Tar and Bituminous Equipments
On the works of road
construction, bitumen is used for surface painting. Bituminous pavements and
wearing surfaces provide a resilient and waterproof layer that projects the
underlying materials from water and traffic. In case of isolated jobs, the
aggregate filler and binder are heated together after being mixed dry in the
required proportions. Mixing is done on a mixing platform from which the mix is
carried to the site. In case of large projects, the mixing is done in a
centrally placed stationary plant mixers and then the material is carried to
the site either in trucks or in dumpers. The bituminous concrete is also mixed
in stationary or portable plant depending upon the magnitude of the project.
There are two types of plants
generally referred to as “Batch Plants” and “Continuous mix Plant”. The
principle of operating both the plants is the same. The component parts of a
tar and bitumen mixing plants are as follows:
1. Bins for
storage of various size aggregate:
The aggregates
are fed into the plant at “Cold Feed” end. A very common method of feeding the
aggregate at the cold feed is by means of storage bins and crane, to charge
them from the stock. Sometimes, the aggregate are stored on the ground and
bulldozer is used to push the aggregates over the feeder.
2. Aggregate
Drier:
The aggregates
of various sizes are fed to the drier through a cold elevator. The drier dries
off most of the moisture in the aggregate at the same time heats the material
to the desired mixing temperature. Drier consists of a long rotating drum with
inside lifting flights which continuously drops the aggregates through hot
gases. The drum is in a tilting position.
Aggregate Drier
3. Hopper and
Screens:
After the
aggregates are dried, they are transferred. Before entering into the hopper,
they are screened into two or more size ranges. The screens are so selected
that the gradation is split according to the specifications.
4. Mixers:
From the
hoppers the aggregates are discharged into the mixer and at the same time they
are weighed. Quantity of hot bitumen is led into the mixer. After mixing
bituminous the concrete is discharged into a truck. Trucks are used for
transportation to the construction site. Mixer consists of a chamber containing
central shaft with paddles and heating appliances. It contains a door which can
be automatically opened for the discharge of mixed material into trucks.
Bitumen Sprinkler:
For surface dressing of large
areas, bitumen sprinklers having a capacity of 3,000 – 15,000 litres are used. The
tanks are insulated and are provided with heaters that may be used to maintain
the temperature of the binder. Tanks are mounted on vehicles and a thermometer
is fitted to check the temperature.
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Distribution of the binder is
done by a spray bar which is fixed at the rear end. The spray bar is properly
nozzled. The rate of spraying bitumen is controlled by speed of vehicle which
is indicated by tachometer reading. A bitumen distributor sprays bitumen
efficiently and quickly.
