What are the Equipment used for Bituminous roads?
There is various equipment used for bituminous roads, it becomes necessary to heat the bitumen and laying properly with compaction.
For small projects and maintenance works; the aggregate filler and binder are heated together after being mixed dry in the required proportions and the binder or bitumen of the specified grade is heated to the required temperature and mixing is done on a specially prepared platform at a central location from which the mix is carried to the site of placement by means of wheelbarrows.
For minor works, maintenance process, patch repairs, providing premix carpet, etc., the mixing and laying are carried out manually. The aggregates and bitumen are heated separately and mixing is done over a specially prepared platform.
In the case of large projects, the mixing plant is centrally located and the prepared mix is carried to the site of placement in trucks or dumpers. The bituminous concrete can also be mixed in stationary or portable plants depending upon the magnitude of the project.
The equipment for bituminous roads can be grouped in the following four categories:
(1) Bitumen heaters (3) Bitumen truck mixers
(2) Bitumen mixers (4) Pavers.
For portable mixing plants as well as for hand mixing, the bitumen heater is an essential piece of equipment. It is an important material for surface painting, primary coats, tack coats, and penetration macadam.
The bitumen heaters are available in various sizes and they are heated either by steam, wood, coal, or kerosene oil. The heated bitumen is carried to the site of work in pouring cans or pots and it is spread over the surface at the predetermined rate of application.
The improved types of bitumen heaters are provided with mechanical pressure distributors. In such a type of bitumen heater, the rate of application is calibrated and hot bitumen is sprayed over a given area so as to give the required coverage.
The application of this type of heater gives a better surface as the binder is spread over the surface more uniformly than by pouring cans or pots.
For isolated and petty works, the bitumen is heated directly in the drums or containers having capacity of about 200 litres.
For big projects, there are number of patented mixing plants available for the construction of bituminous roads. They usually consist of the following components:
(i) Aggregate drier,
(ii) Aggregate heating arrangement, (iii) Bins for storage of aggregates of various sizes,
(iv) Bitumen heater,
(v) Bitumen storage tank,
(vi) Mechanical mixer, and
(vii) Weighing machine.
Following points should be kept in mind for the efficient and successful functioning of a bitumen mixing plant:
- Adequate supply of materials:
The materials will be required in huge quantities and it is, therefore, necessary to ensure an adequate supply of all the materials at the site of the plant before the work of the mixing plant is commenced.
- Arrangements for transport:
The prepared material available from the plant is to be transported by carriers from plant site to the site of work. It is therefore necessary to keep ready the required number of dumpers for this purpose.
- Covering of dumpers: The top surface of dumpers should be covered with tarpaulins to maintain the temperature of the mix and also to prevent the deposition of dust particles from the road surface.
- Pavers and rollers: At the site of work, the necessary number of pavers and road rollers should be provided so that the pavers receive the mix immediately from the dumpers. The laying of mix on the surface is also so arranged that by the time the paver has emptied its contents, the next installment of the dumper is ready to discharge its content.
- Bitumen truck mixers:
For facilitating the preparation of a quick and efficient mix, the bitumen mixing units have been installed in trucks or tractors. Various types of truck mixers are available at present. In one arrangement, the heating of aggregate is done in a separate portable unit and the bitumen is heated in a bitumen heater attached to another portable unit.
The mixing is done in revolving units which are more or less similar to the concrete mixers. The layout is so arranged that the bituminous concrete discharges directly into the paver unit and the entire construction unit along with the mixing unit and laying unit moves forward at the same rate.
The paver unit is a compromise between a pneumatic tractor and a dumper. It consists of the chamber having a capacity equal to that of a dumper bringing bituminous mix from the central mixing plant. The chamber is provided with an adjustable Slot opening. The working of paver is as follows:
(i) The dumper discharges its contents completely into the chamber of paver.
(ii) The chamber is sloped in forward direction and it discharges the mix through adjustable slot opening on the road surface
(iii) The dumped material is laid by means of the following blade whose height above the pavement level corres-ponds to the designed spread thickness of the mix according to the prescribed camber.
(iv) The width of the blade is made equal to the finished width of the pavement surface.
(V) The paver is followed by one or two road rollers so that the compaction of laid mix is carried out while it is hot.
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