Concrete
Cement concrete is an artificial stone obtained by
mixing water in a mixture of cement sand and gravel when it dries. It also
provides reinforcement when cementing in concrete. Sand is used to increase
volume and reduce strength as needed and gravel is added to increase volume and
provide strength. Water combines with other components and allows the concrete
to undergo a chemical process. Concrete is manufactured according to the
strength of the weak. It depends largely on the ratio between the components of
the concrete.
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Concrete |
Types
Of Cement Concrete
There are three types of cement concrete in terms of
structure.
1.
Plain Cement Concrete
2.
Reinforced Cement Concrete
3.
Pre-Stressed Cement Concrete
Plain Cement Concrete
Cement concrete that does not use steel or any other
metal is called plain cement concrete. Such concrete has a particularly high
compressive strength but in tension such concrete is weakened. The compressive strength in such concrete is 10
percent relative to the tension. Such concrete is used only in places where
tension does not apply, such as in floors and foundations.
Reinforced Cement Concrete
In plain cement concrete, steel bars are used to
increase the tensile strength or to increase the compressive strength. Concrete
in which steel is given to reinforce any other metal bars is called Reinforced
cement concrete. This type of concrete is used everywhere in the building. Its
strength is much higher than that of plain cement concrete.
Pre-Stressed Cement Concrete
In this type of concrete the steel bars are
stretched before the use of concrete. Different components of the building are
manufactured in the factory using this type of concrete. It is stronger than
all other types of concrete. Steels bars in this type of concrete are used more
strongly. There are two types of it in terms of preparation.
o
Pre-tension R.C.C.
o
Post tension R.C.C.
Ingredient
Of Concrete:
To make cement concrete, the five components are
mixed in special proportions as required. These are the five components.
o
Cement
o
Fine Aggregate
o
Coarse Aggregate
o
Water
o
Reinforcement Bars
Cement
Ordinary Portland cement is used in common types of
works. Specific types are used for specific tasks. Whichever type is used must
be fresh and in accordance with the specified specification. Cement should be
stored in a dry place as it has a high moisture absorption capacity. If the
cement is frozen or partially frozen, such cement should not be used as the
strength of such cement is very low.
Fine Aggregate
Fine aggregates should be hard and granular and
should not contain soil, organic matter and other densities. The fine aggregate
should conform to the specified specification.
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Coarse Aggregate
Stone gravel, gravel and brick gravel are used as
coarse aggregate to make cement concrete. The size of the aggregate is
determined by the nature of the work. In case of using steel, the size of the
aggregate should not exceed the distance between two steel bars. Coarse
aggregate should not contain dirt and dust. Aggregate made of strong stone
should be used. Should use full baked bricks using brick aggregate. Not all
loaves of bread should be the same size Must be graded this increases the
weight and strength of the concrete.
Water
In the presence of water the cement is solidified by
chemical process. Concrete is weakened due to bad water. Therefore the water
used in making concrete should be clean, potable water is considered suitable
for making concrete also the water should not have lubrication and stagnation. Water
used in concrete should also not contain organic matter.
Reinforcement Bars
Steels used Reinforced
cement concrete are made from mild steel. In which the amount of carbon is less
than 0.25 percent. This steel is soft which can be easily bent. Bending steel,
there should be no cracks in the steel at the bending place Also steel should
be protected from rust. The size of the steel should be according to the
specification.
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Characteristics
Of Good Cement Concrete
A good concrete should have the following
Characteristics:
Strength
Concrete should be strong depending on the nature of
the work. Concrete is strong enough in compression but weak in tension. Steels
bars are used to strengthen the tension
Durability
Concrete should be durable so that it does not lose
its strength due to climatic effects such as wind, rain and temperature
changes. In addition the concrete must be strong enough against the chemical
effects in the atmosphere.
Fire Resistance
Concrete must be strong enough to withstand fire. In
the event of a fire, the building should not collapse too quickly.
Impermeability
Concrete should have a minimum of voids which will
increase the weight of the concrete which will give extra strength. The heavier
the weight, the greater the weight.
toughness
Concrete should be hard enough to prevent wear due
to friction. This feature should be especially in concrete used in floors and
roads.
Workability
The amount of water in the concrete should not be
excessive as it reduces the strength. Concrete should only be thin enough to be
easy to place.
Shrinkage
Concrete should be such that it shrinks to a minimum
when dry, with a slight increase in the amount of sand to remove this defect.
Fatigue
Concrete
should not be prone to breakage after bearing constant and constant weight. The
amount of water in the concrete should not be excessive as it reduces the
strength. Also, concrete should not be weakened by repeated loading and
unloading.
economy
Different types of concrete are produced for
different purposes. The concrete produced should be less costly depending on
the purpose.
Appearance
The finished surface of the concrete should be
beautiful because the right amount of water and the right amount of water
enhances the beauty of the concrete.
Process
Of Concreting
There are
many steps involved in preparing concrete and putting it in place for use which
is like as
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| process of concreting |
o
Mixing
o
Transportation
o
Placing
o
Compacting
o
Curing
Batching Of Concrete
The process of measuring different components of
concrete according to the ratio of concrete is called batching of concrete.
