Correct Answer: C. 50%
Solution:
For brick earth to be suitable, it needs a balanced composition. The combined percentage of clay and silt provides the necessary plasticity, which allows the brick to be molded without cracking. A good brick earth should contain:
- Clay: 20-30%
- Silt: 20-35%
Therefore, the total content of clay and silt should be at least 50% to ensure proper binding and plasticity.
Correct Answer: B. 19 cm x 9 cm x 9 cm
Solution:
It's important to distinguish between the standard (or modular) size and the nominal size of a brick.
- Standard Size: This is the actual size of the brick itself, which is 19 cm x 9 cm x 9 cm.
- Nominal Size: This is the size of the brick plus the mortar joint. With a standard 1 cm mortar joint, the nominal size becomes 20 cm x 10 cm x 10 cm. This simplifies calculations for masonry structures.
The question asks for the standard size of the brick, not the nominal size.
Correct Answer: C. 100 kg/cm²
Solution:
First-class bricks are high-quality bricks used for permanent and structural work. According to standards, their minimum crushing strength should not be less than 100 kg/cm² (which is approximately 10 N/mm²). This high strength ensures they can withstand significant loads without failing.
Correct Answer: B. 19 x 9 x 9 cm
Solution:
The term "modular brick" refers to the standard size of a brick that is designed to fit into a standardized grid for construction. This standard or modular size is 19 cm x 9 cm x 9 cm. When a 1 cm mortar joint is added, it becomes the "nominal size" of 20 x 10 x 10 cm, which fits neatly into a 10 cm grid system.
Correct Answer: D. brick masonary
Solution:
A king closer is a specialized type of cut brick used in brick masonry. It is created by cutting off the corner of a brick, leaving one header face intact. King closers are essential for creating strong bonds at the corners and ends of brick walls, allowing the brick courses to be properly aligned without continuous vertical joints.
Correct Answer: B. 15% of its dry weight
Solution:
Water absorption is a key indicator of a brick's quality and durability. For a good quality (or first-class) brick, the amount of water it absorbs after being soaked for 24 hours should not exceed 15% of its own dry weight. A lower water absorption percentage indicates a denser, more compact brick that is less susceptible to damage from frost action and weathering.
Correct Answer: C. 35 - 70% silica and 10 - 20% alumina
Solution:
The ideal composition of brick earth is crucial for producing good quality bricks. The two main constituents are silica and alumina.
- Silica (Sand): Should be present in a proportion of 35-70%. It prevents cracking, shrinking, and warping of bricks.
- Alumina (Clay): Should be present in a proportion of 10-20%. It imparts plasticity to the earth, making it easy to mould.
This balance ensures the brick is both mouldable and strong after firing.
Correct Answer: A. Alumina
Solution:
Alumina is the chief constituent of clay and is the primary source of plasticity in brick earth. It absorbs water and makes the earth easy to mould into the desired shape. Without sufficient alumina, the brick earth would be too brittle and difficult to shape.
- Silica provides strength and prevents shrinkage.
- Lime acts as a flux during burning but does not contribute to plasticity.
- Magnesia also helps in burning and reduces shrinkage.
Correct Answer: C. 10.5 N/mm²
Solution:
The minimum crushing strength is a key property that defines the class of a brick. For a first-class brick, the crushing strength should not be less than 10 N/mm² or 10.5 N/mm² (approximately 100-105 kg/cm²). This high strength makes them suitable for load-bearing structures.
- Second-class bricks have a minimum strength of around 7-7.5 N/mm².
- Third-class bricks have a strength of around 3.5-5.5 N/mm².
Correct Answer: B. IS: 3102
Solution:
The classification of burnt clay solid bricks based on their compressive strength is specified in IS 3102: 1971. The other codes listed are for different purposes:
- IS: 3101: Specification for aluminium collapsible tubes.
- IS: 3495: Methods of tests of burnt clay building bricks.
