UNIT 4: CONSTRUCTION MATERIALS - EXAM-FOCUSED SHORT NOTES

I. STONES (Aggregates & Natural Building Stones)

A. Geological Classification & Examples

• Igneous Rocks: Formed from cooling magma/lava.

  • Examples: Granite (intrusive, crystalline, strong - used in bridges, dams), Basalt (extrusive, fine-grained, durable - used in road metal, concrete aggregate).

• Sedimentary Rocks: Formed by deposition & consolidation of sediments.

  • Examples: Limestone (calcium carbonate, used in cement, kiln), Sandstone (silica grains, used in masonry, paving).

• Metamorphic Rocks: Formed by transformation of existing rocks under heat/pressure.

  • Examples: Slate (cleavage, used in roofing, flooring), Marble (recrystallized limestone, used in flooring, sculpture), Quartzite (hard, used in heavy engineering).

B. Quarrying & Dressing of Stones

• Quarrying Methods:

  1. Hand: For soft stones & small quarries (using chisels, hammers).

  2. Machine: For large works (using steam/derrick cranes, wire saws).

  3. Blasting: For hard rocks & deep quarries (controlled explosives).

• Dressing Processes: Chisel dressing, Pitched, Hammered, Tooled, Rubbed, Polished.

• Purpose & Necessity of Dressing:

  • Aesthetics: To give regular shape & pleasing appearance.

  • Bonding: To create proper key for mortar.

  • Load Distribution: To provide true, even bearing surface.

  • Durability: To remove weathered, soft outer layer.

C. Properties, Defects & Deterioration

• Engineering Properties: Strength (crushing, shear), Hardness, Toughness, Durability (weathering), Appearance.

• Common Defects: Fissures (cracks), Veins (thin layers of different material), Seams, Nodules (hard inclusions), Cavities.

• Causes of Deterioration:

  • Atmospheric action: Rain, wind, frost (freeze-thaw).

  • Temperature: Thermal expansion stresses.

  • Water: Dissolution, infiltration.

  • Vegetation: Root penetration.

  • Retardation: Use of protective coatings, proper design to avoid water stagnation.

D. Specific Stone Materials

• Marble: Metamorphic (recrystallized limestone). Properties: Hard, takes polish, porous, susceptible to acid attack. Uses: Flooring, wall cladding, sculpture.

• Kota Stone: Sedimentary (fine-grained sandstone from Rajasthan). Properties: Hard, durable, slip-resistant, natural colors (buff, pink, green). Uses: Flooring (commercial), pathways, wall cladding.

II. BRICKS & CLAY PRODUCTS

A. Classification of Bricks

B. Brick Manufacturing Process

1. Selection of earth: Clayey soil with alumina & silica.

2. Preparation: Digging → Weathering (3-4 weeks for impurity removal) → Blending (adding sand/lime).

3. Moulding: Hand or machine (table/ extrusion).

4. Drying: Shade drying (7-10 days) to prevent cracking.

5. Burning: In Kilns:

   • Clamp: Temporary, intermittent, uneven burning.

   • Bull’s Trench: Permanent, continuous, better control.

   • Tunnel: Modern, fully mechanized, best quality.

C. Properties of Good Bricks

• Physical: Uniform size (190x90x90 mm), sharp edges, regular shape, fine texture, red/cherry colour.

• Mechanical: Compressive strength > 3.5 N/mm² (First Class), tensile strength ~ 100-300 kg/cm², hardness (scratch test), soundness (metallic ring).

• Durability: Low porosity/absorption (<20% by weight), no efflorescence (salt deposits), frost resistance.

D. Special Bricks & Tiles

• Fly Ash Bricks: Made from fly ash (60-80%), lime, gypsum, sand. Properties: Lightweight, high strength, good thermal insulation, low water absorption. Uses: Masonry, partitions.

  | Property | Fly Ash Brick | Clay Brick | |--------------------|-------------------|--------------------| | Density (kg/m³) | 1600-1700 | 1800-2000 | | Compressive Strength (N/mm²) | 7.5-10 | 3.5-10 | | Water Absorption (%) | <10% | 15-20% |

• Clay Roofing Tiles: Half-round or flat. Properties: Impervious, durable, good weathering. Uses: Roof covering, curved surfaces.

