Cement – Complete Chapter-wise Study Notes

Cement is the most critical topic in Building Materials for GATE Civil, ESE (IES) and SSC JE. This page covers every chapter — from raw materials and manufacturing through to hydration chemistry, Bogue's compounds, physical & chemical tests, all types of special cements, IS codes, admixtures and exam-focused numerical values.

GATE ESE / IES SSC JE State PSC RRB JE

Ch 1 · Raw Materials Ch 2 · Manufacture Ch 3 · Chemical Composition Ch 4 · Hydration Ch 5 · Physical Properties & Tests Ch 6 · Chemical Properties Ch 7 · Types of Cement Ch 8 · Special Cements Ch 9 · Admixtures Ch 10 · IS Codes & Quick Revision

1Raw Materials of Cement ►

Two Principal Groups

Group	Chemical Nature	Sources	Provides
Calcareous materials	CaCO₃-rich	Limestone, chalk, marl, calcareous shale, sea shells	CaO (lime) — 60–67 % of cement
Argillaceous materials	SiO₂, Al₂O₃, Fe₂O₃-rich	Clay, shale, laterite, blast furnace slag	Silica, alumina, iron oxide

Approximate Oxide Composition of OPC

Oxide	Symbol	% Range	Effect if Excess
Lime	CaO	60–67 %	Unsoundness (free CaO), expansion
Silica	SiO₂	17–25 %	Slow-setting, weak early strength
Alumina	Al₂O₃	3–8 %	Quick setting, low durability
Iron oxide	Fe₂O₃	0.5–6 %	Dark colour; flux during burning
Magnesia	MgO	< 4 %	Delayed unsoundness (periclase)
Sulphur trioxide	SO₃	< 2.5 %	Expansion, sulphate attack
Alkalis	Na₂O + K₂O	< 1 %	Alkali–silica reaction (ASR)
Loss on Ignition	LOI	< 4 %	Indicates pre-hydration / adulteration

⚠ Free lime (f-CaO) and free magnesia (periclase, f-MgO) are the main causes of unsoundness — they expand after setting and cause cracking. Detected by Le Chatelier test (CaO) and Autoclave test (MgO).

Lime Saturation Factor (LSF)

LSF = CaO / (2.8 SiO₂ + 1.2 Al₂O₃ + 0.65 Fe₂O₃)
Ideal range: 0.66 – 1.02 (IS 269 limits: 0.80 – 1.02)

LSF > 1.02 → excess free CaO → unsoundness
LSF < 0.66 → insufficient clinker formation → weak cement

Silica Modulus (SM) / Silica Ratio

SM = SiO₂ / (Al₂O₃ + Fe₂O₃)
Typical value: 1.7 – 4.0

High SM → hard to burn, slow setting
Low SM → easy to burn, but poor strength

Alumina Modulus (AM) / Iron Ratio

AM = Al₂O₃ / Fe₂O₃
Typical value: 1 – 4 (for white cement: > 10)

AM > 0.637 → C₃A forms (normal cement)
AM < 0.637 → no C₃A; C₄AF dominates (sulphate resistant cement)

💡 GATE/ESE Tip: LSF, SM and AM are the three moduli used in raw mix design. Questions on these moduli appear regularly in GATE as numerical-answer-type (NAT) problems.

2Manufacture of Portland Cement ►

Two Main Processes

Feature	Dry Process	Wet Process
Raw material moisture	Low (< 1 %)	High (30–40 %)
Grinding	Dry grinding in ball mills	Wet grinding; slurry formed
Raw mix form	Dry powder (raw meal)	Slurry (33–40 % water)
Kiln length	Shorter (50–90 m)	Longer (150–200 m)
Heat consumption	Lower (3.5 GJ/t)	Higher (5.0–6.0 GJ/t)
Capital cost	Higher (pre-heater)	Lower initial cost
Product homogeneity	Lower (requires blending)	Better (slurry mixing)
Current use	Predominant worldwide	Declining; used where raw materials are wet

Steps in Dry Process (Modern)

Quarrying & crushing: Limestone and clay crushed to <25 mm
Pre-blending & storage: Stacker-reclaimer beds
Proportioning & grinding (Raw Mill): Ball mill or vertical roller mill; raw meal to ~90 µm
Blending silos: Homogenisation of raw meal
Pre-heater tower (cyclones): 4–6 stage; heat exchange raises meal to ~800 °C
Pre-calciner: 60–95 % decarbonation; CaCO₃ → CaO + CO₂
Rotary kiln (burning zone): Peak temperature ~1450 °C; clinker formation
Clinker cooler: Rapid cooling to <100 °C (grate cooler)
Cement grinding (Finish Mill): Clinker + gypsum (3–5 %) + any additions; ground to fineness
Storage & dispatch: Silos then bags or bulk tankers

Reactions in the Rotary Kiln (Temperature Zones)

Temperature (°C)	Zone	Reaction
100 – 300	Drying	Evaporation of free moisture
300 – 600	Pre-heating	Removal of absorbed water; clay dehydration
600 – 900	Calcination	CaCO₃ → CaO + CO₂ (calcination, endothermic)
900 – 1200	Solid-state reaction	C₂S formation; beginnings of C₃A & C₄AF
1250 – 1280	Exothermic	Liquid phase appears; rapid formation of C₃S from C₂S + CaO
1350 – 1450	Burning / Clinkering	C₃S fully formed; peak clinker temperature; nodule formation
Cooling	Clinker cooling	Rapid cooling preserves C₃S; slow cooling causes C₃S → C₂S + free CaO (belite reversion)

⚠ Slow cooling of clinker causes C₃S to revert to C₂S + free CaO → reduced strength and unsoundness. Therefore rapid cooling is essential.

