Building Materials — Part 1 MCQs with Explanations

Gypsum is a mineral that is composed of: Calcium sulfate dihydrate (CaSO₄ · 2H₂O) This means gypsum consists of: Calcium sulfate (CaSO₄), which is the primary component. Water (H₂O), which is combined with calcium sulfate to form gypsum. Gypsum is widely used in construction and building materials, particularly for plaster and drywall.

Initial Setting Time refers to the period after water is added to cement during which the mixture remains workable before it begins to stiffen. For asbestos cement products such as roofing sheets and pipes, a longer setting time is essential to allow for proper mixing, molding, and compaction . According to standard requirements, the minimum initial setting time should be 90 minutes to ensure sufficient workability. Other options like 30, 50, and 75 minutes are too short and do not provide adequate time for the manufacturing process of asbestos cement products.

Permanent magnets must be made from materials that retain magnetism for long periods. High carbon steel is a good base because it can be hardened and magnetized effectively. Adding cobalt to high carbon steel improves its magnetic strength and stability by increasing the material’s ability to resist demagnetization. For conventional permanent magnets, the optimal composition includes around 15% cobalt alloyed with high carbon steel. Higher percentages, like 35%, are not standard in steel-based magnets and are more applicable to specialized magnet alloys such as Alnico, but even then, typical cobalt content does not reach 35%. Therefore, Option A (15% of cobalt) is the correct choice for permanent magnets made from high carbon steel.

Chlorite is a green-colored mineral that belongs to the clay mineral group and is commonly formed during the alteration or decomposition of other minerals. It is primarily formed by the decomposition of minerals like Augite, Biotite, and Hornblende , which are all common minerals in igneous rocks. Option A: Augite is a pyroxene mineral, and when it undergoes weathering, it can transform into chlorite. Option B: Biotite is a mica mineral that can also decompose to form chlorite under certain conditions. Option C: Hornblende , a type of amphibole mineral, can also undergo alteration to form chlorite. Therefore, the correct answer is Option D: All of these , as chlorite can be derived from the decomposition of Augite, Biotite, and Hornblende.

Definition: Silica is a key component of brick earth that influences the strength and durability of bricks. However, its excess can negatively impact the quality of bricks. Step 1: Understanding the role of silica: Optimal amount: Silica in the right proportion (about 50-60%) provides strength and prevents shrinkage. Excess silica: When silica content is too high, it prevents proper bonding between particles, leading to weak bricks. Step 2: Evaluating the options: Cracking and warping of bricks: Usually caused by rapid drying or improper burning, not excess silica. Loss of cohesion: Excess silica reduces the binding property of clay, making the bricks brittle and weak. Enhancing the impermeability of bricks: Impermeability is affected by the proportion of clay and firing temperature, not directly by excess silica. Step 3: Since high silica content leads to poor cohesion, the correct answer is Loss of cohesion (Option B).

Mild steel is a type of steel that is known for its ductility and weldability . One of the key factors determining the properties of steel is its carbon content . A higher carbon content makes steel harder and stronger but also more brittle . Mild steel has a relatively low carbon content , making it a good choice for applications where toughness and formability are important. The question asks about the percentage of carbon in mild steel. Option A: Less than 0.25% is the correct answer because this range defines the carbon content of mild steel. Option B, C, and D represent higher carbon content, leading to different types of steel with different properties (like medium carbon steel or high carbon steel).

Gneiss is a type of rock that forms through a process of metamorphism. Let’s look at the options: Option A: Igneous rocks → Incorrect. Igneous rocks are formed from the cooling and solidification of molten material, such as magma or lava. Gneiss is not derived from igneous rocks. Option B: Metamorphic rocks → Correct. Gneiss is a metamorphic rock that is formed when granite or other rocks undergo high pressure and temperature, leading to the formation of distinct bands. Option C: Sedimentary rocks → Incorrect. Sedimentary rocks form from the deposition of materials over time, such as sand, silt, and clay. Gneiss does not come from sedimentary processes. Option D: Sedimentary metamorphic rocks → Incorrect. Gneiss is specifically a metamorphic rock, not a combination of sedimentary and metamorphic types. Therefore, the correct answer is Option B: Metamorphic rocks , as gneiss is derived from the metamorphism of other rocks, typically granite.

Modular bricks are standardized bricks used in construction to maintain uniformity and ease of calculation in masonry work. The actual size of a modular brick is typically 190 mm × 90 mm × 90 mm . However, when the thickness of mortar joints (usually about 10 mm) is included, the nominal size becomes 200 mm × 100 mm × 100 mm . This nominal size ensures proper bonding and modular coordination in construction. Therefore, the correct answer is 200 mm × 100 mm × 100 mm .

