SPECIAL CONCRETE &
CONCRETING TECHNIQUES
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6.1 Light weight concrete
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6.2 Plum concrete
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6.3 Fibre reinforced concrete
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6.4 Polymer concrete
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6.5 High density concrete
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6.6 No fines concrete
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6.7 Ferro cement
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6.8 Fly ash concrete
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6.9 Ready mix concrete
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6.10 Pumped concrete
Lightweight concrete
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Lightweight concretes can either be lightweight aggregate
concrete, foamed concrete or autoclaved aerated concrete
(AAC). Such lightweight concrete blocks are often used in
house construction.
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Light weight concrete - or foamed concrete - is a versatile
material which consists primarily of a cement based mortar
mixed with at least 20% of volume air. The material is now
being used in an ever increasing number of applications,
ranging from one step house casting to low density void fills.
Lightweight concrete
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Normal concrete has a density of 2,400 kg/m3 while
densities range from 1,800, 1,700, 1,600 down to 300
kg/m3. Compressive strengths range from up to 40 mpa
down to almost zero for the really low densities. Generally it
has more than excellent thermal and sound insulating
properties, a good fire rating, is non combustible and
features cost savings through construction speed and ease of
handling.
Lightweight aggregate concrete
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Lightweight aggregate concrete can be produced using a
variety of lightweight aggregates. Lightweight aggregates
originate from either:
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Natural materials, like volcanic pumice.
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The thermal treatment of natural raw materials like clay, slate
or shale i.e. Leca.
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Manufacture from industrial by-products such as fly ash, i.e.
Lytag.
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Processing of industrial by-products like FBA or slag.
Lightweight
aggregates
Natural lightweight
aggregates
1. Pumice
2 . Scoria
3. Rice husk
4. Saw dust
5. Diatomite
6. Volcanic tuff
7. Foamed lava
Artificial lightweight
aggregates
1. Sintered fly ash
2. Foamed slag
3. Bloated
4. Artificial cinders
5. Expended clay, slate,
shale
6. Coke breeze
7. Expanded polite
8. Exfoliated ermiculite
Fibre reinforced concrete
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Concrete made with portland cement has certain
characteristics: it is relatively strong in compression but weak
in tension and tends to be brittle. The weakness in tension can
be overcome by the use of conventional rod reinforcement and
to some extent by the inclusion of a sufficient volume of
certain fibres. The use of fibres also alters the behaviour of the
fibre-matrix composite after it has cracked, thereby improving
its toughness
The use of fibres
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For the effective use of fibres in hardened concrete:ibres should be significantly
stiffer than the matrix, i.e. have a higher modulu
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Fibre content by volume must be adequate.
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There must be a good fibre-matrix bond.
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Fibre length must be sufficient.
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Fibres must have a high aspect ratio, i.e. they must be long relative to their
diametes of elasticity than the matrix
Types of fibre
1.
Glass
2.
Steel
3.
Synthetic fibres
4.
Carbon
5.
Nylon
6.
Polyester
1. Glass
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Glass-fibre products exposed to outdoor environment have
shown a loss of strength and ductility. The reasons for this are
not clear and it is speculated that alkali attack or fibre
embrittlement are possible causes. Because of the lack of data
on long-term durability, GRC has been confined to nonstructural uses where it has wide applications. Glass fibre is
available in continuous or chopped lengths. Fibre lengths of up
to 35-mm are used in spray applications and 25-mm lengths are
used in premix applications.
2. Steel
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Steel fibres have been used in concrete since the early 1900s.
The early fibres were round and smooth and the wire was cut
or chopped to the required lengths. The use of straight, smooth
fibres has largely disappeared and modern fibres have either
rough surfaces, hooked ends or are crimped or undulated
through their length. Modern commercially available steel
fibres are manufactured from drawn steel wire, from slit sheet
steel or by the melt-extraction process which produces fibres
that have a crescent-shaped cross section. Typically steel fibres
have equivalent diameters (based on cross sectional area) of
from 0,15 mm to 2 mm and lengths from 7 to 75 mm.
3. Synthetic fibres
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Synthetic fibres are man-made fibres resulting from research
and development in the petrochemical and textile industries.
There are two different physical fibre forms: monofilament
fibres, and fibres produced from fibrillated tape
4. Carbon
Carbon fibre is substantially more expensive than other fibre
types. For this reason its commercial use has been limited.
Carbon fibres are manufactured by carbonizing suitable
organic materials in fibrous forms at high temperatures and
then aligning the resultant graphite crystallites by hotstretching. The fibres are manufactured as either Type I (high
modulus) or Type II (high strength) and are dependent upon
material source and extent of hot stretching for their physical
properties. Carbon fibres are available in a variety of forms and
have a fibrillar structure similar to that of asbestos.
5. Nylon
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Nylon is a generic name that identifies a family of polymers.
Nylon fibre’s properties are imparted by the base polymer type,
addition of different levels of additive, manufacturing
conditions and fibre dimensions. Currently only two types of
nylon fibre are marketed for concrete. Nylon is heat stable,
hydrophilic, relatively inert and resistant to a wide variety of
materials
6. Polyester
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Polyester fibres are available in monofilament form and belong
to the thermoplastic polyester group. They are temperature
sensitive and above normal service temperatures their
properties may be altered. Polyester fibres are somewhat
hydrophobic. Polyester fibres have been used at low contents
(0,1% by volume) to control plastic-shrinkage cracking in
concrete
POLYMER CONCRETE
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Low component weight, high strength, smooth surfaces and
extremely high resistance are four reasons why polymer
concrete is the ideal material for professional drainage
channels. Compared to regular concrete, MEA polymer
concrete is an impermeable material with a low porosity;
because of its extremely high stability, products with thin walls
and thus a lower weight can be manufactured.