Clinker Composition

Clinker nodules: 3–25 mm diameter; dark grey
Free lime content in clinker must be < 1.5 %
Gypsum addition: controls setting time by reacting with C₃A to form Ettringite
Over-addition of gypsum: > 3.5 % SO₃ in cement causes false set and expansion

💡 GATE Tip: The temperature 1450 °C (clinkering), 900 °C (calcination) and the reaction CaCO₃ → CaO + CO₂ are frequently tested in MCQ format.

3Chemical Composition & Bogue's Compounds ►

Bogue's Compounds – Complete Table

Compound	Abbreviation	Full Chemical Name	Formula	% in OPC
Alite	C₃S	Tricalcium Silicate	3CaO·SiO₂	40–50 %
Belite	C₂S	Dicalcium Silicate	2CaO·SiO₂	25–35 %
Celite (aluminate phase)	C₃A	Tricalcium Aluminate	3CaO·Al₂O₃	5–12 %
Ferrite phase	C₄AF	Tetracalcium Aluminoferrite	4CaO·Al₂O₃·Fe₂O₃	8–14 %

Bogue Calculation Formulae (from oxide analysis)

C₃S = 4.071 CaO − 7.600 SiO₂ − 6.718 Al₂O₃ − 1.430 Fe₂O₃ − 2.852 SO₃
C₂S = 2.867 SiO₂ − 0.7544 C₃S
C₃A = 2.650 Al₂O₃ − 1.692 Fe₂O₃
C₄AF = 3.043 Fe₂O₃

⚠ GATE PYQ format: Given oxide % → find Bogue compound %. These are direct substitution problems. Always use the Bogue formulae in the order C₃S → C₂S → C₃A → C₄AF.

Properties of Each Compound – Comparison

Property	C₃S	C₂S	C₃A	C₄AF
Rate of hydration	Moderate–fast	Slow	Very fast	Moderate
Early strength (1–7 days)	High	Low	Very high (minor)	Low
Long-term strength (28 d+)	High	High	Low	Low
Heat of hydration (J/g)	~502	~260	~867	~419
Resistance to sulphate	Moderate	High	Very low	Moderate–high
Colour contribution	None (white)	None (white)	None (white)	Grey/brown
Role of gypsum	Delays set slightly	Minor	Critical (prevents flash set)	Minor

Strength Development (% of 28-day strength)

Age	C₃S	C₂S	C₃A	C₄AF
1 day	~46 %	~6 %	~53 %	~30 %
7 days	~72 %	~20 %	~92 %	~60 %
28 days	100 %	100 %	100 %	100 %
1 year	~110 %	~160 %	~105 %	~106 %

💡 C₂S continues gaining strength for years beyond 28 days — 1-year strength can be 160 % of 28-day strength. This is exploited in Low Heat and Portland Pozzolana Cements.

Heat of Hydration (HOH) Order

C₃A (867 J/g) > C₃S (502 J/g) > C₄AF (419 J/g) > C₂S (260 J/g)

Total HOH of OPC at 28 days ≈ 375–525 J/g
Low Heat cement target: ≤ 272 kJ/kg at 7 days; ≤ 314 kJ/kg at 28 days

Cement Notation (Abbreviated Oxide Notation)

Oxide	Full formula	Notation
Calcium oxide (lime)	CaO	C
Silicon dioxide (silica)	SiO₂	S
Aluminium oxide (alumina)	Al₂O₃	A
Iron oxide	Fe₂O₃	F
Water	H₂O	H
Sulphur trioxide	SO₃	S̅

4Hydration of Cement ►

Definition & Mechanism

Hydration is the chemical reaction between cement compounds and water that produces binding products (C–S–H gel) and causes setting and hardening. The process involves both dissolution (ions dissolve from clinker surface) and precipitation (products crystallise from solution).

Hydration Reactions (Complete)

Compound	Hydration Reaction	Products
C₃S (Alite)	2C₃S + 6H → C₃S₂H₃ + 3Ca(OH)₂	C–S–H gel + Portlandite
C₂S (Belite)	2C₂S + 4H → C₃S₂H₃ + Ca(OH)₂	C–S–H gel + less Portlandite
C₃A (initial, with gypsum)	C₃A + 3CS̅H₂ + 26H → C₆AS̅₃H₃₂	Ettringite (AFt phase) — prevents flash set
C₃A (after gypsum exhausted)	2C₃A + C₆AS̅₃H₃₂ + 4H → 3C₄AS̅H₁₂	Monosulphate (AFm phase)
C₄AF	C₄AF + 2Ca(OH)₂ + 10H → C₆AFH₁₂	Calcium aluminoferrite hydrate

💡 C–S–H gel (Calcium Silicate Hydrate) is the primary binding phase in hardened cement paste, constituting ~60–70 % of the hydration products. Its gel-like structure provides cohesion and strength.

