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INTRODUCTION OF THE PRODUCT
Cement concrete hollow/solid blocks have an important place in
modern building
industry. They are cost effective and better alternative to
burnt clay bricks by
virtue of their good durability, fire resistance, partial
resistance to sound, thermal
insulation, small dead load and high speed of construction.
Concrete hollow/solid
blocks being usually larger in size than the normal clay
building bricks and less
mortar is required, faster of construction is achieved.
Also building construction with cement concrete hollow/solid
blocks provides
facility for concealing electrical conduit, water and sewer
pipes wherever so
desired and requires less plastering.
MARKET & DEMAND ASPECTS
Cement concrete hollow/solid blocks are modern construction
materials and as
such are used in all the constructions viz. residential,
commercial and industrial
building constructions. Construction industry is a growing a
sector. The demand
for this product is always high in all cities and other urban
centres due to
construction of residential apartments, commercial buildings and
industrial
buildings.
Growing public awareness of the advantages of the product
coupled with increase
in the government and financial institutions support for housing
which is a basic
human necessity would ensure a healthy growth in the demand.
RAW MATERIALS
Concrete is a mixture of ordinary Portland cement, mineral
aggregate (sand and
stone chips) and water. The water used in preparing the concrete
serves two
purposes:
(1) It combines with the cement to form a hardened paste
(2) It lubricates the aggregates to form a plastic and workable
mass
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The water that combines with the cement varies from about 22 to
28% of the total
amount of mixing water in concrete.
Mineral aggregates (sand and stone chips) are normally divided
into two fractions
based on their particle size. Aggregate particles passing
through the No.4 or 4.7
mm Indian Standard sieve are known as fine aggregate. The
particles retained on
this sieve are designated as coarse aggregate. Natural sand is
often used as fine
aggregate in cement concrete mixture. Coarse aggregate are
crushed stone chips.
Crushed stone chips broken into particle sizes passing through
the 4.7 mm sieve
may also be used as fine aggregate. The maximum size of the
coarse aggregate that
may be used in cement concrete hollow blocks is 12.5 mm.
However, the particle
size of the coarse aggregate should not exceed one third
thickness of the thinnest
web of the hollow blocks.
Ordinary Portland cement is the cementing material used in
cement concrete
hollow blocks. Cement is the highest priced material per unit
weight of the
concrete. Hence, the fine and coarse aggregates are combined in
such proportions
that the resulting concrete is workable and has minimum cement
content for the
desired quality.
MANUFACTURING PROCESS
The process of manufacture of cement concrete hollow blocks
involves the
following 5 stages;
(1) Proportioning
(2) Mixing
(3) Compacting
(4) Curing
(5) Drying
(1) Proportioning:
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The determination of suitable amounts of raw materials needed to
produce concrete
of desired quality under given conditions of mixing, placing and
curing is known
as proportioning. As per Indian Standard specifications, the
combined aggregate
content in the concrete mix used for making hollow blocks should
not be more
than 6 parts to 1 part by volume of Portland cement. If this
ratio is taken in terms
of weight basis this may average approximately at 1:7 (cement :
aggregate).
However, there have been instances of employing a lean mix of as
high as 1:9 by
manufacturers where hollow blocks are compacted by power
operated vibrating
machines. The water cement ratio of 0.62 by weight basis can be
used for concrete
hollow blocks.
(2) Mixing
The objective of thorough mixing of aggregates, cement and water
is to ensure that
the cement-water paste completely covers the surface of the
aggregates. All the
raw materials including water are collected in a concrete mixer,
which is rotated
for about 1 minutes. The prepared mix is discharged from the
mixer and
consumed within 30 minutes.
(3) Compacting
The purpose of compacting is to fill all air pockets with
concrete as a whole
without movement of free water through the concrete. Excessive
compaction
would result in formation of water pockets or layers with higher
water content and
poor quality of the product.
Semi-automatic vibrating table type machines are widely used for
making cement
concrete hollow blocks. The machine consists of an automatic
vibrating unit, a
lever operated up and down metallic mould box and a stripper
head contained in a
frame work.
