Table of Contents
1.1 Introduction
Cement is an extremely fine material having adhesive and cohesive properties which provide a binding medium for the discrete ingredients.
It is a product obtained by pulverizing (to make into a powder form) clinker formed by calcinating the raw material preliminary consisting of Lime (CaO), Silicate (SiO₂), Alumina (Al₂O₃) and Iron oxide (Fe₂O₃).
- When cement is mixed with water it forms a paste which binds aggregates (fine and coarse) together to form a hard durable mass called concrete
- The cement which is fine in nature assumes to have good setting property; finer the grains of the cement, more is the strength of cement
- Cement is having good heat of hydration due to which it sets early as compared to other binding material like lime
- The cement experiences the exothermic chemical reaction when it comes in contact with water
- The cement is assumed to have a specific gravity of 3.15
- Joseph Asp din manufactured cement and called it Portland cement — it produced a material resembling stone from the quarries near Portland in England
- During grinding of clinker, Gypsum (Plaster of Paris) is added to prevent flash setting of the cement. Amount of gypsum is about 3 to 5% by weight of clinker. It also improves soundness of cement
- Common calcareous materials: lime stone, chalk, marine shell and marl
- Argillaceous materials: clay, shale, slate and selected blast furnace slag
- The processes used for manufacture of cement can be classified as dry and wet
- The ideal net weight of cement bag is 50 kg and volume of 0.035 m³
- Ordinary cement achieves 70% of its final strength in 28 days and 90% in 1 year
Key Reference Data
- Specific gravity
- 3.15
- Bag weight / volume
- 50 kg / 0.035 m³
- Gypsum added during grinding
- 3–5% by weight of clinker (prevents flash set; improves soundness)
- Ultimate binding material
- C–S–H gel (Calcium Silicate Hydrate)
- 28-day strength achieved
- 70% of final strength
- 1-year strength achieved
- 90% of final strength
- Calcareous materials
- Limestone, chalk, marine shell, marl
- Argillaceous materials
- Clay, shale, slate, blast furnace slag
1.2 Cement and Lime
| Point | Cement | Lime |
|---|---|---|
| 1 | Used for gain of early strength | Gains strength slowly |
| 2 | Cement and lime colour are different | White/off-white colour |
| 3 | Cement and lime both are binding materials having good ultimate strength; lime experiences less early strength | Less early strength as compared to cement |
1.3 Manufacturing of Cement
- Cement is manufactured by integrating the calcareous component and argillaceous component in ratio of 3 : 1
- Calcareous component: limestone, chalk, marine shells, marl → derives ingredient called lime
- Argillaceous component: shale, clay, blast furnace slag, slate → composed of silica, alumina, iron oxide and other impurities
1.3(a) Wet Process
- It is the old method of manufacturing — now obsoleted
- Costly method — requires higher degree of fuel consumption, power consumption
- In this process the preheater is not used
Figure 1.1 — Wet Process of Cement Manufacturing (Flow Diagram)
1.3(b) Dry Process
- New method of manufacturing — trending now
- Fuel consumption and power consumption has been reduced to a greater extent by modifying the wet process
- In dry process, first calcareous components (limestone) and argillaceous component (clay or shale) is reduced in size to about 25 mm in crushers separately in a ball mill or tube mill
- Before feeding into rotary kiln, raw mix is allowed into preheater at a temperature of 850°C which reduces the burning time of raw mix in rotary kiln
Figure 1.2 — Dry Process of Cement Manufacturing (Flow Diagram)
Rotary Kiln — Zones & Specifications
Figure 1.3 — Rotary Kiln: Longitudinal Section with All Zones
| Zone | Temperature | Process | Chemical Reaction |
|---|---|---|---|
| Nodule Zone | ~700°C | Calcination — limestone disintegrates | CaCO₃ → CaO + CO₂↑ (by heat/calcination) |
| Burning Zone | ~1450°C | Fusion — clinker formed | CaO + SiO₂ + Al₂O₃ + Fe₂O₃ → C₃S, C₂S, C₃A, C₄AF |
| Cooling Zone | <1450°C | Clinker cooled before ball mill | Clinker → Ball mill + 2–3% gypsum → Cement silos |
Burning Zone reactions (from source):
2CaO + SiO₂ → Ca₂SiO₄ = C₂S (Dicalcium Silicate)
3CaO + SiO₂ → Ca₃SiO₅ = C₃S (Tricalcium Silicate)
3CaO + Al₂O₃ → Ca₃Al₂O₆ = C₃A (Tricalcium Aluminate)
4CaO + Al₂O₃ + Fe₂O₃ → Ca₄Al₂Fe₂O₁₀ = C₄AF (Tetra-calcium Alumino-ferrite)
2CaO + SiO₂ → Ca₂SiO₄ = C₂S (Dicalcium Silicate)
3CaO + SiO₂ → Ca₃SiO₅ = C₃S (Tricalcium Silicate)
3CaO + Al₂O₃ → Ca₃Al₂O₆ = C₃A (Tricalcium Aluminate)
4CaO + Al₂O₃ + Fe₂O₃ → Ca₄Al₂Fe₂O₁₀ = C₄AF (Tetra-calcium Alumino-ferrite)
1.3.1 Composition of Cement Clinker — Bougue Compounds
The product from the rotary kiln is called clinker, composed of the major compounds (Bougue Compound) and minor compounds (alkalies — Soda and Potash). The clinker has flash set property — retarder (2–3% by weight) is added to delay this.
