Lightweight concrete has a density between 300-1850 kg/m3, compressive strengths from 20-40 N/mm2, and better thermal insulation and sound absorption properties compared to normal concrete. It reduces structural dead loads, making it attractive for multi-story buildings.

1. SPECIAL CONCRETE
Concrete Technology
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2. Light weight concrete
It has been successfully used since the ancient roman times and it has gained its
popularity property due to its lower density and superior thermal insulation
properties compared with normal weight concrete.
Light weight concrete can significantly reduce the dead load of structural elements,
which makes it specially attractive in multi storey buildings.
General characteristics of light weight concrete are
(1) Light weight concrete has its density in the range of 300-1850 kg/m3
(2) 28-day compressive strength of light weight concrete varies within the range of
20-40 N/mm2 with various waste materials from thermal power plants.
(3) Light weight concrete has relatively low thermal conductivity.
(4) Since light weight concrete contains large percentage of air, it has better sound
absorption, sound proofing properties.
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No fines concrete
It is defined as a type of concrete from which the fine aggregate component is entirely
omitted.
This concrete is made of only coarse aggregate, cement and water.
Very often only single sized coarse aggregate of size passing through 20 mm retained on
10mm is used.
The aggregates are held together by a binder consisting of a paste of hydraulic cement
water giving to it the strength of concrete.
No fines concrete is generally made with the aggregate/cement ratio 6:1 to 10:1.
It has practically no fine capillary pores and hence there is no transfer of moisture by
capillary action.
Owing to its slightly higher thermal insulating property, it can be used for external walls
heat insulation.
Because of rough texture, it gives a good base for plastering.
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High density concrete
The concrete having unit weight ranging from 3360 kg per cubic meter to 3840 kg per cubic
meter which is about 50% higher than the unit weight of the conventional concrete is said to
be high density concrete.
It can however be produce with the densities upto about 5280 kg per cubic meter using iron
as fine and coarse aggregate.
They are mainly used for construction of radiation shield.
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Sulphur Infiltrated Concrete
It is a type of composite which is produced by the recently developed techniques
impregnating porous materials like concrete with sulphur.
Sulphur impregnation results in great improvements in strength and other physical
properties such as water impermeability and resistance to corrosion.
Sulphur Infiltrated Concrete, also known a Sulphur Impregnated Concrete, was
developed as an economical alternative to Polymer Impregnated Concrete (PIC) to
be used for higher strength and durable precast concrete elements.
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Cold Weather Concrete
The production of concrete in cold weather introduces special and peculiar
such as delay in setting and hardening, damage to concrete in plastic condition
exposed to below freezing point owing to the formation of ice lenses.
Therefore, it is essential to maintain the temperature of the concrete positively
0°C, possibly at much higher temperature.
The method of concreting used in such situations is called cold weather concreting.
The reasons for cold weather concreting
(i) Enhance the setting time and hardening,
(ii) Prevent freezing of concrete at early age, and
(iii) Prevent freezing and thawing cycles.
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Hot weather concrete
Hot weather problems are most frequently encountered in the summer, but the associated
climatic factors of high winds and dry air can occur at any time, especially in arid or tropical
climates.
Hot weather conditions can produce a rapid rate of evaporation of moisture from the
of the concrete and accelerated setting time, among other problems.
Higher temperatures tend to accelerate slump loss and can cause loss of entrained air.
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Ferrocement
Ferrocement is a form of reinforced concrete using closely spaced multiple layers of mesh
small diameter rods completely encapsulated in mortar.
The most common type of reinforcement is steel mesh.
Other materials such as organic, natural or synthetic fibres may be combined with metallic
mesh.
As the steel or fibres are placed at closer spacing, they yield uniform force dispersion and
increases strength.
Ferrocement has great strength and economy. It is fireproof, earthquake safe and does not
rust, rot or blow down in storms.
It has a broad range of applications which include home building, creating sculptures,
of existing artifacts and building boats and ships.
