates their quality and durability. It is defined as the percentage increase in the weight of a brick after being soaked in water for a specific period, compared to its dry weight. Lower water absorption generally means a more durable and stronger brick that can withstand weathering and moisture damage better.
Brick Classes and Water Absorption Limits
Building bricks are typically classified into different classes based on their properties, including compressive strength and water absorption. The classification helps determine where a particular type of brick is suitable for use in construction.
According to standard specifications, different classes of bricks have different maximum permissible limits for water absorption when immersed in cold water for 24 hours:
| Brick Class | Maximum Water Absorption (% of Dry Weight) |
|---|---|
| First Class Bricks | Not more than 20% |
| Second Class Bricks | Not more than 20% |
| Third Class Bricks | Not more than 25% |
While the maximum limit for both first class and second class bricks is typically specified as "not more than 20%", standard tests often show that first class bricks absorb less water (often in the 15-20% range or even less), while second class bricks have a slightly higher, but still acceptable, absorption rate, often falling within a specific range for quality checks.
Second Class Bricks Absorption Rate
For second class bricks, the standard requirement specifies that the water absorption should not exceed 20% of their dry weight after immersion in cold water for 24 hours. Options provided usually give a range that meets this maximum limit.
Looking at the options provided, the range 16 - 20 percent falls within the acceptable limit for second class bricks (which is <= 20%) and is a common range indicating the typical absorption characteristics of this class of bricks. Other options like 21-25 percent are too high for second class bricks, while 5-10 percent is characteristic of higher quality or specific types of bricks.
Therefore, when comparing to its dry weight after immersion in cold water for 24 hours, the water absorption for second class bricks should typically be within the 16 - 20 percent range.
The calculation for water absorption is typically done using the formula:
\( \text{Water Absorption} (\%) = \frac{\text{Wet Weight} - \text{Dry Weight}}{\text{Dry Weight}} \times 100 \)
Where Wet Weight is the weight after 24 hours immersion and Dry Weight is the weight before immersion.
Important Questions from Bricks and Mortar
The Indian standard brick size is
Statement (I): Bricks are soaked in water before using in brick masonry for removing dirt and dust.
Statement (II): Bricks are soaked in water before using in brick masonry so that bricks do not absorb moisture from the bonding cement mortar.
Mortars for masonry construction are designated based on their strength as per IS: 2250 and IS: 1905, with classifications including $L_1, L_2, H_1, H_2, M_1$ and $M_2$. What is the correct sequence representing the decreasing order of strength for these designations?
The mortar mix proportion used in brick masonry is generally taken as
As per Indian Standard, the modular size of bricks is-
