BMT

📘 Unit 2: Building Materials

• 2.1 Concrete
  • 2.1.1 Composition and Constituent Materials
  • 2.1.2 Production of Concrete
  • 2.1.3 Microstructure of Concrete
  • 2.1.4 Stress-Strain and Load-Deformation Response
  • 2.1.5 Strength Properties
  • 2.1.6 Durability, Permeability and Water Absorption
  • 2.1.7 Defects in Concrete
  • 2.1.8 Applications in Construction
  • 2.1.9 Relevant IS Codes
• 2.2 Bricks
  • 2.2.1 Composition and Raw Materials
  • 2.2.2 Manufacturing Process
  • 2.2.3 Microstructure
  • 2.2.4 Load–Deformation Response
  • 2.2.5 Strength and Other Properties
  • 2.2.6 Applications
  • 2.2.7 Defects in Bricks
  • 2.2.8 Relevant IS Codes
• 2.3 Steel
  • 2.3.1 Composition and Types
  • 2.3.2 Production
  • 2.3.3 Microstructure
  • 2.3.4 Load–Deformation Response
  • 2.3.5 Strength and Other Properties
  • 2.3.6 Corrosion and Durability
  • 2.3.7 Applications
  • 2.3.8 Relevant IS Codes
• 2.4 Stones
  • 2.4.1 Composition and Classification
  • 2.4.2 Quarrying and Production
  • 2.4.3 Microstructure
  • 2.4.4 Load–Deformation Response
  • 2.4.5 Strength and Other Properties
  • 2.4.6 Applications
  • 2.4.7 Defects in Stones
  • 2.4.8 Relevant IS Codes
• 2.5 Timber
  • 2.5.1 Composition and Structure
  • 2.5.2 Seasoning and Preservation
  • 2.5.3 Microstructure
  • 2.5.4 Load–Deformation Response
  • 2.5.5 Strength and Other Properties
  • 2.5.6 Defects in Timber
  • 2.5.7 Applications
  • 2.5.8 Relevant IS Codes

• 2.6 Comparative Summary

• 2.7 Key IS Codes

• 2.8 Activities and Exercises

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2.1 Concrete

_For detailed content on Concrete visit another dedicated website on ‘Concrete Technology’ - Click Here

2.1.1 Composition and Constituent Materials

Concrete is a composite construction material made primarily from cement, fine aggregates, coarse aggregates, water, and sometimes admixtures. The performance of concrete depends significantly on the properties of each constituent.

Cement

To read more about Cement, its properties and tests - Click Here

• Role: Acts as the binding material, developing strength through hydration.

• Properties:

  • Fineness (affects rate of hydration and strength gain)
  • Setting time (initial & final)
  • Soundness (resistance to volume change)
  • Strength (compressive strength of cement mortar cubes)
• Composition (by oxides):

Oxide Component	Typical % Range in OPC	Role / Function
CaO (Lime)	60 – 67 %	Provides strength and soundness; excess causes unsoundness
SiO₂ (Silica)	17 – 25 %	Contributes to strength development at later stages (C-S-H formation)
Al₂O₃ (Alumina)	3 – 8 %	Lowers clinkering temperature; influences setting time
Fe₂O₃ (Iron oxide)	0.5 – 6 %	Imparts color; contributes slightly to strength; acts as flux
MgO (Magnesia)	0.1 – 4 % (≤ 6% as per IS)	Small amounts improve strength; excess leads to expansion & unsoundness
SO₃ (Sulphur trioxide)	1 – 3 % (≤ 3.5% as per IS)	Controls setting time; regulates expansion
Na₂O + K₂O (Alkalis)	0.2 – 1 %	Can cause efflorescence & alkali-aggregate reaction if high

• Main compounds (Bogue’s):

  • C₃S (early strength)
  • C₂S (later strength)
  • C₃A (initial setting, heat generation)
  • C₄AF (reduces clinkering temperature)

Fine Aggregates (Sand)

To read more about Aggregates - Click Here

• Role: Fills voids between coarse aggregates, improves workability.

• Properties:

  • Grading (as per IS sieve analysis)
  • Fineness modulus
  • Cleanliness (free from silt/clay)
  • Specific gravity & water absorption

Coarse Aggregates

To read more about Aggregates - Click Here

• Role: Provide bulk, strength, and dimensional stability.

• Properties:

  • Size & shape (angular preferred for strength)
  • Crushing value & impact value (measure resistance to failure)
  • Water absorption
  • Grading for proper packing

Water

To read more about Water for making Concrete - Click Here

• Role: Hydration of cement + workability of mix.
• Requirement: Must be free from salts, acids, organic matter.

Admixtures

To read more about Admixtures - Click Here

• Role: Modify properties of concrete for specific needs.