Ca(OH)₂ (Portlandite) constitutes ~20–25 %; it is responsible for the high pH of concrete (~12.5) that passivates steel reinforcement.

Stages of Hydration (Le Chatelier Stages)

Stage	Time	What Happens
Pre-induction / Initial	0 – 15 min	Rapid dissolution of C₃A; first ettringite forms; early heat release spike
Induction / Dormant	15 min – 3 hrs	Slow reaction; cement remains workable; ion concentration builds
Acceleration	3 – 8 hrs	C₃S hydration accelerates; C–S–H nucleates rapidly; initial set
Deceleration	8 – 24 hrs	Reaction slows as products form diffusion barrier around grains; final set
Slow / Long-term	24 hrs onwards	Continued hydration; gradual pore refinement; strength development for months/years

Setting vs Hardening

Feature	Setting	Hardening
Definition	Loss of plasticity / stiffening of paste	Development of strength and rigidity
Time scale	Minutes to hours (IST & FST)	Hours to years (28-day strength and beyond)
Primarily due to	C₃A hydration & Ettringite formation	C₃S & C₂S hydration (C–S–H gel formation)
Temperature effect	Higher temp → faster set	Higher temp → faster early strength but lower 28-day strength

Flash Set vs False Set

Feature	Flash Set	False Set
Cause	Rapid reaction of C₃A with insufficient gypsum	Dehydration of gypsum (CaSO₄·2H₂O → CaSO₄·½H₂O) during hot grinding
Heat release	Significant heat	No significant heat
Remixing	Cannot be restored by remixing	Can be restored by vigorous remixing (re-dissolves CaSO₄·½H₂O)
Product	Ettringite (expansive)	Re-hydrated gypsum (no expansion)

Degree of Hydration (α) and Water Requirements

Theoretical minimum water for complete hydration: w/c ≈ 0.23
Practical minimum for full hydration: w/c ≈ 0.36 (includes gel water)
At w/c < 0.36, unhydrated cement grains remain permanently
Degree of hydration at 28 days for OPC with w/c = 0.50: ≈ 70 %

Products of Hydration and Their Volume

Product	% Volume of Paste	Role
C–S–H gel	50–60 %	Primary binding; strength
Ca(OH)₂ (Portlandite)	20–25 %	High pH; passivation of steel
Ettringite / Monosulphate	15–20 %	Early structure; sulphate reactant
Unreacted cement	Variable	Latent reservoir
Gel pores	Very fine	Intrinsic to C–S–H; ~3 nm
Capillary pores	Variable (reduces with hydration)	Main pathway for aggressive agents

⚠ Capillary porosity is the main factor controlling durability. It decreases as hydration proceeds (pore refinement). Low w/c + prolonged curing → minimal capillary porosity → high durability.

5Physical Properties & Laboratory Tests on Cement ►

Summary of IS 4031 Tests

Test	IS 4031 Part	Apparatus / Method	What it Measures
Fineness (Sieving)	Part 1	90 µm IS sieve; 100 g sample	Coarse particle content
Fineness (Blaine)	Part 2	Air permeability apparatus	Specific surface area (m²/kg)
Standard Consistency	Part 4	Vicat apparatus, 10 mm plunger	Water % for standard paste
Setting Time	Part 5	Vicat apparatus, 1 mm needle & annular needle	IST and FST
Soundness	Part 3	Le Chatelier mould; boiling	Expansion due to free CaO
Soundness (autoclave)	Part 3	Autoclave at 2 MPa, 3 hrs	Expansion due to free MgO
Compressive Strength	Part 6	70.6 mm mortar cubes; 1:3 cement:sand	Strength at 3, 7, 28 days
Heat of Hydration	Part 9	Adiabatic calorimeter	Total heat generated
Tensile Strength (briquette)	Part 8	Briquette mould; tensile testing	Tensile splitting strength

1. Fineness Test (IS 4031 Part 1 – Sieving)

100 g of cement sieved on 90 µm IS sieve for 15 minutes
Residue on sieve expressed as % of original mass
Acceptance: ≤ 10 % residue for OPC
Finer cement → faster hydration, faster strength gain, higher heat of hydration

2. Fineness Test – Blaine's Air Permeability (IS 4031 Part 2)

Measures specific surface area (SSA) in m²/kg
Principle: time for fixed volume of air to flow through compacted cement bed
OPC minimum: 225 m²/kg; PPC: 300 m²/kg; RHPC: 325 m²/kg

SSA (Blaine) = K × √(t / η) [t = flow time; η = viscosity of air; K = apparatus constant]

3. Standard Consistency Test (IS 4031 Part 4)

Vicat apparatus with 10 mm diameter flat-end plunger, mass 300 g
Paste placed in Vicat mould; plunger released from surface level
Standard consistency = % water (P) when plunger penetrates to 5–7 mm from bottom
Typical P value: 26–33 %
Note: subsequent tests use 0.85P for setting time and 0.78P for Le Chatelier test

4. Setting Time Test (IS 4031 Part 5)

Parameter	Initial Setting Time (IST)	Final Setting Time (FST)
Needle used	1 mm square needle	Annular needle (1 mm pin inside 5 mm annular ring)
Criterion	Needle does NOT penetrate to within 5 mm of bottom plate	Annular ring leaves no impression; needle sinks 0.5 mm
Water content	0.85P (P = standard consistency)
Test conditions	27 ± 2 °C; 65 ± 5 % RH (IS 4031)