- IS: 3496: Specification for Dobby lags and pegs (used in textile weaving).
Correct Answer: C. 20%
Solution:
According to the standard classification (IS 1077), the water absorption of a first-class brick after 24 hours of immersion in cold water should not exceed 20% of its dry weight. This property is crucial for ensuring the durability of the brick, especially in damp conditions.
Correct Answer: A. 3.5 N/mm²
Solution:
"Common building bricks" generally refer to third-class bricks, which are used for temporary and non-structural purposes. According to Indian Standards, the minimum compressive strength for these bricks should not be less than 3.5 N/mm².
- First Class Brick: > 10.5 N/mm²
- Second Class Brick: > 7.5 N/mm²
- Third Class Brick: > 3.5 N/mm²
Correct Answer: B. 500
Solution:
This calculation is based on the nominal size of a brick (including mortar). The nominal size of a standard brick is 20 cm x 10 cm x 10 cm.
- Volume of one brick with mortar = 0.20 m x 0.10 m x 0.10 m = 0.002 m³
- Number of bricks in 1 m³ of masonry = Total Volume / Volume of one brick
- Number of bricks = 1 m³ / 0.002 m³ = 500
Correct Answer: C. 19 cm x 9 cm x 9 cm
Solution:
The standard size for a conventional masonry brick, as specified by Indian Standards, is 19 cm x 9 cm x 9 cm. This is also known as the modular size. When used in masonry with a 1 cm mortar joint, it occupies a space of 20 cm x 10 cm x 10 cm, which is its nominal size.
Correct Answer: A. frog
Solution:
The depression or indentation made on the top face of a brick is called a frog. It serves two main purposes:
- It creates a keyway, forming a strong shear-resistant bond with the mortar.
- It often bears the manufacturer's name or trademark.
A pallet is a board used to carry freshly moulded bricks, and a strike is a tool used to level off excess clay from the mould.
Correct Answer: A. soling
Solution:
A layer of brick or stone laid flat below a foundation is called soling. Its purpose is to provide a clean, hard, and level surface for the foundation concrete to be laid upon, especially in soft or uneven soils. This prevents the concrete from mixing with the soil.
- Shoring is a temporary support system for trenches or buildings.
- D.P.C. stands for Damp-Proof Course, which is a barrier to prevent moisture from rising.
Correct Answer: B. providing insulation against heat
Solution:
The primary advantage of hollow bricks is their excellent thermal insulation properties. The air trapped within the hollow cavities is a poor conductor of heat, which helps to keep buildings cooler in the summer and warmer in the winter. While they are also lighter and can sometimes reduce costs, their main purpose is providing insulation against heat and sound.
Correct Answer: A. chuffs
Solution:
Chuffs are a common defect in bricks that occurs when rain falls on hot bricks just after they have been removed from the kiln. The rapid cooling and steam generation cause the surface to deform, resulting in a distorted shape.
- Bloating is the swelling of a brick due to excess carbonaceous matter and sulphur.
- Nodules are lumps of material in the brick, often from lime.
- Lamination is the splitting of the brick into thin layers due to trapped air.
Correct Answer: C. dressing
Solution:
In the context of preparing raw materials, dressing is the process of cleaning and removing unwanted impurities. While the question mentions iron ore, the same term applies to the preparation of clay for brick making, where stones, pebbles, and organic matter are removed. It is a general term for the initial treatment of a raw material before processing.
Correct Answer: D. Any of these
Solution:
Brick masonry can fail in several ways, and all the listed options are valid modes of failure:
- Rupture along vertical joints: Occurs when the bond between bricks is weak, leading to cracks along the vertical mortar lines.
- Shearing along a horizontal plane: Can happen due to lateral forces (like wind or earthquakes) causing one course of bricks to slide over another.
- Crushing due to overloading: Happens when the compressive stress on the masonry exceeds the strength of the bricks or mortar, causing them to break and crumble.
Therefore, any of these conditions can lead to the failure of brick masonry.