plain and reinforcement concert civil engineering 5th semester

1. CE – 308
Credits: 3 + 1
Min. Contact Hours: 48 + 48
Batch: UG CE 2k19
Fall 2021 Semester
Atif Rasheed Baloch
Lecturer Civil Engineering Department
NUST Balochistan Campus, Quetta,
Pakistan
Cell: 92-333-7714643, Email:
atif.rahan82@gmail.com
Plain & Reinforced Concrete-I
Lecture 2 – Cement

2. Plain & Reinforced Concrete – I Fall Semester 2021 (Atif Rasheed
Contents
• Cement
• Advent of Modern Cement
• Portland Cement
• Manufacturing
• Hydration of Cement
• Setting Times
• Types of Cement

3. Cement
 Cements may be defined as adhesive
substances capable of uniting fragments or
masses of solid matter to a compact whole in
general terms.
 Plastic materials employed to produce
adhesion between stones, bricks, etc. in the
construction of buildings and engineering
works is cement in specific context.
 Term 'cements' in this restricted sense then
becomes equivalent to 'calcareous cements.
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4. Adventof ModernConcrete
 Nonhydraulic Cement Concrete
 Use of lime by Romans 6500BC and Chinese 3000BC.
 Use of Gypsum by Egyptians 3000BC
 Production of Hydraulic Lime
 Lime mixed withVolcanic ash by Romans and Greeks.
50BC to 200AD
 John Smeaton (1756) showed that best mortar was
produced when pozalana was mixed wih containing
clayey matter,
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5. PortlandCement
 James Parker (1796) patent natural Hydraulic cement.
Limestone + Clay( Pozzolans)
 Mixture of ground Limestone and pulverised clay
burnt in kiln and fine grinding of material to make
Roman cement.
 Joseph Aspdin(1824) named it as Portland cement
based on colour of limestone found in
Portland(Dorset).
 Issac Johnson (1845)improved burning to Clinkering
stage to produce modern cement.
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6. PortlandCement
 Portland cement is intimately mixing
together calcareous, silica, alumina and iron
oxide-bearing materials
 Burning them to a clinkering temperature
 And grinding to a fine powder

7. Manufactureof
Cement
William Aspdin's
preserved beehive kiln
at Northfleet, Kent,
which operated from
1847 to 1850.This is
the oldest surviving
Portland cement kiln in
the world. Meso-
Portland cement was
manufactured in this
kiln.
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8. ChemicalCompositionofCement
3CaO.SiO2. 2CaO.SiO2. 3CaOAl2O3.
4CaoAl2o3.Fe2O3
Main constituents Cement
Chemist's shorthand
SiO2 S
Al2O3 A
Fe2O3 F
CaO C
H2O H
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10. TypicalcompositionofClinker
Shorthand Chemical Mineral Typical level Typical range
nomenclature formula name (mass %) (mass %)
C3S 3CaO·SiO2 or Ca3SiO5 Alite 57 45–65
C2S 2CaO·SiO2 or Ca2SiO4 Belite 16 10–30
C3A 3CaO·Al2O3 or Ca3Al2O6 Aluminate 9 5–12
C4AF 4CaO·Al2O3·Fe2O3 or
Ca4Al2Fe2O10 Ferrite 10 6–12
MgO,TiO, Mn2O3, K2O and Na2O
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12. Compounds in Clinker
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13. Sequence of reactions taking place during the formation of
Portland cement clinker.
( Source: Reproduced by courtesy of KHD Humbolt Wedag AG.)
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15. Cement Manufacturing
 Steps
 Mixing. Limestone and clay are ground and mixed in
right proportions.
 Burning. Obtaining of clinker from kilns.
 Grinding. Grinding of clinker to fine powder.
 Processes
 Dry process. Dry mixing and grinding of constituents.
Difficult for composition control, slow, costly, now
obsolete process.
 Wet process.Wet mixing and grinding into slurry
which turns into clinker on burning in kiln.
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Cement Manufacturing Process
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Cement Manufacturing
Modern Process
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18. 10/19/2023
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Cement Clinker Composition
 Tri-calcium silicate (Alite)
 Best cementing material. About 57%. Main cause of
hardness and early strength
 Di-calcium silicate (Belite)
 About 16%. Resistance to chemical attacks. Hardens
slow and takes long to add to strength
 Tri-calcium aluminates (Celite)
 About 9%. Rapidly reacts responsible for flash set,
volume changes, cracking and high heat of hydration
 Tetra-calcium alumino ferrite (Felite)
 About 10%. Responsible for flash set.
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19. HydrationofCement
 When water is added to cement , a chemical
reaction starts and new products are formed
which bind the material together in a strong
solid mass giving us concrete. This process is
known as hydration. It is complex process due to
presence of multiple compounds in varying
proportions. Hydration of each compound can
be studied separately to arrive at total picture.
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20. Heat of Hydration
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21.  2C3S + 6H ⇒ C3S2H3 +3CH, heat
 100 +24 = 75+49
 Major component of cement
 Produces C-S-H jel which glues aggregates together.
 Hydrates 50% by 3days and 80% by 28 days.
 Dormant, or induction, period after mixing.
 2C2S +4H ⇒ C3S2H3 + CH, heat
 100+21= 99+22
 Second major component
 Produces C-S-H jel which glues aggregates together.
 No significant reaction till 14 days.
Hydration of cement compounds
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22. Portland Cement

