Question 1

Fire clay used for refractory products contains which principal constituent in a comparatively pure form? Choose the single correct option relevant to refractories and heat resistance.

Accepted Answer

Introduction / Context: Fire clay is the base material for refractory bricks and shapes. Understanding its chemistry explains thermal stability and suitability for furnaces and kilns. Given Data / Assumptions: We are focusing on the main compound present in fire clay. Impurities like iron oxide and lime are kept low because they lower refractoriness. Concept / Approach: Fire clay is rich in kaolinitic minerals, essentially hydrated aluminium silicate. This composition provides high melting point, low fluxing, and good thermal shock resistance compared to clays with higher iron/lime content. Step-by-Step Solution: 1) Identify the desired refractory constituent: aluminosilicate with structural water.2) Hydrated aluminium silicate (kaolinite group) matches fire clay chemistry.3) Therefore, the correct option is hydrated aluminium silicate. Verification / Alternative check: Refractory standards specify Al2O3 and SiO2 within ranges typical of kaolinitic clays, with low Fe2O3 and CaO. Why Other Options Are Wrong: Lime and magnesium act as fluxes reducing refractoriness; iron oxide also lowers softening temperature and can cause deformation under heat. Common Pitfalls: Assuming “iron-rich” clay is better—iron reduces refractoriness. Final Answer: hydrated aluminium silicate

Question 2

Which of the following are classified as ferrous metals in structural and manufacturing practice? Select the best option.

Accepted Answer

Introduction / Context: Ferrous metallurgy deals with iron-based alloys. Recognizing the main ferrous families is foundational for material selection in construction and fabrication. Given Data / Assumptions: We consider common engineering materials containing iron as the base metal. Examples include cast iron, wrought iron, and steels. Concept / Approach: Ferrous metals are iron-based. Cast iron has high carbon and is castable; wrought iron is low carbon with slag fibers; steel is refined iron with controlled carbon and alloying. All are ferrous because iron is the principal constituent. Step-by-Step Solution: 1) Identify iron-based families: cast iron, wrought iron, steel.2) All listed items qualify as ferrous.3) Therefore, select “all of the above”. Verification / Alternative check: Chemical analysis shows Fe as the dominant element in all three, confirming classification. Why Other Options Are Wrong: Picking any single item ignores the others that are equally ferrous. Common Pitfalls: Confusing “ferrous” with magnetic response; some stainless steels are weakly magnetic yet still ferrous. Final Answer: all of the above

Question 3

Blister steel: identify the correct statement about its manufacture and characteristics for historical tool steels. Choose one accurate statement only.

Accepted Answer

Introduction / Context: Before modern steelmaking, “blister steel” was a key intermediate for tool steels. Understanding how it is made and its microstructural features helps explain later developments such as shear steel and crucible steel. Given Data / Assumptions: Blister steel originates from wrought iron exposed to carbon at high temperature. Historic production predates basic oxygen and electric arc routes. Concept / Approach: In the cementation process, bars of wrought iron are packed with charcoal and heated for prolonged periods. Carbon diffuses into the surface, creating a high-carbon outer zone and gas blisters—hence the name. The product is chemically heterogeneous and often shows fissures/cavities. Step-by-Step Solution: 1) Match the correct historical route: carburizing wrought iron in a cementation furnace.2) Evaluate texture: blister steel is not uniform; it exhibits blisters and internal flaws.3) Evaluate weldability: blister steel can be forge-welded to make “shear steel”; hence an absolute claim of non-weldability is false.4) Electric arc melting is modern and not the primary route for blister steel. Verification / Alternative check: Historical metallurgy texts describe conversion of blister steel to single- or double-shear steel by piling and forge welding, confirming weldability and the cementation origin. Why Other Options Are Wrong: Free from fissures: incorrect—blisters and heterogeneity are typical. Cannot be welded: incorrect—forge welding is precisely how shear steels were made. Electric arc route: anachronistic for blister steel. Common Pitfalls: Assuming modern homogeneous properties for historical steels; overlooking carburizing terminology. Final Answer: It is obtained by the cementation process (carburizing wrought iron).