A ferrocement structure is usually 2-3 cm thick, much thinner and lighter than poured
concrete structures.
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Polymer Impregnated Concrete
It is one of the widely used polymers composite.
It is nothing but a pre-cast conventional concrete, cured and dried in oven, or
dielectric heating from which the air in the open cell is removed by vacuum.
Then a low viscosity monomer is diffused through the open cell and
by using radiation, application of heat or by chemical initiation.
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Fibre Reinforced Concrete (FRC)
Fibre Reinforced Concrete is a concrete containing fibrous material which increase its structural
integrity.
Fibre is used in concrete to control shrinkage and drying shrinkage cracking.
They also lower the permeability of concrete and thus reduce bleeding of water.
Plain Concrete possess a very low tensile strength, limited ductility and little resistance to
cracking.
It has been recognized that the addition of small, closely spaced and uniformly dispersed
to concrete would act as crack arrester and would substantially improve its static and dynamic
properties.
Fibre Reinforced Concrete offers many advantages because of their many desirable
characteristics as compared to those of conventional steel reinforcement.
Different types of Fibres used in FRC are
(1) Steel FRC, (2) Glass FRC, (3) Nylon FRC, (4) Polypropylene FRC, (5) Carbon FRC and (6)
Asbestos FRC
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Glass Fibre Reinforced Concrete(GFRC)
GFRC is composed of concrete, reinforced with glass fibers to produce a thin, lightweight,
strong material.
The material offered several benefits to architects and designers.
These are
(1) GFRC has superior fire retardant properties.
(2) GFRC offers a variety of shapes (similar to what terra cotta, carved stone or precast
concrete offer, but at a much reduced weight).
(3) GFRC is lightweight.
(4) GFRC can replicate Terra Cotta, granite, limestone, cast stone or other hard to use
materials.
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Self-Compacting Concrete (SCC)
SCC is a very important advanced technology of concrete in recent time.
Self-compacting concrete, also referred to as self-consolidating concrete, is able to flow and
consolidate under its own weight, almost completely while flowing in the formwork.
It is cohesive enough to fill the spaces of almost any size and shape without segregation or
bleeding.
This makes SCC particularly useful wherever placing is difficult, such as in heavily-reinforced
concrete members or in complicated work.
The materials used in SSC are Cement (Ordinary Portland Cement 43 or 53 grade) ,
Aggregates (well graded cubical aggregates of size 10 to 12 mm), Fine aggregate, Chemical
Admixtures ( Super plasticizers are an essential)
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The major advantages of SCC are as follows.
(1) Ability to completely fill complex formwork and encapsulate areas of congested
steel reinforcement without any compaction and yet with reduced risks of
segregation and bleeding.
(2) Ability to develop higher early and ultimate strengths and enhanced durability
properties compared with conventional vibrated concretes.
(3) Potential for improved surface finish with reduced costs related to ordinary poorly
compacted surfaces.
(4) Low noise-level in the plants and construction sites.
(5) Eliminated problems associated with vibration.
(6) Reduced labour cost.
(7) Construction is faster and so it is suitable for under water construction.
(8) Improved quality and durability can be achieved.
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Shotcrete
Shotcrete or guniting has the same characteristics as ordinary concrete
but it has smaller aggregate size and it is applied under pressure with
low water content.
It requires no framework and can be applied on any surface including
inclined and vertical surfaces and even on ceilings.
This results in very good adhesion between old and new concrete and
good compaction due to application under pressure.
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Shotcrete
Shotcrete or guniting has the same characteristics as ordinary concrete but it has smaller
aggregate size and it is applied under pressure with low water content.
It requires no framework and can be applied on any surface including inclined and vertical
surfaces and even on ceilings.
This results in very good adhesion between old and new concrete and good compaction due
application under pressure.
The low w/c ratio results in high strength and low shrinkage.
The permeability of shotcrete is also lower than that of ordinary concrete and results in better
protection of steel against corrosion.
The main advantage of shotcrete is that it can be used retrofitting materials.
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