Building Materials Study Notes – Cement, Concrete, Aggregates | ESE, GATE & SSC JE

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Building Materials — Detailed Study Notes

8 chapters · GATE, ESE (IES), SSC JE, State PSC

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Building materials form the foundation of civil engineering design and construction. This detailed reference condenses cement chemistry, aggregate testing, concrete mix design, bricks, timber & steel and durability mechanisms into one exam-focused revision resource — complementing the dedicated deep-dive chapters on Cement, Concrete and Timber elsewhere in this subject.

Learning Objectives

After studying this chapter you will be able to:

Recall Bogue compound composition, hydration reactions and cement types/grades with their governing IS codes
Classify and test aggregates (ACV, AIV, LAA, flakiness/elongation, sieve analysis) and interpret IS 383 grading zones
Apply Abrams' law, select workability tests, and read IS 456/IS 10262 concrete grade and mix-design tables
Reproduce cement laboratory test procedures (fineness, consistency, setting time, soundness, strength, heat of hydration) with their IS 4031 acceptance limits
Classify bricks by strength/absorption, identify manufacturing defects, and recall IS 1077/IS 3495 dimensions and test limits
Compare timber and structural steel properties, and explain the steel corrosion mechanism and IS 456 cover requirements
Explain the five major durability-attack mechanisms (sulphate, carbonation, ASR, chloride, acid) and their IS 456 defences
Recall the full set of cross-chapter exam formulae, critical numerical values and mnemonics from a single revision chapter

Exam Relevance

ESE★★★★★

GATE★★★★★

SSC JE★★★★★

State PSC★★★★☆

💡 Use this page as a rapid cross-topic revision sheet in the final days before an exam — every formula, IS-code limit and mnemonic from Cement, Concrete, Bricks, Timber/Steel and Durability is collected in Chapter 8.

Concept Map

Cement (Bogue compounds, types, hydration) → Physical requirements (IS 4031)

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Aggregates (classification, tests, grading zones)

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Concrete (w/c ratio, workability, mix grades, admixtures)

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Lab Tests on Cement — fineness, consistency, setting, soundness, strength

Bricks — composition, dimensions, classification, defects

Timber & Steel — structure, defects, seasoning, grades, corrosion

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Durability — sulphate, carbonation, ASR, chloride, acid, physical deterioration

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Revision — all formulae, key values, mnemonics

Where This Fits

Companion pages: for full chapter-length treatments with worked numericals and diagrams, see Cement — Full Notes, Concrete Technology — Full Notes and Timber — Full Notes. This page is the condensed, cross-topic reference — use it for quick lookups and last-minute revision.

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Ch 1 · Cement — Composition, Types & Properties

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Raw Materials

Calcareous materials ($CaCO_{3}$) — limestone, chalk, marl
Argillaceous materials ($SiO_{2}, Al_{2}O_{3}$) — 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
$C_3S$	Tricalcium Silicate	40–50%	Early & ultimate strength (most important)
$C_2S$	Dicalcium Silicate	25–35%	Long-term / later-age strength
$C_3A$	Tricalcium Aluminate	5–12%	Very early strength; flash set; highest heat
$C_4AF$	Tetracalcium Aluminoferrite	8–14%	Grey/brown colour; minor strength; low heat

⚠ $C_3A$ is responsible for sulphate attack. Low-heat cement has reduced $C_3A$ and $C_3S$ content.

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 $C_3S$; early strength; road repairs
Low Heat Cement	IS 12600	High $C_2S$, low $C_3A$; mass concrete, dams
Sulphate Resistant Cement (SRC)	IS 12330	$C_3A < 5\%$; 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 $C_4AF$; 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 ($m^2$/kg)	≥ 225	≥ 225	≥ 225

Hydration Reactions

$C_3S + H_2O \to$ C–S–H gel (primary binding phase) + $Ca(OH)_2$
$C_2S + H_2O \to$ C–S–H gel + smaller amount of $Ca(OH)_2$
$C_3A$ + gypsum $\to$ Ettringite (prevents flash set)
Heat of hydration order: $C_3A > C_3S > C_4AF > C_2S$

💡 Flash set = rapid stiffening without heat (cannot be remixed). False set = rapid stiffening with heat (can be remixed).