Question 4

Field efflorescence test on bricks: after immersing a brick in water for 24 hours and drying, classify the extent of efflorescence based on surface coverage by grey/white deposits. Select the most complete and correct statement.

Accepted Answer

Introduction / Context: Efflorescence indicates soluble salts migrating to the surface and crystallizing as the brick dries. This classification guides acceptance of brick lots for masonry. Given Data / Assumptions: Test: soak brick 24 hours, dry, observe deposit coverage. Thresholds: none, slight (~10%), serious (~50%). Concept / Approach: Higher coverage means more soluble salts. No deposit implies acceptable salts level. Slight efflorescence may be tolerable for hidden work; serious efflorescence is typically unacceptable. Step-by-Step Solution: 1) Apply the standard visual criteria to each observation.2) All three statements correctly map observations to standard classifications.3) Therefore the comprehensive correct choice is “All the above”. Verification / Alternative check: Site QC manuals use deposit area coverage and presence of powdering/peeling to grade efflorescence severity. Why Other Options Are Wrong: Selecting any single condition ignores the full correct set of criteria. Common Pitfalls: Confusing slight with moderate; ignoring flaking/spalling that upgrades severity. Final Answer: All the above

Question 5

In painting and interior finishes, identify the base material traditionally used for preparing distemper for walls and ceilings. Pick the correct single base.

Accepted Answer

Introduction / Context: Distemper is an economical wall finish made from a base pigment/binder system. Recognizing the base material helps in understanding mixing, application, and performance. Given Data / Assumptions: Traditional distemper comprises a base (pigment/filler), binder (usually animal glue or casein historically), and water. Modern products may add polymers, but the classic base remains the same. Concept / Approach: Classic distemper uses finely ground chalk (whiting) as the main base/filler, which provides body and opacity. Limewash and cement wash are different finishing systems. Lime putty may be added to some formulations but is not the primary base of traditional distemper. Step-by-Step Solution: 1) Identify the conventional filler: chalk (calcium carbonate) in fine powder form.2) Recognize that limewash relies on calcium hydroxide carbonation, not distemper chemistry.3) Therefore, select “chalk (whiting)”. Verification / Alternative check: Older specifications list whiting plus glue size as the essential composition, confirming the base material. Why Other Options Are Wrong: Lime/lime putty: indicate limewash or tempera variants, not standard distemper base. Cement wash: a different material with cement binder. Common Pitfalls: Assuming any white powder equals distemper base; confusing distemper with limewash. Final Answer: chalk (whiting)

Question 6

Stone testing in civil engineering: pick the correct statement(s) about standard laboratory tests used to assess suitability of stones for construction and roads. Choose the most comprehensive correct option.

Accepted Answer

Introduction / Context: Different tests characterize stones for durability and loading conditions. This question checks your ability to match tests with the engineering property they quantify. Given Data / Assumptions: We consider common tests: acid, attrition, crushing, and impact. Each test targets a distinct property required in practice. Concept / Approach: Acid test indicates resistance to chemical weathering. Attrition test simulates abrasion in road traffic. Crushing test provides compressive strength values. Impact test measures toughness, important for aggregates under impact loads. Step-by-Step Solution: 1) Map each test to its primary property.2) All four mappings are correct as per standard practice.3) Therefore, “All the above” is the comprehensive correct choice. Verification / Alternative check: Codes and handbooks list these test-property pairs; results inform material selection for masonry and pavement layers. Why Other Options Are Wrong: Selecting any single item ignores other correct statements and provides an incomplete answer. Common Pitfalls: Confusing impact with crushing; assuming attrition equals polishing value—though related, the specific apparatus and metrics differ. Final Answer: All the above

Question 7

Building finishes – understanding distemper (water-based wall paint) Which statement best defines distemper used in civil engineering and architectural painting?

