Raw Materials

• Calcareous materials (CaCO₃) – limestone, chalk, marl
• Argillaceous materials (SiO₂, Al₂O₃) – clay, shale
• Manufacturing: Dry process (most common) or Wet process
• Clinker formed at ~1450 °C; gypsum (3–5 %) added to control setting time

Bogue's Compounds – Major Compounds in OPC

Compound	Full Name	% in OPC	Role
C3S	Tricalcium Silicate	40–50 %	Early & ultimate strength (most important)
C2S	Dicalcium Silicate	25–35 %	Long-term / later-age strength
C3A	Tricalcium Aluminate	5–12 %	Very early strength; flash set; highest heat
C4AF	Tetracalcium Aluminoferrite	8–14 %	Grey/brown colour; minor strength; low heat

Types of Cement (IS Classification)

Type	IS Code	Special Feature / Use
Ordinary Portland Cement (OPC 33 / 43 / 53)	IS 269	General construction
Rapid Hardening Cement	IS 8041	High C3S; early strength; road repairs
Low Heat Cement	IS 12600	High C2S, low C3A; mass concrete, dams
Sulphate Resistant Cement (SRC)	IS 12330	C3A < 5 %; marine / deep foundations
Portland Pozzolana Cement (PPC)	IS 1489	Fly ash blended; better durability, less heat
Blast Furnace Slag Cement	IS 455	GGBS + OPC; good sulphate resistance
White Cement	IS 8042	Very low C4AF; decorative work
Expansive Cement	–	Compensates shrinkage; grouting, rigid pavements
High Alumina Cement (HAC)	IS 6452	High-temperature resistance; refractory lining

Physical Requirements of OPC (IS 4031)

Property	OPC 33	OPC 43	OPC 53
Initial Setting Time (min)	≥ 30	≥ 30	≥ 30
Final Setting Time (min)	≤ 600	≤ 600	≤ 600
Soundness – Le Chatelier (mm)	≤ 10	≤ 10	≤ 10
Compressive Strength 28 days (MPa)	≥ 33	≥ 43	≥ 53
Specific Gravity	~3.15
Fineness – Blaine (m2/kg)	≥ 225	≥ 225	≥ 225

Hydration Reactions

• C₃S + H₂O → C–S–H gel (primary binding phase) + Ca(OH)₂
• C₂S + H₂O → C–S–H gel + smaller amount of Ca(OH)₂
• C₃A + gypsum → Ettringite (prevents flash set)
• Heat of hydration order: C₃A > C₃S > C₄AF > C₂S

Storage of Cement

• Store in dry, waterproof godowns; bags stacked ≤ 10 high
• Use within 3 months; older cement loses ~10–20 % strength
• Bags must not touch walls or floor directly

Classification of Aggregates

Basis	Type	Description
Size	Fine Aggregate (FA)	Passes 4.75 mm IS sieve; e.g. river sand, crushed stone dust
Size	Coarse Aggregate (CA)	Retained on 4.75 mm sieve; e.g. gravel, crushed stone
Size	All-in-aggregate	Mix of FA & CA; used in lean / blinding concrete
Origin	Natural	River gravel, pit sand, natural sand
Origin	Artificial	Broken brick, blast furnace slag
Density	Lightweight	Pumice, cinder; thermal insulation panels
Density	Heavyweight	Baryte, magnetite; radiation-shielding concrete

Requirements of Good Aggregate

• Clean, hard, strong, durable and well-graded
• Free from organic impurities, clay coatings and mica
• Chemically inert with cement paste
• Cubical / angular shape preferred (better interlocking, higher strength)

Fineness Modulus (FM)

• Fine sand: FM = 2.2 – 2.6
• Medium sand: FM = 2.6 – 2.9
• Coarse sand: FM = 2.9 – 3.2
• Higher FM → coarser aggregate → higher strength but lower workability

Standard Tests on Aggregates (IS 2386)

