Cement pptx

Unit- 1
CEMENT
CONCRETE TECHNOLOGY

Cement is a fine, soft, powdery-type substance
• It is made from a mixture of elements that are
found in natural materials such as limestone,
clay, sand and/or shale
• When cement is mixed with water, it can bind
sand and aggregates into a hard, solid mass
called concrete
- NEIL ARMSTRONG

Cement
Cement is a fine, soft, powdery-type substance
• It is made from a mixture of elements that are found in natural
materials such as limestone, clay, sand and/or shale
• When cement is mixed with water, it can bind sand and
aggregates into a hard, solid mass called concrete

History of Cement
In 1824, Joseph Aspdin, a British stone mason, heated a mixture of
finely ground limestone and clay in his kitchen stove and ground the
mixture into a powder to create a hydraulic cement—one that
hardens with the addition of water.
He took a patent for this cement
• A variety of sandstone is found in abundance in Portland in
England
• Hence it is called as “ORDINARY PORTLAND CEMENT”
In India, the first cement factory was installed at Tamil Nadu (1904)
by South India Industry Limited

History of Cement
Four essential elements are needed to make cement. They are
Calcium, Silicon, Aluminum and Iron
• Calcium (which is the main ingredient) can be obtained from
limestone, whereas silicon can be obtained from sand
• Aluminum and iron can be extracted from bauxite and iron
ore, and only small amounts are needed

Chemical Composition of Cement
The raw materials used for the manufacture of cement consist
mainly of lime, silica, alumina and iron oxide
• These oxides interact with one another in the kiln at high
temperature to form more complex compounds
• The relative proportions of these oxide compositions are
responsible for influencing the various properties of cement, in
addition to rate of cooling and fineness of grinding

Chemical Composition of Cement

Functions of Ingredients of Cement
Lime (CaO)
• Major ingredient of cement
• Excess quantity of lime makes the cement unsound
• If it is less, it decreases the strength and allows the cement to set
quickly
Silica (SiO2)
• An important ingredient which gives strength to cement
• If it is in excess silica allows the cement to set slowly

Alumina(Al2O3)
• This imparts quick setting time to the cement
• If it is in excess quantity, it weakens the cement
• It also lowers the temperature of clinkers
Iron Oxide (Fe2O3)
• It helps the fusion of the raw materials during burning stage
• It gives colour, strength and hardness to cement

Magnesium Oxide (MgO)
• If present in small quantities, MgO imparts hardness and colour to
cement
• If becomes excess quantity, weakens the cement
Sulphur Trioxide (SO3)
• A very small quantity is required in the manufacturing of cement
• If it is in excess, SO3 makes the cement unsound

Alkalies
• A small quantity are required
• Alkalies and other impurities present in raw
materials are carried by the flue gases during
heating
• If it is in excess quantity, efflorescence is caused

Production and Composition
of Portland Cement

Hydration of Cement
During the manufacturing of cement, various constituents combine in burning and
form certain compounds
• These compounds formed during burning, react with water help in setting and
hardening of cement
• These compounds are called bogue compounds they are

Hydration of Cement
When water is added to cement a chemical reaction
starts between active components of cement
(C4AF,C3A,C3S andC2S) and water which is
exothermic in nature and liberate a significant amount
of heat
• This is known as hydration and the liberated heat is
called heat of hydration

Hydration Mechanism
When mixed with water, Portland cement hydrates and forms
heat.
Tricalcium silicate hydrates rapidly and forms earlier strength
and earlier heat of hydration.
Tricalcium silicate is formed in a kiln when the charge contains
an abundance of lime, and hence the greater amount of CaO in
the reaction.
3CaO·SiO2+H2O  CaO·2SiO2·3H2O+Ca(OH)2

Dicalcium silicate hydrates slowly and is
responsible for strength increase in concrete at
later ages.
The heat of hydration is liberated slowly.
More dicalcium silicate is formed when the raw
materials contain less lime.
2CaO·SiO2+H2O  3CaO·2SiO2·3H2O+Ca(OH)2
Hydration Mechanism