Definition: The slenderness ratio of a masonry wall is the ratio of its effective height or effective length (whichever is less) to its thickness. Purpose: This ratio indicates the wall’s susceptibility to buckling under compressive loads. A higher value means the wall is taller and thinner, making it less stable. Code requirement: As per standard building codes such as IS 1905:1987, the slenderness ratio for masonry walls should not exceed 20 to ensure stability and safety. Reason: Limiting the slenderness ratio reduces the risk of lateral deflection, buckling, and failure under axial loads. Conclusion: For structural safety, the effective height or length of a masonry wall divided by its thickness should be ≤ 20 .

Whitworth compressed steel is a special type of high-quality steel produced by applying pressure to molten steel during the solidification process. This process removes air bubbles, blowholes, and internal imperfections , resulting in a more compact and uniform steel structure. The key to this method is the application of high pressure while the steel is still molten . The correct pressure applied in this process is 9 kg/mm 2 . Therefore, the correct answer is Option B: 9 kg/mm 2

Asbestos is a naturally occurring mineral fiber known for its excellent fire resistance and heat insulation properties . It is classified as an incombustible and fireproof material , which is why it has been widely used in construction for insulation and fire protection. Although asbestos is used in making corrugated roofing sheets , it itself is not a sheet but a material , so Option A is not correct. Asbestos is not an organic substance ; it is an inorganic mineral , so Option C is incorrect. Therefore, the correct answer is an incombustible fireproof material .

Definition: In plastic bitumen, a filler is a fine material added to the bitumen mix to improve its binding properties and performance. Role of filler: It increases the viscosity of bitumen, fills the voids, and enhances the strength and durability of the paving material. Specific filler used: Asbestos powder is commonly used as the filler in plastic bitumen due to its fine texture, high resistance to heat, and good binding compatibility with bitumen. Reason: The addition of asbestos powder improves the stability, wear resistance, and lifespan of the bituminous layer. Conclusion: For plastic bitumen, asbestos powder is the standard filler material used to achieve the desired strength and performance.

A first-class brick is characterized by its high quality and durability. It is required that when such a brick is immersed in cold water for 24 hours, it should not absorb water more than 20% of its dry weight. This specification ensures the brick has good strength and resistance to weathering. Hence, the correct answer is Option B: 20% .

Cement setting is a chemical reaction that causes it to harden. To control this process and prevent it from setting too quickly, we add certain compounds. Gypsum (calcium sulfate) is specifically added to cement to retard , or slow down, the initial setting time. This ensures that the cement has enough time to be mixed and placed before it hardens. The other options listed (tri-calcium silicate, di-calcium silicate, and tri-calcium aluminate) are all components of cement itself, but they do not primarily control the initial setting time in the same way gypsum does. Therefore, the correct answer is B: Gypsum .

The correct answer is Option B: Cellulose paints Here's why: * Duco paints are a type of lacquer. * Lacquers are known for their fast-drying, durable, and glossy finish. * Cellulose paints are a common type of lacquer. * They use cellulose nitrate or cellulose acetate as the main film-forming ingredient. Let's look at the other options: * Plastic paints: While they might contain plastics, this is too broad a term. Duco is a specific type of paint, not just any paint with plastic in it. * Emulsion paints: These are water-based paints, and Duco paints are generally solvent-based. * Oil paints: Oil paints dry slowly and have a different composition than Duco paints.

According to IS: 10080 - 1982, the recommended size for testing the compressive strength of cement cubes is indeed 70.6 mm. Thank you for providing the accurate information. The size of 150 mm is typically used for testing the compressive strength of concrete cubes, not cement cubes.

Lime concrete is a mixture of lime, aggregate, and water used in construction for various purposes. Wall foundations often utilize lime concrete due to its strength and durability, especially in older or traditional buildings. Flooring at ground level also commonly uses lime concrete as it provides a smooth, durable surface. Thus, both (A) and (B) are correct applications of lime concrete.

Option A: Tri-calcium silicate (C3S) - This is the most important compound in cement. It's responsible for the early strength development (within the first week). A higher percentage of C3S means faster setting and hardening , which is generally desired in good quality cement. Option B: Di-calcium silicate (C2S) - This contributes to strength gain over a longer period (after the first week). While important, it's not the primary factor determining early strength and overall cement quality as much as C3S. Option C: Tri-calcium aluminate (C3A) - This contributes to very early hydration and heat generation. A high percentage of C3A can lead to flash set and reduced durability, especially in sulfate-rich environments. Good quality cement generally has a controlled amount of C3A , not a higher percentage. Option D: Tetra calcium alumino ferrite (C4AF) - This reduces the clinkering temperature during cement production. It has minimal contribution to the strength of cement. Therefore, the correct answer is: Option A: Tri-calcium silicate , as it contributes to faster setting and hardening and higher early strength of the cement.