Cement Type	Min IST (min)	Max FST (min)
OPC 33, 43, 53	30	600
Rapid Hardening (RHPC)	30	600
Low Heat Cement	60	600
Sulphate Resistant (SRC)	30	600
High Alumina Cement	30	360
Masonry Cement	90	1440
Super Sulphated Cement	30	600

Factors affecting setting time:
↑ Temperature → shorter IST and FST
↑ Fineness → shorter IST and FST
↑ w/c ratio → longer IST and FST
↑ C₃A content → shorter IST
↑ Gypsum → longer IST
Retarders (sugar, lignosulfonates) → longer IST
Accelerators (CaCl₂) → shorter IST

5. Soundness Test (IS 4031 Part 3)

(a) Le Chatelier Method — detects free CaO expansion

Brass split-cylinder mould (30 mm dia, 30 mm high) with two steel indicators
Paste of 0.78P water content; sealed and kept 24 hrs at 27 ± 2 °C
Initial reading (d₁) taken; then boiled for 3 hrs; cooled; final reading (d₂) taken
Expansion = d₂ − d₁ ≤ 10 mm for OPC (IS 269)
After re-testing: ≤ 5 mm

(b) Autoclave Method — detects free MgO expansion

Cement bar (25 mm × 25 mm × 285 mm) with neat cement paste
Cured 24 hrs at 27 °C; then autoclaved at 2.0 MPa steam pressure for 3 hrs
Expansion ≤ 0.80 % after autoclave treatment

6. Compressive Strength Test (IS 4031 Part 6)

Standard mortar cubes: 70.6 mm × 70.6 mm × 70.6 mm (face area = 50 cm²)
Mix ratio: 1 cement : 3 standard Ennore sand; w/c = 0.40 (water = P/4 + 3 %, where P = standard consistency)
Compacted in vibration table or hand compaction; demoulded after 24 hrs
Moist curing at 27 ± 2 °C in water; tested at 3, 7 and 28 days
Loading rate: 35 N/mm²/min; average of 3 cubes

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

Physical Requirements Summary (OPC IS 269:2015)

Property	OPC 33	OPC 43	OPC 53
Specific gravity	3.10 – 3.15
Bulk density (loose)	~1440 kg/m³
Normal consistency (P)	26 – 33 %
Fineness (sieve, 90 µm)	≤ 10 % residue
Fineness (Blaine)	≥ 225 m²/kg	≥ 225 m²/kg	≥ 225 m²/kg
IST	≥ 30 min
FST	≤ 600 min
Soundness (Le Chatelier)	≤ 10 mm
Autoclave expansion	≤ 0.80 %
Compressive strength 3 days	≥ 16 MPa	≥ 23 MPa	≥ 27 MPa
Compressive strength 7 days	≥ 22 MPa	≥ 33 MPa	≥ 37 MPa
Compressive strength 28 days	≥ 33 MPa	≥ 43 MPa	≥ 53 MPa

6Chemical Properties & Requirements of Cement ►

Chemical Requirements as per IS 269:2015

Chemical Property	Requirement (OPC)	Significance
Ratio (Al₂O₃ / Fe₂O₃)	≥ 0.66	Ensures C₃A forms; important for setting & strength
Lime Saturation Factor (LSF)	0.80 – 1.02	Ensures no excess free CaO; proper clinker composition
Insoluble residue	≤ 2.0 %	Indicates purity; siliceous adulterants detected
Magnesia (MgO)	≤ 6.0 %	Excess MgO (periclase) causes delayed expansion
Sulphur trioxide (SO₃)	≤ 3.0 % (C₃A ≤ 5 %); ≤ 3.5 % (C₃A > 5 %)	Excess SO₃ causes expansion and cracking
Loss on Ignition (LOI)	≤ 5.0 %	Indicates pre-hydration, adulteration or excess gypsum
Chloride (Cl⁻)	≤ 0.05 %	Excess chloride causes corrosion of steel reinforcement
Total alkalis (Na₂O equivalent)	≤ 0.60 % (low alkali cement)	High alkalis trigger alkali–silica reaction (ASR) with reactive aggregates

Alkali Equivalent

Na₂O_eq = Na₂O + 0.658 × K₂O
Low-alkali cement: Na₂O_eq ≤ 0.60 %

High alkali content + reactive silica in aggregate + moisture → ASR → swelling gel → map cracking
Prevention: use low-alkali cement, pozzolans (fly ash, GGBS), or non-reactive aggregates

Sulphate Attack Mechanism

External SO₄^2– from soil / groundwater reacts with C₃A hydration product
Ca(OH)₂ + SO₄^2– → CaSO₄ (gypsum) → reacts with C₃A → Ettringite (expansive)
MgSO₄ also attacks C–S–H gel directly → most destructive sulphate
Prevention: Use SRC or GGBS cement; low w/c; dense concrete; membranes / coatings

Chloride Content in Concrete (IS 456:2000)

Type of Concrete	Max Cl⁻ (% by mass of cement)
Prestressed concrete	0.10 %
RCC in humid / aggressive environment	0.20 %
RCC in normal environment	0.30 %
Plain concrete (PCC)	0.60 %

