Pavement is the actual travel surface especially made durable and serviceable to withstand the traffic load commuting upon it. Pavement grants friction for the vehicles thus providing comfort to the driver and transfers the traffic load from the upper surface to the natural soil.
In earlier times before the vehicular traffic became most regular, cobblestone paths were much familiar for animal carts and on foot traffic load.
Pavements are primarily to be used by vehicles and pedestrians. Storm water drainage and environmental conditions are a major concern in the designing of a pavement.
The first of the constructed roads date back to 4000 BC and consisted of stone paved streets or timber roads. The roads of the earlier times depended solely on stone, gravel and sand for construction and water was used as a binding agent to level and give a finished look to the surface. All hard road pavements usually fall into two broad categories namely
- Flexible Pavement
- Rigid Pavement
Flexible pavement is composed of a bituminous material surface course and underlying base and subbase courses. The bituminous material is more often asphalt whose viscous nature allows significant plastic deformation. Most asphalt surfaces are built on a gravel base, although some 'full depth' asphalt surfaces are built directly on the subgrade. Depending on the temperature at which it is applied, asphalt is categorized as hot mix asphalt (HMA), warm mix asphalt, or cold mix asphalt. Flexible Pavement is so named as the pavement surface reflects the total deflection of all subsequent layers due to the traffic load acting upon it. The flexible pavement design is based on the load distributing characteristics of a layered system.
It transmits load to the subgrade through a combination of layers. Flexible pavement distributes load over a relatively smaller area of the subgrade beneath. The initial installation cost of a flexible pavement is quite low which is why this type of pavement is more commonly seen universally. However, the flexible pavement requires maintenance and routine repairs every few years. In addition flexible pavement deteriorates rapidly; cracks and potholes are likely to appear due to poor drainage and heavy vehicular traffic.
A valuable advantage of flexible pavement is that it can be opened for traffic within 24 hrs after completion. Also the repair and maintenance of flexible pavement is easy and cost effective.
Today 96% of all paved roads and streets in Pakistan are surfaced with asphalt. Almost all paving asphalt used today is obtained by processing crude oils. Man-made asphalt consists of compounds of hydrogen and carbon with minor proportions of nitrogen, sulfur and oxygen.
Rigid pavement is composed of a concrete surface course and underlying base and subbase course (optional) and is stiffer than the flexible pavement. The cement concrete may be plain, reinforced or prestressed concrete. In the rigid pavement the load transfer phenomenon is quite different than the flexible pavement. The concrete surface layer alone provides most of the rigid pavement
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