• Types:

  • Plasticizers & Superplasticizers – improve workability
  • Accelerators – reduce setting time
  • Retarders – increase setting time
  • Air-entraining agents – improve frost resistance
  • Mineral admixtures – fly ash, silica fume, slag (improve durability & reduce heat of hydration)

2.1.2 Production of Concrete

To read more about Properties & Production of Concrete

1. Click Here

and 2. Click Here

Concrete production involves several stages to ensure uniformity, strength, and durability.

Batching (Measuring Quantities of Ingredients)

• Weight Batching (preferred): Ingredients measured by mass → accurate & consistent.
• Volume Batching: Ingredients measured by volume → less accurate, prone to errors.

Weight vs. Volume Batching

Feature	Weight Batching	Volume Batching
Accuracy	High	Low
IS Code Reference	Recommended	Not recommended for important works
Cost	Higher (needs weigh batcher)	Lower
Consistency	Excellent	Variable
Usage	Major projects	Small, unimportant works

Mixing (Uniform Blending of Materials)

• Hand Mixing: For small works, not very uniform.
• Machine Mixing: Using drum or pan mixers, ensures uniformity.

Transporting and Placing

• Transport Methods: Wheelbarrows, transit mixers, pumps.
• Key Requirement: Prevent segregation and loss of water.

Compaction

• Hand Ramming / Rodding (small works)
• Vibration (internal/needle, surface, formwork vibrators)

Curing

• Ensures hydration continues to achieve strength & durability.
• Methods: Water curing, wet coverings, membrane curing, steam curing.
• Duration: Minimum 7–14 days depending on cement type.

Segregation vs. Bleeding

Aspect	Segregation	Bleeding
Definition	Separation of coarse aggregates from mortar	Water rising to surface
Cause	Excess water, improper handling, vibration	High water content, poor grading
Effect	Non-uniform concrete, honeycombing	Weak surface layer, cracks
Prevention	Proper mix design, controlled vibration	Use of fines, proper w/c ratio

2.1.3 Microstructure of Concrete

• The microstructure consists of hydrated cement paste (C–S–H gel, CH crystals), unhydrated cement particles, aggregates, and pores.

• Strength and durability depend on porosity, interfacial transition zone (ITZ), and bond between aggregates and paste.

• The microstructure of hydrated concrete consists primarily of calcium silicate hydrate (C–S–H) gel, a complex, fibrous, or gel-like material formed from the reaction of cement and water, and calcium hydroxide (CH) crystals, which are thin, hexagonal plates. These hydration products, along with remaining unhydrated cement particles and a network of pores, interlock to create a rigid, hardened matrix that binds aggregates together. The overall microstructure is a heterogeneous composite of these phases, the exact nature of which significantly influences the mechanical properties and durability of the concrete.

Fig: Microstructure of Hydrated Concrete

Key Components of the Hydrated Microstructure

• C–S–H gel: This is the main binding phase in concrete and is formed from the hydration of calcium silicates (alite and belite) in Portland cement. C–S–H is a poorly crystalline material with a high surface area and variable composition, providing much of the concrete’s strength.

• Calcium Hydroxide (CH): Also known as portlandite, this is a product of cement hydration and appears as larger, dense hexagonal crystals. While it contributes to the mass of the hardened paste, it is often considered a less significant factor in strength than C–S–H and can be susceptible to acid attack.

• Unhydrated Cement Particles: Even after hardening, some cement particles remain unreacted. These are residual components within the microstructure that continue to hydrate and contribute to strength over time.

• Pores:
  The microstructure contains various pores, including the gel pores within the C–S–H gel and larger capillary pores. The distribution and size of these pores affect the concrete’s permeability and overall durability.

• Aggregates: Concrete also contains large aggregates (sand and gravel) that are encapsulated by the hydrated cement paste. These are not part of the cement paste microstructure itself but are essential components of the composite material.

Formation and Properties

1. Hydration: When water is added to Portland cement, the cement compounds begin a series of chemical reactions.
2. Product Formation: The reactions produce C–S–H gel, calcium hydroxide crystals, and other hydration products.
3. Microstructure Development: These products grow and interlock, filling the space and solidifying into a rigid, hardened mass that binds the aggregates.
4. Variability: The exact microstructure, including the ratio of C–S–H to CH and the pore network, is influenced by the cement’s composition, the water-to-cement ratio, and curing conditions.

Significance

The microstructure of hydrated concrete dictates its properties. A well-developed microstructure, with a dense C–S–H network and well-distributed pores, leads to high strength and low permeability, which is crucial for the durability and performance of concrete structures.

2.1.4 Stress-Strain and Load-Deformation Response

• Stress–strain curve of concrete is non-linear.
• In compression: Rapid rise, peak, followed by descending branch (brittle failure).
• In tension: Very low strength, sudden brittle failure.