Test	Purpose	Apparatus / Method	Acceptance Limit
Aggregate Crushing Value (ACV)	Resistance to crushing	Steel cylinder (150 mm dia), plunger, compression machine	≤ 30 % pavement; ≤ 45 % other
Aggregate Impact Value (AIV)	Resistance to dynamic shock	Impact machine; 15 blows of 14 kg hammer from 380 mm	≤ 30 % pavement; ≤ 45 % other
Los Angeles Abrasion Value	Resistance to wear	Rotating drum + steel balls (IS 2386 Part IV)	≤ 30–50 % (by use)
Flakiness Index	Shape – flatness	Thickness gauge; flaky if least dim < 0.6 × mean size	≤ 15 % preferred
Elongation Index	Shape – elongation	Length gauge; elongated if longest dim > 1.8 × mean size	≤ 15 % preferred
Specific Gravity & Water Absorption	Density, void ratio, moisture	Wire basket, balance, water bath	SG 2.6–2.8; WA ≤ 2 %
Soundness Test	Weathering resistance	Na2SO4 / MgSO4 solution cycles	≤ 10–12 % loss
Sieve Analysis	Particle size distribution	IS sieves + mechanical shaker; FM calculated	As per IS 383 zones

Grading Zones of Fine Aggregate (IS 383)

Zone	Nature	Remarks
Zone I	Coarsest	High-strength mixes; low workability
Zone II	Medium coarse	Best for most concrete – recommended
Zone III	Medium fine	Acceptable; slightly higher water demand
Zone IV	Finest	Avoid for structural concrete; excessive water demand

Ingredients of Concrete

• Cement: Binding material
• Fine Aggregate: Fills voids between CA particles; improves workability
• Coarse Aggregate: Provides bulk, stiffness and compressive strength
• Water: Hydrates cement; w/c ratio is the single most important strength parameter
• Admixtures: Chemical or mineral additions to modify fresh and hardened properties

Water-Cement (w/c) Ratio

• Lower w/c → higher strength; lower workability
• Higher w/c → lower strength; higher workability
• Theoretical minimum for complete hydration ≈ 0.23
• Practical range: 0.40 – 0.60 for most structural concrete
• Abrams' Law: Strength is inversely proportional to the w/c ratio

Workability Tests

Test	Apparatus	Range / Values	Suitable For
Slump Test	Abrams' cone (h = 300 mm; top ⌀ 100 mm; base ⌀ 200 mm)	0 – 175 mm	Medium workability
Compaction Factor Test	Two conical hoppers + cylindrical mould	0.70 – 0.95	Low to medium workability
Vee-Bee Consistometer	Vibrating table + cylindrical container	3 – 25 seconds	Stiff / very low workability
Flow Test	Flow table + truncated cone mould	Diameter spread (mm)	High workability / SCC

Slump Values for Different Structural Members

Structure Type	Slump (mm)
Mass concrete – dams, pavements	25 – 50
Foundations (lightly reinforced)	25 – 75
Beams, columns, slabs (RCC)	50 – 100
Pumped concrete	75 – 150

Concrete Mix Grades (IS 456 & IS 10262)

Grade	fck (MPa)	Nominal Mix (C : FA : CA)	Typical Use
M5	5	1 : 5 : 10	Lean / blinding concrete
M7.5	7.5	1 : 4 : 8	–
M10	10	1 : 3 : 6	PCC, non-structural
M15	15	1 : 2 : 4	Light structures
M20	20	1 : 1.5 : 3	Minimum for RCC (mild exposure)
M25	25	1 : 1 : 2	RCC slabs, beams, columns
M30 and above	30+	Design mix only	Bridges, prestressed, high-rise

Strength Formulae

• Tensile strength ≈ 10–12 % of compressive strength
• Cubes 150 mm × 150 mm × 150 mm tested at 28 days (IS 516)

Special Types of Concrete

Type	Key Feature	Use
Ready Mix Concrete (RMC)	Batched at plant; delivered by transit mixer	Large urban projects
Self Compacting Concrete (SCC)	High flowability; no vibration needed	Congested reinforcement zones
High Performance Concrete (HPC)	w/c ≤ 0.35; silica fume; superplasticizer	Bridges, offshore structures
Fibre Reinforced Concrete (FRC)	Steel / polypropylene / glass fibres	Pavements, tunnels, crack control
Lightweight Concrete	Density < 1900 kg/m3; lightweight aggregates	Thermal insulation, precast panels
Shotcrete / Gunite	Sprayed pneumatically at high velocity	Tunnels, slopes, structural repairs
Pervious Concrete	High void content; permeable to water	Stormwater management pavements

