Introduction
What is ''Concrete''?
Recyclable
Strong
Plentiful
Science
Versatile
Everywhere
Natural
Inexpensive
It is the material that widely used in construction field such as domestic, commercial, recreational, rural and education. There are variety of concrete such as reinforced concrete, pre-stressed concrete, and mass concrete.
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| Most of the materials that use in the construction site are make out of concrete. |
So What is concrete huh?
Concrete is the mixture of cement, water, and aggregates. There are 2 types of aggregates have been used such as coarse aggregates and fine aggregates.
Both aggregates provide a different workability and compressive strength to the concrete. Example of coarse aggregates are limestone and granite while the fine aggregates is sand. Admixtures are also added to the concrete to change it properties to shorter the time concrete take to harden and improve its workability. Hydration is a chemical process carry by water to solid the mixture of concrete by bonding the component together. Concrete has a high compressive strength and lower tensile strength. So reinforcement is added to the concrete to increase the tensile strength of the concrete.
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| Concrete structure |
Composition of concrete
Cement
Cement is the basic ingredient of the concrete.
Calcium oxide and silicon dioxide is the most important ingredients in
manufacturing cement. Portland cement is the mixture of calcium oxide, silicon
and aluminium. Cement powder mixed with water to form a paste. Paste acts like glue
to bond the aggregates together.
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| Cement |
Is it Concrete = Cement ?
let's us look at the video below⇊⇊⇊⇊
Now let's us look at another video showing manufacturing process for cement step by step.
WATER
Water is the components that carry
out hydration to bond all the other materials together to form concrete.
Different types of water will produce different types of concrete. Impure water
can cause problems when setting and premature failure of structure. Excessive
water will produce concrete with higher slump while less water will improve the
strength and durable of the concrete.
Equation
C3S + H → C-S-H
+ CH
Ca3SiO5 +
H2O → (CaO)·(SiO2)·(H2O)(gel) + Ca(OH)2
2Ca3SiO5 +
7H2O → 3(CaO)·2(SiO2)·4(H2O)(gel) + 3Ca(OH)2
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| Cement mix with the water |
What is Hydration?
Hydration is the chemical reaction between cement and water that binds the cement, water and aggregate into concrete. The strength of the finished concrete depends on proper and sufficient hydration.
So here is the video talking bout Hydration of cement.
AGGREGATES
Hydration is the chemical reaction between cement and water that binds the cement, water and aggregate into concrete. The strength of the finished concrete depends on proper and sufficient hydration.
So here is the video talking bout Hydration of cement.
AGGREGATES
There are two basic types of aggregates, coarse
aggregates and fine aggregates. Coarse aggregates mostly made up of crushed
rock and gravel while fine aggregates made up of sand. Aggregates that have
been chosen must be strong and hard. Crumble or flakey rock should be avoided.
Aggregates chosen must chemically inactive to prevent reaction between cement
and aggregates. Clean the aggregates before mix them with concrete to prevent
the dirt weaken the bond between paste and aggregates. Cohesiveness of the
concrete is affected by the aggregate grading. Well-graded aggregates give a
more cohesive mix, too much coarse aggregate gives a boney mix.
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Fine aggregates
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Coarse aggregates
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| Mix aggregates |
REINFORCEMENT
We all know that concrete is strong in compression force due to the
aggregate efficiently carries the compression load. It is weak in tension
stress and reinforcement is added inside concrete to withstand the tensile
force.
ADMIXTURES
Materials that added to the concrete to alter the
original properties of the concrete. There are 5 types of admixtures such as
plasticisers, pigments, accelerators, retarders, and air entraining agents. CaCl2, Ca(NO3)2 andNaNO3
is the accelerators that speed up the hydration process. However excessive use
of chlorides may cause corrosion in the reinforcing. Sugar, sucrose, sodium
gluconate, glucose and tartaric acid which are retarders to slow down the
hydration process when concrete are used in large or difficult pour, hot
weather, or long distances delivery. Air entraining agents controlling the
quantity of air between the concrete to prevent honeycomb. Pigments is a colour
agent which give a colour to the concrete. So the concrete can be more
attractive. Plasticisers increase the
workability of the concrete by reducing the water inside the concrete.
Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (vibration) and without reducing the concrete's quality and depends on water content, aggregate(shape or size), cementitious content and age(level of hydration). Concrete workability will increase by raising the water content or adding chemical admixtures. Concrete slump test can be measured the workability. Slump can be increased by addition of chemical admixtures without changing the water-cement ratio. After mixing, concrete is a fluid and can be pumped to the location where needed.
For workability, it have 4 test which are slump test, compacting factor test, vebe test and flow table test.
Properties
A basic desired property of concrete is good workability when the concrete is newly mixed. For example the concrete can be transport from the mixer, handled, placed in the moulds and compacted satisfactory. Concrete has high compressive strength and hardness, but lower tensile strength. This is because reinforced with materials that are strong in tension. This often refers to steel. Concrete also has adequate durability as a long term for all the building.
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Concrete Admixtures |
Concrete
production
The processes
of concrete production are from hand tools to heavy industry and probably used
of high technology advanced. Portland cement and water rapidly form a gel,
formed of chains of crystals when they mixed together. The fluid gel aiding by
improving workability through react over the time. Besides, the chains of
crystals join and form a rigid structure, gluing the aggregate particles. Most
of the cement reacts with the residual water that mean hydration during curing.
Mixing Concrete
For a production of uniform, high quality concrete, mixing of concrete is
essential. And equipment and methods should be capable to contain the largest
amount of mixing concrete materials. In order to increase the compressive
strength, the mixing of cement and water into the paste is needed before
combining these materials with aggregates. The paste is mixed in high-speed.
The cement paste premix may include admixtures such as accelerators or
retarders, superplasticizers, pigments, or silica fume. A plasticizer or a
superplasticizer is then added to the activated mixture, which can later be
mixed with aggregates in a conventional concrete mixer.
Workability
Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (vibration) and without reducing the concrete's quality and depends on water content, aggregate(shape or size), cementitious content and age(level of hydration). Concrete workability will increase by raising the water content or adding chemical admixtures. Concrete slump test can be measured the workability. Slump can be increased by addition of chemical admixtures without changing the water-cement ratio. After mixing, concrete is a fluid and can be pumped to the location where needed.
For workability, it have 4 test which are slump test, compacting factor test, vebe test and flow table test.
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| Slump test |
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| Compacting factor test |
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| Vebe test |
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| Flow table test |
Properties
A basic desired property of concrete is good workability when the concrete is newly mixed. For example the concrete can be transport from the mixer, handled, placed in the moulds and compacted satisfactory. Concrete has high compressive strength and hardness, but lower tensile strength. This is because reinforced with materials that are strong in tension. This often refers to steel. Concrete also has adequate durability as a long term for all the building.
Use
of concrete in infrastructure
Mass concrete structures
Large structures typically include gravity dams, such as the
Hoover Dam, Itaipu Dam and the Three Gorges Dam: arch dams, navigation locks
and large breakwaters.
Such large structures will generate excessive heat and
associated expansion, even though it is individually placed in formed
horizontal blocks. Post-cooling provided in the design is commonly used to
mitigate these effects.
A network of pipes between vertical concrete placements is installed
to circulate cooling water during the curing process and avoid damaging
overheating.
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| Mass concrete structure the Baths of Caracalla, in 2003 |
Pre-stressed concrete structures
Pre-stressed concrete is a form of reinforced concrete that
builds in compressive stresses during construction to oppose those found when
in use.
Weight of beams or slabs can be reducing by better
distributing the stresses in the structure to make optimal use of the
reinforcement.
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Pre-stressed concrete structures |
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| Bridge over the Sungai Selangor, Kuala Selangor, Malaysia |
