Cement as construction Material : Important Properties|Types and use
What is cement??
Cement can defined as a powdery brown substance, Which get harden after
mixing with water due to hydration.
Cement is generally use as a binder in mortar. Which is made up of
calcium,silica and aluminium as primary substance.
Cement is most important construction material, Because it act as binder
material in mortar and concrete. It help aggregate and sand to adhere tight
to form solid structure.
Important Properties:
Hydration of Cement:
Hydration is nothing but chemical reaction between water and cement. Whole
process can be divided into three stages based on time period.
Setting of Cement:
When we add water in cement it becomes plastic. With passing of time it
become solid. This process of converting cement in solid state from plastic
state is known as setting of cement.
It can be further divided into two types
Initial setting:
settlement of cement between mixing and moulding is known as initial
hardening. It time frame should be as high as possible to facilitate more
time for transporting and casting of it.
Generally as per IS 456, It should me minimum 30 minute
Final setting:
Settlement of cement after placing is known as final settlement. It should
occure as early as possible to get early strength to cement.
It should be maximum 10 hour as per IS 456
Hardening of Cement:
After the final settlement cement gain strength. This gaining of strength
is known as hardening of cement. This is years long process.
Cement mortar cube
Crushing strength of Cement:
This is nothing but compressive strength of cement mortar after 28 days of
curing. This testing cube having 70.71mm wide and surface area 50 cm².
Specific surface of cement:
Surface area of all cement micro particles in 1 gm. It is measure in
cm²/gm
Grades of Cement:
According to IS 516-1959, Cement can be divided in three grade based on
specific surface.
Grade 33: 2250 cm²/gm
Grade 43: 3400 cm²/gm
Grade 53: 3400 cm²/gm
Note
: major differences between grade 43 and 53 are that Grade 53 have more
shrinkage and gain early strength in short time period, So it can be use
where early strength is require.
Types of Cement and their use:
There are different types of cement, which use in construction. All have
different properties,advantages and dis-advantages.
We can use suitable cement based on our requirement,if we know it
well.
Lets discuss important types of cement one by one.
Ordinary Portland Cement:
This is most use and common types of cement. Which is also known as
OPC.
This cement gets hardening slowly, so less crack and shrinkage
occure.
But major disadvantage is that it posses less chemical resisting strength,
so it can't be use in soil, which contain high sulphur.
This type of cement is suitable for all types of general
construction.
Rapid Hardening Cement:
As per name this type cement gain strength early, so it is also known as
Hight Early Strength cement.this early strength is due to high amount of tri
calcium silica and low amount of dia calcium silica. Normally this type of
cement contain less weight compare to other.
Major advantages of this cement are that it require less period of curing
and formwork, so it is economical.
But as It get strength faster, so there are more chances of developing of
cracks, so it can't be use for massive concrete work like dam.
This cement should be use, where early strength is require likewise road
construction, cold region.
Quick setting cement:
In quick setting cement high amount of alumina is uses, because it is
responsible for quick setting of cement
This cement is used, where quick setting of cement is require like running
water.
Note: difference between rapid hardening cement and quick setting cement is
that however quick setting cement set quickly, but it gain strength at
normal as OPC.
Portland pozzolana cement:
Portland pozzolana cement is made by adding 30% pozzolana in ordinary
Portland cement.
Pozzolana contain 80% silicious material, mostly clay.
In hydraulic structures like dam and canal, this cement is use.
Low heat Portland cement:
In this type of cement high amount of dia calcium silica is use, which is
responsible for rapid hardening and high heat. So there are less production
of heat
Due to less amount of tri calcium silica, hardening of cement will be slow,
so there are less compression strength. So it should not use for thin
structure.
This cement is mostly use in retaining wall.
Sulphate resisting Portland cement:
In Sulphate resisting Portland cement tri calcium aluminate is keep less
than 5%. Because of it chemical resistant capacity of cement is get
higher.
In alkaline land this kind of cement is use.
This cement is use in canal linings and culverts.
High Alumina cement:
Aluminium is responsible for hardening and strength of cement. This cement
contain 35% of alumina. So it settle quickly and get harden fast.
This types of cement is use, where quick hardening is require. In sea water
construction, chemical plants and furnaces, this type of cement is
use.
Blast furnace slag cement:
By mixing ordinary Portland cement clinker with blast furnace slag, this
cement is made. Due to it, it is cheaper as compare to OPC.
This cement develops low heat, so it contain less strength.
This one is mostly use in dams, bridge abutments and retaining wall.
Coloured cement:
This one is also known as colocrete. It is formed by adding 5% to 15%
require colouring pigment.
It is mostly use in finishing work, like wise floor,wall and other external
surfaces.
|
| White cement rendering work |
This cement is produce by raw material free from iron oxide, so it is white
ordinary Portland cement. It is costly as compare to other
cements.
White cement is mostly use for architectural purpose. Such as a building
external and internal rendering, precast Decorative structure,ceiling
etc.
Air Entraining Cement:
This cement is made by adding air entraining agent during grinding of
cement. Sodium salt and glue are use as air entraining agent.
This cement contain more workability, due to less water cement ratio, so
less cement is require for mortar and concrete.
This cement is suitable for cool region where frist action taken
place.
Hydrophobic cement:
During production water reppelling chemical is mix. Due to this, it contain high workability and
strength.
This cement unaffected by water, so this cement is use for hydraulic
structure like dams,retaining wall,spillway etc.
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