Components of concrete are measured in two ways
By Volume
By Weight
Batching
Of Concrete By Volume
For general types of construction work, different
components of concrete are measured in terms of volume. A box equal to the volume of a cement stall is
made to measure the components. The volume of a bag of cement is 35.5 liters ie
0.035(1.125cft) cubic meters. The amount of sand and gravel to be used in a
cement bag is measured according to the ratio of concrete. Usually the amount of sand is three times or
four times the amount of cement while the amount of gravel is kept twice the
amount of sand. In this way, their quantities are measured and the cement is
used without measuring. If there is moisture in the sand, then some more sand
is added according to the moisture content.
Batching
Of Concrete By Weight
It is better to weigh the concrete components
according to the set ratio. This is the method used in important works. In this respect the finished concrete is
stronger than the components. A concrete stall weighs five kilograms. To
measure the amount of sand and gravel according to the prescribed ratio, 50 kg
sand and 50 kg aggregate are prepared on a scale which is matched according to
the ratio. Heavy machinery is used for large works. There are 500 kg and 1000
kg scales made by weight. Balance weight is also used to measure the weight.
Mixing Of Concrete
The concrete components are mixed well. If the
concrete components are not mixed well, the amount of cement in some parts of
the concrete will increase and in some parts it will decrease. Which will
reduce the amount of cement will not be able to achieve the desired strength. Concrete
components are mixed in two ways.
o
Hand Mixing
o
Machine Mixing
Hand
Mixing
Concrete components are usually mixed by hand on
small projects. This method is not considered better. Since machinery is
expensive. Therefore it cannot be used on small projects and has to be shaken
hands. The first suitable size is made for shaking the concrete components. It
should be water tight so that the water used in the preparation of concrete is
not wasted. On this platform cement and sand are mixed well with the desired
ratio. After mixing, the two ingredients are stirred until the whole material
becomes one color. The gravel is then smoothed by placing it on the platform
according to the ratio and then a mixture of cement and sand is poured on it. The
three ingredients are then stirred until the whole material becomes one. Then a
certain amount of water is added to it and it is taken well so that the
concrete is ready.
Machine
Mixing
The concrete components on the large project are
mixed with the machine. This machine is called concrete mixing machine. Batching plants are used for this purpose in
very large projects. The speed of
performance is very high while the quality of extensions is also good. According to this method, the concrete
components are poured into the machine according to the prescribed ratio to mix
the concrete. The drum of the machine combines all the ingredients. If the machine is rotated for too long, it
begins to separate from the concrete components.
Transportation Of Concrete
Concrete is not prepared in the place where it is
used but in a suitable place near it. After mixing the concrete, it is
transported to a suitable place of use. The transport of concrete to the place
of use after mixing is called transportation of concrete. This process requires
great care as there is a risk of dissolving dissolved water in the concrete and
separation of the concrete components. Concrete should be transported in such a
way that the concrete can be delivered to the desired location within the initial
time period. The different methods of transportation of concrete are as follows.
·
Steel pan method
·
By wheel barrow
·
By dumper
·
By tripper
·
By truck mixer
·
By tower lift
·
By cable ways
·
By crane
·
By belt conveyor
·
By pumping
Placing Of Concrete
The concrete should be put in place immediately
after mixing. You should use the concrete before the start of the initial setting
time of the cement. The initial hardening time of ordinary Portland cement
begins 30-45 minutes after pouring, so ordinary cement concrete should be used
within that time. In no case should concrete be used after the start of the
initial time nor should it be re-mixed with water. Putting the finished concrete
in its proper place is called Placing of concrete. Concrete should be poured in
a thin layer and each layer should be pressed well. After pressing well,
another layer should be laid. Concrete should not be dropped from a height
while pouring; otherwise its components will fall apart. The separation of
concrete components in this way is called segregation.
Compaction Of Concrete
After preparing the concrete and putting it in the
relevant place, it is pressed well so that no vacuum remains inside the concrete.
Concrete is made workable for this purpose. In the normal type of work, it is
pressed with the help of rod and with the help of trowel. In the process of
pressing, care is taken that no corner etc. is left empty. In the case of
concrete is pressed exclusively around the steel bars. When pressing, care is
taken that the steel does not move out of place. In large works, the process of pressing
concrete is done with the help of vibrators. There are three types of vibrators.
·
Internal Vibrator
·
External Vibrator
·
Surface Vibrator
The internal vibrator is used by inserting fresh
concrete. External vibrator is used
outward with formwork. The surface vibrator consists of vibrating hit plates
that are used to compress low-thickness components of concrete.
Curing Of Concrete
Different methods are used to preserve the amount of
water in fresh concrete. The process by which the waste amount of water is
added back to the concrete is called curing of concrete.
There are two ways to do this.
·
The surface of fresh concrete is covered
in a moisture barrier layer which saves the amount of water present in the
concrete. The moisture barrier layer contains tar, paint and other chemicals.
·
The concrete surface is watered
periodically and covered with empty cement bags, patson bags or sand to prevent
water loss. After 24 hours of concrete, the work of plowing is started and the
plowing is done for three weeks. In no case should the curing take less than
ten days.
(https://civilengineeringlec.blogspot.com/2021/02/what-is-civil-engineering-scope.html)
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