Tricalcium aluminate hydrates rapidly and liberates a
large amount of heat.
If this reaction were not controlled, concrete would
set so rapidly (flash set) that it could not be used in
modern construction.
3CaO·Al2O3+H2O  3CaO·Al2O3·6H2O
Hydration Mechanism

Water Requirement for Hydration
About an average 23 percent of water by weight of cement is required for
complete hydration of Portland cement
• This water combines chemically with the cement compounds
• Some quantity of water, about 15 percent by weight of cement, is required to
fill the cement gel pores
• A total of 38 percent of water by weight of cement is required to complete the
chemical reaction If excess water is present, it will lead to capillary cavities
• In a month’s time 85 to 90 % of the cement gets hydrated and cement attains
almost its full strength
• Hydration still continues and cement grows stronger with time
• Total 50% of water by weight of cement is required for complete hydration

Types of Cement
Ordinary
Portland
Cement(OPC
)
Quick Setting
Cement
High Alumina
Cement
White
Cement
Low heat
Cement
Rapid
Hardening
Cement
Sulphate
Resisting
Cement
Portland
Pozzolana
Cement
Coloured
Cement

Ordinary Portland Cement(OPC)
It is a common variety of cement
It is suitable for the construction of all civil engineering works except under water
constructions
Uses of Ordinary Portland Cement
• Structures requiring great strength such as heavy buildings and bridges light houses,
docks, reservoirs, etc.
Foundations in wet places, and structures subjected to the action of water such as
• Retaining walls
• Watertight floors
• Cement mortar for plastering, pointing etc
• Plain concrete

Ordinary Portland Cement(OPC)
Uses of Ordinary Portland Cement
For making
• Reinforced cement concrete for laying floors ,roofs, lintels, beams, etc,.
• Reinforced brick work
• In drainage and water supply works like water storage tanks, septic, tanks, etc,.
• For protecting the external faces of buildings or engineering structures from
weathering action
• For thin masonry works, where strength is required
• Making joints for drains, pipes etc,.
• Manufacturing of precast pipes, piles, garden benches, fencing posts, flower pots,
etc,.
• Preparation of foundations, watertight floors, footpaths, etc,.

Quick Setting Cement
• As the name indicates, it sets very fast
• The early setting property is brought out by reducing the amount of gypsum during
the grinding process
• This cement is costlier than ordinary Portland cement
• Initial setting time starts within 5 minutes, after adding water
• Final setting time: within 30 minutes
• It is ground much finer than OPC
Advantages
• It is used in construction of structures under water, in water logging areas, rivers, in
running water like canals and streams and pipe lines etc.
• It is also used in emergency circumstances where quick setting of cement is needed.

White Cement
Raw materials like china clay and pure lime stone are used to get pure white colour
• It is a variety of OPC
• It is prepared from such materials which are practically free from colouring oxides of
iron and manganese
• For burning of this cement, the oil fuel is used instead of coal
• It is white in colour
Uses
• It is used for floor finish, plaster work, ornamental work, etc
• It is also used to fill the small holes during sanitary, water supply fittings, wall tiles
etc

TESTING OF CEMENT
Testing of cement can be brought under two
categories:
(a) Field testing
(b) Laboratory testing.

