Mould for a pair of wall panels:
suited for panels that require a smooth surface on both sides.
1. A large
no of units can be produced in a small space.
the units proceeds fast.
3. No need
to spread the concrete
finishing not necessary due to smooth mould faces.
5. Heat of
hydration developed is conserned and accelerates curing.
These are employed for casting
volumetric elements such as sanitary units, ventilates shafts and refuse
chuter. Battery moulds are employee for internal panel walls and floor panels.
The swing down moulds are used for simultaneous manufacture of two wall panels.
Flow Line Production :
This is a travelling horizontal
mould system in which the moulds are moved and the element from one position to
the rest a series of stations, such as demoulding, mould cleaning and oiling,
placing of reinforcements concreting vibration, surface finishing and curiving
a stream chamber forms the part of the continuous travelling a chain and the
chain can be in the horizontal plane or in the vertical plane.
Schematic diagram of flow line production:-
should have volumetric stability to ensure dimensional accuracy.
2. They can
be reused a large no of times with minimum maintenance cost.
should be easy to handle and close tightly so that no liquid can lead out.
should not have adhesion to concrete and easy to clean.
They can be sued for various cross sections shapes
of the components. Wooden moulds:
1. Concrete sticks more easily. to
prevent this, a coating of mould oil or wood lequer is given.
2. It can be used 30 to 40 times. The dimensions
should be checked frequently.
They are used fro smaller
production programmes. Steel Moulds :
of the smooth surface demoulding is fairless easy.
Indiscreminate harmmering by workmen should be
avoided. Concrete moulds:
1. These are
used in vertical battery moulding.
workability is low
moulds enable hish degree of dimensional accuracy, but are un-suitable for
moulds are stationary not often transported.
surface of the mould must be absolutely smooth of otherwise excessive adherion
may cause difficulties in demoulding.
made of glass fibre reinforce plastics are commonly used.
2. They have
the advantage of freedom of shaping and low weight.
4. They are
The same mould can be used 70 to 80 times without
repair. Manufacture Of Precast Elements:
Type of moulding depends upon the
constructional features and the surface finish. In the case of internal panel
wall-vertical battery wall. In the case of external panel wall-horizontal
moulding is usually done.
2. Roof or Floor Elements:
Depends on the type of building
we construct whether residential or public building with large span. In the
case of residential building the entire roof or floor is cast as a single unit.
In the case of public building where long spans are encountered. The elements
are east in the form of hollow core floor slabs. Trough units and ribbed slabs
which are normally of PSC.
3. Beams and Column :
horizontal moulding is done. In the case of staircases vertical or horizontal
of concrete by strips slips
of concrete is done manually or mechanically.
by vibrators or by vacuum process or pressing.
case of vibration it is effected by means of internal vibrations and external
vibrations. Internal vibrations in the form of immersion vibrators is used in
places where we have conjusted reinforcements. External vibrators ae generally
used with steel moulds. Vacuum process is suitable for components with large
surface area or relatively thin elements. In the case of compaction by
pressing. The freshly poured concrete is subjected to a pressure of about 70
ksc. It sequences out excessive water forming a cohesive slab which can be
curing -1 cycle -(Steam curring)
1. Preheating period -3hrs-35ºC
Rise Period -2hrs -35 to 8.
at max temp - 6hrs - 80ºC
period - 3hrs - 80ºC-45ºC
Accelerated curing techniques are
adopted for quicker turnover. It may be in the form of steam curing or heat
treatment. Hot water or hot air. The duration of stream curing cycle is
influenced by the factors like type of cement, water cement ratio, size of the
members, the desired strength. With proper steam curing it is possible to
achieve 60% of the moist curned 28 days strength of the concrete in 24 hours.
In open casting yard for steam using specially made hoods are used which are
insulated and sealed to prevent excessive loss of heat and moisture. In the
case of flow line product.
The chamber is sufficiently long
to ensure that the products remain wihin the chamber for the desired time.
Demoulding and storage:
are first demoulded from the sides and then from the bases and the earthwork
required to separate the unit from the base is more than the weight of the unit
to account the adhesion of the unit to the base. Wall element are stored
vertically. Floor and roof elements are stacked horizontally with & wooden
strips in between two elements.
formed in the mould.
treatement of surface.
surfaces are obtained by lining the mould with suitably patterned rubber
linings, plastic steel or timber. Smooth surfaces are obtained by resin coated
or plastic zined mould surfaces.
b) This can
be applied by freshly cast concrete or by the hardened concrete. In the case of
freshly cast concrete. It is done by hand travelling or by rolling with a
smooth steel tube on the compact concrete or by tamping with the edge of long
wooden floor. In the case of hardened concrete. It is done by point tooking or
by grinding the surface when soft aggregate are used.
By production tolerance use mean
the limiting value of admissible deviations in the actual dimensions. The
deviations may be caused.
fitting of joints.
Joints and mould sides under pressure of concrete.
The limiting values are
1. Length ± 10mm
2. Width ± 3mm
3. Thickness ± 3mm
Flatness - 1/300 of the length. Planning of
precast concrete works:-
Requirement of space and
facilities. Space for production :
It is based on height and no
moulds horizontal moulds -larger areas - vertical battery moulds -least amount
of floor space. Height of the casting shed is based on space required. To lift
and move one precast corpponent over another. The head room can be sufficiently
decreased by having moulds in pits. Extra space must be provides for making the
reinforcements stages cleaning and up the demoulded units.
Space for storage yard:
depends on the daily output and the demand. The space must be sufficient to
store minimum of 3 weeks production. The storage yard may be preferably aligned
with the casting shed to facilitate movement of overhead cranes.
Space for facilities:
This depends on the type &
single of ancillary facilities required namely storage of raw materials such as
cement, coarse aggregate & fire aggregate, reinforcement steel. Conc
batching plaint, fitters and joiness shop, Boiler and compress house.
Laboratory & Office.
Modular co-ordination, standardization and Tolerance
Basic Dimensions :
This is the dimension between the
axis defined by the dimensional grid. The dimensional grid is the two
dimensional co-ordinate system of reference line defining the layout of the
Nominal or Theoretical Dimensions :
It is the
planned dimension of the prefabricate arrived from its basic dimension and its
Actual Dimensions :
It is the dimension of the
prefabricated when produced and its differs from the nominal dimension by the
production discrepancies which are unavoidable.
The tolerance is the sum of
acceptable positive and negative discrepancies of actual dimensions from the
theoretical one. The limits of tolerance are based on the manufacturing and
Modular Co-ordination :
If the inter dependent
arrangements based on the Pre Fabrication and System Building
Pre-fabrication means that the
structure is disunited in its members and these are precast either in factories
built and equipped particularly for this purpose or in temporary plants
established n the site. Then the precise reinforced concrete members are
shifted to the place where they are to be used, here they are hoisted, set into
their final places, and assembled to form a complete structure.
Stages involved in pre-fabrication
structure divided into number of units.
different units are precast in permanent factories (plant fabrication) or
temporary plants (site prefabrication).
to the site.
Hoisted set into their final places and assembled to
or total saving of material used for scaffoldings.
use of shuttering
of far more accurate and better work manship.
time can be shortened.
expansion joints are required.
is connection can be omitted.
7. The work
can be carried out with a high degree of mechanization.
in man power decrease.
9. Re use of