Highway Stones Requirements
Highway Stones Requirements
The highway is consist of five layers. These are subgrade, Cushion, subbase, roadbase , wearing course. Each layer has different demands on stones materials.
Sub-grade:
The sub-grade layer of a pavement is, essentially, the underlying ground. It is also known as the "Formation Level", which can be defined as the level at which excavation ceases and construction starts: it's the lowest point of the pavement structure. This layer need large stones which do not be crushed.
Cushion:
The cushion is between base and ground whose role is drainage, antifreeze. when the water temperature is in poor conditions, improve the soil base status, improve the pavement structure of water stability and anti-frost skills, and the proliferation of load, in order to reduce land-based deformation.
Subbase:
In highway engineering, subbase is the layer of aggregate material laid on the subgrade, on which the base course layer is located. It may be omitted when there will be only foot traffic on the pavement, but it is necessary for surfaces used by vehicles.
Subbase is often the main load-bearing layer of the pavement. Its role is to spread the load evenly over the subgrade. The materials used may be either unbound granular, or concrete-bound. The quality of subbase is very important for the useful life of the road.
Unbound granular materials are usually crushed stone, crushed slag or concrete, or slate.
Concrete-bound materials come in multiple types. Mass concrete is used where exceptional loads are expected, with thickness usually 100-150 mm, and optional reinforconcrete with steel mesh or polymer fibers. Other concrete bound materials (CBM), with less strength but also lower cost, are used. They are rated by strength, from the weakest CBM 1 (also formerly known as soil concrete) through CBM 2 to CBM 3, 4, and 5, which are more similar to concrete and are called "lean mix".
The thickness of subbase can range from 75-100 mm for garden paths through 100-150 mm for driveways and public footpaths, to 150-225 mm for heavy used roads, and more for highways.
Base course:
Base Course in pavements refers to the sub-layer material of an asphalt roadway and is placed directly on top of the undisturbed soil so as to provide a foundation to support the top layer(s) of the pavement. Generally consisting of a specific type of construction aggregate, it is placed by means of attentive spreading and compacting to a minimum of 95% relative compaction, thus providing the stable foundation needed to support either additional layers of aggregates or the placoncrete of asphalt concrete which is applied directly on top of an asphalt sealed Base Course, all resulting in a roadway pavement.
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