| S.No. | Principal Mineral Compound | Formula | Name | Symbol | Percentage |
|---|---|---|---|---|---|
| 1 | Tricalcium silicate | 3CaO·SiO₂ | Alite | C₃S | 30–50% |
| 2 | Dicalcium silicate | 2CaO·SiO₂ | Belite | C₂S | 20–45% |
| 3 | Tricalcium aluminate | 3CaO·Al₂O₃ | Celite | C₃A | 8–12% |
| 4 | Tetracalcium alumino ferrite | 4CaO·Al₂O₃·Fe₂O₃ | Felite | C₄AF | 6–10% |
Figure 1.4 — Bougue Compounds: Percentage Composition & Heat of Hydration
Figure 1.5 — Development of Strength of Pure Compounds with Age (Log Scale)
Properties of Each Bougue Compound
C₃S — Tricalcium Silicate
Alite · 30–50% · Heat of hydration: 500 J/gm
- Very good strength compound; enables clinker to grind easily
- Hydrates rapidly → generates high heat → early hardness and strength
- Increases resistance to freezing and thawing
- Mainly responsible for 7-day and 28-day strength
- It is the compound which has maximum contribution in 28 days strength
- Raising C₃S content beyond limit → heat of hydration increases
C₂S — Dicalcium Silicate
Belite · 20–45% · Heat of hydration: 260 J/gm
- Hydrates and hardens slowly — responsible for ultimate strength
- Imparts resistance to chemical attack
- Raising C₂S → decreases early strength and heat of hydration
- Contribution starts from 14 days, remains up to 1 year
- After 28 days, gain of strength is due to C₂S
- Stable compound — in low heat cement C₂S content is more
C₃A — Tricalcium Aluminate
Celite · 8–12% · Heat of hydration: 865 J/gm
- Rapidly reacts with water → responsible for flash set of finely ground clinker
- Flash set prevented by retarder gypsum (2–3%)
- Least stable compound; maximum heat of hydration
- Very less durable — susceptible to cracks in structure
- Any cement having high C₃A content is liable for sulphur attacks
- Contributes in 24-hour strength but less contribution overall
C₄AF — Tetracalcium Alumino Ferrite
Felite · 6–10% · Heat of hydration: 420 J/gm
- Also responsible for high heat (less than C₃A but more than C₂S)
- Contribution in strength is very less
- Contribution within 24 hours of adding water to the cement
- Imparts colour to cement
Heat of hydration (descending): C₃A (865) > C₃S (500) > C₄AF (420) > C₂S (260) J/gm |
Rate of hydration (descending): C₄AF > C₃A > C₃S > C₂S
Heat of Hydration at Various Ages (J/g) — Source Data
| Compound | 3 Days (J/g) | 90 Days (J/g) | 13 Years (J/g) |
|---|---|---|---|
| C₃S | 242.44 | 434.72 | 508.95 |
| C₂S | 50.16 | 175.56 | 246.62 |
| C₃A | 860.15 | 1299.98 | 1354.32 |
| C₄AF | 288.42 | 409.64 | 426.36 |
1.3.2 Functions of Various Cement Ingredients
| Constituent | % | Range | Function / Effect |
|---|---|---|---|
| Lime (CaO) | 62 | 62–67% | Most important. Excess → unsound cement. Deficiency → decreased strength + quick set. |
| Silica (SiO₂) | 22 | 17–25% | Imparts strength via dicalcium & tricalcium silicates. Excess → prolonged setting time. |
| Alumina (Al₂O₃) | 5 | 3–8% | Quick setting property; acts as flux; lowers clinkering temperature. Excess → weakens cement. |
| Calcium Sulphate (CaSO₄) | 4 | 3–4% | Present as gypsum. Increases initial setting time of cement. |
| Iron Oxide (Fe₂O₃) | 3 | 3–4% | Imparts colour, hardness and strength to the cement. |
| Magnesia (MgO) | 2 | 0.1–3% | Small amount → hardness & colour. High content → unsound cement. |
| Sulphur (S) | 1 | 1–3% | Very small amount → sound cement. Excess → unsoundness. |
| Alkalies (Na₂O + K₂O) | 1 | 0.5–1.3% | Excess → alkali-aggregate reaction, efflorescence and staining when used in concrete/mortar. |