Correct Answer: Option C: Both (i) and (iii) (i) Sedimentary rock – ✅ Correct Sandstone is definitely a sedimentary rock . It forms through the compaction and cementation of sand-sized mineral particles over time, often in layers. (ii) Aqueous rock – ❌ Not a standard classification While sandstone forms in environments involving water (like rivers, lakes, or oceans), the term “aqueous rock” is not a formal geological classification . In geology, rocks are usually grouped as igneous, sedimentary, or metamorphic . “Aqueous” may be used descriptively, but not as a standalone rock type. (iii) Siliceous rock – ✅ Correct Sandstone is primarily composed of quartz , which is silicon dioxide (SiO₂) . This makes sandstone a siliceous rock due to its high silica content. Final Conclusion: Sandstone is a sedimentary and siliceous rock, but not formally an aqueous rock. Therefore, the correct answer is Option C: Both (i) and (iii) .

Thinner is a solvent added to paint to reduce its viscosity, making it easier to apply. Let's look at the options: Option A: Naphtha - Naphtha can be used as a solvent, but it is not as common as turpentine in oil paints. Option B: Turpentine - Turpentine is a widely used and very effective thinner for oil paints. Option C: Both (A) and (B) - Since Turpentine is more commonly used, this option is a possibility. Option D: None of these - We know Turpentine is used, so this is incorrect. Therefore, the commonly used thinner in oil paints is Turpentine , though Naphtha can also be used. So the best answer is Option C: Both (A) and (B) .

The ultimate tensile strength is a measure of the maximum stress that a material can withstand while being stretched or pulled before necking, which is a point where the specimen's cross-section starts to significantly contract. For structural mild steel, the ultimate tensile strength is typically in the range of: Option B: 260 N/mm 2 So, Option B is the correct answer for the ultimate tensile strength of structural mild steel, which is approximately 260 N/mm 2 .

Lime putty is prepared by slaking quicklime with water. During this process, quicklime (CaO) reacts vigorously with water to form calcium hydroxide [Ca(OH)₂], which is then kept under water for a period to mature and form a smooth paste known as lime putty. Option A: Incorrect, because lime putty is not made from hydraulic lime. Hydraulic lime sets under water due to the presence of clay impurities and is not suitable for making lime putty. Option B: Correct, because lime putty is obtained by adding quicklime to water and allowing it to slake and mature. Option C: Incorrect, since lime putty improves with age and can be stored for a long time (even months or years) if kept properly under water. Option D: Incorrect, because only option B is true while A and C are false.

When a tree is freshly felled, it typically contains a significant amount of moisture, often equal to or even exceeding its own dry weight. This moisture content can be measured as: The percentage of water relative to the dry weight of the wood. In a freshly felled tree, the moisture content can be as high as 100% or more, meaning the water weight can equal or exceed the dry weight of the wood. Hence, a freshly felled tree may contain water up to 100% based on its dry weight.

Hydraulic lime is a type of lime that can set and harden when mixed with water. It is obtained through a specific process. Let's examine each option: Option A: Burning of lime stone This option refers to the production of quicklime (calcium oxide) by heating limestone. Quicklime is not hydraulic lime; it is a different product. Option B: Burning of kankar Kankar is a type of nodular limestone, and burning it can result in hydraulic lime. This option is correct. Option C: Adding water to quick lime Adding water to quicklime results in the formation of slaked lime (calcium hydroxide) and is not the process for obtaining hydraulic lime. Option D: Calcination of pure clay Calcination of pure clay results in the production of other materials, such as clay bricks or ceramics, and is not the process for obtaining hydraulic lime. So, the correct answer is Option B: Burning of kankar . Hydraulic lime is obtained by burning kankar, a type of nodular limestone that has hydraulic properties.

Honey combing in concrete refers to the presence of voids or air pockets in the concrete mass, particularly around the reinforcement bars or in corners. It occurs due to improper mixing, inadequate compaction, or poor workability of concrete. When cement concrete is not mixed properly, the coarse aggregates do not bind well with the mortar, leading to gaps and cavities. This results in a weak structure, poor durability, and may expose reinforcement to environmental effects like corrosion. While segregation and bleeding are also issues related to poor concrete practices, they are more associated with excessive water content or improper handling rather than just bad mixing. Therefore, the most specific result of badly mixed cement concrete is honey combing.