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

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Ch 1 · Key Reference Values

Bogue Compound Proportions (OPC)

$$ C_3S{:}40\text{–}50\%,\;C_2S{:}25\text{–}35\%,\;C_3A{:}5\text{–}12\%,\;C_4AF{:}8\text{–}14\% $$

$C_3S$ governs early strength; $C_2S$ governs long-term strength

Heat of Hydration Order

$$ C_3A > C_3S > C_4AF > C_2S $$

Decreasing order of heat released during hydration

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Clinkering Temperature

$$ T \approx 1450^\circ C $$

Gypsum (3–5%) added afterward to control setting time

°C

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Ch 1 · Applied Scenario

Common ESE descriptive style

A dam's mass-concrete pour is at risk of thermal cracking from hydration heat, and separately, its foundation sits in sulphate-rich groundwater. Which single cement property should be minimised to address BOTH risks simultaneously, and which cement type achieves this?

Approach hint

Check which Bogue compound is both the highest heat-generator AND the one responsible for sulphate attack.

$C_3A$ generates the most heat of hydration of all four compounds
$C_3A$ is also the compound that reacts with sulphates to form expansive ettringite
Minimising $C_3A$ content addresses both the thermal-cracking risk and the sulphate-attack risk together
Sulphate Resistant Cement (SRC, IS 12330) specifically caps $C_3A < 5\%$

✓ Minimise $C_3A$; Sulphate Resistant Cement (SRC) is the correct choice, addressing both the heat and sulphate concerns with one specification

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Ch 1 · Diagrams

Click any diagram to zoom

Fig 1 – (a) Typical proportion of the four Bogue compounds in OPC; (b) Relative heat of hydration order — C3A releases the most heat (and is the compound responsible for sulphate attack), while C2S releases the least.

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Ch 1 · Quick Quiz

3 questions · tap an option to reveal answer

Question 1

Which Bogue compound is primarily responsible for the EARLY strength of OPC?

$C_3S$ (tricalcium silicate, 40–50% of OPC) hydrates fastest among the silicates and governs early and ultimate strength ✓

Question 2

Sulphate Resistant Cement (IS 12330) achieves its resistance mainly by limiting which compound?

$C_3A$ reacts with sulphates to form expansive ettringite; SRC caps $C_3A < 5\%$ to resist this attack ✓

Question 3

"Flash set" in cement is best described as:

Flash set is rapid, irreversible stiffening without significant heat (unlike false set, which occurs with heat and can be remixed by further mixing) ✓

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Ch 2 · Aggregates — Types, Properties & Tests

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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	$Na_2SO_4/MgSO_4$ solution cycles	≤ 10–12% loss
Sieve Analysis	Particle size distribution	IS sieves + mechanical shaker; FM calculated	As per IS 383 zones

⚠ Mica reduces bond strength and raises water demand. Organic impurities retard setting of cement and reduce early strength.

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

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Ch 2 · Formulas

Fineness Modulus

$$ FM = \frac{\Sigma(\text{cumulative \% retained on IS sieves})}{100} $$

Fine sand 2.2–2.6, medium 2.6–2.9, coarse 2.9–3.2

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Aggregate Crushing Value

$$ ACV\% = \frac{B}{A} \times 100 $$

B = fines passing after crushing; A = original mass

Water Absorption

$$ WA\% = \frac{W_2 - W_1}{W_1} \times 100 $$

$W_1$ = oven-dry mass, $W_2$ = saturated surface-dry mass

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Ch 2 · Solved Example

GATE CE / ESE level

A 500 g sample of coarse aggregate is tested for ACV. After crushing and sieving, 145 g passes through the specified sieve as fines. Compute the ACV and state whether it is acceptable for a road pavement wearing course.

Approach hint

Apply $ACV\% = (B/A)\times100$ and compare against the pavement limit of ≤ 30%.

