|Components of Flexible Pavements|
It is one of the most convenient,safe and cost effective method of road construction throughout the world. It consists of HMA ( Hot Mix Asphalt) layers on the top surface of the road which is flexible due to contain of bitumen content and it is black in color, that's why it is called flexible pavement or black top pavement.
Components of Flexible Pavements
Flexible pavements are consists of the following Components:
It is the natural soil which acts like foundation for the pavement. The stability of pavement depends upon Subgrade. In order to stabilize the road, the subgrade is compacted to achieve its maximum density. Through compaction all the voids are removed from the soil particle. To achieve required compaction, various laboratory test has to be conducted e.g FDT ( Field Density Test), Moisture Content etc.
It is the layer of coarse aggregate of the size 0.5" to 1". It is an optional layer and provide a base and level surface for its subsequent layer. It can increase the load carrying capacity of the road.
3) Base Course
It consists of broken rocks or coarse aggregate of size 2.5". Its is compact by roller to thoroughly compact the layer. Most of the strength provides by this layer of the pavement. To fill all the voids among the aggregates a thin layer of stone dust is provided on it and then water is sprinkle on it and again compact it. Then by brushes the surface dust is removed.
4) HMA (Hot Mix Asphalt)
i) Binder Course & Tack Coat
Binder is mixture of Bitumen and Lubricating oil. It is sprayed on the Base Course layer and then traffic is on for 3 to 4 months to thoroughly compact the pavements components and any rutting that can cause in future. After that another thin layer of bitumen called tack coat is sprayed on it in order to make a perfect bond between Base course and subsequent layer.
ii) Asphalt Wearing Course and Seal Coat
After Binder Course and Tack Coat, Asphalt Wearing Course is laid on it and it is the final layer of the flexible pavement. Its normal thickness is almost 4" to 6" and then compact it by roller. Its thickness can be increase according the traffic capacity. After that seal coat is sprayed on it which consists of Bitumen and emulsion in order to fully seal the wearing course. Th e rain water cannot percolate through Seal Coat.