Accepted Answer

Introduction: Distemper is a traditional, water-based decorative coating commonly used on interior walls and ceilings. This question tests basic materials knowledge in building finishes—specifically, what distemper is made of and how it differs from waterproofing compounds, cement paints, and chemical additives such as driers. Given Data / Assumptions: Context is architectural finishes for walls and ceilings. Distemper refers to the classic water-based coating used in many low- to medium-cost applications. We compare distemper to waterproofing agents, cement paints, and drying additives. Concept / Approach: Distemper is formulated using whiting (finely ground chalk or calcium carbonate), colored pigments for shade, and water as the medium. A small amount of glue size or binder may be used in some recipes, but the defining concept is a simple, economical water-thinnable paint that offers a matte finish for interiors. It is not a waterproofing product, nor is it a cement-based paint. Step-by-Step Solution: 1) Identify the constituents: powdered chalk + pigments + water are the essentials of distemper.2) Recognize performance: provides a soft, matte decorative finish; breathes reasonably well; economical for large areas.3) Contrast with alternatives: waterproofing agents are different chemistries aimed at stopping water ingress; cement paint uses cement as binder and needs curing; driers are additives for oil-based systems, not water-based distemper. Verification / Alternative check: Standard references in building construction consistently describe distemper as a simple water-based coating with chalk and pigments, sometimes with minimal binder. Practical site use confirms it is suited for low-cost interior finishes but not for high-moisture or external waterproofing duties. Why Other Options Are Wrong: Waterproofing agent: Distemper is decorative, not a waterproofing membrane. Coloured cement paint: Cement paints are cement-based and require water curing; distemper is chalk- and pigment-based. Drying agent: Driers are additives for oil/alkyd paints and are not the paint itself. Common Pitfalls: Assuming any wall coating can waterproof surfaces; confusing cement paint with distemper because both are economical; expecting oil-paint additives (driers) to apply to water-based systems. Final Answer: A paint consisting of powdered chalk (whiting), pigments, and water

Question 8

Varnishes – identifying the most critical constituent for film formation In a conventional varnish system, which constituent is the most important?

Accepted Answer

Introduction: Varnish is a transparent or translucent protective finish used on wood, metal, and other substrates. This question examines the core chemistry of varnish and asks you to identify the single most important ingredient that determines the final protective film and its performance characteristics. Given Data / Assumptions: We consider traditional oil or spirit varnishes used in building and furniture work. Typical components include resin (film former), solvent (vehicle), and drier (for oxidative cure in oil systems). We focus on which component is fundamentally critical to the final film. Concept / Approach: The resin is the primary film-forming substance in a varnish. It creates the continuous, protective layer that provides gloss, hardness, chemical resistance, and durability. Solvent thins the resin for application and then evaporates. Driers accelerate oxidation in oil-based systems, but without the resin there would be no functional film to harden or protect the surface. Step-by-Step Solution: 1) Identify roles: resin = film former; solvent = application aid; drier = curing accelerator (when applicable).2) Determine what remains after drying/curing: primarily the resinous film persists.3) Conclude that resin governs key properties like gloss, hardness, adhesion, and resistance. Verification / Alternative check: Product datasheets and coatings science texts consistently center the performance discussion on the resin or binder family (alkyd, polyurethane, phenolic, etc.), because the binder defines the final film properties. Solvents and driers support application and cure but are not the film itself. Why Other Options Are Wrong: Drier: Useful only in certain systems; not the main film former. Solvent: Evaporates after application; does not provide lasting film properties. All of the above: Not correct because resin stands out as the crucial film-forming component. Common Pitfalls: Overvaluing solvents due to application ease; assuming driers are universally needed; overlooking that the binder (resin) dictates performance class and durability. Final Answer: Resin

Question 9

Production of lime for construction – identifying the correct source process Which statement correctly describes how quicklime (CaO) is obtained for use in building works?