$ACV\% = (145/500)\times100 = 29\%$
Pavement acceptance limit is ≤ 30%

✓ ACV = 29%, which is just within the ≤ 30% pavement limit — acceptable, though with little margin

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Ch 2 · Quick Quiz

3 questions · tap an option to reveal answer

Question 1

Which IS 383 grading zone of fine aggregate is recommended as the best general-purpose choice for concrete?

Zone II (medium coarse) is recommended as the best general-purpose grading for most concrete ✓

Question 2

An aggregate particle is classed as "flaky" when its least dimension is:

Flakiness is defined by thickness less than 0.6 × the mean sieve size; elongation is defined by length greater than 1.8 × the mean size ✓

Question 3

The presence of mica in fine aggregate primarily:

Mica's platy, smooth surface reduces the cement-aggregate bond and raises water demand, both harmful to concrete quality ✓

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Ch 3 · Concrete — Mix Design, Properties & Types

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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	$f_{ck}$ (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

⚠ As per IS 456:2000, minimum grade for RCC is M20 (mild exposure) and M25 (moderate exposure).

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/$m^3$; 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	$CaCl_2$, 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

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Ch 3 · Formulas

Water-Cement Ratio

$$ w/c = \frac{\text{Weight of water}}{\text{Weight of cement}} $$

Practical range 0.40–0.60; theoretical minimum ≈ 0.23

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Target Mean Strength

$$ f'_m = f_{ck} + 1.65 \times \sigma $$

σ = standard deviation, per IS 10262 Table 1

MPa

Modulus of Elasticity

$$ E_c = 5000\sqrt{f_{ck}} $$

IS 456; $f_{ck}$ in MPa

MPa

Flexural Strength (Modulus of Rupture)

$$ f_r = 0.7\sqrt{f_{ck}} $$

IS 456; $f_{ck}$ in MPa

MPa

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Ch 3 · Solved Example

GATE CE / ESE level

For M25 concrete with standard deviation σ = 4.0 MPa, find (a) the target mean strength, and (b) the modulus of elasticity $E_c$.

Approach hint

Apply $f'_m = f_{ck}+1.65\sigma$ and $E_c = 5000\sqrt{f_{ck}}$ with $f_{ck}=25$.

$f'_m = 25 + 1.65(4.0) = 25 + 6.6 = 31.6$ MPa
$E_c = 5000\sqrt{25} = 5000 \times 5 = 25{,}000$ MPa

✓ Target mean strength ≈ 31.6 MPa; $E_c = 25{,}000$ MPa (25 GPa)

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Ch 3 · Diagrams

Click any diagram to zoom

Fig 2 – Water-cement ratio vs compressive strength (Abrams' Law): strength falls steeply as w/c ratio increases. Theoretical minimum w/c for complete hydration ≈ 0.23; practical structural range is 0.40–0.60.

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Ch 3 · Quick Quiz

3 questions · tap an option to reveal answer

Question 1

Abrams' Law states that concrete compressive strength is:

Abrams' Law: strength decreases as the w/c ratio increases — an inverse relationship ✓

Question 2

Per IS 456:2000, the minimum concrete grade permitted for RCC under mild exposure is:

M20 is the minimum grade for RCC under mild exposure; moderate exposure requires at least M25 ✓

Question 3

A superplasticizer (HRWR) is defined by a water reduction of at least:

Superplasticizers (high-range water reducers) achieve > 20% water reduction at equal workability, versus a smaller reduction for ordinary plasticizers ✓

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Ch 4 · Important Laboratory Tests on Cement

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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 $m^2$/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/$mm^2$/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)

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Ch 4 · Key Reference Values

Fineness (Dry Sieving)

$$ \text{Residue on 90}\mu\text{m} \leq 10\% $$

100 g sample; Blaine specific surface ≥ 225 m²/kg for OPC

Compressive Strength Loading Rate

$$ 35\ \text{N/mm}^2\text{/min} $$

70.6 mm mortar cubes, 1:3 cement:Ennore sand, average of 3 cubes

N/mm²/min

Low Heat Cement Limit

$$ \leq 272\ \text{kJ/kg (7 d)},\; \leq 314\ \text{kJ/kg (28 d)} $$

Measured by adiabatic calorimeter, IS 4031 Part 9

kJ/kg

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Ch 4 · Applied Scenario

Common SSC JE / ESE style

A lab technician performs the standard consistency test before running setting-time and soundness tests. Why must consistency be determined first, and what is the acceptance criterion for the plunger penetration?