Field Testing
It is sufficient to subject the cement to field tests when it is used for
minor works.
The following are the field tests:
(a) Open the bag and take a good look at the cement. There should not
be any visible lumps. The colour of the cement should normally be
greenish grey.
(b) Thrust your hand into the cement bag. It must give you a cool feeling.
There should not be any lump inside.
(c) Take a pinch of cement and feel-between the fingers. It should give a
smooth and not a gritty feeling.
(d) Take a handful of cement and throw it on a bucket full of water, the
TESTING OF CEMENT

Field Testing
(e) Take about 100 grams of cement and a small quantity of water and make
a stiff paste.
From the stiff paste, pat a cake with sharp edges.
Put it on a glass plate and slowly take it under water in a bucket.
See that the shape of the cake is not disturbed while taking it down to the
bottom of the bucket.
After 24 hours the cake should retain its original shape and at the same
time it should also set and attain some strength.
TESTING OF CEMENT

Laboratory Testing
1. Fineness test.
2. Standard Consistency Test
3. Setting time test.
4. Strength test.
5. Soundness test.
6. Heat of hydration test.
7. Chemical composition test.
TESTING OF CEMENT

1. Fineness of Cement
Influences the rate of hydration and hence on the rate of gain of strength and the rate of
evolution of heat.
Finer cement offers a greater surface area for hydration and hence faster the development of
strength.
Size of a cement particle < 100 micron and > 1.5 micron and an average size of the cement
particles 10 micron.
The particle size fraction below 3 microns has been found to have the predominant effect on the
strength at one day while 3-25 micron fraction has a major influence on the 28 days strength.
Increase in fineness of cement is also found to increase the drying shrinkage of concrete.
In commercial cement it is suggested that there should be about 25-30 per cent of particles of
less than 7 micron in size.
Disadvantage: Fine grinding may lead to airset and early deterioration

1. Fineness of Cement
Fineness of cement is tested in two ways :
(a) By seiving.
(b) By determination of specific surface (total
surface area of all the particles in one gram of
cement) by air-permeability apparatus.
Expressed as cm2/gm or m2/kg. Generally
Blaine Air permeability apparatus is used.

Sieve Test
Weigh correctly 100 grams of cement and take it on a standard IS Sieve No. 9 (90
microns). Break down the air-set lumps in the sample with fingers. Continuously sieve the
sample giving circular and vertical motion for a period of 15 minutes. Mechanical sieving
devices may also be used. Weigh the residue left on the sieve. This weight shall not exceed
10% for ordinary cement. Sieve test is rarely used

Air Permeability Method
To determine the fineness of cement by total
surface area in sq. cm/gm. of cement or in
m2/kg..
Can measure the specific surface of cement
using this apparatus .
Principle: Relation between the flow of air
through the cement bed and the surface area of
the particles comprising the cement bed.
From this the surface area per unit weight of the
body material can be related to the permeability
of a bed of a given porosity.
The cement bed in the permeability cell is 1 cm.
high and 2.5 cm. in diameter.
The weight required to make a cement bed of
porosity of 0.475 can be calculated from the
density of cement. Lea and Nurse Air Permeability Appartus

Air Permeability Method
This quantity of cement is placed in the
permeability cell in a standard manner.
Slowly pass on air through the cement bed
at a constant velocity.
Adjust the rate of air flow until the flowmeter
shows a difference in level of 30-50 cm.
Read the difference in level (h1) of the
manometer and the difference in level (h2)
of the flowmeter.
Repeat these observations to ensure that
steady conditions have been obtained as
shown by a constant value of h1/h2

Specific surface Sw is calculated from the following formula:
where, ξ= Porosity, i.e., 0.475
A = Area of the cement bed
L = Length (cm) of the cement bed
d = Density of cement, and
C = Flowmeter constant
Fineness can also be measured by Blain Air Permeability apprartus.