7Types of Portland Cement – Properties & IS Codes ►

Ordinary Portland Cement (OPC)

Grade	IS Code	28-day Strength	Application
OPC 33	IS 269:2015	≥ 33 MPa	Plastering, masonry mortar, less critical structures
OPC 43	IS 8112:2013	≥ 43 MPa	General RCC, precast, pre-stressed (mild exposure)
OPC 53	IS 12269:2013	≥ 53 MPa	High-performance RCC, bridges, high-rise (preferred)

Rapid Hardening Portland Cement (RHPC)

IS Code: IS 8041:1990
Key change: Higher C₃S content (up to 70 %) and finer grinding (Blaine ≥ 325 m²/kg)
Strength at 3 days ≈ 28-day strength of OPC 33
Uses: Road / pavement repair, emergency works, prefabrication, cold weather concreting
Higher heat of hydration → not suitable for mass concrete

Low Heat Portland Cement (LHPC)

IS Code: IS 12600:1989
Composition: Low C₃S (max 35 %) & low C₃A (max 6 %); High C₂S (min 40 %)
Heat of hydration: ≤ 272 kJ/kg at 7 days; ≤ 314 kJ/kg at 28 days
Setting: IST ≥ 60 min (slower)
Uses: Mass concrete — dams, raft foundations, large piers, thick retaining walls
Slower strength gain; long-term strength ultimately same as OPC

Sulphate Resisting Portland Cement (SRPC)

IS Code: IS 12330:1988
Composition: Very low C₃A ≤ 5 %; C₃A + C₄AF ≤ 25 %
When Al₂O₃/Fe₂O₃ ratio ≈ 0.64 → no C₃A forms; all aluminate present as C₄AF
Uses: Foundations in sulphate-bearing soils, marine structures, sewers, coastal construction
Slightly lower early strength; grey colour; somewhat less workable

Portland Pozzolana Cement (PPC)

IS Code: IS 1489:1991 (Part 1: Fly ash based; Part 2: Calcined clay based)
Composition: OPC clinker + 15–35 % pozzolana (fly ash or calcined clay)
Pozzolanic reaction: SiO₂ (reactive) + Ca(OH)₂ → C–S–H (secondary)
Blaine fineness: ≥ 300 m²/kg
Strength: 28-day ≥ 33 MPa; slower early strength than OPC
Advantages: Lower heat of hydration, better workability, improved long-term durability, reduced permeability, resistance to sulphate and chloride attack, utilises industrial waste
Uses: General construction, mass concrete, marine works, underground structures

Portland Blast Furnace Slag Cement (PBFSC)

IS Code: IS 455:1989
Composition: OPC clinker + granulated blast furnace slag (GBFS) 25–65 %; GGBS (Ground Granulated)
Slag is latently hydraulic; activated by Ca(OH)₂ released during OPC hydration
Blaine fineness: ≥ 225 m²/kg
Advantages: Low heat, sulphate resistance, lower permeability, better workability, long-term strength
Uses: Marine structures, foundations, mass concrete, road base

Masonry Cement

IS Code: IS 3466:1988
Composition: OPC + inert or pozzolanic filler (≥ 40 %)
IST ≥ 90 min; FST ≤ 1440 min (24 hrs)
Lower strength; improved workability and plasticity for mortar
Uses: Masonry mortar, plastering, jointwork — never structural concrete

White Portland Cement

IS Code: IS 8042:1989
Composition: Very low Fe₂O₃ (< 0.5 %) and MnO → white colour; AM very high
Raw materials: white chalk/limestone + white kaolin clay; special fuel (oil/gas not coal)
More expensive; similar strength to OPC
Uses: Decorative finishes, floor tiles, architectural concrete, swimming pools

Coloured Cement

White cement + suitable pigments (3–10 %)
Pigments: red (Fe₂O₃), green (Cr₂O₃), blue (cobalt oxide), yellow (iron hydroxide)
Pigments must be alkali-resistant and non-fading

Air-Entraining Portland Cement

IS Code: IS 8043:1991
Interground air-entraining agent (AEA) added during clinker grinding
Produces uniformly distributed micro air bubbles (25–250 µm) in concrete
Uses: Cold climate regions; freeze-thaw resistance; road concrete

Hydrophobic Portland Cement

IS Code: IS 8043:1991
Oleic acid / stearic acid coats cement grains → prevents moisture absorption during storage
Shelf life extended; used in tropical / humid storage conditions
The coating wears off during mixing — no long-term effect on concrete

Expansive Cement

No dedicated IS code; used in special applications
Types: Ettringite-based (Type K, M, S), Calcium oxide–based, Metallic powder–based
Expansion mechanism: controlled formation of Ettringite after setting → compensates shrinkage
Uses: Chemical-prestressed concrete, grouting bolt holes, shrinkage-compensating overlays

8Special Cements – Composition, Properties & Uses ►

High Alumina Cement (HAC / Aluminous Cement / Ciment Fondu)

Feature	Details
IS Code	IS 6452:1989
Raw materials	Bauxite (Al₂O₃ source) + limestone; fusion process at ~1500 °C
Main compound	Monocalcium Aluminate (CA = CaO·Al₂O₃) — ~40 %
Al₂O₃ content	> 32 %
IST	≥ 30 min
FST	≤ 360 min (6 hrs)
24-hour strength	> 40 MPa — extremely rapid strength gain
28-day strength	≥ 45 MPa
Heat of hydration	~560 kJ/kg (very high)
Temperature resistance	Retains strength up to 1000 °C (refractory grade)
Conversion	Metastable CAH₁₀ converts to stable C₃AH₆ (cubic) over time — significant strength loss (30–50 %); promoted by heat and moisture

⚠ Conversion of HAC: CAH₁₀ (hexagonal) → C₃AH₆ (cubic) + Al(OH)₃ + H₂O
This conversion increases porosity and reduces strength by 30–50 %. HAC must NOT be used in structural concrete where loads are sustained. Used only for refractory/high-temperature applications.