1.4 Hydration of Cement
- Chemical reactions that take place between cement and water = hydration of cement
- Visualized in two ways: “through solution” and “solid state” type of mechanisms
- Reaction of cement with water is exothermic — liberates considerable heat (heat of hydration)
- Hydration is not instantaneous — faster in early periods, continues indefinitely at a decreasing rate
- During hydration, C₃S and C₂S react with water → Calcium Silicate Hydrate (C–S–H) formed along with Ca(OH)₂
- C–S–H gel is the most important product of hydration — determines the good properties of concrete
Figure 1.6 — Cement Hydration: Reactions, Products & Water Requirements
Permissible Limits for Impurities in Water
| Impurity | Permissible Limit |
|---|---|
| Organic | 200 mg/l |
| Inorganic | 3000 mg/l |
| Sulphates (SO₄²⁻) | 400 mg/l |
| Chlorides (Cl⁻) | 2000 mg/l (plain concrete); 500 mg/l (reinforced concrete) |
| Suspended matter | 2000 mg/l |
1.5 Types of Cements (BIS Classification)
Figure 1.7 — Classification of Cements as per Bureau of Indian Standards (BIS)
Ordinary Portland Cement (OPC)
IS 269-1989 / IS 8112-1989 / IS 12269-1987
- 3 grades: 33, 43, 53 (= 28-day strength in MPa)
- OPC-33 recommended for M20 concrete
- Most commonly used in general construction where no exposure to sulphates
Rapid Hardening Cement (RHC)
IS 8041-1990
- Higher C₃S, lower C₂S than OPC
- 1-day strength = 3-day strength of OPC
- Shuttering removed earlier; road works
- Cost 10–15% more than OPC
Extra Rapid Hardening (ERHC)
No IS code
- RHC + CaCl₂ ≤ 2% by weight
- Very suitable for cold weather concreting
- 1–2 day strength 25% more than RHC
- Prohibited in prestressed concrete
- Max time of use: 20 minutes
Low Heat Cement (LHC)
IS 12600-1989
- Reduced C₃S & C₃A; increased C₂S
- 7d ≤ 65 cal/gm; 28d ≤ 75 cal/gm heat
- Used in dams, retaining walls, mass structures
- Ultimate strength same as OPC
Portland Blast Furnace Slag
IS 455-1989
- Portland clinker + granulated BF slag (25–65%)
- Gains strength more slowly than OPC
- Lower heat of hydration; high sulphate resistance
- Used in dams, foundations, bridge abutments
Portland Pozzolana Cement (PPC)
IS 1489-1991 (Part 1 & 2)
- Pozzolana 15–35% (earlier 10–25%)
- Ca(OH)₂ + Pozzolana + H₂O → C-S-H gel
- Less heat; marine and hydraulic constructions
- 28-day onward strength = OPC; lower early strength
Sulphate Resisting Cement (SRC)
IS 12330-1988
- Low C₃A & C₄AF; C₃S and C₂S ≈ 45% each
- Resists MgSO₄, CaSO₄, Na₂SO₃ attack
- 3d=10 N/mm²; 7d=16; 28d=33 N/mm²
High Alumina Cement (HAC)
IS 6452-1989
- Very low C₂A; resistant to sulphur & chemical attacks
- 1-day ≈ 40 N/mm²; 3-day ≈ 50 N/mm²
- Initial set = 3.5 hr; Final set ≈ 5 hr
- Do NOT mix with any other cement type
1.6 Field Tests for Cements
| Field Test | Observation (Good Cement) |
|---|---|
| Colour | Grey colour with a light greenish shade |
| Physical properties | Cement should feel smooth when rubbed in between the fingers |
| Hand insert | If hand is inserted in a bag or heap of cement, it should feel cool |
| Water float test | A small quantity of cement thrown in a bucket of water should sink and should NOT float on the surface |
| Presence of lumps | Cement should be free from lumps |
1.7 Laboratory Tests for Cements
Tests on cement performed per IS: 4032-1985 and IS: 4031 (Parts 1 to 15)–1988-99 to assess: chemical composition, normal consistency, initial/final setting times, soundness, strength, fineness, heat of hydration, specific gravity.
