Transcript Cement.pptx

Cement
Cement
• Ordinary Portland Cement
(OPC)
• Rapid Hardening Portland Cement
(RHPC)
• Sulphate Resistant Portland Cement
(SRPC)
• White Portland Cement
(WPC)
Specialised Portland Cements:
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Masonry Portland Cement
Low Heat Portland Cement
Hydrophobic Portland Cement
Oil-well Portland Cement
Alternative Cement Replacement Materials
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Blastfurnace Slag Cement
Pulverised-fuel Ash Cement
Metakaolin
Rice Husk Ash
Silica Fume
(GGBS)
(PFA)
Cements in Europe are classed as CEM1 (OPC or RHPC),
CEM2-4 (OPC with limestone, PFA or GGBS) in varying
proportions pre-blended
• Chemistry of OPC
• Manufacture
1. Cement Manufacture
2. Water
• Should be free from impurities
• Unsuitable if it contains - sugars
- sulphates
- chlorides
• Sea water must not be used for reinforced
concrete
• Section A.1
Basic Materials
Hydration
• Setting and hardening results from a chemical reaction between the cement and
the water, not from a drying process.
• The reaction is exothermic and is irreversible. The heat produced is known as the
“Heat of Hydration” C3A and C3S are the compounds primarily responsible.
• The paste is usually workable up to two hours before it begins to harden
• Strength gain is initially rapid becoming progressively less rapid
• Strength gain continues indefinitely provided moisture is present.
“Curing”
Section A.2 Fresh Concrete Properties
2.
Cement hydration
Cement + H2O = Calcium Silicate Hydrate (C-S-H) +Ca (OH)2 +H2O
Section A.2 Fresh Concrete Properties
2.
Cement hydration and heat generation
• Section A.1
Basic Materials
2. Cement paste strength gain
Basic components of the cement production process
Portland Cement Manufacturing
Process
cement is a binder, a substance
that sets and hardens
independently, and can bind other
materials together.
Composition of Ordinary Cement
i)Argillaceous - Clay predominates
ii)Calcareous - Calcium carbonate predominates
Ingredient
% Responsible for
Lime
62 strength characteristics to the cement
Silica
22 strength to the cement
Alumina
Gypsum
5
Setting action of the cement
4
Prolonging the initial setting action
3
Imparting colour to the cement,
Iron Oxide
Magnesia
Alkalies
Sulphur
increasing strength & hardness
2
Imparting strength & hardness
1
Produces ellforescent.
1
Imparting soundness to cement.
THE CEMENT MANUFACTURING PROCESS
quarry
dumper
loader
Quarry face
1. BLASTING
2. TRANSPORT
storage at
the plant
crushing
conveyor
3. CRUSHING & TRANSPORTATION
1. BLASTING : The raw materials that are used to manufacture cement (mainly limestone and clay) are blasted
from the quarry.
2. TRANSPORT : The raw materials are loaded into a dumper.
3. CRUSHING AND TRANSPORTATION : The raw materials, after crushing, are
transported to the plant by conveyor. The plant stores the materials before they are
homogenized.
Next
THE CEMENT MANUFACTURING PROCESS
Raw grinding and burning
storage at
the plant
Raw mill
conveyor
preheating
Raw mix
1. RAW GRINDING
kiln
cooling
clinker
2. BURNING
1. RAW GRINDING : The raw materials are very finely ground in order to produce the raw mix.
2. BURNING : The raw mix is preheated before it goes into the kiln, which is heated by a flame that can
be as hot as 2000 °C. The raw mix burns at 1500 °C producing clinker which, when it leaves the kiln, is
rapidly cooled with air fans. So, the raw mix is burnt to produce clinker : the basic material needed to
make cement.
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THE CEMENT MANUFACTURING PROCESS
Grinding, storage, packing, dispatch
Gypsum and the secondary additives are added
to the clinker.
clinker
storage
Finish grinding
1. GRINDING
silos
dispatch
bags
2. STORAGE, PACKING, DISPATCH
1.GRINDING : The clinker and the gypsum are very finely ground giving a “pure cement”. Other secondary
additives and cementitious materials can also be added to make a blended cement.