Accepted Answer

Introduction: Lime is a fundamental binder used historically in mortars, plasters, soil stabilization, and whitewashing. The question checks your understanding of the industrial process used to produce quicklime (calcium oxide) from natural raw materials such as limestone and chalk. Given Data / Assumptions: Calcium carbonate sources: limestone, chalk, shells, etc. Target product: quicklime (CaO), not hydrated lime (Ca(OH)2). Process temperature is approximately in the neighborhood of 900°C or higher depending on kiln and material. Concept / Approach: The key reaction is thermal decomposition of calcium carbonate (calcination). Heating CaCO3 drives off carbon dioxide and yields calcium oxide, which is then slaked with water to produce hydrated lime. Dissolving carbonates in water does not yield CaO, and calcium chloride is a different compound entirely. Step-by-Step Solution: 1) Start with limestone (CaCO3).2) Apply heat in a kiln: CaCO3 → CaO + CO2 (gas).3) Collect CaO as quicklime; optionally slake to Ca(OH)2 for mortars or whitewash. Verification / Alternative check: Industry practice and civil engineering texts universally describe lime manufacture as calcination of carbonate rocks. Operational temperatures around 900°C–1000°C are typical for efficient decomposition. Why Other Options Are Wrong: Free state: Lime does not occur naturally in a stable free state; it reacts readily with moisture and CO2. Dissolving CaCO3 in water: Produces a slurry/suspension, not CaO. Calcium chloride: CaCl2 is a different salt used as a set accelerator or dehumidifier, not lime. None of these: Incorrect because calcination is correct. Common Pitfalls: Confusing lime types (quicklime vs hydrated lime); mixing up CaO with CaCl2; overlooking that calcination releases CO2. Final Answer: Lime is obtained by calcining calcium carbonate at about 900°C

Question 10

Oil varnish – typical composition used in building and furniture work Oil varnish generally consists of which combination of ingredients?

Accepted Answer

Introduction: Varnishes are classified broadly into oil varnishes and spirit varnishes based on the vehicle and curing mechanism. This item asks for the standard composition of an oil varnish as used for wood finishing and certain protective coats in buildings and furniture manufacture. Given Data / Assumptions: Oil varnish is being contrasted with spirit varnish. Typical ingredients include a resin, a drying oil, and a volatile solvent for application. Wax is not a defining component in standard oil varnish. Concept / Approach: Oil varnishes use a drying oil (e.g., linseed or tung) with resins (natural or modified) dissolved in a volatile solvent such as turpentine or mineral spirits. After application, solvent evaporates and the oil-resin system cures by oxidation and polymerization to form a durable film. Step-by-Step Solution: 1) Identify key functional roles: resin = film former; drying oil = cures by oxidation; turpentine/mineral spirits = solvent.2) Exclude spirit varnish composition (resin + alcohol) as it is not an oil varnish.3) Exclude wax as it is not a standard primary component of oil varnish. Verification / Alternative check: Coatings references list classic oil varnish compositions as resin + drying oil + hydrocarbon/terpene solvent, confirming option C as the correct combination. Why Other Options Are Wrong: Synthetic resin and spirit: That describes spirit varnish, not oil varnish. Oil, wax, and resin / Spirit, oil, and wax: Wax is not essential and changes film properties; these are not standard oil varnish recipes. Common Pitfalls: Mixing up spirit varnish with oil varnish; assuming wax is a universal component; ignoring the role of the solvent. Final Answer: Resin, drying oil, and turpentine (or mineral spirits)

Question 11

Physical properties of stones – specific gravity of marble What is the typical specific gravity value closest to that of good quality marble?

Accepted Answer

Introduction: Specific gravity is a key indicator of a building stone’s density and, indirectly, certain mechanical properties. For marble—widely used in flooring, cladding, and monumental work—knowing the typical range helps in selection and quality control on site and in specifications. Given Data / Assumptions: We refer to calcitic marbles typically used in construction. Acceptable specific gravity range for marble is roughly around 2.65–2.75 depending on composition and porosity. We choose the option closest to a representative value. Concept / Approach: Marble is metamorphosed limestone dominated by calcite. The theoretical specific gravity of calcite is about 2.71. Commercial marbles hover near this figure, with minor variation due to impurities and void content. Hence, a value near 2.72 is a sound representative pick for good quality material. Step-by-Step Solution: 1) Recognize calcite’s specific gravity ≈ 2.71.2) Note marble’s composition and low porosity lead to similar values.3) Select the option that best matches this benchmark: 2.72. Verification / Alternative check: Handbooks and testing data for commercial marbles routinely indicate specific gravity values around 2.70–2.73, confirming 2.72 as a representative figure. Why Other Options Are Wrong: 2.50 / 2.60 / 2.66: Lower than typical dense marble; may correspond to more porous or different rock types. 3.00: High for calcitic marble; closer to denser minerals/rocks. Common Pitfalls: Confusing marble with granite or dolomitic stones; ignoring porosity’s effect; assuming a single exact value rather than a representative range. Final Answer: 2.72

Question 12

Timber defects – identifying swellings from irregular branch removal Curved swellings formed by growth around wounds where branches were cut off irregularly are called what?