Uses: Refractory lining of furnaces, kilns, chimneys; chemical plant floors; emergency/repair work; cold-weather concreting
Good resistance to weak acids, seawater (calcium aluminate pastes are acid-resistant)
Not suitable for prolonged contact with alkalis

Supersulphated Cement (SSC)

IS Code: IS 6909:1990
Composition: 80–85 % granulated GGBS + 10–15 % calcium sulphate (anhydrite or gypsum) + small amount of OPC or lime as activator
Very low C₃A; hydration produces Ettringite as primary phase → dense microstructure
Strength: Slow early gain but good 28-day and long-term strength
Heat of hydration: Very low (~167–180 kJ/kg at 7 days)
Chemical resistance: Excellent against sulphates, acids, seawater
Uses: Sewers, foundations in sulphate soils, marine structures, chemical plants
Must be used with higher water content; sensitive to temperature (do not use in hot weather)

Oil Well Cement

IS Code: IS 8229:1986 (based on API standards)
Designed to be pumped and set at high temperatures (up to 150 °C) and high pressures (> 100 MPa)
API grades A–J; Grade G and H most common internationally
Low C₃A (< 3 %) and coarser grind → slower setting at surface; retarder admixtures added
Uses: Cementing steel casings in oil/gas wells to seal formation fluids

Tricalcium Silicate Cement (Mineral Trioxide Aggregate – MTA)

Used in dentistry / endodontics — not a construction material but occasionally mentioned in ESE
Biocompatible; sets in moist conditions

Pozzolana Cement (Natural Pozzolana)

IS Code: IS 1344:1981 (calcined pozzolana)
Natural pozzolanas: volcanic ash (trass), diatomite, rice husk ash, silica fume, fly ash
Definition: Pozzolana is a siliceous and/or aluminous material that has little or no cementitious value alone but reacts chemically with Ca(OH)₂ in the presence of water to form compounds with cementitious properties

Comparison of Special Cements

Cement	HOH	Early Strength	Sulphate Resistance	Key Use
RHPC	High	Very High	Low	Emergency repairs
Low Heat	Very Low	Low	Moderate	Mass concrete
SRC	Moderate	Moderate	Very High	Marine / sulphate soil
HAC	Very High	Extremely High	High (acids)	Refractory concrete
SSC	Very Low	Low	Excellent	Sewers, chemical plants
PPC	Low	Low–Moderate	Good	General / mass concrete
PBFSC	Low	Moderate	Good	Marine / mass concrete

9Admixtures for Cement & Concrete ►

Definition & Classification

Admixtures are materials other than cement, water and aggregates that are added to a concrete mixture immediately before or during mixing to modify its properties in the fresh or hardened state.

Category	Type	Mechanism
Chemical admixtures	Plasticizers (Water Reducers)	Disperse cement particles → improve workability at same w/c
	Superplasticizers (HRWR)	Steric / electrostatic repulsion; reduce water > 20 %
	Retarders	Delay C₃A / C₃S hydration
	Accelerators	Speed up C₃S hydration
	Air Entraining Agents (AEA)	Surfactants; stabilise micro air bubbles
Mineral admixtures	Fly Ash (Class F & C)	Pozzolanic; Class C also cementitious
	GGBS (Slag)	Latent hydraulic; activated by Ca(OH)₂
	Silica Fume (Microsilica)	Highly reactive pozzolan; ultra-fine (0.1 µm)
	Metakaolin	Calcined kaolin; reactive pozzolan

Chemical Admixtures – Detailed

Plasticizers (Normal Water Reducers)

Feature	Details
IS Code	IS 9103:1999
Water reduction	5–10 %
Chemical types	Lignosulfonates (LS), Hydroxylated carboxylic acids, Gluconates
Effect	Same workability at lower w/c; or increased slump at same w/c
Retarding effect	Mild; adds ~30–60 min to setting time

Superplasticizers (High Range Water Reducers – HRWR)

Feature	Details
IS Code	IS 9103:1999
Water reduction	15–30 %
Dosage	0.2–3 % by mass of cement
Types	1st gen: SNF (Sulfonated Naphthalene Formaldehyde), SMF (Sulfonated Melamine Formaldehyde); 2nd gen: Modified lignosulfonates; 3rd gen (latest): PCE (Polycarboxylate Ether) — most effective; comb-polymer structure
Slump life	SNF/SMF: 30–60 min; PCE: 60–90 min or more
Applications	SCC, HPC, ready-mix concrete, pumped concrete