Fig: Typical stress-strain curve for concrete

A stress-strain curve for concrete plots compressive stress (y-axis) against compressive strain (x-axis) to show its behavior under load. The curve starts linear, then becomes nonlinear as micro-cracks form, eventually reaching a peak stress and failing. The slope of the initial linear portion is the modulus of elasticity, while the curve’s overall shape, particularly the parabolic-to-constant form in some standards, is crucial for structural design.

Components of the Stress-Strain Curve

Stress (Y-axis): This represents the force per unit area applied to the concrete. Strain (X-axis): This represents the deformation or change in shape of the concrete under the applied load.

Key Characteristics

1. Nonlinear Behavior: Unlike initially linear materials, concrete’s stress-strain curve quickly becomes nonlinear due to micro-cracks forming at the aggregate-cement paste interface and within the paste itself as load increases. 2. Modulus of Elasticity (E): The initial, nearly linear part of the curve’s slope provides the modulus of elasticity, indicating concrete’s stiffness and resistance to deformation. 3. Ultimate Strength: The curve reaches a peak value representing the ultimate compressive strength of the concrete. 4. Rupture Point: After reaching its peak, the concrete begins to crush and fails, which is known as the rupture point. 5. Design Standards: For design purposes, an idealized stress-strain curve is often used, which is typically parabolic up to a certain strain (e.g., 0.002) and then constant until the failure point (e.g., 0.0035).

Fig: Idealized Stress–Strain Curve for Concrete (IS 456)

The idealized stress–strain curve for concrete is codified in the Indian Standard IS:456-2000, where it’s defined as a parabolic-rectangular curve. This idealized curve, used for designing reinforced concrete structures, shows stress increasing parabolically with strain up to 0.002, then remaining constant at a reduced design stress level (0.67fck/1.5 = 0.45fck) up to an ultimate strain of 0.0035.

2.1.5 Strength Properties

Compressive Strength

\[f_{ck} = \frac{P}{A}\]

where

• $f_{ck}$ = Compressive strength (MPa)
• $P$ = Load at failure (N)
• $A$ = Loaded area (mm²)

Target Mean Strength

\[f_{t} = f_{ck} + 1.65 \times \sigma\]

where

• $f_{t}$ = Target mean strength
• $f_{ck}$ = Characteristic strength
• $\sigma$ = Standard deviation

Difference between Characteristic Compressive Strength $(f_{ck})$ and Target Mean Strength $(f_{t})$

Aspect	Characteristic Compressive Strength $(f_{ck})$	Target Mean Strength $(f_{t})$
Definition	Minimum compressive strength below which not more than 5% of test results are expected to fall	Strength of concrete mix designed to ensure that the obtained strength is always greater than or equal to fck
Purpose	Used as the basis for structural design	Used in mix design calculations to account for variability
Value	Specified in IS codes (e.g., M20 → fck = 20 MPa)	Higher than fck by a margin (depends on standard deviation)
Formula	—	fcm = fck + 1.65 × σ (where σ = standard deviation)
Margin Considered	No margin included	Includes margin to cover variations in materials, workmanship, and testing
Role in Practice	Ensures minimum safety requirement for structures	Ensures that designed mixes actually achieve the required fck in practice

2.1.6 Durability, Permeability and Water Absorption

• Water–Cement Ratio (Abram’s Law): Lower w/c ratio → higher strength & durability.

• Factors affecting strength & durability:

  • Quality of materials
  • Mix proportions
  • Curing method & duration
  • Environmental exposure conditions
• Water absorption test (as per IS 516).
• Permeability: Resistance to ingress of water, chloride, sulfate.

2.1.7 Defects in Concrete

Common defects include:

• Honeycombing
• Cracks (plastic shrinkage, drying shrinkage, thermal)
• Efflorescence
• Alkali–aggregate reaction
• Cavities due to poor compaction

2.1.8 Applications in Construction

• Structural components: beams, columns, slabs, foundations
• Pavements, dams, bridges
• Precast elements: pipes, blocks, panels
• Mass concrete works

2.1.9 Relevant IS Codes

• IS 456 – Plain and Reinforced Concrete – Code of Practice
• IS 10262 – Concrete Mix Proportioning Guidelines
• IS 516 – Methods of Tests for Strength of Concrete
• IS 1199 – Methods of Sampling and Analysis of Concrete
• IS 2386 – Methods of Test for Aggregates

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2.2 Bricks

2.2.1 Composition and Raw Materials

Bricks are primarily made from clay and other additives that improve performance.

• Clay Minerals

  • Kaolinite, Illite, Montmorillonite.
  • Provide plasticity and binding properties.

• Silica (50–60%)

  • Prevents shrinkage, imparts strength.

• Alumina (20–30%)

  • Provides plasticity and workability.

• Lime (2–5%)

  • Improves binding, prevents cracking.

• Iron Oxide (5–6%)

  • Provides red/brown coloration, adds strength.

• Magnesia (less than 1%)

  • Improves color, reduces shrinkage.