Approach hint

Think about what "standard paste" means and why setting time/soundness need a fixed, repeatable water content.

Setting time and soundness tests are sensitive to the water content of the paste — too much or too little water changes the result independent of the cement's actual properties
The standard consistency test finds the exact % water (typically 26–33%) that produces a paste of standardised stiffness
Using this fixed consistency for all subsequent tests ensures results are comparable across cement samples and batches
Acceptance: Vicat plunger penetrates to 5–7 mm from the bottom of the mould

✓ Standard consistency must be found first because setting-time and soundness results depend on paste water content; the criterion is 5–7 mm plunger penetration from the bottom

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Ch 4 · Quick Quiz

3 questions · tap an option to reveal answer

Question 1

The Le Chatelier soundness test limits expansion (after boiling) to:

Le Chatelier expansion must not exceed 10 mm; the separate autoclave test (for MgO/periclase) limits expansion to ≤ 0.8% ✓

Question 2

Compressive strength testing of cement uses mortar cubes made with cement and:

IS 4031 Part 6 specifies 70.6 mm mortar cubes made at a 1:3 cement:Ennore standard sand ratio ✓

Question 3

Which cement type is REQUIRED to have the longest minimum initial setting time?

Low Heat Cement requires IST ≥ 60 minutes, longer than the ≥ 30 minutes required for OPC, RHC and HAC ✓

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Ch 5 · Bricks — Composition, Properties & Tests

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Composition of Good Brick Earth

Component	% (approx.)	Role
Silica ($SiO_2$)	50–60%	Prevents cracking & warping; excess makes bricks brittle
Alumina ($Al_2O_3$)	20–30%	Plasticity for moulding; excess → cracking on drying
Lime (CaO)	< 5%	Aids binding; excess → efflorescence and swelling
Iron oxide ($Fe_2O_3$)	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: $(W_{soaked} - W_{dry})/W_{dry} \times 100$; 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

Ceramic Products

Ceramics are inorganic, non-metallic materials made by firing clay and other minerals at high temperature — bricks are the archetypal structural ceramic, but the family extends to a range of finishing and specialist products:

Product	Nature	Typical use
Earthenware	Porous, low-fired, glazed for water resistance	Drain pipes, tiles, pottery
Stoneware	Dense, vitrified, high-fired; strong & hard	Sewer pipes, floor tiles
Porcelain / Vitreous china	Fully vitrified, non-porous, white	Sanitary ware, electrical insulators
Glazed & vitrified tiles	Ceramic body with a fused glassy surface	Wall & floor finishes
Refractories (fire-clay)	High alumina/silica; withstand very high temperature	Furnace & kiln linings

Key properties valued in ceramics are hardness, chemical inertness, low water absorption (for vitrified products) and heat resistance — at the cost of brittleness and low tensile strength.

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Ch 5 · Formulas

Water Absorption

$$ WA\% = \frac{W_{soaked} - W_{dry}}{W_{dry}} \times 100 $$

Max ≤ 20% for Class 1 bricks (24-hour cold-water immersion)

Modular Brick Size (with joint)

$$ 200 \times 100 \times 100\ \text{mm} $$

Nominal brick 190×90×90 mm + 10 mm mortar joint

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Ch 5 · Solved Example

GATE CE / ESE level

A brick weighs 3.20 kg dry and 3.68 kg after 24-hour immersion in cold water. Compute the water absorption and classify the brick per IS 1077.

Approach hint

Apply $WA\% = (W_{soaked}-W_{dry})/W_{dry}\times100$, then compare against the Class 1/2/3 limits.