Accepted Answer

Introduction: Timber defects arise from growth characteristics, environmental stresses, and improper pruning or conversion. Recognizing the names and causes of common defects is vital for selecting structural and joinery timber with acceptable appearance and performance. This question targets the swelling formed after irregular branch removal. Given Data / Assumptions: A branch has been removed or broken off irregularly. The tree subsequently grows new layers over the wound. The result is a characteristic swelling on the surface. Concept / Approach: When branches are cut improperly or torn, the cambium overgrows the wound unevenly. The overgrowth encapsulates bark or cambium pockets, forming rind galls. These can include discontinuities and are considered defects that affect appearance and, at times, workability. Step-by-Step Solution: 1) Identify the cause: irregular branch removal leaves a wound.2) Tree response: overgrowth creates a curved swelling over time.3) Name the defect associated with such overgrowth and enclosed bark: rind galls. Verification / Alternative check: Timber technology references distinguish rind galls from knots (embedded branch bases) and burls (abnormal rounded growths due to cambial disturbances). The description here matches rind galls specifically. Why Other Options Are Wrong: Knots: Are remains of branches within the wood structure, not surface swellings from wound overgrowth. Burls: Large, rounded, warty growths from cambial proliferation; not necessarily linked to pruning wounds. None of these: Incorrect because rind galls precisely fit the description. Common Pitfalls: Using the terms knot and burl interchangeably; assuming any surface swelling is a burl; overlooking the role of enclosed bark in rind galls. Final Answer: Rind galls

Question 13

Rock-forming minerals – matching common names and properties Which of the following statements about hornblende, muscovite, and biotite is correct?

Accepted Answer

Introduction: Minerals such as hornblende and the micas (muscovite and biotite) occur widely in igneous and metamorphic rocks used as construction stone and aggregates. Identifying their common names and basic properties aids in geological classification and in anticipating behavior such as cleavage and durability. Given Data / Assumptions: We compare three minerals and their commonly cited properties/names. Focus is on standard descriptive mineralogy used in civil engineering contexts. Concept / Approach: Hornblende (an amphibole) is typically brittle with prismatic cleavage. Muscovite is the light-colored mica, often called white mica or potash mica because of its potassium content. Biotite is the dark mica, commonly called black mica. Each statement provided is a conventional fact in introductory mineralogy. Step-by-Step Solution: 1) Hornblende: brittle silicate, prismatic habit, characteristic cleavage; statement is true.2) Muscovite: K-rich, light/transparent sheets; known as white mica/potash mica; statement is true.3) Biotite: Fe-Mg-rich, dark sheets; known as black mica; statement is true.4) Therefore, all listed statements are correct. Verification / Alternative check: Standard mineral tables consistently list these synonyms and physical properties, reaffirming that each individual statement holds. Why Other Options Are Wrong: Any single-choice option would omit other true statements; only the combined option captures all truths. Common Pitfalls: Confusing amphiboles (hornblende) with pyroxenes; mixing up muscovite and biotite based on color; forgetting that potash mica refers to muscovite due to potassium content. Final Answer: All of the above

Question 14

Portland cement chemistry – earliest reacting compound on hydration Which compound of Portland cement reacts immediately with water and is responsible for the earliest set?