Reference: IS 1077 – Common Burnt Clay Building Bricks

2.2.2 Manufacturing Process

The production of bricks involves four main stages:

1. Preparation of Clay

   • Winning/excavation.
   • Weathering to improve plasticity.
   • Blending with additives.

2. Moulding

   • Hand Moulding: Ground moulded, table moulded.
   • Machine Moulding: For mass production, more uniform.

3. Drying

   • Sun drying or artificial drying.
   • Reduces moisture to prevent cracking in kilns.

4. Burning

   • Done in clamps or kilns (Bull’s Trench Kiln, Hoffman’s Kiln).
   • Burning temperature: 900–1100°C.
   • Develops strength, hardness, and durability.

Fig: Brick Manufacturing Process

Fig: Block diagram of brick manufacturing.

2.2.3 Microstructure

• Bricks are heterogeneous ceramic materials with pores and crystalline phases.
• Amorphous silica, alumina, and iron oxides form the primary matrix.
• Pores influence water absorption and durability.
• Microstructural features such as voids, cracks, and orientation of clay particles impact strength.

Fig: SEM image of Clay Brick Microstructure

A scanning electron microscope (SEM) image of brick microstructure reveals a complex, heterogeneous material composed of fired clay particles, mineral aggregates, and a network of pores. The exact appearance varies depending on the raw materials used, the firing temperature, and any additives.

2.2.4 Load–Deformation Response

• Stress–strain behavior of bricks is non-linear and brittle.
• Bricks generally fail without much plastic deformation.
• Modulus of Rupture (MOR): Indicates flexural strength.
• Toughness: Low compared to concrete or steel.

📌 [Placeholder for Graph: Stress–Strain Curve for Brick under Compression]

2.2.5 Strength and Other Properties

1. Compressive Strength

• Tested using IS 3495 (Part 1).

• Typical values:

  • First Class Bricks: ≥ 10.5 MPa
  • Second Class Bricks: ≥ 7.5 MPa
  • Third Class Bricks: ≥ 3.5 MPa

\[\text{Compressive Strength (MPa)} = \frac{\text{Maximum Load (N)}}{\text{Loaded Area (mm}^2\text{)}}\]

2. Water Absorption

• Tested as per IS 3495 (Part 2).
• Requirement: Should not exceed 20% by weight after 24 hours immersion.

3. Efflorescence

• White deposits due to soluble salts.
• Tested as per IS 3495 (Part 3).

4. Dimensional Tolerance & Shape

• As per IS 1077.
• Length, width, and height must be within permissible tolerance.

Classification of Bricks

Bricks are classified based on quality and strength:

• First Class Bricks

  • Uniform shape, smooth surface, sharp edges.
  • High strength (≥ 10.5 MPa).
  • Low water absorption (< 15%).
  • Used in permanent, load-bearing structures.

• Second Class Bricks

  • Slightly irregular, small surface cracks allowed.
  • Strength ≥ 7.5 MPa.
  • Used in internal walls, where plastering is required.

• Third Class Bricks

  • Rough, poor strength (~3.5 MPa).
  • High water absorption.
  • Used for temporary structures.

• Fourth Class Bricks

  • Over-burnt, dark color, brittle.
  • Not suitable for masonry.
  • Used as aggregate in road construction.

2.2.6 Applications

• Load-Bearing Walls – Residential, low-rise buildings.
• Partition Walls – Non-load bearing.
• Pavements and Pathways – Bricks laid in herringbone or stretcher bond.
• Special Bricks – Fire bricks, engineering bricks, perforated bricks.
• Refractory Applications – High-temperature furnaces and kilns.

2.2.7 Defects in Bricks

1. Efflorescence – White patches due to soluble salts.
2. Lamination – Thin layers due to improper mixing.
3. Cracks – During drying or burning.
4. Chuff – Formation of cracks when clay lumps burn.
5. Warping – Uneven shape due to improper drying.
6. Bloating – Swelling due to excessive heating.
7. Black Core – Due to incomplete burning.

📌 [Placeholder for Figure: Common Defects in Bricks]

2.2.8 Relevant IS Codes

• IS 1077 – Common burnt clay building bricks.
• IS 2180 – Burnt clay building bricks (heavy duty).
• IS 2222 – Burnt clay perforated building bricks.
• IS 3495 (Parts 1–4) – Methods of testing bricks.
• IS 5454 – Method for sampling of clay.
• IS 2691 – Burnt clay facing bricks.

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2.3 Steel

Steel is one of the most important construction materials due to its high tensile strength, ductility, and versatility. It is extensively used in reinforced concrete, structural frameworks, bridges, industrial buildings, and modern infrastructure projects.