$WA\% = (3.68-3.20)/3.20 \times 100 = 15\%$
Class 1 limit is ≤ 20% water absorption, with minimum strength 10.5 MPa

✓ Water absorption = 15% — within the Class 1 limit (≤ 20%), provided the compressive strength also meets 10.5 MPa

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Ch 5 · Diagrams

Click any diagram to zoom

Fig 3 – (a) Modular brick: 190×90×90 mm nominal, 200×100×100 mm with a 10 mm mortar joint. (b) Traditional (non-modular) brick: 230×115×75 mm. Classification limits per IS 1077 shown at right.

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Ch 5 · Quick Quiz

3 questions · tap an option to reveal answer

Question 1

The nominal modular brick size per IS 1077 is:

190×90×90 mm is the nominal modular brick size; adding a 10 mm mortar joint gives the modular co-ordinating size of 200×100×100 mm ✓

Question 2

Excess lime (CaO) in brick earth primarily causes:

Excess lime causes efflorescence (soluble salt migration) and can cause unsoundness/swelling as unslaked lime particles hydrate and expand ✓

Question 3

A "black core" defect in a fired brick indicates:

Black core results from incomplete combustion of carbon at the centre of the brick when firing temperature or duration is insufficient ✓

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Ch 6 · Timber & Steel — Properties & Uses

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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

💡 For a full chapter-length treatment of timber (structure, classification, felling, conversion, seasoning, defects, preservation, mechanical properties, engineered wood products), see Timber — Full Notes.

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

$E_s = 2 \times 10^5$ MPa (200 GPa)
Coefficient of thermal expansion ≈ $12 \times 10^{-6}$/°C (matches concrete — no differential thermal stress)
High ductility; excellent weldability (low carbon grades)

Corrosion of Steel Reinforcement

Carbonation ($CO_2$) or $Cl^-$ ingress destroys passive $Fe_2O_3$ 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

🪵

Ch 6 · Key Reference Values

Modulus of Elasticity of Steel

$$ E_s = 2 \times 10^5\ \text{MPa} $$

200 GPa; roughly 8× the modulus of concrete for M25

MPa

Rust Expansion Factor

$$ V_{rust} \approx 2\text{–}6 \times V_{steel} $$

Volume increase causes expansive cracking and spalling of concrete cover

—

IS 456 Cover by Exposure

$$ 20\text{–}30\text{–}45\text{–}50\ \text{mm} $$

Mild – Moderate – Severe – Very Severe/Extreme

🪵

Ch 6 · Applied Scenario

Common ESE descriptive style

A coastal RCC column shows surface cracking and spalling of concrete cover, with no visible external impact damage. Explain the most likely mechanism, tracing it from cause to visible effect.

Approach hint

Coastal exposure is the key clue — think about which aggressive ion is most associated with marine environments.

Coastal exposure exposes the column to airborne/splash chloride ($Cl^-$) ions
Chloride ions penetrate the concrete cover and destroy the passive $Fe_2O_3$ protective film on the reinforcing steel
Once depassivated, the steel corrodes; rust occupies 2–6× the volume of the original steel
This volumetric expansion generates internal tensile stress in the surrounding concrete, causing cracking and eventual spalling of the cover — with no external impact needed

✓ Chloride-induced reinforcement corrosion: $Cl^-$ ingress → passive film breakdown → rust volume expansion → cover cracking/spalling

🪵

Ch 6 · Diagrams

Click any diagram to zoom

Fig 4 – (a) Steel corrosion mechanism: chloride/carbonation attack destroys the passive oxide film; rust forms at 2–6× the volume of the original steel, cracking and spalling the concrete cover. (b) IS 456 nominal cover requirements rise with exposure severity, from 20 mm (mild) to 75 mm (extreme).

🪵

Ch 6 · Quick Quiz

3 questions · tap an option to reveal answer

Question 1

Rusted steel occupies approximately how many times the volume of the original unrusted steel?