Definition: Expansion joints are deliberate gaps introduced in long masonry walls to permit thermal expansion and contraction, as well as movements due to moisture changes, without causing cracking or structural damage. Purpose: Masonry, like most construction materials, changes in size when exposed to temperature variations and moisture. These movements, though small in magnitude, accumulate over long wall lengths. If the wall is built without any provision for movement, internal stresses develop. Since masonry is strong in compression but weak in tension, these stresses can easily lead to visible cracks. Code requirement: As per standard building construction practices and IS 3414:1968 (Code of Practice for Design and Installation of Joints in Buildings), expansion joints should be provided in masonry walls when the uninterrupted length exceeds 20 m . This spacing is considered safe for most climatic conditions to control cracking and maintain durability. Reason: By limiting the length between joints to about 20 m , the potential expansion or contraction in each wall panel is kept within a range that the masonry and jointing materials can safely accommodate. This reduces the likelihood of structural distress and ensures the longevity of the wall. Conclusion: In masonry construction, expansion joints must be placed at intervals not exceeding 20 m to allow for natural material movements and to preserve both the appearance and structural integrity of the wall.

In brick masonry, the term "hearting" refers to the interior filling of a thick wall between the two outer faces. For thicker walls, especially those more than one brick thick, proper filling of the internal space (hearting) is essential to ensure strength and stability. Brick bats , which are pieces of bricks (often broken or cut), are commonly used for this purpose. They help fill the space effectively and maintain the bond between the outer layers of the wall. Using full bricks like headers or stretchers for hearting is not economical or practical in most cases. Queen closers are used at corners and junctions to maintain bond and are not suitable for hearting. Therefore, the correct answer is: Brick bats (Option C).

Linseed oil is the commonly used drying oil for oil paints. It is extracted from the seeds of the flax plant. It polymerizes upon exposure to air, forming a tough, elastic film that binds the pigment particles together and provides protection to the painted surface.

In brick masonry, various types of bonds are used to enhance the structural integrity and aesthetic appeal of the construction. Let's examine each option: Option A: English bond - This bond is formed by laying alternate courses of headers and stretchers. Headers are bricks laid with their ends facing outwards, while stretchers are bricks laid with their faces parallel to the face of the wall. This pattern provides good strength and stability to the wall, making it a commonly used and efficient bond in brick masonry. Option B: Double Flemish bond - This bond consists of alternate courses of stretchers and headers, with each header being centered over the stretcher below it and vice versa. This creates a pattern of alternating headers and stretchers on each face of the wall. While the double Flemish bond is visually appealing and offers good strength, it requires more skill and effort to construct compared to the English bond. Option C: Zigzag bond - This bond involves the use of bricks laid in a zigzag pattern, with each course consisting of bricks laid diagonally or at an angle to the face of the wall. While the zigzag bond may provide some decorative effects, it lacks the structural integrity and stability offered by bonds such as the English bond. Option D: Single Flemish bond - This bond is similar to the double Flemish bond but with only one header placed over each stretcher and vice versa. While the single Flemish bond is easier to construct compared to the double Flemish bond, it still requires more skill and effort than the English bond. Additionally, it may not provide as much strength and stability as the English bond due to the lack of headers in every course. Conclusion: Among the options provided, Option A: English bond is the correct choice for a bond produced by laying alternate headers and stretchers in each course. It offers a balance of structural integrity, stability, and ease of construction, making it a widely used and effective bond in brick masonry.

Run at right angles is the correct answer to “For the manufacture of plywood, veneers are placed so that grains of adjacent veneers”. This question is standard in competitive examination syllabi for Building Materials.

All the above is the correct answer to “The most important constituent of an oil paint, is”. This question is standard in competitive examination syllabi for Building Materials.

Both (A) and (B) is the correct answer to “Stucco paints are suitable for”. This question is standard in competitive examination syllabi for Building Materials.

All the above is the correct answer to “Depending on the chemical composition and mechanical properties, iron may be classified as”. This question is standard in competitive examination syllabi for Building Materials.

500 is the correct answer to “Number of bricks required for one cubic metre of brick masonry is”. This question is standard in competitive examination syllabi for Building Materials.

75 kg/cm2 is the correct answer to “The minimum compressive strength of 2 nd class bricks should be”. This question is standard in competitive examination syllabi for Building Materials.

100 kg/cm2 is the correct answer to “The minimum compressive strength of 1 st class bricks should be”. This question is standard in competitive examination syllabi for Building Materials.

Shrinkage is the correct answer to “Addition of pozzolana to ordinary Portland cement increases”. This question is standard in competitive examination syllabi for Building Materials.

10 hours is the correct answer to “As per IS specifications, the maximum final setting time for ordinary Portland cement should be”. This question is standard in competitive examination syllabi for Building Materials.

Compact sand stone is the correct answer to “Which of the following has more fire resisting characteristics”. This question is standard in competitive examination syllabi for Building Materials.

Quartzite is the correct answer to “Which of the following metamorphic rocks has the most weather resisting characteristics”. This question is standard in competitive examination syllabi for Building Materials.