Wooden pallet is kept on the vibrating platform of the machine.
The mould box is
lowered on to the pallet. Concrete mix is poured into the mould
and evenly leveled.
The motorized vibrating causes the concrete to settle down the
mould by
approximately 1 to 1 inches. More of concrete is then raked
across the mould
level. The stripper head is placed over the mould to bear on the
leveled material.
Vibration causes the concrete come down to its limit position.
Then the mould box
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is lifted by the lever. The moulded hollow blocks resting on the
pallet is removed
and a new pallet is placed and the process repeated. The machine
can
accommodate interchangeable mould for producing blocks of
different sizes of
hollow or solid blocks.
(4) Curing
Hollow blocks removed from the mould are protected until they
are sufficiently
hardened to permit handling without damage. This may take about
24 hours in a
shelter away from sun and winds. The hollow blocks thus hardened
are cured in a
curing yard to permit complete moisturisation for at least 21
days. When the
hollow blocks are cured by immersing them in a water tank, water
should be
changed at least every four days.
The greatest strength benefits occur during the first three days
and valuable effects
are secured up to 10 or 14 days. The longer the curing time
permitted the better the
product.
(5) Drying
Concrete shrinks slightly with loss of moisture. It is therefore
essential that after
curing is over, the blocks should be allowed to dry out
gradually in shade so that
the initial drying shrinkage of the blocks is completed before
they are used in the
construction work. Hollow blocks are stacked with their cavities
horizontal to
facilitate thorough passage of air.
Generally a period of 7 to 15 days of drying will bring the
blocks to the desired
degree of dryness to complete their initial shrinkage. After
this the blocks are ready
for use in construction work.
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Quality measurement:
Casting Platform
The blocks are produced on a smooth, level and hard surface of
30 mm. thick 1:3:6
cement concrete platform simultaneously finished smooth with 1:3
mortar. A base
of brick soling of 12 cm thick lean concrete 1:8:16 may be used
as a sub grade.
The platform shall be cast in bays of 2m to avoid random
surface-cracks. A
casting platform of about 80 m (10m x 8m preferably) is required
for production
of 500 blocks per day.
Mould
A battery of single moulds fabricated with mild steel plate is
used to cast the
blocks. Steel moulds yield clean, sharp edged blocks with
prefinished faces. It is
advisable to use 8 to 20 moulds arranged in a row with no gap in
between to form a
battery. Moulds are provided with handles to facilitate
lifting.
Concrete mix
Properly selected, clean ingredients of concrete should be used
in appropriate
proportions. Mixing of concrete should be done preferably in a
mixer. Basically
two types of mixes are proposed to carter for situations (i)
where coarse sand is
available and (ii) where coarse sand is not available. Although
it is advisable to do
precise mix design with the available ingredients at a place,
the following two
mixes could be followed in general with local modifications.
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Release Agents
Before starting and also after completion of the work, the
platform and the moulds
are cleaned properly. Lubricating oil is applied inside the
moulds and on the area
of platform under the moulds, to act as release agent. This
helps in an easy, clean
release of blocks and avoids the breakage of platform. The
blocks may also be cast
over alkathene sheet for easy release from the casting
floor.
Dimensional Tolerance
Deviation in the block length should not be more than () 5mm,
and that in the
height and width of the block should not be more than (3mm)
these tolerance
limits can be achieved without any difficulty with the help of
steel moulds
fabricated to an accuracy of 3.0mm in length and 1.5mm in height
and width.
Masonry Strength using solid blocks:
The wall made of solid concrete masonry blocks is designed like
other masonry
wall. The values of basic permissible stresses given in IS:
1905-1980. "Structural
Safety of Building Masonry Wall" hold good for solid concrete
masonry blocks
also. (Although the actual values achieved are about 30%
higher). Provision of
vertical reinforcement at corners and opening to impart desired
protection to the
structure in seismic regions can easily be made by using special
blocks with recess.
Masonry Construction of solid blocks:
Mortar Composition
Commonly used 1:6 cement sand mortar is compatible to solid
concrete blocks.