2.3.1 Composition and Types

• Composition:

  • Iron (Fe): Base element.
  • Carbon (C): Primary strengthening element (0.05–2%).
  • Manganese (Mn): Improves toughness.
  • Sulphur (S) and Phosphorus (P): Undesirable impurities, reduce ductility.
  • Alloying elements (in special steels): Nickel, Chromium, Vanadium, Molybdenum.

• Types of Steel (based on composition and application):

  • Mild Steel (Low carbon, 0.05–0.25%) → ductile, widely used in RCC.
  • Medium Carbon Steel (0.25–0.6%) → higher strength, used for rails, gears.
  • High Carbon Steel (0.6–1.5%) → very strong but brittle, used for springs, cutting tools.
  • Alloy Steels → Stainless steel (Cr & Ni), Weathering steel, Tool steels.
  • Structural Steel → Used in building frames, IS sections.
  • Reinforcing Steel (Rebars) → HYSD bars, TMT bars.

• Grades of Steel used in RCC (as per IS 1786):

  • Fe 250 → Yield strength = 250 MPa (mild steel, used in older RCC).
  • Fe 415 → Yield strength = 415 MPa (widely used TMT grade).
  • Fe 500 → Yield strength = 500 MPa (higher strength rebars).
  • Fe 550 → Yield strength = 550 MPa (used in heavy structures).
  • Fe 600 → Yield strength = 600 MPa (special high-strength applications).

👉 In these designations, “Fe” indicates iron/steel and the number indicates the minimum yield strength (in N/mm² or MPa).

2.3.2 Production

• Iron Ore to Steel (basic steps):

  1. Extraction of iron from ore in blast furnace.
  2. Conversion to pig iron.
  3. Steel making in open-hearth furnace, Bessemer converter, or Basic Oxygen Furnace.
  4. Secondary refining → Removal of impurities, alloying additions.
  5. Casting and rolling → Billets, sheets, rebars, structural sections.

• Modern processes:

  • Electric Arc Furnace (EAF) – used for recycling scrap steel.
  • Continuous Casting – improves uniformity of steel products.

📌 Figure Placeholder: Steel production flow chart

2.3.3 Microstructure

• Steel microstructure depends on carbon content and heat treatment.

• Main phases:

  • Ferrite (α-Fe) → soft, ductile, low strength.
  • Pearlite → alternating layers of ferrite & cementite, stronger than ferrite.
  • Cementite (Fe₃C) → hard, brittle phase.
  • Martensite → obtained by quenching, very hard and brittle.
  • Austenite (γ-Fe) → stable at high temperature, FCC structure.

📌 Figure Placeholder: Microstructure of steel (Ferrite–Pearlite, Martensite)

2.3.4 Load–Deformation Response

• Steel shows an elastic–plastic behavior.

• Stress–strain curve of mild steel:

  • Proportional Limit → Hooke’s law valid.
  • Elastic Limit → material regains shape after unloading.
  • Yield Point → permanent deformation starts.
  • Ultimate Strength → max stress before necking.
  • Fracture Point → failure.

• For High Strength Steels (TMT, HYSD) → No clear yield point; yield strength is determined by 0.2% proof stress method.

📌 Figure Placeholder: Stress–strain curve for mild steel and HYSD steel

2.3.5 Strength and Other Properties

• Mechanical Properties:

  • Tensile Strength (UTS).
  • Yield Strength.
  • Ductility (Elongation %).
  • Toughness.
  • Hardness.

• Physical Properties:

  • Density ≈ 7850 kg/m³.
  • Melting point ≈ 1500°C.
  • Thermal conductivity ≈ 50 W/mK.
  • Coefficient of expansion ≈ 12 × 10⁻⁶ /°C.

• Factors affecting strength:

  • Carbon content.
  • Heat treatment.
  • Rate of cooling.
  • Presence of impurities.

2.3.6 Corrosion and Durability

• Corrosion Types:

  • Uniform corrosion.
  • Galvanic corrosion.
  • Pitting corrosion.
  • Stress corrosion cracking.

• Factors influencing corrosion:

  • Moisture and oxygen.
  • Chlorides, sulphates, industrial pollutants.
  • Inadequate cover in RCC structures.

• Protection Methods:

  • Providing adequate cover (as per IS).
  • Coatings → Galvanization, Epoxy coating, Bituminous paints.
  • Cathodic protection.
  • Using stainless steel or corrosion-resistant steel.

📌 Figure Placeholder: Rusting process of steel reinforcement

2.3.7 Applications

• Reinforcement in concrete structures (RCC).
• Structural steel sections → beams, columns, trusses.
• Prestressing tendons (high-strength steel wires and strands).
• Bridges, industrial buildings, transmission towers.
• Tools, machinery, pipelines, tanks, railways.

2.3.8 Relevant IS Codes

• IS 2062 – Hot rolled medium and high tensile structural steel.
• IS 1786 – High strength deformed steel bars and wires for concrete reinforcement.
• IS 432 – Mild steel and medium tensile steel bars for concrete reinforcement.
• IS 1608 – Mechanical testing of metals (tensile testing).
• IS 1599 – Method for bend test.
• IS 800 – Code of practice for general construction in steel.