Accepted Answer

Introduction: Understanding the hydration behavior of cement compounds is central to controlling setting time, early strength, and durability. This question targets the compound that reacts most rapidly with water and largely governs the initial set if not moderated by gypsum. Given Data / Assumptions: Ordinary Portland cement (OPC) composition includes C3S, C2S, C3A, and C4AF. Gypsum is added to regulate flash set. We focus on the earliest, fastest reaction with water. Concept / Approach: Tricalcium aluminate (C3A) hydrates very quickly, releasing significant heat. Without gypsum, C3A would cause flash setting. Gypsum supplies sulfate to form ettringite initially, controlling the rapid reaction and enabling a workable setting time. C3S contributes mainly to early strength but does not react as instantly as C3A in terms of setting behavior. Step-by-Step Solution: 1) Identify fastest-reacting phase: C3A is highly reactive with water.2) Recognize gypsum’s role: sulfate from gypsum moderates C3A via ettringite formation.3) Distinguish early strength vs earliest set: C3S aids early strength; C3A governs initial set rate. Verification / Alternative check: Cement chemistry literature consistently describes C3A as the phase responsible for flash set and early heat evolution, confirming it as the earliest reacting compound. Why Other Options Are Wrong: C3S: Important for early strength, but slower than C3A for immediate set. C2S: Contributes to later strength; slower hydration. C4AF: Reactivity is moderate and not dominant in setting. Common Pitfalls: Equating early strength with earliest set; overlooking gypsum’s regulatory role; confusing heat evolution profiles among phases. Final Answer: Tricalcium aluminate (C3A)

Question 15

Selection of building stones – minimum specific gravity requirement For a good building stone, the specific gravity should generally be greater than which value?

Accepted Answer

Introduction: Specific gravity is a practical indicator of a stone’s density and often correlates with strength and durability. This question checks the commonly cited threshold used in many construction texts for evaluating whether a stone is suitable for high-quality building work. Given Data / Assumptions: We consider natural stones commonly used in masonry and structural applications. Higher specific gravity often implies greater density and potential strength. We choose the accepted benchmark value from standard references. Concept / Approach: Many civil engineering handbooks use 2.7 as a benchmark for the specific gravity of good building stones (e.g., granite, basalt). Stones significantly below this may be weaker or more porous, which can affect durability, abrasion resistance, and water absorption traits important for weathering and load-bearing use. Step-by-Step Solution: 1) Review typical specific gravity ranges: lighter stones can be 2.0–2.5; dense igneous stones often exceed 2.7.2) Adopt the threshold commonly recommended in texts: SG > 2.7.3) Therefore select 2.7 as the minimum benchmark. Verification / Alternative check: Engineering property tables for building stones frequently list SG around or above 2.7 for preferred structural stones, supporting the threshold. Why Other Options Are Wrong: 1.5 / 1.7: Far too low; would indicate very light, usually unsuitable stones. 2.2: Still low for many structural applications compared with high-quality dense stones. Common Pitfalls: Assuming any stone with SG above 2.2 is adequate; ignoring that other properties (water absorption, compressive strength) must also be checked in addition to SG. Final Answer: 2.7

Question 16

Magnetic materials – cobalt content in cobalt steel for permanent magnets Permanent magnets are made from high carbon steel alloyed with approximately what percentage of cobalt?

Accepted Answer

Introduction: Permanent magnet materials must exhibit high coercivity and good retentivity. Historically, cobalt steels and later AlNiCo and rare-earth magnets have been used for strong permanent magnets. This question targets a classic composition range for cobalt steel magnets used in engineering contexts. Given Data / Assumptions: Material class: cobalt steel (prior to or alongside AlNiCo developments). High carbon steel is alloyed with cobalt to increase coercivity. We choose the commonly quoted cobalt percentage. Concept / Approach: Cobalt addition to high carbon steel significantly improves magnetic hardness (coercive force). Traditional references describe cobalt steels for permanent magnets containing roughly one-third cobalt by weight, i.e., about 35%. This composition yields improved ability to retain magnetization compared with plain carbon steel. Step-by-Step Solution: 1) Identify the alloy system: cobalt steel based on high carbon steel.2) Recall typical cobalt range used to raise coercivity: around 35% is widely cited.3) Select the option that matches the established figure: 35% cobalt. Verification / Alternative check: Classic materials texts list cobalt steels with ~35% cobalt for permanent magnets, preceding the extensive use of AlNiCo and rare-earth magnets. This aligns with the option given. Why Other Options Are Wrong: 15% / 20%: Lower cobalt content typically does not deliver the same coercivity as the established 35% composition. 45%: Higher than common cobalt steel compositions cited for traditional permanent magnets, impacting cost and properties. Common Pitfalls: Confusing cobalt steel compositions with AlNiCo alloys; assuming any cobalt addition is sufficient without considering the established optimum ranges. Final Answer: 35% cobalt