However, it is preferable to use 1:2:9 composite mortars if good
quality lime is
available. The composite mortar has a quality of autogenous
healing of shrinking
cracks. In case the mortar should be such that the minimum flow
after suction
should be 60% to 70% of that before suction.
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Masonry Bonds
Typical 'T' and 'L' junctions occurring generally in various
combinations of wall
thickness are illustrated in figure. Alternate courses are
clearly indicated in the
sketches. The figures illustrate two typical wall to pilaster
junctions. These also
indicate how bonding for 20cm thick wall with special grooved
blocks is provided,
which facilitates introduction of vertical reinforcement at
opening and corners,
wherever desired.
Pictures of masonry bond
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Advantages of using concrete block:
The solid Concrete Block Masonry has following advantages
1) It is a labour intensive appropriate technique and hence does
not call for heavy
capital investment.
2) It is suitable for site oriented production. Thus
transportation cost can be
eliminated.
3) Quality control is easy.
4) The wall thickness is reduced to 20 cm for load bearing wall
and 10cm for
partition walls. Thereby reducing the cubic contents of the
material, obviously
resulting in to saving in substructure as well as
superstructure. It also offers larger
floor area for the same plinth area as compared to conventional
random rubble
masonry or even non modular brick walling.
5) Internal plaster can be eliminated with proper care during
production and laying.
When plastered, the thickness of the plaster required is also
lesser as compared to
that in the case of brick wall.
6) Can be produced in remote areas without power supply by using
a portable 1
KW generator.
Do's and Don'ts for making concrete blocks:
1) Plan the building to a 10 cm module to avoid cutting of the
blocks.
2) Check the accuracy of new moulds before starting the
production. Check
accuracy of the angles of the mould every day, before starting
the work.
3) Keep strict watch on quality and the proportions of
ingredients used in concrete.
4) Modify the mix to suit the local sand and coarse aggregate.
Confirm result of the
trial mixes before commencement of the production of blocks. It
is a must.
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5) Do not forget to use release agent or alkathene sheet on the
platform before
casting.
6) Clean the moulds, alkathene sheet and, the production floor
as soon as the day's
production is closed.
7) Do not disturb the freshly cast blocks before 24 hrs, in any
case.
8) Do temporary stacking near the casting yard on a level ground
provided with
sand cushioning. Each day's production is accommodated in not
more than 2 tiers.
9) Cure the blocks by sprinkling water for three weeks and then
air dry for two to
three weeks depending upon weather conditions.
10) Do not use a partially dry block in masonry.
11) Do not soak the block before using in the masonry. It should
be only surface
wet. So, a light water spray, about half an hour an hour before
use, is enough.
12) Do not use harsh mortar in masonry.
13) Fill up the vertical joints with extra care.
14) Provide control joints at appropriate locations for wall
more than 10 meter
long.
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Block Making Machine:
Design Parameters
Compaction of concrete in mould depends on frequency. Amplitude
and duration
of vibration, these in turn depend on the conditions of
vibrating system comprising
the mould and the concrete to it. For concrete having coarse
fraction of aggregate,
a lower frequency of vibration and high amplitude are required
whereas for
concrete containing fine fractions, the high frequency with low
amplitude is
necessary. Since concrete normally contains particles of varying
sites, the most
satisfactory compaction is obtained by using vibrators with
different speed of
vibration as in case of poly frequency vibrators. This however,
makes the vibrating
system costly. The vibrators used in practice therefore work
only at single
frequency suitable for average particle size of the concrete to
be compacted. By
using increased frequency of vibration, it is possible to obtain
high values of
exciting forces with a much lighter vibrating system, but with
increased vibration
frequencies, the resistance of wear of the vibrator is markedly
reduced. The most
widely used form of vibrators therefore have vibration
frequencies varying from
2800 to 6000 VPM and amplitude of vibrations correspondingly
varying from 1.0
to 0.1 mm. Besides frequency and amplitude, the acceleration of
vibration is also
an important factor. For external vibration of concrete (as in
case of block making
machines in general), the criterion for effective compaction at
constant workability
and constant time of vibrations acceleration with the provision
that at frequencies
up to 6000 VPM, the acceleration is greater than 1.5 g and at
frequencies greater
than 0.04 mm. The available block making machines work at higher
side of
frequency range, 6000 VPM and lower amplitudes and are therefore
more suitable
for concrete with smaller aggregates. Since the new block making
machine was
required to primarily cast the stone blocks and the large
aggregate concrete block
wherein lean mixes of concrete with larger size aggregates are
involved, a lower
frequency of 3000 VPM and a corresponding higher amplitude of
1.5 mm with an
acceleration of about 7 g were considered desirable in the light
of the
recommendations of IS: 4656 1968 Specifications for Form
Vibrators for Concrete.