III. TIMBER & WOOD PRODUCTS

A. Structure & Properties of Timber

• Macrostructure:

  • Sapwood: Outer, living, lighter colour, moist, perishable.

  • Heartwood: Inner, dead, darker, durable, resistant to fungi/insects.

  • Annual Rings: Growth rings (spring/summer wood). Density ∝ number of rings.

• Engineering Properties:

  • Mechanical: Strength (parallel/perpendicular to grain), stiffness, toughness.

  • Physical: Density (300-800 kg/m³), Moisture Content (MC) = (W_wet - W_dry)/W_dry × 100%. Oven-dry MC ~ 10-12%.

  • Thermal: Low conductivity (good insulator).

  • Acoustic: Good sound absorption.

B. Defects in Timber

C. Seasoning of Timber

• Need & Importance:

  • Prevent fungal/insect attack (dry timber resists).

  • Increase strength (dry timber stronger).

  • Reduce weight & transportation cost.

  • Improve workability, paint/adhesive bonding.

• Methods:

  1. Natural/Air Seasoning: Stacking under shade with spacers (6-12 months). Slow, cheap, but uneven.

  2. Water Seasoning: Immersion in water (logs) to remove sap, then air drying. Removes extractives but may reduce toughness.

  3. Artificial/Kiln Seasoning: Controlled temp/humidity (60-90°C, 65-75% RH). Fast (days), uniform, but costly.

D. Wood Products & Substitutes

• Need for Substitutes: Timber scarcity, high cost, inconsistent quality, better performance (size, strength, stability).

• Applications:

  • Plywood: Layers (veneers) bonded at right angles. Uses: Furniture, partitions, shuttering.

  • Block Board: Core of softwood strips, outer veneers. Uses: Doors, partitions.

  • Batten Board: Similar to block board but wider battens.

  • Fibre Board (Hardboard): Made from wood fibres under pressure. Uses: Paneling, furniture.

  • Particle Board: Wood chips/flakes bonded with resin. Uses: Low-cost furniture, underlayment.

  • Laminated Board (Glulam): Laminations bonded with adhesives. Uses: Beams, columns, arches.

E. Advantages & Disadvantages of Timber

• Advantages: High strength/weight ratio, renewable, good insulator, workable, aesthetic.

• Disadvantages: Anisotropic, combustible, perishable (decay, insects), dimensional changes with MC, cost, scarcity.

IV. GLASS

A. Nature, Structure & Manufacturing

• Nature: Amorphous solid (non-crystalline). No long-range atomic order.

• Molecular Structure: Disordered network of SiO₄ tetrahedra (in soda-lime glass) with network modifiers (Na⁺, Ca²⁺).

• Manufacturing (Float Glass Process): Molten glass floated on molten tin bath → forms flat, smooth sheet. Controlled cooling (annealing).

B. Properties of Glass

• Optical: Transparency (visible light), Refractive index (~1.5), can be coloured (additives: Co²⁺=blue, Au³⁺=red).

• Thermal: Low thermal conductivity (insulator), high thermal expansion coefficient (needs care), poor thermal shock resistance (tempered improves).

• Mechanical: Brittle (fails catastrophically), Hard (6-7 on Mohs), elastic until fracture.

C. Coatings on Glass

D. Types of Glass

• Soda-Lime: 70% SiO₂, 15% Na₂O, 10% CaO. Common window/bottle glass.

• Borosilicate: SiO₂ + B₂O₃. Low thermal expansion (Pyrex). Lab ware, cookware.

• Lead: PbO added. High refractive index, brilliance. Optical lenses, decorative.

• Toughened/Tempered: Heat-treated for strength/safety.

• Laminated: As above.

• Insulating Units (IGU): Two+ panes with sealed air/argon gap. Reduces U-value.

V. ROOFING & FLOORING MATERIALS

A. Roofing Materials

B. Flooring Materials

Selection Factors Impact:

• Load: Heavy load → concrete, stone.