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It is made from natural minerals such as quartz, basalt and
granite which are mixed with a polymer binder. MEA polymer
concrete is the basis for highly resilient, heavy-duty drainage
channels. The high resistance of MEA polymer concrete to
most chemical liquids is beneficial for the environment.
Main components:
Polymer-impregnated concrete (PIC)
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produced by impregnating or infiltrating a hardened concrete
with a monomer and subsequently polymerizing the monomer
in situ.
Polymer Concrete (PC)
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Polymer concrete uses a polymer binder in place of Portland
cement. Potassium silicate polymer concretes are more like
Portland cement concrete in that they achieve compressive
strengths in the 3,500-4,500 psi range and have a certain
degree of absorption. Unlike Portland cement concrete,
potassium silicate concrete offers exceptional resistance to
non-fluoride acids including nitric, hydrochloric, sulfuric, and
phosphoric.
RMC
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Ready mix concrete that is manufactured in a factory or
batching plant, according to a set recipe, and then delivered to
a worksite, by truck mounted transit mixers . This results in a
precise mixture, allowing specialty concrete mixtures to be
developed and implemented on construction sites.
It is popularly called as RMC, specially manufactured for
delivery to the customers construction site in a freshly mixed
and plastic or unhardened state. It is sold by volume expressed
in cubic meters.
ADVANTAGES
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A centralized concrete batching plant can serve a wide area.
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The plants are located in areas zoned for industrial use, and yet the
delivery trucks can service residential districts or inner cities.
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Better quality concrete is produced.
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Elimination of storage space for basic materials at site.
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Elimination of hiring of plant and machinery.
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Wastage of basic materials is avoided.
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Labours associated with production of concrete is eliminated.
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Time required is greatly reduced.
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Noise and dust pollution at site is reduced.
No fines concrete
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No-fines concrete (NFC) consists of coarse aggregate and
cement paste. In the hardened state, aggregate particles are
covered by a thin layer of cement paste and are in point-topoint contact with each other. At each contact point the paste
forms a small fillet; these fillets hold the particles together and
give strength to the concrete.
Or
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No-fines concrete can be defined as a lightweight concrete
composed of cement and fine aggregate. Uniformly distributed
voids are formed throughout its mass. No-fines concrete
usually used for both load bearing and non-load bearing for
external walls and partitions.
Mass Concrete
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Concrete in a massive structure, e.g., a beam, columns, pier,
lock, or dam where its volume is of such magnitude as to
require special means of coping with the generation of heat and
subsequent volume change.
Ferro cement
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Ferro cement is a type of thin wall reinforced concrete,
commonly constructed of hydraulic cement mortar,
reinforced with closely spaced layers of continuous and
relatively small size wire mesh. The mesh may be made
of metallic or other suitable materials”
The term Ferro cement is most commonly applied to a
mixture of Portland cement and sand applied over layers
of woven or expanded steel mesh and closely spaced
small-diameter steel rods rebar. It can be used to form
relatively thin, compound curved sheets to make hulls
for boats, shell roofs, water tanks, etc. It has been used in
a wide range of other applications including sculpture
and prefabricated building components.
Ferro cement
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Ferro cement has a very high tensile strength-to-weight ratio
and superior cracking behaviour in comparison to reinforced
concrete. This means that Ferro cement structures can be
relatively thin, light and water-tight.
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In India, ferro concrete is used often because the constructions
made from it are more resistant to earthquakes. Earthquake
resistance is dependent on good construction technique and
additional reinforcement of the concrete.
High density concrete
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High density or heavyweight concrete is concrete with a
density greater than 2600kg/m3. Its primary use is in radiation
shielding, either in nuclear power plants or in radiation therapy
units. It can also be used as ballast in offshore locations such as
pipelines.
6.2 Plum concrete
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It is a fluid, concrete can be pumped to where it is
needed. Here, a concrete transport truck is feeding concrete to
a concrete pumper, which is pumping it to where a slab is
being poured
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A concrete pump is a machine used for transferring liquid
concrete by pumping. There are two types of concrete pumps.
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The first type of concrete pump is attached to a
truck. It is known as a trailer-mounted boom
concrete pump because it uses a remotecontrolled articulating robotic arm (called a boom)
to place concrete with pinpoint accuracy. Boom
pumps are used on most of the larger construction
projects as they are capable of pumping at very
high volumes and because of the labour saving
nature of the placing boom. They are a
revolutionary alternative to truck-mounted concrete
pumps.
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The second main type of concrete pump is either
mounted on a truck and known as a truck-mounted
concrete pump or placed on a trailer, and it is
commonly referred to as a line pump or trailermounted concrete pump. This pump requires steel
or flexible concrete placing hoses to be manually
attached to the outlet of the machine. Those hoses
are linked together and lead to wherever the
concrete needs to be placed. Line pumps normally
pump concrete at lower volumes
Fly ash concrete
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Flyash is defined in Cement and Concrete Terminology (ACI
Committee 116) as “the finely divided residue resulting from
the combustion of ground or powdered coal, which is
transported from the firebox through the boiler by flue gases.”
Flyash is a by-product of coal-fired electric generating plants.
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In India, fly ash bricks are used for construction. Leading
manufacturers use an industrial standard known as "Pulverized
fuel ash for lime-Pozzolana mixture" using over 75% postindustrial recycled waste, and a compression process. This
produces a strong product with good insulation properties and
environmental benefits