A top pressure of 30 to 100 gm/cm2 has been reported to improve
the flow ability
of concrete during vibration and is particularly helpful in
handling stiff mixes. A
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top pressure of about 50 to 80 gm/cm2 was found effective in
case of stone blocks
and large aggregate blocks respectively.
Features
The block making machine comprises a four wheel trolley with
front pair of
wheels having steering arrangement and a portal frame which its
top carries a
horizontal power shift connected to an electric motor through V
belt and pulleys
mould block with a number of mould cavities placed centrally
inside the portal
frame. Two vertical power screws, onset each end of the mould
block are used to
raise or lower down the mould block. The lower end of the power
screw after
passing through the edge of mould block is supported in a
bearing which in turn is
supported with the trolley. The top end of power screw is
connected with the
aforesaid horizontal power shaft through gears. The arrangement
helps in lifting or
lowering down the mould block by motor power. The mould block
has a number of
cavities or moulds for castling more than one block at a time.
On form vibrator is
rigidly fixed with each opposite face of longer side of the
mould block. A bridge
arranged just above the mould block carries as many number
pressure platens as
there are mould cavities in the mould block. The pressure
platens keep the concrete
pressed in the mould during vibration and later help during
ejection of the new
casts blocks from the moulds. The bridge also carries a system
which provides
required amount of to pressure through the pressure platens on
the concrete in
moulds at the time of the compaction of concrete. The vertical
upward movement
of the bridge is achieved through the mould block when the later
is lifted up with
the help of two power screws. The connection between the power
screws and the
mould block is through two lifting pads each fitted on the edge
of opposite shorter
faces of the mould block. The lifting pads have built-in
vibration isolating devices
that help in confining the vibrations (during compaction of
concrete) only to the
mould block. Salient features of the machine are given in the
following:
A portable egg laying type machine.
Six blocks of size 30x20x15 cm case in one operation.
Output of 120 to 150 blocks of above size in one hour.
Better compaction ensured through pressure vibration.
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Two vibrators each of 0.5 KW capacity and frequency 3000 VPM
used for
consolidation of concrete.
Suitable for casting stone block, large aggregate concrete
blocks traditional
concrete block and hollow blocks.
Operator's access right upto the moulds help in easy placement
of stone
spalls in casting stone blocks and screeding of concrete in the
moulds while
casting large aggregate blocks.
Power required: 3KW
Working and trials
The machine is placed on the casting platform which should be a
leveled and well
finished concrete floor. Waste newspapers or polythene sheets
are laid on the
platform for easy removal of the block next day. The mould block
is first made to
rest on the platform by operating the powers screws. Concrete
prepared in a
concrete mixer is received in special trolleys and brought to
the block making
machine and dumped in the moulds. Screeding of concrete is done
manually to
bring the concrete to the same level in all moulds. The operator
then allows the
bridge to drop freely. These results in sudden impact which
passes through the
pressure platens on the concrete filled in the moulds. Vibration
of concrete is later
carried out by switching vibrators simultaneously. The vibration
is maintained till
the full height of the compacted block is achieved. The height
of the compacted
block is achieved. The mould block is the lifted up leaving cast
concrete blocks on
the platform. During upward moving when mould block completely
clears the cast
blocks, the former comes in contact with the bottom face of
bridge. From this stage
onwards. the bridges also lifted up along with the mould block
resulting in
simultaneous breaking of the contact between all pressure
platens and the top face
of the cast blocks. When both the mould block and the bridge are
raised to a certain
height, their upward movement is automatically stopped with a
limit switch. The
machine is then moved forward on its wheels to a new position of
casting while
leaving the newly cast blocks behind on the floor.