Rust occupies 2–6× the volume of the original steel, generating the expansive stress that cracks and spalls the concrete cover ✓

Question 2

Per IS 456, the nominal cover required for "Severe" exposure is:

Severe exposure requires 45 mm nominal cover (Mild=20, Moderate=30, Very Severe=50, Extreme=75) ✓

Question 3

The most commonly used steel grade for RCC reinforcement in India is:

TMT Fe 415 (HYSD) bars are the most widely used reinforcement grade for general RCC construction in India ✓

🛡

Ch 7 · Durability of Concrete & Building Materials

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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/$m^3$)	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

$SO_4^{2-}$ reacts with $C_3A$ → expansive Ettringite → cracking
$MgSO_4$ also attacks C–S–H gel; most aggressive sulphate form
Prevention: SRC ($C_3A < 5\%$); low w/c; PPC or GGBS; dense concrete

(b) Carbonation

$CO_2 + Ca(OH)_2 \to CaCO_3 + H_2O$
pH drops from ~12.5 to < 9 → passive film destroyed → steel corrosion begins
Carbonation depth $\propto \sqrt{t}$ (diffusion-controlled)
Prevention: dense concrete, low w/c, adequate cover, proper curing

(c) Alkali–Silica Reaction (ASR)

Reactive $SiO_2$ + alkalis ($Na_2O, K_2O$) → expansive gel → map cracking
Prevention: low-alkali cement ($Na_2O_{eq} < 0.6\%$), fly ash, GGBS

(d) Chloride Attack

$Cl^-$ ions destroy passive $Fe_2O_3$ film → pitting corrosion
Sources: seawater, de-icing salts, $CaCl_2$ 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: $H_2S \to H_2SO_4$ (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

🛡

Ch 7 · Formulas

Carbonation Depth

$$ d \propto \sqrt{t} $$

Diffusion-controlled; t = exposure time

Chloride Corrosion Threshold

$$ Cl^- > 0.4\%\text{ by mass of cement} $$

Free chloride content above which corrosion risk becomes significant

Freeze Expansion of Water

$$ \Delta V \approx 9\% $$

Volume increase on freezing drives freeze-thaw spalling

🛡

Ch 7 · Applied Scenario

Common ESE descriptive style

A concrete sewer pipe develops progressive surface erosion at its crown (top inner surface) even though it carries no abrasive solids. What chemical mechanism is most likely responsible, and how does it operate?

Approach hint

Think about what gas accumulates above the flow line in sewers and what it converts into on the moist pipe crown.

Sewers generate $H_2S$ gas from anaerobic decomposition of organic matter in the wastewater
$H_2S$ rises and accumulates in the air space above the flow line, condensing as moisture on the crown
Bacteria on the moist crown oxidise $H_2S$ to biogenic $H_2SO_4$ (sulphuric acid)
This acid dissolves $Ca(OH)_2$ and C–S–H gel, progressively eroding the crown — a form of acid attack, not mechanical abrasion

✓ Biogenic sulphuric acid attack: $H_2S \to H_2SO_4$ at the crown, dissolving the cement paste — commonly called "crown corrosion"

🛡

Ch 7 · Diagrams

Click any diagram to zoom

Fig 5 – The five major durability-attack mechanisms on concrete: Sulphate, Carbonation, ASR, Chloride and Acid attack, with their chemistry and IS 456 defences. All five are ultimately slowed by the same core defence: low permeability (low w/c) plus adequate cover and curing.

🛡

Ch 7 · Quick Quiz

3 questions · tap an option to reveal answer

Question 1

Carbonation reduces the pore-water pH of concrete from about 12.5 down to:

Carbonation drops pH below about 9, at which point the passive oxide film on steel is no longer stable and corrosion can begin ✓

Question 2

Per IS 456:2000 Table 3, which exposure condition requires the maximum permitted w/c ratio to be limited to 0.40?