Admixtures

Type	Function	Example
Plasticizer (Water Reducer)	Increases workability without extra water	Lignosulfonates
Superplasticizer (HRWR)	Water reduction > 20 % at same workability	SNF, PCE-based
Retarder	Delays setting; hot weather / long hauls	Sugar, lignosulfonates
Accelerator	Speeds up setting; cold weather	CaCl2, sodium silicate
Air Entraining Agent	Micro air bubbles; freeze-thaw resistance	Vinsol resin, fatty acids
Pozzolanic (Mineral)	Reacts with Ca(OH)2; refines pore structure	Fly ash, GGBS, silica fume

1. Fineness Test (IS 4031 Parts 1 & 2)

• Purpose: Measure particle surface area; governs rate of hydration and strength gain
• Dry sieving: 100 g cement on 90 μm IS sieve; residue ≤ 10 %
• Blaine Air Permeability: Specific surface ≥ 225 m²/kg for OPC
• Finer cement → faster strength gain; higher heat of hydration; greater thermal cracking risk

2. Standard Consistency Test (IS 4031 Part 4)

• Purpose: Determine % water for standard paste (prerequisite for setting time & soundness tests)
• Apparatus: Vicat apparatus with 10 mm diameter plunger
• Criterion: Plunger penetrates to 5–7 mm from bottom
• Typical value: 26–33 % by mass of cement

3. Setting Time Test (IS 4031 Part 5)

• IST: 1 mm square needle does NOT penetrate to within 5 mm of bottom
• FST: Annular collar needle leaves no impression on surface

Cement Type	IST (min)	FST (min)
OPC (all grades)	≥ 30	≤ 600
Rapid Hardening Cement	≥ 30	≤ 600
Low Heat Cement	≥ 60	≤ 600
High Alumina Cement	≥ 30	≤ 360

4. Soundness Test (IS 4031 Part 3)

• Purpose: Ensure no harmful expansion from free CaO or free MgO after setting
• Le Chatelier Method: Brass split-cylinder mould; expansion ≤ 10 mm after boiling
• Autoclave Test: For periclase (MgO); 2 MPa steam for 3 hrs; expansion ≤ 0.8 %

5. Compressive Strength Test (IS 4031 Part 6)

• 70.6 mm × 70.6 mm mortar cubes; 1 : 3 cement : Ennore standard sand
• Cured in water at 27 °C ± 2 °C; tested at 3, 7 and 28 days
• Loading rate: 35 N/mm²/min; average of 3 cubes reported

Age	OPC 33 (MPa)	OPC 43 (MPa)	OPC 53 (MPa)
3 days	≥ 16	≥ 23	≥ 27
7 days	≥ 22	≥ 33	≥ 37
28 days	≥ 33	≥ 43	≥ 53

6. Heat of Hydration (IS 4031 Part 9)

• Measured using adiabatic calorimeter
• Low heat cement: ≤ 272 kJ/kg at 7 days; ≤ 314 kJ/kg at 28 days
• Excessive heat causes thermal cracking in mass concrete (dams, raft foundations)

Composition of Good Brick Earth

Component	% (approx.)	Role
Silica (SiO2)	50–60 %	Prevents cracking & warping; excess makes bricks brittle
Alumina (Al2O3)	20–30 %	Plasticity for moulding; excess → cracking on drying
Lime (CaO)	< 5 %	Aids binding; excess → efflorescence and swelling
Iron oxide (Fe2O3)	5–6 %	Red colour; excess → dark, over-burned brittle bricks
Magnesia (MgO)	< 1 %	Yellow tint; excess → cracking and unsoundness

Standard Dimensions (IS 1077)

• Modular brick: 190 mm × 90 mm × 90 mm (with mortar joint: 200 × 100 × 100 mm)
• Traditional / non-modular: 230 mm × 115 mm × 75 mm

Classification of Bricks (IS 1077)

Class	Min. Compressive Strength (MPa)	Max. Water Absorption (%)
Class 1 (First class)	10.5	20
Class 2 (Second class)	7.0	22
Class 3 (Third class)	3.5	25

Tests on Bricks (IS 3495)