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2.4 Stones

2.4.1 Composition and Classification

• Composition: Stones are naturally occurring aggregates of minerals. The primary minerals found are silica, alumina, lime, iron oxides, and magnesia. Their properties depend upon mineral content and bonding.

• Classification of Stones:

  1. Geological Classification

     • Igneous rocks: Granite, Basalt, Trap.
     • Sedimentary rocks: Sandstone, Limestone.
     • Metamorphic rocks: Marble, Slate, Quartzite.

  2. Physical Classification

     • Stratified (Sandstone, Limestone).
     • Unstratified (Granite, Trap).
     • Foliated (Slate, Gneiss).

  3. Chemical Classification

     • Siliceous (Granite, Quartzite).
     • Argillaceous (Slate, Laterite).
     • Calcareous (Limestone, Marble).

  📌 [Figure Placeholder: Flowchart of classification of stones]

2.4.2 Quarrying and Production

• Quarrying Methods:

  1. Digging and Excavation
  2. Heating (fire setting method)
  3. Wedging with steel wedges
  4. Blasting with controlled explosives (for hard stones like granite)

• Production Steps:

  1. Quarrying
  2. Dressing (manual or machine cutting to required shapes)
  3. Seasoning (air-drying to remove moisture)
  4. Transportation to site

📌 [Figure Placeholder: Quarrying and dressing process diagram]

2.4.3 Microstructure

• Stones have crystalline or granular structures depending on their mineral origin.
• Granite: crystalline quartz, feldspar, mica.
• Sandstone: granular silica bound with natural cementing materials.
• Marble: crystalline calcite interlocking crystals.

📌 [Figure Placeholder: Microstructure of granite vs. marble vs. sandstone]

2.4.4 Load–Deformation Response

• Stones are brittle in nature.

• Stress–strain curve shows:

  • Linear elastic behavior up to failure.
  • No yielding like steel.

• Modulus of elasticity (E):

  • Granite: 50–70 GPa
  • Marble: 30–50 GPa
  • Sandstone: 20–40 GPa

📌 [Graph Placeholder: Stress–strain curve of stone vs. concrete vs. steel]

2.4.5 Strength and Other Properties

• Compressive Strength:

  • Granite: 100–250 MPa
  • Basalt: 200–350 MPa
  • Sandstone: 20–170 MPa
  • Limestone: 30–250 MPa

• Other Properties:

  • Toughness index: measured by impact test.
  • Water absorption: should not exceed 1–5% for building use.
  • Specific gravity: 2.4–3.0.
  • Hardness: tested by Moh’s scale (Granite – 6 to 7, Marble – 3).
  • Durability: resistance to weathering, frost action, and chemical attack.

📌 [Table Placeholder: Comparison of properties of granite, marble, sandstone, limestone]

2.4.6 Applications

• Granite: Foundations, columns, flooring, monuments.
• Marble: Flooring, cladding, decorative finishes.
• Sandstone: Wall construction, ornamental works.
• Slate: Roofing tiles, damp-proof courses.
• Limestone: Building blocks, raw material for cement.
• Quartzite: Railway ballast, retaining walls.

2.4.7 Defects in Stones

• Common Defects:

  1. Cracks/Seams – reduce strength.
  2. Sand Holes – uneven texture.
  3. Spots – stains due to iron oxide.
  4. Pores – increase water absorption.
  5. Shake – separation of layers due to weathering.

📌 [Figure Placeholder: Photographs of common defects in stones]

2.4.8 Relevant IS Codes

• IS 1121 (Part 1–4): Methods of test for determination of strength properties of natural building stones.
• IS 1122: Determination of true specific gravity of natural building stones.
• IS 1123: Identification of natural building stones.
• IS 1124: Determination of water absorption, apparent porosity and specific gravity of natural building stones.
• IS 1125: Determination of weathering of natural building stones.
• IS 1130: Marble (blocks, slabs and tiles).
• IS 3620: Laterite stone building blocks.
• IS 3316: Structural granite.

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2.5 Timber

2.5.1 Composition and Structure

• Constituents of Timber:

  • Cellulose (40–50%): Provides tensile strength.
  • Hemicellulose (20–30%): Binds cellulose fibers.
  • Lignin (20–30%): Provides rigidity and compressive strength.
  • Extractives (tannins, resins, oils): Provide durability and resistance.
  • Ash and minerals (≤1%): Minor but influence durability.

• Anatomical Structure:

  • Pith: Central core of the tree.
  • Heartwood: Inner matured portion, stronger and darker.
  • Sapwood: Outer younger layer, lighter, less durable.
  • Cambium Layer: Growing zone between sapwood and bark.
  • Bark: Protective outer covering.
  • Annual Rings: Growth rings indicating age and climate conditions.

