Bituminous mixing and laying plant
The mixing and laying of bitumen for roads and pavements can be undertaken using a range of different types of plant. The type of plant used will be determined by the type of material that is required and the process adopted.
 Heaters and boilers
Bitumen heaters and boilers range from small mobile units to large permanent plant. The most common types are:
- Mobile boilers: Mounted on a steel chassis and towed from place to place. The furnace at the base of the boiler is either gas or oil-fired.
- Static heating and storage tanks: These are heated by oil-fired burners and are available for high outputs as they can have capacities of up to 18,000 litres. They will usually be transported on a low loader.
 Binder distributors
The most common type of binder distributor is the bulk tank sprayer. The binder is kept at the required temperature by fitted heating units. A static heating unit feeds the binder into the bulk tanker which can have a range of tank capacities. A horizontal spray bar and power-driven pump mounted at the rear of the unit is used to spray the binder over the road surface.
These are commonly used in resurfacing projects. The road is sprayed with hot binder and then coated with grit from a slow-moving machine. A lorry follows behind the chip-spreader to keep it supplied with chippings. These are fed into a rear hopper and carried on a conveyor to the spreader.
These are either permanent plant installations or small mobile units. They perform a complete sequence of operations, from drying, to aggregate heating and mixing, to coating them with binder, to delivering them ready to be laid.
- Drying units: A long rotating cylindrical drum is heated internally by hot gases through which the aggregate is passed, ensuring that it is thoroughly dry before being coated with a binder.
- Batch-mixing plants: These have several individual sections – aggregate feeder, drier unit, binder heater, weighing plant and mechanical mixer.
- Mixing units: These are a form of paddle mixer that enables a thorough mix in a short space of time.
 Spreading and finishing plant
Large machines are used for spreading and finishing the surface coating, ideally in a single pass. They are available with different laying speeds and hopper capacities. Rollers on the front of the lorry’s hopper are connected to the tyres and so push the lorry forward whilst unloading. The screed plate is hydraulically adjusted so as to control the thickness of the surface finish.
 Related articles on Designing Buildings Wiki
- Cherry pickers.
- Compressed air plant.
- Concreting plant.
- Construction plant.
- Construction tools.
- Crane supports.
- Earth-moving plant.
- Excavating plant.
- Forklift truck.
- Power float.
- Road construction.
- Road joints.
- Runway construction.
- Types of crane.
- Types of road and street.
- Types of roller.
 External references
- ‘Introduction to Civil Engineering Construction’ (3rd ed.), HOLMES, R., The College of Estate Management, (1995)
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