• Wear: High traffic → ceramic, stone.

• Moisture: Wet areas → ceramic, PVC (non-slip).

• Aesthetics/Cost: Luxury → marble; budget → ceramic, vitrified.

• Thermal Comfort: Cold climates → timber, carpets.

VI. PIPES & PIPE FITTINGS

A. Classification by Material

B. Selection Criteria for Pipes

1. Pressure Rating: Must withstand operating + surge pressure.

2. Temperature: Hot water → CPVC, steel; cold → PVC, HDPE.

3. Corrosion Resistance: Chemical lines → stoneware, PVC; potable water → PVC, CPVC.

4. Cost & Jointing: PVC (solvent weld), steel (welding/flange), cast iron (spigot & socket).

5. Soil Conditions: Aggressive soil → PVC, avoid steel.

VII. PAINTS, VARNISHES & WALL FINISHES

A. Ideal Paint Characteristics

• Good flow & levelling, high coverage (spreading rate), durable (weathering, abrasion), excellent colour retention, appropriate drying time, easy application (brush/roller/spray), cost-effective, resistance to fungi/algae.

B. Paint Composition & Types

• Composition of Oil Paints:

  1. Pigment: Provides colour & opacity (TiO₂ white, ochres, carbon black).

  2. Vehicle/Oil: Binder (linseed, soybean, alkyd). Forms film.

  3. Solvent/Thinner: Adjusts viscosity (turpentine, mineral spirits).

  4. Additives: Driers (cobalt), fillers, anti-settling agents.

• Comparison of Finishes:

C. Varnishes & Polishes

• Varnish: Transparent protective coating. Composition: Resin (shellac, polyurethane), solvent, drying oil.

  • Types: Oil varnish (slow), Spirit varnish (fast, alcohol-based), Water varnish (acrylic), Acrylic varnish.

  • Uses: Protect/beautify wood, metal, paintings.

• French Polish: Process of applying shellac dissolved in alcohol with a rubber (pad). Characteristics: High gloss, deep colour, but poor heat/moisture resistance. Uses: Antique furniture, musical instruments.

• Wax Polish: Beeswax/carnauba wax in solvent. Characteristics: Soft sheen, easy application, needs frequent reapplication. Uses: Furniture maintenance, floor polish.

D. Painting Process for Wooden Surfaces

1. Surface Preparation: Clean (remove dirt/grease), sand (smooth), Knotting (apply knotting compound to seal resin knots), Priming (apply primer/sealer to seal pores, prevent absorption).

2. Application:

   • Apply undercoats (2-3) to build opacity & seal.

   • Sand lightly between coats.

   • Apply finishing coat(s) (enamel/lacquer).

3. Specific Considerations:

   • Moisture Content: Timber should be well-seasoned (MC < 12%) to prevent blistering.

   • Grain Filling: For open-grained wood (oak), use grain filler before undercoats.

   • Sanding Between Coats: Ensures smooth finish.

   • Environmental Conditions: Avoid high humidity/dust during application.

VIII. WALL & CEILING FINISHING MATERIALS

A. Gypsum Boards (Plasterboards)

• Core: Gypsum plaster (CaSO₄·½H₂O) sandwiched between paper/fibre mats.

• Types & Uses:

  • Regular: General partitions, ceilings.

  • Fire-resistant: Contains glass fibres/ additives. Fire-rated walls/ceilings.

  • Moisture-resistant (Green board): For bathrooms, kitchens.

  • Sound-resistant: Denser core, higher STC. Acoustic partitions.

  • Thermal-resistant: With insulating core. Energy-efficient walls.

• Advantages: Fast installation, smooth finish, lightweight, fire-resistant (core), some types moisture/sound resistant.

B. Plasters & Renders (Brief)

• Cement Plaster: 1:4 or 1:6 cement:sand. Strong, durable, used externally & internally.

• Lime Plaster: Lime + sand + hair. Flexible, breathable, used in old buildings, internal.

• Gypsum Plaster: Ready-mix, quick setting, smooth finish. Internal walls/ceilings.