(Insert Figure Placeholder: Cross-section of tree showing pith, heartwood, sapwood, cambium, bark, annual rings)

2.5.2 Seasoning and Preservation

• Seasoning of Timber (removal of excess moisture):

  • Air Seasoning: Natural drying, low cost, but slow.
  • Kiln Seasoning: Artificial drying using controlled heat and humidity, faster and more uniform.
  • Solar Seasoning: Uses solar energy, intermediate method.
  • Chemical Seasoning: Salts and chemicals used to accelerate drying.

• Advantages of Seasoning:

  • Increases strength, reduces shrinkage and warping.
  • Improves durability and resistance to decay.
  • Enhances workability and surface finish.

• Preservation of Timber:

  • Chemical Preservatives: Creosote oil, coal tar, copper sulphate, sodium fluoride.

  • Methods:

    • Brushing, spraying, dipping – surface protection.
    • Pressure treatment (full-cell/empty-cell process) – deep penetration for durability.

(Insert Figure Placeholder: Timber seasoning methods – air and kiln seasoning)

2.5.3 Microstructure

• Timber is an anisotropic material.

• Microstructure consists of:

  • Fibers (tracheids): Provide mechanical strength.
  • Vessels (pores): Conduct water and nutrients.
  • Rays: Radial structures for storage and transport.

• Hardwoods vs. Softwoods:

  • Hardwoods → presence of vessels, denser.
  • Softwoods → mainly tracheids, lighter but strong.

(Insert Figure Placeholder: Microscopic view of hardwood vs. softwood structure)

2.5.4 Load–Deformation Response

• Timber shows orthotropic behavior (properties differ along longitudinal, radial, tangential directions).

• Stress–strain curve:

  • Linear up to elastic limit.
  • Nonlinear beyond due to fiber crushing and buckling.

• Load-bearing behavior:

  • Stronger along grain (longitudinal direction).
  • Weak across grain (radial/tangential).
• Exhibits creep under long-term loading.

(Insert Figure Placeholder: Stress–strain curve of timber along and across grain)

2.5.5 Strength and Other Properties

• Mechanical Properties:

  • Compressive strength (parallel to grain): 30–60 N/mm².
  • Tensile strength (parallel to grain): 50–150 N/mm².
  • Modulus of Elasticity (E): 7–20 GPa.

• Physical Properties:

  • Density: 300–1000 kg/m³ depending on species.
  • Moisture content: Affects strength, decay, and weight.
  • Permeability: Controls preservative treatment efficiency.
  • Water absorption: Higher in sapwood.

• Durability: Heartwood more durable than sapwood.

2.5.6 Defects in Timber

• Natural Defects:

  • Knots: Branch bases within timber.
  • Shakes: Cracks due to shrinkage or seasoning.
  • Rind galls: Swollen wood due to injury.

• Seasoning Defects:

  • Warping: Distortion in shape.
  • Twisting: Spiraled deformation.
  • Splitting/checking: Surface cracks due to drying.

• Biological Defects:

  • Fungal decay: Dry rot, wet rot.
  • Insect attack: Termites, beetles.

(Insert Figure Placeholder: Timber defects – knots, shakes, warping, termite attack)

2.5.7 Applications

• Construction: Beams, rafters, doors, windows, flooring.
• Furniture and Interior: Chairs, tables, cabinets.
• Marine Structures: Boats, ships (teak, sal wood).
• Railway Sleepers: Sal, teak, deodar.
• Plywood, Laminates, Engineered wood: For structural and decorative purposes.

2.5.8 Relevant IS Codes

• IS 287 – Recommendations for maximum permissible moisture content of timber.
• IS 1708 – Methods of testing small clear specimens of timber.
• IS 401 – Preservation of timber.
• IS 303 – Plywood for general purposes.
• IS 3629 – Glossary of terms relating to timber technology.