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Concrete Block Making Machine
Types of Concrete block making machines:
Heavy duty concrete block making machine
The product is used in the construction and civil works. This
range of high density
paver blocks are widely used in swimming pools, petrol pumps,
parking areas,
courtyards, container yards, road side foot-path. Due to this
heavy duty, the blocks
have to be built according to the nature of use. Heavy Duty
Paver Block Machine
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are developed to bring about looking into this requirement. This
machine on an
average can produce 1400 to 1500 nos per day of 8 hrs. The
latest model machine
are highly specialized with Total Motor 7.5 HP, 3 Phase 1440 RPM
Pressing Load
40 to 50 Ton Cylinder Bore Size 125 mm Hydraulic Oil 120 Ltr.
Same size mould
or any different two types mould can be used simultaneously. Any
type mould as
per customers specification can be manufactured.
Cover block making machine
Cover Block Making Machine offered by us are widely used in the
construction
industry to making high quality cover blocks. In this process
highly flowing
pigments with concrete is poured in to the rubber moulds and
compacted in vibro forming vibrating tables. The various customized
size & thickness with design and
attractive.
Technical Specifications:
Power Consumption: 1.5 HP / single phase
Mixer Muller Machine: 2 hp / single phase
Vibrator cum manual machine
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Designed and developed by the professionals using advanced
technologies and
quality raw material in adherence with the international
standards. The offered
machines are widely used for making blocks that are suitable for
construction
purposes.
Features:
Easy operations
Minimum maintenance
Excellent performance
Interlock soil block making machine
Interlock Soil Block Making Machine machines can be availed by
the customers in
varied capacities and are widely used at construction sites to
reduce the labor cost.
Before the end delivery, these machines are stringently checked
by the quality
analyzers on varied parameters to ensure their flawlessness.
Features:
Optimal performance
Compact design
Low power consumption
Precise engineering
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Economy in production
It has been observed in the field that the contractors normally
employ a gang of
about 20 persons to produce 1000 large aggregate concrete blocks
of size
30x20x15 cm in one shift of 8 hours with manual, method of
casting. The gang
includes labour for mixing concrete in moulds vibrating the
concrete with two
plate vibrators. Demoulding the blocks and preparing moulds for
next filling.
Normally the labour cost of production estimated in the manual
method at Rs. 0.50
per block. An estimate was also prepared for labour charged for
making blocks
with newly developed machine. The operating charges for the
machine are Rs.
160.00 per day per shift of eight hours. Considering a
production rate of 1000 large
aggregate concrete blocks of size 30x20x15 cm in one shift and
using concrete
mixer of 200 liters capacity with Rs. 80.00 per day labour
charges the total cost of
labour was estimated at Rs. 0.24 per block which is 50 percent
of the labour cost of
manually made blocks. Since in the field the labour charges are
about 20 % of the
total cost of a block, the mechanized production of blocks
brings in substantial
savings in the labour charges in addition to improving strength
and other properties
of the block.
Labour cost per a single block is
Rate of cement per bag(50kg) =Rs 280
Sand or crushed stone per 1 ton = Rs 350
Crushed stone chips per 1 ton =Rs 600
As a single cube size is 30cmx20cmx15cm the volume is 0.009cum
per
cube and for M10 (1:3:6) the required mass of
1. cement is 2kg (Rs 5/kg)
2. sand or crushed stone sand is 6kg (Rs 0.35/kg)
3. crushed stone chips is 11 kg (Rs 0.60/kg)
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Then the cost of materials per cube is
1) cement = Rs 10
2) sand or crushed stone sand= Rs 2
3) crushed stone chips= Rs 7
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Total Rs 19/per block (30cmx20cmx15cm)
Then we can say the total cost of a single block including
labour cost &
material cost is Rs 19.24