IX. WATERPROOFING & INSULATION MATERIALS

A. Waterproofing Materials

• Bitumen & Tar:

  • Composition: Hydrocarbon from petroleum/coal tar. Viscous, black.

  • Properties: Waterproof, adhesive, flexible, but temperature-sensitive (softens in heat, brittle in cold), degrades in UV.

  • Application: Hot (heated to 150-200°C, applied with mop/brush), Cold (emulsions/solvent-based). Used as membranes (felt, sheet) or coatings.

  • Advantages: Excellent waterproofing, good adhesion, relatively cheap.

  • Disadvantages: Temperature sensitivity, UV degradation (needs protection), flammable when hot, health hazards (fumes).

• Other Materials:

  • Cementitious Coatings: Polymer-modified cement slurries. Good for tanks, basements.

  • Polymer Coatings: Acrylic, polyurethane, epoxy. Seamless, flexible, chemical resistant.

  • Membranes: HDPE, EPDM, PVC sheets (welded/seamed).

B. Thermal Insulating Materials

• Importance: Reduce heat transfer → energy conservation (lower HVAC load), thermal comfort, prevent condensation on cold surfaces.

• Types & Properties:

X. SOUND INSULATING MATERIALS

• Principles:

  1. Mass: Heavier materials block sound (mass law).

  2. Damping: Convert sound energy to heat (viscoelastic materials).

  3. Absorption: Porous materials absorb sound within pores (fibrous, foamed).

• Common Materials:

  • Mass-Loaded Vinyl (MLV): Flexible, heavy sheet. Adds mass to walls/floors.

  • Acoustic Boards: Fibrous (mineral wool) or perforated panels with absorbent backing.

  • Fibrous Materials: Glass/rock wool in wall/ceiling cavities.

  • Double Walls/Air Gaps: Decoupling + absorption in cavity.

XI. METALS IN CONSTRUCTION

A. Aluminium

• Key Properties:

  • Lightweight: Density ~ 2.7 g/cm³ (1/3 steel).

  • Corrosion Resistant: Forms protective oxide film.

  • Ductile & Malleable: Easy to extrude/form.

  • Conductive: Electrical & thermal.

  • Non-magnetic, Non-sparking.

• Forms & Uses:

  • Extrusions: Window/door frames, curtain wall mullions.

  • Sheets: Cladding, roofs, signboards.

  • Foil: Insulation, packaging.

B. Steel

• Structural Properties:

  • Yield Strength (f_y): Stress at permanent deformation.

  • Ultimate Tensile Strength (f_u): Max stress before fracture.

  • Ductility: Measured by % elongation/area reduction. Allows redistribution of stresses.

  • Toughness: Ability to absorb energy (impact resistance).

  • Weldability: Ability to weld without cracking (carbon content < 0.3%).

• Types:

  • Mild Steel (MS): Low carbon (0.15-0.25%). Ductile, weldable. General structures.

  • High-Yield Strength Deformed (HYSD): Higher strength, ribbed surface for bond. Reinforcement.

  • TMT (Tempcore) Bars: Quenched & self-tempered. High strength, ductility, corrosion resistant. Main reinforcement.

XII. CONCRETE (Advanced/Revisited)

A. Grades of Concrete

• Notation: M followed by characteristic compressive strength in N/mm² at 28 days (e.g., M20, M25).

• Characteristic Strength: Strength below which not more than 5% of test results are expected to fall.

• Mix Proportions (IS 10262): Given as Cement : Fine Aggregate : Coarse Aggregate (by weight or volume) for a target strength. Example: M20 ≈ 1:1.5:3.

• Standard Grades: M5 to M80 (special). Common: M15 (mass), M20 (plinth), M25 (superstructure), M30+ (RCC, prestressed).

B. Special Concretes

\boxed{\text{Characteristic Strength } f_{ck} = f_{cm} - 1.64\sigma} (where \(f_{cm}\) = mean strength, \(\sigma\) = std. deviation)

Exam Tip: For special concretes, remember HSC (strength), HPC (all-round performance), SCC (no vibration), FRC (fibres for toughness), Lightweight (density). Focus on specs (w/c ratio, admixtures) and applications.