• Compressive Strength: Average of 5 bricks; range 3.5 – 10.5 MPa
• Water Absorption: (W_soaked − W_dry) / W_dry × 100; max ≤ 20 % (Class 1)
• Efflorescence: Brick half-submerged in distilled water; rated nil / slight / moderate / heavy / serious
• Hardness: No impression left when scratched firmly with fingernail
• Soundness: Two bricks struck together → clear metallic ringing sound
• Shape & Size: 10 bricks stacked; overall dimensions checked

Defects in Bricks

• Efflorescence: White salt patches; soluble salts leached by moisture
• Chuffs: Shape deformation due to rain falling on bricks during burning
• Bloating: Spongy, swollen surface; excess carbon in raw material
• Black core: Carbon not fully burned; insufficient firing temperature
• Over-burning: Vitrified, dark, hard, brittle; warped shape
• Under-burning: Soft, weak, porous; water absorption exceeds permissible limit

Classification of Timber

• Exogenous: Grow outward year by year; visible annual rings (teak, deodar, sal, pine) – used in construction
• Endogenous: Grow inward (bamboo, coconut palm) – light / temporary work only

Internal Structure of Timber

• Pith (Medulla): Central core; oldest, weakest, softest part
• Heartwood: Dark, dense, durable inner rings; no active sap flow; preferred for structural use
• Sapwood: Lighter colour; less durable; young wood actively conducting sap
• Annual rings: One ring = one year; closer rings indicate denser, stronger wood
• Medullary rays: Radial lines from pith to bark; impart cross-grain stiffness
• Cambium layer: Between bark and sapwood; new wood cells formed here annually

Defects in Timber

Defect	Cause	Effect
Knots	Branch bases embedded in trunk	Local stress concentration; difficult machining
Star shake	Radial cracks from pith; wind / frost	Severe strength reduction
Cup shake	Separation along annual ring	Circular crack; reduces cross-section strength
Warping	Unequal shrinkage during drying	Dimensional distortion
Dry rot	Fungi in poorly ventilated damp wood	Wood crumbles to dry powder
Wet rot	Alternate wetting and drying	Soft, dark, mushy texture

Seasoning of Timber

• Target moisture content: ~15 % (interior); ~20 % (exterior)
• Natural (Air) Seasoning: Stacked in open yard; ~1 year per 25 mm thickness
• Artificial (Kiln) Seasoning: Controlled humidity & temperature; most reliable; few weeks
• Water Seasoning: Submerged in running water to leach sap; then air dried
• Chemical Seasoning: Immersed in salt solution (urea) to equalise moisture rapidly

Structural Steel – Grades (IS 1786)

Grade	Yield Strength (MPa)	Use
Mild Steel Fe 250	250	Plain smooth bars; mild exposure zones
TMT Fe 415 (HYSD)	415	Most common RCC reinforcement
TMT Fe 500 (HYSD)	500	High-rise buildings, heavy structures
Fe 550	550	Bridges, heavy load-bearing members

Key Properties of Steel

• E_s = 2 × 10⁵ MPa (200 GPa)
• Coefficient of thermal expansion ≈ 12 × 10⁻⁶ /°C (matches concrete – no differential thermal stress)
• High ductility; excellent weldability (low carbon grades)

Corrosion of Steel Reinforcement

• Carbonation (CO₂) or Cl⁻ ingress destroys passive Fe₂O₃ film → active corrosion begins
• Rust occupies 2–6 × volume of steel → expansive cracking and spalling of cover
• Cover per IS 456: 20 mm (mild), 30 mm (moderate), 45 mm (severe), 50 mm (very severe / extreme)
• Prevention: low w/c, dense concrete, epoxy-coated bars, cathodic protection

Definition

Durability is the ability of concrete to resist weathering, chemical attack, abrasion and other deterioration while retaining its engineering properties over its design life. Per IS 456, governed by: w/c ratio, minimum cement content, cover depth, permeability and curing quality.