Question 17

In materials engineering, a cermet (ceramic–metal composite) combines high-temperature hardness of ceramics with the toughness and thermal conductivity of metals. What are the usual proportions (by percentage) of ceramic (clay-based ceramic phase) a…

Accepted Answer

Introduction / Context: Cermets are composite materials engineered by combining a ceramic phase (often alumina, titanium carbide, or similar refractory ceramics sometimes colloquially referred to as clay-based ceramic constituents) with a ductile metallic binder (such as nickel, cobalt, or molybdenum). The concept examined here is the typical composition balance that gives cermets their hallmark performance in cutting tools, wear plates, and high-temperature components. Given Data / Assumptions: Cermets must retain ceramic advantages: hot hardness, abrasion resistance, and chemical stability. They also require metallic benefits: toughness, thermal conductivity, and reduced brittleness. We seek a common, practical proportion used in industry-standard compositions. Concept / Approach: The ceramic fraction must dominate to deliver wear resistance and hardness. The metallic binder must be sufficient to provide crack-bridging toughness and to enable densification during sintering. In practice, many formulations cluster around a ceramic-majority range of roughly two-thirds to four-fifths ceramic, with the remainder metal binder. Among these, approximately 70% ceramic with 30% metal is widely cited as a balanced baseline for general-purpose cermets. Step-by-Step Solution: 1) Identify the required properties: high hardness (ceramic) + workable toughness (metal).2) Ensure ceramic fraction dominates to preserve hardness and wear resistance.3) Provide enough metal (about one-third) to toughen and aid sintering densification.4) Compare options: 70/30 aligns best with the balanced property target for common tool-grade cermets. Verification / Alternative check: Reference compositions for TiC–Ni or Al2O3–Ni based cermets commonly hover near the 70/30 region, with variants tuned for specific wear, speed, and temperature conditions by shifting a few percent either way. Why Other Options Are Wrong: 50/50: Metal fraction too high; hardness and wear resistance drop notably. 60/40: Still metal-rich; lower hot hardness than typical tool-grade targets. 80/20: Toughness can become marginal for impact or interrupted cuts. Common Pitfalls: Assuming a single exact ratio fits all; in reality, the 70/30 value is a practical midpoint, not a rigid rule—final choice depends on application (continuous cut vs intermittent, dry vs lubricated, temperature limits). Final Answer: 70% ceramic, 30% metal

Question 18

In building and woodworking adhesives, which of the following are synthetic resins used for bonding and laminating? Consider common construction-grade resins used in panels, joinery, and exterior/interior woodwork.

Accepted Answer

Introduction / Context: Synthetic resins are man-made polymers formulated to act as binders and adhesives in woodworking, laminates, and construction products. The question tests recognition of common resin families used across interior and exterior applications in building practice. Given Data / Assumptions: We are focusing on adhesives and binders in panels and timber assemblies. Durability, water resistance, and cure conditions vary by resin chemistry. All listed options are well-known synthetic systems. Concept / Approach: Each listed resin—melamine, phenolic, resorcinol, and urea—belongs to established families used in plywood, particle boards, laminates, finger joints, and structural timber bonding. Their chemistry (amino resins and phenolic types) enables controlled curing and reliable bond strengths. Step-by-Step Solution: 1) Melamine (often melamine-formaldehyde): high hardness and heat resistance; widely used in laminates.2) Phenolic (phenol-formaldehyde): robust exterior-grade panels; excellent water/boil resistance.3) Resorcinol: premier cold-setting structural wood adhesive; excellent durability.4) Urea (urea-formaldehyde): common in interior panels where moisture exposure is limited.5) Since each is a synthetic resin, the inclusive choice is 'All of these'. Verification / Alternative check: Standards and product datasheets for plywood and laminates consistently list these resins by name for specific moisture and strength classes (e.g., BWR, BWP, MR). Why Other Options Are Wrong: Any single-resin option is incomplete because multiple resin chemistries are used across applications. Common Pitfalls: Confusing interior-grade urea-based bonds with exterior structural grades; overlooking the superior durability of phenolic and resorcinol systems in wet or load-bearing situations. Final Answer: All of these