23. Portland Cement

24. Hydration of cement compounds
 Hydration of C3A and C4AF
 C3A Reacts rapidly to form C2AH6 resulting in immediate
set.
 When gypsum (CaSO4·2H2O) is added, the reaction
becomes
C3A + 3C + 3 S + 32H ⇒ C3A·3CS ·32H (ettringite).
Avoid immediate set.
On consumption of Gypsum the reaction turns to (ettringite).
C3A·3CS· 32H + 2C3A + 4H ⇒ 3(C3A·CS ·12H).
C4AF is variable but generally slow.
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25. Hydration of Cement

26. Hydration of Cement
Mixing Period
Different ions are
dissolved .
Process is rapid and
Exothermic
C-S-H is formed on
surface of cement.
Ettringite is formed by
Cellite.
Reaction slows down
due to protective layer
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27. Dormant Period
Reaction slows
down between
1-2 hours.
Silicates (alite
And belite) slowly
dissolve, releasing
calcium ions in
solution
Hydration of Cement
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28.  Hardening (2–4 hours)
 The solution eventually becomes
supersaturated with calcium ions,
triggering the formation of new
compounds.
 (C-S-H, fiber-like particles), which
adheres to aggregate and gives
concrete its strength.
 Calcium hydroxide (CH, crystals).
 “Initial set” occurs when enough C-S-
H and CH form to mesh together,
causing the mix to stiffen
 Final set” occurs when the concrete
achieves a defined stiffness, about
when the concrete is hard enough to
walk on.
 needle-like solid (Ettringite) that
contributes somewhat to early
strength.
Hydration of Cement
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29. Hydration of Cement
 Cooling
 Soon after final set, the
buildup of C-S-H and CH
begins to limit access of
water to undissolved cement.
Silicate reactions slow. Heat
peaks and begins to drop.
 Sulfate will be depleted. Any
remaining aluminate then
reacts .This has little effect
on concrete properties except
for a brief increase in heat.
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30.  Densification or
Hardening
 Alite hydrate and provide
early strength.
 Belite dissolves slowly than
alite and start to have an
impact on concrete
strength after 10-14 days.
Hydration of Cement
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31. Portland Cement
On Mixing 6 hours
After 7 Days After 1 Year