2. Standard Consistency Test
Consistency that permits a Vicat plunger having 10 mm diameter and 50 mm
length to penetrate to a depth of 33-35 mm from the top of the mould.
This appartus is used to find out the percentage of water required to produce a
cement paste of standard consistency.
The standard consistency of the cement paste is some time called normal
consistency (CPNC)

Standard Consistency Test
Take about 500 gms of cement and prepare a paste with
a weighed quantity of water (say 24 per cent by weight
of cement).
The paste must be prepared in a standard manner and
filled into the Vicat mould within 3-5 minutes.
After completely filling the mould, shake the mould to
expel air.
A standard plunger, 10 mm diameter, 50 mm long is
attached and brought down to touch the surface of the
paste in the test block and quickly released allowing it to
sink into the paste by its own weight
Take the reading by noting the depth of penetration of
the plunger.
First
Trail

Conduct a 2nd trial (say with 25 per cent of water) and
find out the depth of penetration of plunger.
Similarly, conduct trials with higher and higher
water/cement ratios till such time the plunger penetrates
for a depth of 33-35 mm from the top
That particular percentage of water which allows the
plunger to penetrate only to a depth of 33-35 mm from the
top is known as the percentage of water required to
produce a cement paste of standard consistency.
This percentage is usually denoted as ‘P’.
The test is required to be conducted in a constant
temperature (27° + 2°C) and constant humidity (90%).
Standard Consistency Test

Setting Time of Cement
For There are two type of setting time:-
1. Initial setting time:-
2. Final setting time:-
An arbitrary division has been made for the setting time of cement as
initial setting time and final setting time.

In actual construction dealing with cement paste, mortar or concrete certain
time is required for mixing, transporting, placing, compacting and finishing.
During this time cement paste, mortar, or concrete should be in plastic
condition.
The time interval for which the cement products remain in plastic condition is
known as the initial setting time
Normally a minimum of 30 minutes is given for mixing and handling
operations.
The constituents and fineness of cement is maintained in such a way that the
concrete remains in plastic condition for certain minimum time.

Once the concrete is placed in the final position, compacted and finished, it should lose
its plasticity in the earliest possible time so that it is least vulnerable to damages from
external destructive agencies.
This time should not be more than 10 hours which is often referred to as final setting
time.
The Vicat Appartus is used for setting time test also.
 Take 500 gm. of cement sample and guage it with 0.85 times the water required to
produce cement paste of standard consistency (0.85 P).
The paste shall be gauged and filled into the Vicat mould in specified manner within 3-5
minutes.
Start the stop watch the moment water is added to the cement. The temperature of water
and that of the test room, at the time of gauging shall be within 27°C ± 2°C.

Initial setting time is regarded as the time elapsed
between the moment that the water is added to the
cement, to the time that the paste starts losing its
plasticity.
The time interval for which the cement products
remain in plastic condition is known as the initial
setting time.
Normally a minimum of 30 minutes is given for
mixing and handling operations.

Lower the needle gently and bring it in contact with the surface
of the test block and quickly release.
Allow it to penetrate into the test block. In the beginning, the
needle will completely pierce through the test block.
But after some time when the paste starts losing its plasticity,
the needle may penetrate only to a depth of 33-35 mm from the
top.
The period elapsing between the time when water is added to
the cement and the time at which the needle penetrates the test
block to a depth equal to 33-35 mm from the top is taken as
initial setting time.

The final setting time is the time elapsed between
the moment the water is added to the cement, and
the time when the paste has completely lost its
plasticity and has attained sufficient firmness to
resist certain definite pressure.
This time should not be more than 10 hours.

Replace the needle (C) of the Vicat appartus by a
circular attachment (F) The cement shall be
considered as finally set when, upon, lowering the
attachment gently cover the surface of the test block,
the centre needle makes an impression, while the
circular cutting edge of the attachment fails to do so.
The paste then has attained such hardness that the
centre needle does not pierce through the paste
more than 0.5 mm.

Strength Test
The compressive strength of hardened cement
is the most important of all the properties.
Strength tests are not made on neat cement
paste because of difficulties of excessive
shrinkage and subsequent cracking of neat
cement.
Strength of cement is indirectly found on
cement sand mortar in specific proportions.
The standard sand is used for finding the
strength of cement.
It shall conform to IS 650-1991.