Extreme exposure has the tightest w/c limit (0.40) and highest minimum grade (M40) and cover (75 mm) among the five exposure classes ✓

Question 3

Alkali-Silica Reaction (ASR) requires three conditions together: reactive silica, moisture, and:

ASR needs reactive silica aggregate, moisture, AND sufficient alkalis from cement (or environment) to form the expansive gel ✓

📚

Ch 8 · Quick Revision — Key Values, Formulae & Mnemonics

Cross-topic recall sheet, mini quiz and practice questions

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Important Numerical Values

Item	Value
Specific gravity of OPC	3.15
Density of structural steel	7850 kg/$m^3$
$E_s$ (steel)	$2 \times 10^5$ MPa (200 GPa)
$E_c$ (concrete, IS 456)	$5000\sqrt{f_{ck}}$ MPa
Flexural strength of concrete	$0.7\sqrt{f_{ck}}$ MPa
Bulk density of cement (loose)	~1440 kg/$m^3$
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 $m^2$/kg
Unit weight – RCC	25 kN/$m^3$
Unit weight – PCC	24 kN/$m^3$
Unit weight – brick masonry	~19–20 kN/$m^3$
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)	$12 \times 10^{-6}$/°C

Key Formulae

Fineness Modulus

$$ FM = \frac{\Sigma(\text{cumulative \% retained on IS sieves})}{100} $$

—

Target Mean Strength

$$ f'_m = f_{ck} + 1.65 \times \sigma $$

—

MPa

Modulus of Elasticity (Concrete)

$$ E_c = 5000 \times \sqrt{f_{ck}} $$

IS 456

MPa

Modulus of Rupture

$$ f_r = 0.7 \times \sqrt{f_{ck}} $$

—

MPa

Aggregate Crushing Value

$$ ACV\% = \frac{B}{A} \times 100 $$

B = fines after crushing; A = original mass

Water Absorption

$$ WA\% = \frac{W_2 - W_1}{W_1} \times 100 $$

—

Carbonation Depth

$$ d \propto \sqrt{t} $$

t = exposure time in years

—

Mnemonic – Bogue Compounds Decreasing % in OPC

💡 "Some Silly Cats Are Fighting"
$C_3$S (~50%) → $C_2$S (~25%) → $C_4$AF (~12%) → $C_3$A (~10%)

Mnemonic – Heat of Hydration (Decreasing Order)

💡 $C_3A > C_3S > C_4AF > C_2S$
"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.

Mini Quiz

For M20 concrete, what is $E_c$ per IS 456?

$E_c = 5000\sqrt{20} = 5000 \times 4.472 \approx 22{,}360$ MPa ✓

Which Bogue compound has the SMALLEST typical proportion in OPC?

Per the "Some Silly Cats Are Fighting" order (C3S ~50% → C2S ~25% → C4AF ~12% → C3A ~10%), $C_3A$ has the smallest typical share ✓

What is the minimum curing period for OPC concrete per standard practice?

OPC concrete requires a minimum of 7 days curing; PPC/SRC need 10 days and blended cements up to 14 days ✓

The unit weight typically assumed for RCC in design is:

RCC = 25 kN/m³ (PCC = 24 kN/m³; the extra 1 kN/m³ accounts for the embedded reinforcement) ✓

Per IS 456 Table 3, the minimum cement content required for "Very Severe" exposure is:

Very Severe exposure requires ≥ 340 kg/m³ (Mild/Moderate = 300, Severe = 320, Extreme = 360) ✓

Practice Questions

EasyState the target mean strength formula and compute it for M30 concrete with σ = 5.0 MPa.

$f'_m = f_{ck}+1.65\sigma = 30 + 1.65(5.0) = 38.25$ MPa.

EasyWhy does Sulphate Resistant Cement specifically limit $C_3A$ content rather than any other Bogue compound?

Sulphates react specifically with $C_3A$ (not the other compounds) to form expansive ettringite, which cracks hardened concrete — limiting $C_3A$ to below 5% removes the reactive pathway for this specific attack.

MediumA precast yard needs to cast, cure and de-mould identical column segments as fast as possible without compromising the required 28-day strength. Which cement type and curing method would you recommend, and why?

Rapid Hardening Cement (high $C_3S$, IS 8041) combined with steam curing: RHC gains strength quickly at early ages, and steam curing further accelerates hydration without harming later strength, allowing faster mould turnaround while still meeting the 28-day design strength.

