Types of Concrete

Concrete is one of the widest used construction material
whether it is a dam or a house or a bridge or flyover. Concrete is basically of
three components water, aggregate and cement. Aggregate acts as a filling agent
while cement mostly Portland cement act as a binding agent.

Types of Concrete
Concrete is basically the most popular artificial material
on earth. It has many advantages beside easy availability of the constituents it
is powerful in compression however weak in tension which can be compensated by
using reinforcing bars of steel as in Reinforced Cement concrete.
Concrete is easily and readily prepared and fabricated in
all sorts with advantage being turned into any shape desired at site. Concrete is
leveled by screeding and smoothed out with trowel or a float. Normally it would
be poured into a wood formwork and then finished.
There are different types of concrete out there depending
upon type of constituents used in there 
keeping in view of the demand at site.
Some common types are as follows :-

1.      
Normal concrete
2.      
High performance concrete
3.      
High strength concrete
4.      
Air entrained Concrete
5.      
Light weight concrete
6.      
Self compacting Concrete
7.      
Shortcrete
8.      
Pervious concrete
9.      
Roller compacted concrete

Normal Concrete

Normally concrete also known as normal weight concrete is
relatively strong in compression and weak in tension. It has low
coefficient of thermal expansion and it shrinks while setting. Density of
concrete is around 2240 – 2400 Kg/meter cube. (150 lb/cu.ft.). Compressive
strength is usually around 3000 to 6000 psi.  Normal concrete has 1-2 % air content but is
not durable for severe conditions like freezing and thawing. A freshly poured
concrete usually sets within 30 – 90 minutes depending upon local temperature
and moisture conditions. Just after coming in contact with water the normal
hydration reaction starts and concrete sets. It mostly develops its strength
after 7 days and usually attain more than 80% strength after 28 days.

High Strength Concrete

Whenever we are talking about strength of non-reinforced
concrete we are talking about compression strength or compressive strength
denoted by fc’. As the name suggests this type of concrete has extraordinary
strength than normal strength or normal concrete. By one definition HSC is
mostly the one having cube strength between 60 to 100 N/mm2, although higher
strengths can also be achieved. Mix design of high strength concrete is
influenced by properties of cement, sand aggregates and water cement ratio. The
strength according to one standard is said to be greater than 40 MPa. Mostly
high strength is achieved by lowering water cement ratio upto 0.35 or even
lower. Often Silica fume is also added to prevent the formation of free calcium
hydroxide crystal in the cement matrix. It is usually less workable and thus if
needed super-plasticizers can be used.

High Performance concrete

As the name suggests high performance concrete refers to all
those sorts of concrete which are optimum in all the standards usually adopted
in common application of concrete, thus not only strength it has ease of
placement, optimum heat of hydration, compaction without segregation, have
early age strength, permeability is sufficient, density is more, life is more
even in severe environments, toughness is more.
High workability is attained by super plasticizers, they
lower the water cement ratio to 0.25 which is the amount required only for
hydration process.
High durability is attributed to fly ash and silica fume
which modify the e mineralogy of the cement; it enhances the compatibility of
ingredients in concrete mass and reduces the CH amount. Fly ash also causes
ball bearing effect increasing workability.
The admixtures are 20-25% fly ash of partial replacement of
cement and rest 70% is Ordinary Portland Cement.
As it is not usually durable against freezing and thawing so
air entrained agents can also be utilized.
Properties of high performance concrete mix
Strength of high performance concrete ranges from 10000 psi
– 15000 psi
Water cement ratio can be reduced to 0.25

Air entrained Concrete

In this type of concrete tiny air bubbles are intentionally created.
Mostly an air entraining agent called surfactant (a type of chemical) is used.
Air bubbles are created during mixing of the plastic concrete which mostly
survive upto end as hardened concrete. The basic purpose of air entrainment is
to make it durable for concrete in extreme climate where freeze-thaw effect is
there while second purpose is to increase workability of concrete while in
plastic state.
Normal concrete will have small capillaries produced by the
evaporation of water in concrete. These capillaries are invaded by water from
the environment and the freezing of this water can cause a lot of stress in
concrete because of expansion in volume that accompanies the freezing. An Air
entrained concrete allows the expansion to take place without causing any
further stresses as air bubbles are capable of being compressed.
The amount of entrained air is maintained between 4 and 7
percent for best freezing thawing resistance though variations can be made
depending on specific conditions.
Normally air entrained concrete has a drawback it has low
strength as compared to normal concrete.