Strength Test
Take 555 gms of standard sand (Ennore sand), 185 gms of
cement (i.e., ratio of cement to sand is 1:3) in a non-porous
enamel tray and mix them with a trowel for one minute,
Then add water of quantity P/4 +3.0 per cent of combined
weight of cement and sand and mix the three ingredients
thoroughly until the mixture is of uniform color, for not less than
3 minutes nor more than 4 minutes.
Immediately after mixing, the mortar is filled into a cube mould
of size 7.06 cm.
The area of the face of the cube will be equal to 50 sq cm.
Compact the mortar either by hand compaction in a standard
specified manner or on the vibrating equipment (12000 RPM)
for 2 minutes..

Strength Test
Keep the compacted cube in the mould at a temperature of 27°C ± 2°C
and at least 90 per cent relative humidity for 24 hours.
Where the facility of standard temperature and humidity room is not
available, the cube may be kept under wet gunny bag to simulate 90
per cent relative humidity.
After 24 hours the cubes are removed from the mould and immersed in
clean fresh water until taken out for testing.
Three cubes are tested for compressive strength at the periods
mentioned in Table 2.5.
The periods being reckoned from the completion of vibration.
The compressive strength shall be the average of the strengths of the
three cubes for each period respectively.
The strength requirements for various types of cement is shown in
Table 2.5.

4. SOUNDNESS TEST
It is very important that the cement after setting shall not undergo any
appreciable change of volume.
This test is to ensure that the cement does not show any subsequent
expansions.
The unsoundness in cement is due to the presence of excess of
lime combined with acidic oxide at the kiln.
This is due to high proportion of magnesia & calcium sulphate.
Therefore magnesia content in cement is limited to 6%. Gypsum 3-5.

APPARATUS FOR SOUDNESS TEST
It consists of a small split cylinder of spring brass.
It is 30mm diameter & 30mm high.
Cement is gauged with 0.78 times & filled into the mould & kept on
a glass plate & covered with another glass plate.
This is immersed in water at a temperature 270c-320c for 24
hours.
Measure the distance between indicators.
Heat the water & bring to boiling point of about 25-30min.
Remove the mould from the water after 3 hours.
Measure the distance between the indicators.
This must not exceed 10mm for ordinary, rapid hardening, low
heat Portland cements.
If this expansion is more than 10mm the cement is said to be
unsound.

Heat of Hydration
The reaction of cement with water is exothermic. The reaction
liberates a considerable quantity of heat.
This can be easily observed if a cement is gauged with water and
placed in a thermos flask. Much attention has been paid to the heat
evolved during the hydration of cement in the interior of mass
concrete dams.
It is estimated that about 120 calories of heat is generated in the
hydration of 1 gm. of cement. From this it can be assessed the total
quantum of heat produced in a conservative system such as the
interior of a mass concrete dam.
A temperature rise of about 50°C has been observed.
This unduly high temperature developed at the interior of a concrete
dam causes serious expansion of the body of the dam and with the
subsequent cooling considerable shrinkage takes place resulting in
serious cracking of concrete.

Heat of Hydration
The use of lean mix, use of pozzolanic cement, artificial cooling of constituent materials
and incorporation of pipe system in the body of the dam as the concrete work
progresses for
circulating cold brine solution through the pipe system to absorb the heat, are some of
the
methods adopted to offset the heat generation in the body of dams due to heat of
hydration
of cement.
Test for heat of hydration is essentially required to be carried out for low heat cement
only.
This test is carried out over a few days by vaccum flask methods, or over a longer
period
in an adiabatic calorimeter.

Chemical Composition Test
It is sufficient to give the limits of chemical requirements.
The Table 2.6 shows the various chemical compositions of all types of cements.
Ratio of percentage of lime to percentage of silica, alumina and iron oxide, when
calculated by the formulae,
Not greater than 1.02 and not less than 0.66
The above is called lime saturation factor per cent.
Table 2.5 gives the consolidated physical requirements of various types of cement.
Table 2.6 gives the chemical requirements of various types of cement

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