32. Portland Cement

33. Heat of Hydration
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35. SettingofCement
 Stiffening of the cement paste
 Change from fluid to a rigid state
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36. Setting of cement
Stiffening of cement paste to defined consistency is called
setting.
 Flash Set
 True Set
 False Set
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37. Setting
False Set Flash Set
 Abnormal premature
stiffening of cement within
few minutes of mixing of
water
 No appreciable heat is
evolved
 Remixing the cement paste
without additional water
restores plasticity
 No loss in strength
 Cement sets in quickly
 Difficult to work with
 C3A is main cause of flash
set
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39. Fineness of Cement
 Surface area of cement particles in square
meter per kg (1.1x10¹² particles/kg) 160-300
m²/kg
 Better workability
 Finer the cement better is hydration
 Cost of grinding is higher
 Finer the cement, it requires more gypsum
 Storage life less
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Cement Types
 Portland Cement
 Ordinary Portland Cement
 Rapid Hardening or High Early Strength Portland
Cement
 Low Heat Portland Cement
 Sulphate Resistant Portland Cement
 Water Repellent Portland Cement
 Water Proof Portland Cement
 Air Entraining Portland Cement
 Pozzolan Portland Cement
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Cement Types
 OtherVarieties of Cement
 High Alumina Cement
 Quick Setting Cement
 Blast Furnace Slag Cement
 White Cement
 Colored Cement
 Expanding Cement
 HydrophobicCement
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Cement Types
 Rapid Hardening or High Early Strength Cement
 Gains strength faster than OPC. In 3 days develops 7
days strength of OPC with same water cement ratio
 Initial and final setting times are same as OPC
 Contains more tri-calcium silicate at the expense of
di-calcium silicate
 more finely ground
 Emits more heat during setting, therefore unsuitable
for mass concreting
 Lighter and costlier than OPC. Short curing period
makes it economical
 Used for structures where immediate loading is
required e.g. repair works
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Cement Types
 Quick Setting Cement
 Sets faster than OPC
 Initial setting time is 5 minutes
 Final setting time is 30 minutes
 Used for concreting in underwater or running
water
 Mixing and placing has to be faster to avoid initial
setting prior to laying
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Cement Types
 Low Heat Cement(LHPC)
Heat of hydration - 250 j/gm as compared to opc
which is 420-500j/gm
 Low percentage (5%) of tri-calcium aluminates and
silicate and high (46%) of di-calcium silicate to keep heat
generation low
 Initial and final setting times nearly same as OPC
 Very slow rate of developing strength
 Not suitable for ordinary structures
 Shuttering required for long duration so cost will increase
 Prolonged curing is required
 Structure utilization will be delayed
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Cement Types
 Air Entraining Cement
 OPC with small quantity of air entraining
materials (resins, oils, fats, fatty acids) ground
together
 Air is entrained in the form of tiny air bubbles
during chemical reaction
 Concrete is more plastic, more workable, more
resistant to freezing
 Strength of concrete reduces somewhat
 Quantity of air entrained should not be more than
5% to prevent excess strength loss
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Cement Types
 White Cement
 OPC with pure white color produced with white
chalk free from iron oxide
 Instead of coal, oil fuel is used for burning
 Much more costlier than OPC
 Colored Cement
 Suitable pigments used to impart desired color
 Pigments used should be chemically inert and
durable under light, sun or weather
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Cement Types
 Sulphate Resistant Portland Cement
 Percentage of tricalcium aluminate is kept below
5% resulting in increase in resisting power against
sulphates
 Heat developed is almost same as Low Heat
Cement
 Theoretically ideal cement. Costly manufacturing
because of stringent composition requirements
 Used for structures likely to be damaged by severe
alkaline conditions like bridges, culverts, canal
lining, siphons, etc
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Cement Types
 Portland Pozzolana Cement
 OPC clinker and pozzolana (calcined clay, surkhi
and fly ash) ground together
 Properties same as OPC
 Produces less heat of hydration and offers great
resistance to attacks of sulphates and acidic
waters
 Used in marine works and mass concreting
 Ultimate strength is more than OPC but setting
timings are same as OPC
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49. Cement Properties
 Chemical composition shown earlier
 Fineness. Finer cements react quicker with water and increase shrinkage
and cracking of concrete. Fineness 280-400 m²/kg
 Shrinkage. Change in volume of concrete after setting. It may cause
cracks, distortion and disintegration of concrete
 Setting time
 Initial setting time is that stage after which any cracks that may appear
do not reunite. 30 minutes for OPC
 Final setting is that stage when it has attained sufficient strength and
hardness. Maximum final setting time is 600 min.
 Compressive strength of cement and sand mortar should not be less than
 115 kg/cm² after 3 days
 175 kg/cm² after 7 days
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50. Plain & Reinforced Concrete – I Fall Semester 2021 (Atif Rasheed
Thank you for your attention