1.7.1 Chemical Composition Test
- Lime Saturation Factor (LSF): [CaO − 0.7SO₃] / [2.8SiO₂ + 1.2Al₂O₃ + 0.65Fe₂O₃] — shall be ≤ 1.02 and ≥ 0.66
- Ratio of Al₂O₃ to Fe₂O₃ shall not be less than 0.66
- Weight of insoluble residue shall not be more than 4%
- Weight of magnesia shall not be more than 6%
- Total loss on ignition shall not be more than 5%
- Total sulphur content (as sulphuric anhydride) ≤ 2.5% (when C₃A ≤ 5%); ≤ 3% (when C₃A > 5%)
1.7.2 Normal Consistency Test — Vicat Apparatus
Figure 1.8 — Vicat Apparatus: Normal Consistency, Initial & Final Setting Time Tests
1.7.3 Initial Setting Time
- Time elapsed from water added to cement until paste starts losing its plasticity
- Paste consistency 0.85P; square needle; when needle penetrates only 33–35 mm (5–7 mm from bottom) = initial set
- Minimum: 30 minutes for OPC; 60 minutes for Low Heat Cement
1.7.4 Final Setting Time
- Time from water added until paste has completely lost plasticity and has sufficient firmness to resist definite pressure
- Annular collar needle used: if needle makes impression while collar fails to do so = finally set. Needle does not pierce paste more than 0.5 mm
- Maximum: 10 hours
Significance of setting times: (a) Concrete must NOT be disturbed till final setting completes. (b) Transport from preparation place to placing must be within initial setting time. (c) Final setting test: concrete should achieve desired strength as early as possible so shuttering can be removed and reused.
1.7.5 Soundness Test
Figure 1.9 — Soundness Tests: Le Chatelier Method & Autoclave Test
1.7.6 Strength Test
(a) Compressive Strength Test
- Mix: 185 gm standard Ennore sand + 55 gm cement (ratio 1:3); water = (P/4 + 3.0)% of combined weight
- Cube mould 7.06 cm; face area = 50 cm²; vibrations = 1200 ± 400/min
- Store at 27°±2°C, ≥90% RH for 24 hr; then in clean fresh water till testing
- Three cubes tested at 1, 3, 7 and 28 days; load applied at 0 to 35 N/mm²/min on UTM
- 7-day strength of concrete should be at least 2/3 of 28-day strength
| Grade | 3 Days (min MPa) | 7 Days (min MPa) | 28 Days (min MPa) |
|---|---|---|---|
| OPC 33 | 16 | 22 | 33 |
| OPC 43 | 23 | 33 | 43 |
| OPC 53 | 27 | 37 | 53 |
(b) Tensile Strength Test (Briquette Test)
- Cement:Sand = 1:3 by weight; water = (P/5 + 2.5)%
- Briquette mould area = 6.45 cm²; kept 27°±2°C, 90% RH for 24 hr
- Six briquettes tested; load at 0.7 N/mm² in 12 seconds
- OPC: ≥2.0 MPa (3 days), ≥2.5 MPa (7 days)
- Tensile strength = 10–15% of compressive strength generally
1.7.7 Fineness Test
- Fineness = size of cement particles expressed as specific surface (surface area per unit mass)
- Rate of gain of strength is rapid for finer cement; final strength not affected by fineness