Retarders

Delay initial and final setting time by 1–4 hours
Types: Sugar / sucrose (most effective retarder; 0.1 % reduces strength; 0.3 % = total retardation), lignosulfonates, hydroxycarboxylic acids, phosphates
Uses: Hot weather concreting (T > 35 °C), long transport in transit mixers, large pours, complex formwork
Caution: Excess sugar acts as a set retarder → completely inhibits setting

Accelerators

Speed up hydration → faster set and early strength
Calcium Chloride (CaCl₂): Most effective; 1–2 % by mass; reduces IST by 30–50 %; BUT causes corrosion of steel → NOT permitted in RCC or prestressed concrete
Non-chloride accelerators: Calcium formate, calcium nitrite, triethanolamine; safer for RCC
Uses: Cold weather concreting (T < 5 °C), precast, emergency works

Air Entraining Agents (AEA)

Create uniformly distributed, stable spherical micro air voids (25–250 µm diameter)
Air content: 3–7 % by volume
Types: Vinsol resin, fatty acid salts (sodium oleate), neutralised wood resins, synthetic surfactants
Benefits: Freeze-thaw resistance, improved workability, reduced bleeding and segregation
Effect on strength: Each 1 % increase in air reduces compressive strength by ~5 %
Uses: Concrete in cold climates; roads in freeze-thaw zones; pavements

Mineral Admixtures – Detailed

Fly Ash (FA)

Feature	Class F (Low Calcium)	Class C (High Calcium)
Source	Sub-bituminous / bituminous coal	Lignite coal; high CaO (15–40 %)
SiO₂ + Al₂O₃ + Fe₂O₃	≥ 70 %	≥ 50 %
Activity	Pozzolanic only	Pozzolanic + cementitious
Replacement level in concrete	15–35 %	Up to 50 %
IS Code	IS 3812:2013

Particle size: 1–100 µm; spherical glassy particles (improve workability — ball bearing effect)
Pozzolanic reaction: SiO₂ + Ca(OH)₂ + H₂O → C–S–H (secondary)
Benefits: Reduced HOH, improved long-term strength, better durability, reduced permeability, ASR mitigation

Ground Granulated Blast Furnace Slag (GGBS)

IS Code: IS 12089:2013
By-product of iron manufacture; rapidly quenched → glassy, latent hydraulic material
Chemical composition: CaO 30–45 %; SiO₂ 30–37 %; Al₂O₃ 8–20 %; MgO 1–12 %
Hydraulic activity index: ≥ 70 % at 7 days; ≥ 90 % at 28 days (compared to OPC control)
Replacement level: 30–70 % (up to 80 % in some applications)
Benefits: Very low HOH, excellent sulphate and chloride resistance, low permeability, high long-term strength

Silica Fume (SF / Microsilica)

IS Code: IS 15388:2003
By-product of silicon / ferrosilicon alloy production (electric arc furnace)
Ultra-fine (average 0.1–0.15 µm; 100× finer than cement); amorphous SiO₂ > 85 %
Very high pozzolanic activity (much faster than fly ash)
Pore refinement: fills spaces between cement particles → dramatically reduces capillary porosity
Addition: 5–10 % replacement; always use with superplasticizer
Benefits: Very high strength (70–150+ MPa possible), extremely low permeability, excellent durability
Used in HPC, bridge decks, offshore structures, parking structures

10IS Codes, Key Values & Exam Quick Revision ►

Complete IS Code Reference for Cement

IS Code	Year	Subject
IS 269	2015	Ordinary Portland Cement (OPC 33 grade) specification
IS 8112	2013	Ordinary Portland Cement (OPC 43 grade) specification
IS 12269	2013	Ordinary Portland Cement (OPC 53 grade) specification
IS 8041	1990	Rapid Hardening Portland Cement
IS 12600	1989	Low Heat Portland Cement
IS 12330	1988	Sulphate Resisting Portland Cement
IS 1489 Pt1	1991	Portland Pozzolana Cement – Fly Ash based
IS 1489 Pt2	1991	Portland Pozzolana Cement – Calcined Clay based
IS 455	1989	Portland Blast Furnace Slag Cement
IS 6452	1989	High Alumina Cement
IS 6909	1990	Supersulphated Cement
IS 8042	1989	White Portland Cement
IS 8043	1991	Hydrophobic Portland Cement / Air Entraining Portland Cement
IS 3466	1988	Masonry Cement
IS 8229	1986	Oil Well Cement
IS 1344	1981	Calcined Natural Pozzolana Cement
IS 4031	Various	Methods of physical tests for hydraulic cement (Parts 1–15)
IS 4032	1985	Methods of chemical analysis of hydraulic cement
IS 3812	2013	Pulverised Fuel Ash (Fly Ash) specification
IS 12089	2013	Granulated Slag for Portland Slag Cement
IS 15388	2003	Silica Fume specification
IS 9103	1999	Admixtures for Concrete

All-in-One Cement Properties Quick Table

Cement Type	HOH	Early Str.	Sulphate R.	Blaine (m²/kg)	IST (min)
OPC 33/43/53	Medium	Medium–High	Low	≥ 225	≥ 30
RHPC	High	Very High	Low	≥ 325	≥ 30
Low Heat	Very Low	Low	Medium	≥ 320	≥ 60
SRC	Medium–Low	Medium	Very High	≥ 225	≥ 30
PPC	Low	Low–Med	Good	≥ 300	≥ 30
PBFSC	Low	Medium	Good	≥ 225	≥ 30
HAC	Very High	Extremely High	Good (acids)	≥ 225	≥ 30
SSC	Very Low	Low	Excellent	–	≥ 30
White	Medium	Medium	Low	≥ 300	≥ 30
Masonry	Low	Low	Low	–	≥ 90

