MCQ on Building Materials (General)

Correct Answer: A. 20%

Solution:

According to the Indian Standard IS 3495 (Part 2): 1992, which outlines the methods for testing burnt clay building bricks, the acceptable water absorption limit is defined based on the class of the brick.

• 🔹 For First Class Bricks: Water absorption should not exceed 20% by weight after 24 hours of immersion in cold water.
• 🔹 For Second Class Bricks: Water absorption should not exceed 22% by weight after 24 hours.

Since the question asks about a "good quality brick," the standard for a First Class Brick is the most appropriate reference.

Correct Answer: A. Quartzite

Solution:

A rock is a naturally occurring solid aggregate of one or more minerals. A mineral is a naturally occurring inorganic solid with a definite chemical composition and crystalline structure.

• (a) Quartzite: This is a metamorphic rock formed from sandstone. It's an aggregate of quartz minerals, making it a rock.
• (b) Mica: This refers to a group of silicate minerals, not a rock.
• (c) Gypsum: This is a soft sulfate mineral. While it can form a rock (rock gypsum), the term by itself refers to the mineral.

Therefore, quartzite is the only option that is unambiguously a rock.

Correct Answer: D. 10 to 12%

Solution:

Seasoning of timber is the process of reducing its moisture content to an appropriate level. This is crucial for several reasons: it increases the timber's strength, stability (reduces warping and shrinking), and resistance to decay and insects.

• A moisture content of 10 to 12% is the standard for well-seasoned timber intended for most construction and structural purposes. This level is considered the equilibrium moisture content (EMC) for many environments, meaning the wood will not significantly gain or lose moisture after installation.
• Lower percentages (like 6-8%) are typically required for interior woodwork and furniture, especially in centrally heated buildings.
• Higher percentages would indicate that the timber is not fully seasoned and is prone to defects.

Correct Answer: B. decreases

Solution:

The strength of cement decreases over time with storage. This is because cement is a hygroscopic material, meaning it absorbs moisture from the atmosphere. This moisture causes a slow, partial hydration process, leading to the formation of lumps and a reduction in its binding properties and overall strength.

• Cement: Loses strength due to pre-hydration from atmospheric moisture. The longer it is stored, especially in damp conditions, the more strength it loses.
• Concrete: In contrast, properly mixed and placed concrete gains strength over time through a continuous hydration process known as curing.

Approximate Reduction in Strength:

Correct Answer: B. Di-calcium silicate

Solution:

Dicalcium Silicate (C₂S): This compound, also known as Belite, hydrates and hardens slowly. It is responsible for the later-stage or "ultimate" strength of concrete. Its proportion in cement is typically 25-40%.

Correct Answer: D. 120 minutes

Solution:

It's important to distinguish between "lime-pozzolana" and "Portland Pozzolana Cement (PPC)".

• Lime-pozzolana mixture: As per standards like IS 4098, the initial setting time can be 120 minutes (2 hours). This reflects the slower reaction of lime compared to Portland cement.
• Portland Pozzolana Cement (PPC): This is a blended cement where pozzolana is added to Portland cement. For PPC, Indian Standards (like IS 1489) specify a much quicker initial setting time of not less than 30 minutes.

Correct Answer: C. 500

Solution:

To determine the number of bricks required for one cubic metre of masonry, we first need to calculate the volume of a single brick including the mortar joint.

• Standard brick size (as per IS 1077): 190 mm × 90 mm × 90 mm
• Standard mortar joint thickness: 10 mm

1. Calculate the volume of one brick with mortar:

We add the mortar thickness to each dimension to get the 'nominal size' of the brick.

• Length = 190 mm + 10 mm = 200 mm (or 0.20 m)
• Width = 90 mm + 10 mm = 100 mm (or 0.10 m)
• Height = 90 mm + 10 mm = 100 mm (or 0.10 m)

Volume of one brick with mortar = 0.20 m × 0.10 m × 0.10 m = 0.002 m³

2. Calculate the number of bricks per cubic metre:

Number of Bricks = (Total Volume of Masonry) / (Volume of one brick with mortar)

Number of Bricks = 1 m³ / 0.002 m³ = 500 bricks

Therefore, 500 bricks are required for one cubic metre of brick masonry.

Correct Answer: D. arches

Solution:

Here’s the reasoning:

• Bull Nose Brick: Its defining feature is one or more smoothly rounded corners. Its entire purpose is to soften sharp angles.
• Rounding off sharp corners (A): This is the primary and most common use of a bull nose brick.
• Pillars (B): They can be used to create rounded pillars or pillars with soft edges.
• Decoration purpose (C): The rounded edge is itself a decorative feature, creating a more finished look.
• Arches (D): Arches require specially tapered, wedge-shaped bricks called voussoirs. These bricks are shaped to fit the curve of the arch and transfer the load correctly down to the supports. A bull nose brick is the wrong shape for this structural purpose.

Correct Answer: A. Sulphur

The properties of iron and steel are dramatically affected by the presence of small amounts of other elements. Some are added intentionally as alloying agents (like carbon), while others are undesirable impurities left over from the manufacturing process.

• Red Shortness (or Hot Shortness): This is a condition where a metal, like iron, becomes brittle and cracks when it is heated to red-hot temperatures for forging, rolling, or bending. This is caused by Sulphur.
• Cold Shortness: This is the opposite condition, where a metal is brittle at normal or low temperatures but can be worked without cracking when hot. This is caused by Phosphorus.

Correct Answer: A. the monsoon

Solution:

Weathering is a critical step in brick manufacturing where raw clay is exposed to the elements to improve its quality. This process helps to soften the clay, increase its plasticity, and homogenize its composition.

For large-scale projects, the clay is typically excavated and left in heaps on the ground for an extended period. Allowing it to weather throughout at least one full monsoon season is especially effective. The rain penetrates the clay, breaking down large lumps and washing away soluble impurities, which makes the clay more uniform and easier to mould into high-quality bricks.

Correct Answer: D. Low thermal conductivity

Solution:

The primary purpose of thermal insulation is to reduce the rate of heat transfer. The property that measures a material's ability to conduct heat is thermal conductivity. Therefore, an effective insulation material must have a low thermal conductivity.

Correct Answer: A. Polyester fibre

Solution:

Fibres are classified as natural or synthetic.

• Synthetic fibres are man-made through chemical synthesis. Polyester is a classic example.
• Natural fibres are derived from plants (like Jute) or minerals (like Basalt).
• Steel fibre is a manufactured fibre but is typically classified separately from synthetic polymers.

Correct Answer: B. Statement B is correct, and statement A is incorrect.

Solution:

Statement A is incorrect: The changes to asbestos when heated are permanent. It undergoes dehydration and loses its properties, which are not restored upon cooling.
Statement B is correct: This describes the fibrous nature of asbestos. The strong bonds along the fibre's length give it high tensile strength, while the weak lateral bonds allow it to be easily separated into threads.

Correct Answer: B. Transmission

Solution:

Acoustical properties relate to how a material interacts with sound. Sound transmission is a key acoustical property, referring to the ability of sound to pass through a material. Creep is a mechanical property, hygroscopicity is related to moisture, and thermal resistivity is a thermal property.

Correct Answer: B. Magnesite

Solution:

Acid refractories are materials resistant to acidic environments. They are primarily made of acidic materials like silica, quartz, and ganister (a type of silica rock). Magnesite is a basic material (magnesium oxide) and is used to make basic refractories, not acidic ones.