Question 19

In civil engineering works, why is sea sand generally avoided for concrete and masonry? Identify the most likely consequences when chloride- and sulphate-laden sea sand is used in structural work.

Accepted Answer

Introduction / Context: Aggregates and sand quality critically affect durability of concrete and masonry. Sea sand naturally contains soluble salts such as chlorides and sulphates. This question examines the practical problems that arise when such contaminated sand is used without proper treatment. Given Data / Assumptions: Sea sand contains chlorides/sulphates even after casual washing. Concrete and masonry components may be exposed to moisture cycles. Reinforcement in concrete is susceptible to corrosion from chlorides. Concept / Approach: Chlorides accelerate steel corrosion; sulphates react with cement hydrates to form expansive products that crack the matrix. In walls, soluble salts migrate with moisture and crystallize near surfaces, creating efflorescence and attracting dampness by hygroscopic action, compounding deterioration. Step-by-Step Solution: 1) Identify salt sources: sea sand contributes chlorides/sulphates.2) In concrete: chlorides break down passivation on rebar, initiating rust and cracking.3) In mortar: sulphate attack forms expansive compounds, weakening joints.4) In masonry surfaces: salts migrate and crystallize, causing efflorescence and persistent damp patches.5) Combine effects: material disintegration, visible efflorescence, and dampness. Verification / Alternative check: Durability specifications often cap chloride and sulphate contents in fine aggregates; desalination or prohibition of sea sand is commonly mandated unless rigorous washing and testing are performed. Why Other Options Are Wrong: A/B/C individually capture only part of the problem; the comprehensive, correct impact is all of them together. Common Pitfalls: Assuming a single freshwater rinse removes salts; neglecting long-term migration and crystallization; ignoring code limits for chloride content in reinforced concrete. Final Answer: All of these

Question 20

In timber technology, why is seasoning of freshly felled wood carried out before use? Choose the fundamental objective of seasoning related to moisture content and dimensional stability.

Accepted Answer

Introduction / Context: Green timber contains a high proportion of moisture (free and bound water). Seasoning is the controlled process of reducing this moisture content to levels compatible with service conditions, improving strength, stability, and durability of wood products used in joinery and construction. Given Data / Assumptions: Freshly cut wood can exhibit 30–200% moisture content (based on oven-dry weight). Performance issues (shrinkage, warping, fungal decay) correlate with excess moisture. Seasoning may be air-based or kiln-based depending on urgency and specification. Concept / Approach: By lowering moisture to equilibrium with ambient conditions (equilibrium moisture content), timber gains dimensional stability, better finishes, superior fastener holding, and resistance to biological attack. The key purpose is water removal, not superficial temperature rise or mere paint preparation. Step-by-Step Solution: 1) Identify problems with green timber: shrinkage, checks, decay risk.2) Apply seasoning to reduce free water (in cell lumens) and bound water (in cell walls).3) Target moisture consistent with end-use (e.g., 8–12% for interiors, higher for exterior works).4) Verify improvements: increased strength/ stiffness and reduced movement. Verification / Alternative check: Specifications for joinery require seasoned wood to minimize post-installation movement that would otherwise split joints or misalign fittings. Why Other Options Are Wrong: Waterproofing: Seasoning does not render wood waterproof; finishes and treatments do. Painting: Seasoning is more fundamental than surface prep; painting may follow. Increasing temperature: Any heat is incidental to moisture removal, not an end goal. Common Pitfalls: Over-rapid kiln schedules causing case-hardening; ignoring acclimatization to the installation environment; assuming air-seasoning alone suffices for thick sections without checks. Final Answer: To remove water (reduce moisture content to a suitable level)

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