Critical Numerical Values to Memorise

Parameter	Value
Specific gravity of OPC	3.10 – 3.15
Bulk density of cement (loose)	~1440 kg/m³
Normal consistency (P)	26 – 33 %
Water for setting time test	0.85 P
Water for Le Chatelier test	0.78 P
IST (OPC, RHPC, SRC, PPC, PBFSC, HAC)	≥ 30 min
IST (Low Heat)	≥ 60 min
IST (Masonry Cement)	≥ 90 min
FST (most cements)	≤ 600 min (10 hrs)
FST (HAC)	≤ 360 min (6 hrs)
FST (Masonry)	≤ 1440 min (24 hrs)
Soundness – Le Chatelier limit	≤ 10 mm (OPC)
Soundness – Autoclave expansion	≤ 0.80 %
Fineness (sieve) limit	≤ 10 % on 90 µm sieve
Blaine fineness (OPC)	≥ 225 m²/kg
Blaine fineness (RHPC)	≥ 325 m²/kg
Blaine fineness (PPC)	≥ 300 m²/kg
Clinker burning zone temperature	1350 – 1450 °C
Calcination temperature	~900 °C
C₃A limit in SRC	≤ 5 %
C₃A + C₄AF limit in SRC	≤ 25 %
C₃S in Low Heat Cement	≤ 35 %
C₂S in Low Heat Cement	≥ 40 %
C₃A in Low Heat Cement	≤ 6 %
HOH at 7 days (Low Heat)	≤ 272 kJ/kg
HOH at 28 days (Low Heat)	≤ 314 kJ/kg
MgO limit in OPC	≤ 6 %
SO₃ limit in OPC	≤ 3.0 % (C₃A ≤ 5 %); ≤ 3.5 % (C₃A > 5 %)
LOI limit in OPC	≤ 5.0 %
LSF range (IS 269)	0.80 – 1.02
Shelf life of cement	3 months from manufacture
Min. w/c for complete hydration (theory)	0.23
Min. w/c for complete hydration (practical)	0.36
C₃S HOH	~502 J/g
C₂S HOH	~260 J/g
C₃A HOH	~867 J/g
C₄AF HOH	~419 J/g
Al₂O₃/Fe₂O₃ min ratio (OPC)	≥ 0.66
Air entraining agent water reduction	None; air content 3–7 %
Superplasticizer water reduction	15–30 %
Plasticizer water reduction	5–10 %
HAC: 24-hr compressive strength	> 40 MPa

Bogue Formulae (exam-ready)

C₃S = 4.071(CaO) − 7.600(SiO₂) − 6.718(Al₂O₃) − 1.430(Fe₂O₃) − 2.852(SO₃)
C₂S = 2.867(SiO₂) − 0.7544(C₃S)
C₃A = 2.650(Al₂O₃) − 1.692(Fe₂O₃)
C₄AF = 3.043(Fe₂O₃)

LSF = CaO / (2.8·SiO₂ + 1.2·Al₂O₃ + 0.65·Fe₂O₃)    [target: 0.80 – 1.02]
SM = SiO₂ / (Al₂O₃ + Fe₂O₃)    [typical: 1.7 – 4.0]
AM = Al₂O₃ / Fe₂O₃    [typical: 1 – 4; > 10 for white cement]
Na₂O_eq = Na₂O + 0.658 × K₂O    [≤ 0.60 % for low-alkali cement]

Mnemonics

Bogue compounds by decreasing % in OPC:
"Some Silly Cats Are Fighting"
C₃S (~50%) → C₂S (~25%) → C₄AF (~12%) → C₃A (~10%)

Heat of hydration (decreasing):
"Three-Aluminate is the Hottest; Two-Silicate is the Coolest"
C₃A > C₃S > C₄AF > C₂S

Which cement for which problem:
Hot weather / mass concrete → Low Heat or PPC
Sulphate soil / marine → SRC or PBFSC
Emergency repair → RHPC or HAC
High-strength concrete → OPC 53 + Silica Fume
Decorative work → White Cement
Grouting wells → Oil Well Cement
Chemical plant sewers → SSC or SRC

GATE / ESE Previous Year Pattern

Topic	Frequency	Question Type
Bogue compound calculation (from oxide %)	Every alternate year (GATE)	NAT / MCQ
Setting time and soundness test values	Very high	MCQ
Which cement to use for a given situation	Very high (ESE)	MCQ
Heat of hydration order / values	High	MCQ
LSF / Moduli calculation	Moderate (GATE)	NAT
Flash set vs false set	Moderate	MCQ
IS codes for cement types	High (ESE / SSC JE)	MCQ
Hydration products (C–S–H, ettringite)	Moderate	MCQ
HAC conversion reaction and consequences	Moderate (ESE)	MCQ / Descriptive
Admixture types and effects	Moderate	MCQ
Pozzolana definition and reaction	Moderate	MCQ