2. STORAGE, PACKING, DISPATCH :The cement is stored in silos before being dispatched either in
bulk or in bags to its final destination.
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Clinker
cement mill
Characteristics of Portland cement
1) Colour – uniform
2) Uniform fineness & free of lumps.
3) The average compressive strength
3 days - 16 Mpa &
7 days - 22 Mpa
4) The average tensile strength,
3 days - 2 MPa at & 7 days - 2.5 Mpa
4) Initial setting time > 30 minutes & final
setting time < 10 hours.
5) The residue by weight should be less than
10%, when cement is seived on 90 micron IS
seive.
6) The loss of ignition should be lesser than 4%.
7) The insoluble residue in cement should be
lesser than 1.5%
8) The ratio of percentage of alumina to that of
iron oxide should be greater than 0.66.
Uses of Cement
•Cement mortar can be used for masonry work,
pointing, plastering etc.,
•Concrete for laying floors, roofs and
constructing lintels, beams, weather sheds, stairs,
columns.
•Construction of most important engineering
structures such as Bridges,
dams, culverts,
tunnels, storage reservoirs, lighthouses, docks
and harbours.
•Construction of water tanks, walls, roads.
•Making joints for drains, pipes.
•Manufacture of precast pipes.
•Preparation of foundation, watertight floors, etc.
•Special cements like expansive cement is used for
repairs of cracks and white cement for ornamental
finish.
•High alumina cement is used for furnace
insulation.
•Low heat cement is used for construction of
dams.
•Quick setting cement is used for constructing
structures near sea coast.
•For normal reinforced concrete work Grade 33
cement may be used
•For making precast concrete components and
pre-stressed concrete railway sleepers Grade 43
cement is used
•For construction of major bridges, frames of
high rise buildings Grade 53 cement is used.
Field Test
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Colour
Physical properties
Presence of lumps
Strength
Colour should be uniform
Typical cement colour (gray colour with light greenish shade)
It gives an indication of excess of lime or clay and the degree
of burning.
Physical properties
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Feel smooth when touched or rubbed in between fingers.
If felt rough, indicates adulteration with sand.
If hand is inserted in cement bag, hand feels cool and not warm.
If it immersed in water, it should sink and should not float
• A paste of cement feel sticky
• If it contains clay & silt as adulterant, it give earthy smell.
Presence of Lumps
• It should free from hard lumps.
• It is due to the absorption of moisture from atmosphere.
• If a bag contains lumps it should be rejected.
Fineness
• Sieve test is conducted with the standard BIS sieve no. 9.
• 100g is taken and sieved for 15 min
• The residue should < 10%
Compressive strength
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Mortar of cement & sand is prepared, 1:3.
Water is added, water cement ratio 0.4:1
It is placed in moulds & form cubes of sides 70.6 or 76 mm.
The cement required is 185 or 235g
Compacted in vibrating machine in 2 min.
For 3 days: > 115 kg/cm2 or 11.5 N/mm2
for 7 days: > 175 kg/cm2 or 17.5 N/mm2
Tensile Strength
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Formerly used to have indirect indication for compressive
strength
At present used for rapid hardening test.
• After 3 days: > 20 kg/cm2
• After 7 days: > 25 kg/cm2
Consistency
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It is used to determine the % of water required for
preparing cement pastes for other tests
Types of cement
• General purpose porland cements
• Special purpose cements – additives
• OPC-based
• Rapid-hardening Portland cement
• Extra rapid-hardening cement
• Quick setting cement
• Low-heat Portland cement
• Sulphate-resisting cement
• Coloured Portland cement
• Water proof Portland cement
• Hydrophobic cement
• Air-entraining cement
• Expansive cement
• Oil-well cement
• Masonry cement
• Non OPC-based
• High alumina cement
• Composite or Multiple Blended Cements