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2.6 Comparative Summary

Aspect	Concrete	Bricks	Steel	Stones	Timber
Composition / Constituent Materials	Cement, fine & coarse aggregates, water, admixtures	Clay, sand, lime, iron oxide, magnesia	Iron with carbon and alloying elements (Mn, Cr, Ni, V)	Silica, alumina, lime, iron oxides, magnesia	Cellulose, hemicellulose, lignin, extractives
Production	Batching, mixing, transporting, placing, compaction, curing	Preparation of clay, molding, drying, burning in kiln	Extraction of ore → Refining → Steel making (BOF/EAF) → Rolling/forming	Quarrying, dressing, finishing, polishing	Felling, seasoning (natural/kiln), preservation
Microstructure	Hydrated cement matrix binding aggregates; capillary pores	Fine crystalline clay structure with vitrified bonds	Ferrite, pearlite, cementite, martensite (depending on type)	Interlocked crystalline structure (igneous, sedimentary, metamorphic)	Cellular structure with annual growth rings, fibers, tracheids
Load–Deformation Response	Nonlinear, brittle in tension, ductile in compression (with reinforcement)	Brittle, crushing failure under load	Elastic–plastic, high ductility, clear yield plateau (mild steel)	Brittle, sudden fracture without warning	Initially elastic, non-linear, anisotropic (differs along grain)
Strength & Other Properties	Compressive: 20–80 MPa; Tensile: 2–5 MPa; W/C ratio governs strength; durable but porous	Compressive: 3.5–35 MPa; low tensile strength; high water absorption	Yield strength grades (Fe 250, Fe 415, Fe 500…); Toughness, ductility; corrosion prone	Compressive: 20–300 MPa; strong, durable, heavy; low tension strength	Compressive: 5–50 MPa; Tension (parallel to grain) ~ 50–150 MPa; Tough but moisture-sensitive
Other Material Properties	Toughness low; water absorption 5–15%; permeability depends on curing & W/C ratio	Toughness low; water absorption high; porous	Excellent toughness & ductility; impermeable; corrosion reduces durability	Tough, durable, impermeable when dense; porosity varies with type	Moderate toughness; high water absorption & permeability if unseasoned
Characteristic Strength: Determination & Reporting	Cube/cylinder compression test; reported as fck	Compressive test on brick samples; reported as class (1st, 2nd, 3rd)	Tensile test (stress–strain curve); yield strength (Fe 250, 415…) reported	Crushing test on stone specimen; reported in MPa	Compression, bending, shear tests; reported along & across grain
Applications	RCC, PCC, pavements, dams, buildings, bridges	Masonry walls, partitions, paving, lining of furnaces	RCC reinforcement, structural sections, pre-stressed concrete	Foundations, retaining walls, flooring, cladding, monuments	Roof trusses, beams, doors, windows, flooring, furniture

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2.7 Key IS Codes

For the most current versions and detailed specifications, please refer to the official BIS Standards Portal.

Here’s your table with the IS codes de-linked as requested:

Material	Relevant IS Codes	Description
Concrete	IS 456	Code of Practice for Plain and Reinforced Concrete
	IS 10262	Guidelines for Concrete Mix Design Proportioning
	IS 516	Methods of Tests for Strength of Concrete
	IS 1199	Methods of Sampling and Analysis of Concrete
Bricks	IS 1077	Common Burnt Clay Building Bricks – Specification
	IS 3495	Methods of Tests of Burnt Clay Building Bricks
	IS 2212	Code of Practice for Brickwork
Steel	IS 1786	High Strength Deformed Steel Bars and Wires for Concrete Reinforcement
	IS 2062	Hot Rolled Medium and High Tensile Structural Steel
	IS 800	General Construction in Steel – Code of Practice
	IS 1608	Mechanical Testing of Metals – Tensile Testing
Stones	IS 1121-1	Methods of Test for Determination of Compressive Strength of Natural Building Stones
	IS 1121-2	Methods of Test for Determination of Transverse Strength of Natural Building Stones
	IS 1121-3	Methods of Test for Determination of Tensile Strength of Natural Building Stones
	IS 1597	Construction of Stone Masonry – Code of Practice
Timber	IS 287	Permissible Moisture Content for Timber Used for Different Purposes
	IS 1708	Methods of Testing Small Clear Specimens of Timber
	IS 1141	Code of Practice for Seasoning of Timber
	IS 401	Code of Practice for Preservation of Timber

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2.8 Activities and Exercises

For Theory Learning and Conceptual Understanding

1. Conceptual Discussion Questions

1. Explain how water–cement ratio affects concrete strength and durability.
2. Compare the stress–strain response of steel and timber under tensile loading.
3. Discuss why certain stones are preferred for bridges but not for decorative facades.
4. Explain the role of admixtures in concrete production.
5. Compare mild steel and HYSD/TMT steel for reinforcement in concrete structures.

2. Comparative Analysis Exercises

• Prepare a table or concept map comparing the following properties for concrete, bricks, steel, stones, and timber:

  • Composition / Constituent materials
  • Typical applications
  • Strength and toughness
  • Water absorption and permeability
  • Common defects and durability issues

3. Case Study Discussions

1. A coastal building is exposed to high chloride content. Identify the most suitable construction materials and justify your choices.
2. A masonry wall shows cracking under load. Based on material properties, what could be the possible reasons?
3. For a multi-story building in an earthquake-prone zone, analyze the combination of materials to maximize strength, ductility, and durability.

4. Self-Assessment / Reflection

• Explain in 3–4 sentences why TMT steel is preferred in earthquake-resistant structures.
• List two advantages and two limitations of clay bricks compared to fly ash bricks.
• Reflect on how microstructure of a material influences its load–deformation behavior and strength.

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