Light weight concrete

Structural light weight concrete has an in-place density or
unit weight on the order of 90 to 115 lb/ft3 or 1440 to 1840 kg/m3. Lightweight
concrete is defined as having an air dry density not exceeding 2000 Kg/m3, but
can be as low as 400 kg/m3.
One of the most common uses for light weight concrete is
with floor, roof or bridge decks; other include pavement system, masonry blocks
etc.
Lightweight aggregates used in structural lightweight
concrete are typically expanded shale, clay or slate materials that have been
fired in a rotary kiln to develop a porous structure. Other products such as
air-cooled blast furnace slag are also used. There are other classes of
non-structural LWC with lower density made with other aggregate materials and
higher air voids in the cement paste matrix, such as in cellular concrete.
The required properties of the lightweight concrete will
have a bearing on the best type of lightweight aggregate to use. If little
structural requirement, but high thermal insulation properties, are needed then
a light, weak aggregate can be used. This will result in relatively low
strength concrete.

Self Compacting Concrete

Self compacting concrete or SCC is a flowing concrete
mixture that is able to consolidate under its own weight. The high fluid nature
of SCC makes it suitable for placing in difficult conditions and in sections
with congested reinforcement. Use of SCC can also help minimize the bearing
related damages on the formwork that are induced by vibration of concrete.
Another advantage of SCC is that the time required to place large sections is
considerably reduced.
Self compacting concrete has more finer content and less
coarser aggregate. Self compacting concrete also uses superplasticisers in
large amount and a viscosity modifying agent (VMA) in small doses.
As a high-performance concrete, SCC delivers these
attractive benefits while maintaining all of concrete’s customary mechanical
and durability characteristics. Adjustments to traditional mix designs and the
use of superplasticizers creates flowing concrete that meets tough performance
requirements. If needed, low dosages of viscosity modifier can eliminate
unwanted bleeding and segregation.

Shortcrete

Shortcrete is basically not a product or something you can
pick or touch, it is basically a process of placing concrete to achieve high
strengths and low permeability.
Shortcrete is a concrete conveyed through a hose and
pneumatically projected at high velocity onto a receiving surface.
They are strong, durable, resistant to disasters, fires,
mold, insects and vermin, and have low permeability, good thermal mass, and
create tight envelopes. Although the hardened properties of Shotcrete are
similar to conventional cast-in-place concrete, the nature of the placement
process provides additional benefits, such as very fast erection, particularly
on complex forms or shapes, including curved walls and arches.
Shotcrete is frequently used against vertical soil or rock
surfaces, as it eliminates the need for formwork. It is sometimes used for rock
support, especially in tunneling. Shotcrete is also used for applications where
seepage is an issue to limit the amount of water entering a construction site
due to a high water table or other subterranean sources. This type of concrete
is often used as a quick fix for weathering for loose soil types in
construction zones.

Pervious Concrete

Pervious concrete (also called porous concrete, permeable
concrete, no fines concrete and porous pavement) is a special type of concrete
with a high porosity used for concrete flatwork applications that allows water
from precipitation and other sources to pass directly through, thereby reducing
the runoff from a site and allowing groundwater recharge. When set, typically
between 15% and 25% of the concrete volumes are voids, allowing water to drain.
The majority of pervious concrete pavements function well
with little or no maintenance. Maintenance of pervious concrete pavement
consists primarily of prevention of clogging of the void structure.
In preparing the site prior to construction, drainage of
surrounding landscaping should be designed to prevent flow of materials onto
pavement surfaces. Soil, rock, leaves, and other debris may infiltrate the
voids and hinder the flow of water, decreasing the utility of the pervious concrete
pavement.  

Roller Compacted Concrete

Mostly abbreviated as R.C.C but it must not be confused with
Reinforced Cement Concrete. The word is enough to define itself; roller
compacted concrete is a relatively stiff concrete mix that is spread with a
paving machine and is than compacted with the help of a roller which is usually
steel drum vibratory roller.
Method of construction used for roller compacted concrete is
simple and conventional.
Roller-compacted concrete has the same basic ingredient as
conventional concrete: cement, water, and aggregates, such as gravel or crushed
stone.
But unlike conventional concrete, it’s a drier mix—stiff
enough to be compacted by vibratory rollers. Typically, RCC is constructed
without joints. It needs neither forms nor finishing, nor does it contain
dowels or steel reinforcing.
These characteristics make roller-compacted concrete simple,
fast, and economical.
These qualities have taken roller-compacted concrete from
specialized applications to mainstream pavement. Today, RCC is used for any type
of industrial or heavy-duty pavement. The reason is simple. RCC has the
strength and performance of conventional concrete with the economy and
simplicity of asphalt. Coupled with long service life and minimal maintenance,
RCC’s low initial cost adds up to economy and value.
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Saad Iqbal
Hi there, I am Saad Iqbal from Pakistan. I am an enthusiastic blogger, passionate content creator, construction geek, and a creative graphic designer. Connect with me at my social channels.