Cement ingredients, composition and Test on cement
Cement is one of most important construction material, because it provide
strength and durability to the structure, so Right choice of it is greatly
affect the structure quality and life.
Before proceed ahead, We should know difference between below terms.
What is Ingredient and Composition of cement?
Ingredient means raw materials use in manufacturing of cement. Strength
and setting time of cement is greatly affected by this, so proper quantity
of each raw material is require.
There are enlisted ingredient use in manufacturing of cement.
- Lime
- Silica
- Alumina
- Iron Oxide
- Magnesium Oxide
- Sulphur Trioxide
- Alkalies
Composition is nothing but compound form after the chemical process and
heating of raw material.
Composition of cement is listed below.
- Tricalcium silicate (C3S)
- Dicalcium silicate (C2S)
- Tricalcium Aluminate (C3A)
- Dicalcium Alumino Ferrite (C2AFe)
Ingredients of Cement and their function:
Proportion of each Ingredient:
Lime :
Lime is one of main and most important ingredient in manufacturing of
cement. Cement consist almost 63% of lime.
it is responsible for strength and soundness of cement. Excess amount of
lime makes cement unsound.
Here what is Soundness?
Soundness can be define as gaining strength in Cement within acceptable
expansion.
So excess lime cause excess expansion in cement, which cause
disintegration of cement.
Cement consist 22% of silica. Silica provide strength to cement. It make
dicalcium silicate and tricalcium silicate. Surplus amount of silica cause
slow setting of cement.
Alumina:
6% of Alumina is use in production of cement. Alumina is responsible for
formation of foam in cement. It produce TricalciumAluminate, Dicalcium Alumino Ferrite. This two compositions are responsible for
quick setting to cement and development of temperature during
hydration.
Cement consist 3% iron oxide. Iron oxide deliver colour, hardness and
strength to cement. It also very useful during kiln process of
manufacturing of cement.
Magnesium oxide:
Cement comprise 2.5% Magnesium oxide. Small amount of Magnesium oxide
gives hardness and colour to cement, But excess of it make cement
unsound.
Sulphur trioxide:
1.5% of sulphur trioxide present in cement. It's function is almost same
as Magnesium oxide, because small quantity of it make cement sound and
high cause unsoundness in cement.
Alkalies:
There are 1.5% Alkalies in cement. It should be very less in quantity
because it cause efflorescence.
Composition of Cement:
During the kiln process in manufacturing of cement, this chemical
composition is produce. Which are in following composition.
Tricalcium silicate:
Cement consists 40% tricalcium silicate in clinker. Tricalcium silicate
is responsible for the rapid hardening of cement.
Due to Tricalcium silicate hydration of cement taken place rapidly, so it
is responsible for early strength of cement, and due to quick hydration
more heat will be generate in cement.
Disadvantage of tricalcium silicate is that due to high hydration heat,
there are more chances of development of crack. It consist less resistance
against sulphate attack.
Dicalcium silicate:
There are 32% dicalcium silicate in cement clinker. Dicalcium silicate
provide ultimate strength to cement. It hydrate at slow pace. It harden
slowly, due to it there are less hydration heat.
It consists high resistance against sulphate attack.
Note: up to here, we have understood that tricalcium silicate and dicalcium
silicate are responsible for early strength and production of high
hydration heat in cement.
By increasing tricalcium silicate and reducing in dicalcium silicate,
we can make rapid hardening cement. Which suitable for cementing in cold
region
At high percentage of dicalcium silicate and low percentage of
tricalcium silicate in cement get harden slowly, less hydration heat,
more resistance to sulphate attack.
Tricalcium aluminate:
There are 10.5% tricalcium aluminate in cement. It is first composition
in cement to react with water. It is responsible for the initial setting
of cement. As it react very fast with water so there are high hydration
heat.
Tetra calcium alumino ferrite:
Cement comprise 9% tetra calcium alumino ferrite. It can not react easily
with water, so it produce very low hydration heat.
Hint:
according to upper both composition we can say that initial setting time
of cement is depend upon it. By increase tricalcium aluminate in cement
clinker, we can reduce initial setting time of cement.
Tests on cement:
Quality of cement greatly affects on quality of construction, so to
decide best quality some tests on it should be conducted.
This test can be divided in two parts. Test conducted in lab and second one
on site. In this part we will focus on test conducted in lab in
detail.
Tests in Lab
Fineness test:
Cement should be well grind. To check it this test is adopted. Fine
cement have more surface area per unit weight and fast gaining of
strength. It can be perform two way either sieve method or air
permeability method.
Sieve method:
This method is rarely use now a day. In this method cement is sieve
through 90 micron sieve by shaking horizontal and vertical direction. For
well graded cement residue should not more than 10% by sample
weight.
Air Permeability method:
Blaine's apparatus is use for air permeability method. In this method
fineness is define in specific surface term. Here specific surface means
total surface area per unit weight in gram. It is measure in cm²/
gm.
For good ordinary Portland cement specific surface should be 2250 cm²/
gm.
Consistency Test:
This test is adopted for determination of consistency of cement, initial
and final setting time.
To conduct this test vicat's apparatus is use. Plunger of it is 10mm dia
and consist 40mm to 50mm length.
In this test plunger is allow to penetrate through freshly mix cement mortar up to 33mm to 35mm depth at 25°C to 29°C temprature and 20% humidity.
This test is conducted for three times.
Consistency of cement can be define as amount of water content, which
allow plunger to penetrate in cement mortar at 33mm to 35mm depth within 3
to 5 minute of mixing.
Consistency of cement should be 25% by weight of cement.
Initial setting time:
To decide initial setting time vicat's apparatus is use. In it time
require by cement past to penetrate plunger to depth of 33mm to 35mm is
counted.
It must be greater than 30 minutes.
Final setting time:
To decide it cement is allow to hard until plunger can not penetrate
more than 0.5mm in cement paste. This hardening time is known as final
setting time.
Final setting time should not more than 10 hour.
Soundness test:
We have discussed soundness of cement already. To decide it Le Chatelier
apparatus is use. This test is conducted to decide amount of lime and
magnesium in cement, because excess amount make cement unsound and cause
expansion.
Expansion of cement should not more than 10mm to avoid cracking and
disintegration.
Tensile strength of Cement:
This test is conducted on briquettes in tensile testing machine. Mortar
for it is made in 1:3 ratio. Which should be well cured for 3 to 7 days at
25°C tempreture.
Tensile strength of briquettes are measured at 3rd and 7th day after
curing. Which are not less than 2 N/mm² after 3 day and 2.5N/mm² after
7 days.
Compression test:
Compression test is carried out on universal testing machine on cement
mortar cube of 1:3 proportion.
Total six cube are being tested in it. Three cubes are tested after 3 days
of curing and remaining after 7 days of curing.
Compression strength of cement should not less than 11.5 N/mm² after 3
days and 17.5 N/mm² after 7 days.
Field Tests
Following tests should be adopted on cement on field to check
suitability of it for construction.
Manufacturing and expiry date:
cement lost it's strength with passing of time. It must be use within 90
days of manufacturing.
Colour:
colour of cement must be evenly light brow.
Presence of Lumps:
Cement bag with lump must be rejected because it indicate reaction of
cement with atmospheric water. Lumpy cement resolve less strength.
Rubbed test:
Cement should smooth, when you rubbed it between fingers. If it is not,
than it indicate impurity in it.
Floating test:
Cement should float on water for some time before sinking in water.
We will publish more detail blog on tests on cement.
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