MediumA 400 g coarse aggregate sample gives an AIV test result of 96 g of fines passing the specified sieve after impact. Is this aggregate suitable for a pavement wearing course?

AIV% = 96/400 × 100 = 24%. The pavement limit is ≤ 30%, so this aggregate is suitable (comfortably within limit).

HardExplain why lowering the w/c ratio is the single defence that appears against nearly every durability-attack mechanism (sulphate, carbonation, ASR, chloride, acid), tracing the shared underlying reason.

All five attack mechanisms require an aggressive species (SO4²⁻, CO2, alkalis, Cl⁻, or acid) to first penetrate the concrete's pore network and reach either the cement paste or the embedded steel. A lower w/c ratio leaves less unreacted (capillary) water after hydration, producing a denser paste with a finer, more discontinuous pore structure. This directly slows the diffusion/permeation rate of every aggressive species, regardless of its specific chemistry — which is why low w/c is the universal first line of defence across all five mechanisms, even though each operates by a different chemical reaction once it reaches its target.

Compound	Full Name	% in OPC	Role
\(C_3S\)	Tricalcium Silicate	40–50%	Early & ultimate strength (most important)
\(C_2S\)	Dicalcium Silicate	25–35%	Long-term / later-age strength
\(C_3A\)	Tricalcium Aluminate	5–12%	Very early strength; flash set; highest heat
\(C_4AF\)	Tetracalcium Aluminoferrite	8–14%	Grey/brown colour; minor strength; low heat

Component	% (approx.)	Role
Silica (\(SiO_2\))	50–60%	Prevents cracking & warping; excess makes bricks brittle
Alumina (\(Al_2O_3\))	20–30%	Plasticity for moulding; excess → cracking on drying
Lime (CaO)	< 5%	Aids binding; excess → efflorescence and swelling
Iron oxide (\(Fe_2O_3\))	5–6%	Red colour; excess → dark, over-burned brittle bricks
Magnesia (MgO)	< 1%	Yellow tint; excess → cracking and unsoundness

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Learning Objectives

Exam Relevance

Concept Map

Where This Fits

Raw Materials

Bogue's Compounds — Major Compounds in OPC

Types of Cement (IS Classification)

Physical Requirements of OPC (IS 4031)

Hydration Reactions

Storage of Cement

Classification of Aggregates

Requirements of Good Aggregate

Fineness Modulus (FM)

Standard Tests on Aggregates (IS 2386)

Grading Zones of Fine Aggregate (IS 383)

Ingredients of Concrete

Water-Cement (w/c) Ratio

Workability Tests

Slump Values for Different Structural Members

Concrete Mix Grades (IS 456 & IS 10262)

Strength Formulae

Special Types of Concrete

Admixtures

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

2. Standard Consistency Test (IS 4031 Part 4)

3. Setting Time Test (IS 4031 Part 5)

4. Soundness Test (IS 4031 Part 3)

5. Compressive Strength Test (IS 4031 Part 6)

6. Heat of Hydration (IS 4031 Part 9)

Composition of Good Brick Earth

Standard Dimensions (IS 1077)

Classification of Bricks (IS 1077)

Tests on Bricks (IS 3495)

Defects in Bricks

Ceramic Products

Classification of Timber

Internal Structure of Timber

Defects in Timber

Seasoning of Timber

Structural Steel – Grades (IS 1786)

Key Properties of Steel

Corrosion of Steel Reinforcement

Definition

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

(a) Sulphate Attack

(b) Carbonation

(c) Alkali–Silica Reaction (ASR)

(d) Chloride Attack

(e) Acid Attack

Physical / Mechanical Deterioration

Curing of Concrete

Important Numerical Values

Key Formulae

Mnemonic – Bogue Compounds Decreasing % in OPC

Mnemonic – Heat of Hydration (Decreasing Order)

Mnemonic – Exposure Grade (Steps of 5 MPa)

Mini Quiz

Practice Questions

Related Topics & Continue Learning