- Three methods: (i) Sieve method, (ii) Air permeability — Nurse and Blaine’s method, (iii) Sedimentation — Wagner’s turbidimeter
- Sieve method: 100 gm cement on 90 micron sieve, sieved 15 min. Residue: OPC ≤10%; RHC ≤5%; PPC ≤5%
Blaine specific surface: S = [14 / (d(1−v))] × √(Aρ²/KL) × √(h₁/h₂)
where d = density, v = porosity of cement (0.475), h₁ = manometer reading, h₂ = flowmeter reading, K = flow meter constant
where d = density, v = porosity of cement (0.475), h₁ = manometer reading, h₂ = flowmeter reading, K = flow meter constant
1.7.8 Heat of Hydration Test
- Apparatus = calorimeter
- 60 gm cement + 24 ml distilled water mixed 4 min at 15°–25°C; three glass vials (100 mm × 20 mm) filled, corked, sealed with wax; stored at 27°±2°C
- Heat of hydration = heat of solution of hydrated cement − heat of solution of unhydrated cement (nearest 0.1 calorie)
- Low heat Portland cement: ≤66 cal/gm (7 days); ≤75 cal/gm (28 days)
1.7.9 Specific Gravity Test
- Apparatus = Le Chatelier’s flask; filled with kerosene (sp. gr. ≥0.7313) to 0–1 ml mark
- Cement introduced; air bubbles removed; flask in water bath; final reading taken
- Specific gravity of Portland cement ≈ 3.15
Specific Gravity = Weight of cement (gm) / Weight of displaced volume of liquid (ml)
Note: Specific gravity is NOT an indication of quality of cement. It is used only in calculation of mix proportions. Long seasoning is the chief cause for low specific gravity in an unadulterated cement.
Comprehensive Comparison — Cement Types (from source)
| Type of Cement | Fineness m²/kg (Min) | LC Max (mm) | Autoclave Max (%) | Init. Set Min (min) | Final Set Max (min) | 1 Day MPa | 7 Day MPa | 28 Day MPa |
|---|---|---|---|---|---|---|---|---|
| 33 Grade OPC (IS 269-1989) | 225 | 10 | 0.8 | 30 | 600 | NS | 16 | 33 |
| 43 Grade OPC (IS 8112-1989) | 225 | 10 | 0.8 | 30 | 600 | NS | 23 | 43 |
| 53 Grade OPC (IS 12269-1987) | 225 | 10 | 0.8 | 30 | 600 | NS | 27 | 53 |
| SRC (IS 12330-1988) | 225 | 10 | 0.8 | 30 | 600 | NS | 10 | 33 |
| PPC Part 1 (IS 1489-1991) | 300 | 10 | 0.8 | 30 | 600 | NS | 16 | 33 |
| RHC (IS 8041-1990) | 325 | 10 | 0.8 | 30 | 600 | 16 | 27 | NS |
| Slag Cement (IS 455-1989) | 225 | 10 | 0.8 | 30 | 600 | NS | 16 | 33 |
| High Alumina (IS 6452-1989) | 225 | 5 | NS | 30 | 600 | 30 | 35 | NS |
| Low Heat (IS 12600-1989) | 320 | 5 | 0.8 | 60 | 600 | NS | 10 | 35 |
| Masonry (IS 3466-1988) | 90 | 10 | 1.0 | 90 | 1440 | NS | NS | 2.5 |
| SSC (IS 6909-1990) | — | 5 | 0.8 | 30 | 600 | NS | 15 | 30 |
| IRT-40 (IS designation) | 370 | 5 | 0.8 | 60 | 600 | NS | NS | 37.5 |
NS = Not specified. LC = Le Chatelier expansion. All strength values are minimums. Source: IS 4031 specifications.
Chapter 1: Cement — Civil Engineering · Construction Materials
All technical data as per Bureau of Indian Standards (BIS) specifications · IS 4031