Exposure Conditions & Requirements (IS 456:2000 Table 3)

Exposure	Max w/c	Min cement (kg/m3)	Min grade	Min cover (mm)
Mild	0.55	300	M20	20
Moderate	0.50	300	M25	30
Severe	0.45	320	M30	45
Very Severe	0.45	340	M35	50
Extreme	0.40	360	M40	75

(a) Sulphate Attack

• SO₄²⁻ reacts with C₃A → expansive Ettringite → cracking
• MgSO₄ also attacks C–S–H gel; most aggressive sulphate form
• Prevention: SRC (C₃A < 5 %); low w/c; PPC or GGBS; dense concrete

(b) Carbonation

• CO₂ + Ca(OH)₂ → CaCO₃ + H₂O
• pH drops from ~12.5 to < 9 → passive film destroyed → steel corrosion begins
• Carbonation depth ∝ √t (diffusion-controlled)
• Prevention: dense concrete, low w/c, adequate cover, proper curing

(c) Alkali–Silica Reaction (ASR)

• Reactive SiO₂ + alkalis (Na₂O, K₂O) → expansive gel → map cracking
• Prevention: low-alkali cement (Na₂O_eq < 0.6 %), fly ash, GGBS

(d) Chloride Attack

• Cl⁻ ions destroy passive Fe₂O₃ film → pitting corrosion
• Sources: seawater, de-icing salts, CaCl₂ admixture
• Risk threshold: free Cl⁻ > 0.4 % by mass of cement
• Prevention: low w/c, adequate cover, silica fume, epoxy-coated bars

(e) Acid Attack

• Acids dissolve Ca(OH)₂ and C–S–H gel → progressive surface erosion
• In sewers: H₂S → H₂SO₄ (biogenic) → crown corrosion of concrete pipes
• Prevention: acid-resistant coatings or linings; GGBS / silica fume concrete

Physical / Mechanical Deterioration

Type	Mechanism	Prevention
Freeze-Thaw Damage	Water expands ~9 % on freezing → internal pressure → spalling	Air entraining agent; low w/c
Abrasion / Erosion	Traffic or water flow wears surface	Hard aggregates; surface hardeners
Thermal Cracking	Temperature gradient during hydration in mass concrete	Low heat cement; pipe cooling
Plastic Shrinkage	Rapid evaporation from fresh surface before set	Windbreaks; evaporation retarder; early curing
Drying Shrinkage	Moisture loss from hardened concrete → tensile cracks	Low w/c; adequate curing; control joints

Curing of Concrete

• Minimum curing: 7 days (OPC); 10 days (PPC / SRC); 14 days (blended cements)
• Methods: wet hessian / burlap, ponding, sprinkler, curing compounds, steam curing (precast)
• Inadequate curing → reduced strength, increased permeability, surface cracking

Important Numerical Values

Item	Value
Specific gravity of OPC	3.15
Density of structural steel	7850 kg/m3
Es (steel)	2 × 105 MPa (200 GPa)
Ec (concrete, IS 456)	5000 √fck MPa
Flexural strength of concrete	0.7 √fck MPa
Bulk density of cement (loose)	~1440 kg/m3
Normal consistency of OPC	26 – 33 %
Initial setting time (OPC)	≥ 30 min
Final setting time (OPC)	≤ 600 min
Soundness – Le Chatelier	≤ 10 mm
Fineness – Blaine (OPC)	≥ 225 m2/kg
Unit weight – RCC	25 kN/m3
Unit weight – PCC	24 kN/m3
Unit weight – brick masonry	~19 – 20 kN/m3
Aggregate crushing value (pavement)	≤ 30 %
Aggregate impact value (pavement)	≤ 30 %
Fineness modulus – medium sand	2.6 – 2.9
Min. grade for RCC (mild exposure)	M20
Min. curing period (OPC)	7 days
Specific gravity – aggregates	2.6 – 2.8
Thermal expansion coeff. (steel & concrete)	12 × 10−6 /°C

Key Formulae

Mnemonic – Bogue Compounds Decreasing % in OPC

"Some Silly Cats Are Fighting"
C₃S (~50 %) → C₂S (~25 %) → C₄AF (~12 %) → C₃A (~10 %)

Mnemonic – Heat of Hydration (Decreasing Order)

C₃A > C₃S > C₄AF > C₂S
"Three-Aluminate is the Hottest; Two-Silicate is the Coolest."

Mnemonic – Exposure Grade (Steps of 5 MPa)

Mild = M20  |  Moderate = M25  |  Severe = M30  |  Very Severe = M35  |  Extreme = M40
Each step up in exposure adds 5 MPa to the minimum concrete grade.