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What is Road Pavement? what are the key functions of Road Pavement?
If you would like to know all these details along with the types of road pavement, please read this interesting blog.
Let’s crack on.
The road pavement is multiple layered surfaces constructed to allow the movements of vehicles and provide a smooth and comfortable ride to the road users.
There are two primary purposes of road pavement, first to provide a controlled friction level to the running vehicle, and second to transmit the vehicle load to the underlying ground.
There are numerous types of road pavements as per the road usage, local environment, ground condition, etc and all pavement types come with some pros/cons and advantages/limitations, etc.
Broadly Road Pavements are classified into three distinct categories based on the pavement material types
There are three key types of pavements depending upon the materials used as shown below:
Flexible pavement is made of multiple layers named surface course, base course, sub-base, capping, and lastly the Geogrid. The surface layer is made of Asphalt material.
It is further categorized into two materials named Thin Surface course System (TSCS) and Hot Tolled Asphalt (HRA).
Surface Course which is made of Asphalt material is a mix of asphalt cement and aggregate (5% and 95% respectively). In surface course treatment, larger size aggregates are placed in the lower section and small size aggregates are placed in the upper section.
Asphalt materials are made robust enough to withstand the local climate, which means in a colder climate, they are made softer and for a hot climate, they are made harder.
Following are two types of material commonly used as surface Course:
Thin Surface Course System (TSCS):
This Surface Course System is considered as high-end Stone Mastic Asphalt and preferred for the urban road for low-level noise generation from vehicle tyres friction. It is easy for placement, and compaction.
Riding quality over the TSCS is also very smooth compare to HRA. TSCS comes in three sizes:
Hot Rolled Asphalt (HRA):
Hot Rolled Asphalt (HRA) is a composition of bitumen, aggregate, and sand. It is a highly dense and pre-coated chipping asphalt and comes with a high skid resistance ability. A high PSV (polished stone value) value chipping makes the HRA more skid-resistant.
As a result, it generates a high level of noise due to vehicle tyres friction and so, it's not suitable for the urban road but useful for rural high-speed roads or motorways. It needs less maintenance and resurfacing compare to TSCS.
Milling of Pavement Course is required when it is recommended to restrengthen the existing road pavement. Milling is a delicate task and needs high-level workmanship and expertise.
Base Course is laid just below the surface course and above the Sub-base layer. The thickness of the base course varies from 100mm to 160mm.
It is laid to support the foundation and transmit the load of the vehicle and upper pavement layer to the sub-base and underlying soil.
The sub-base is laid just below the Base-course and above the Capping Layer. The sub-base is considered as the foundation layer (unbound layer) and made to bear a load of the above layer plus vehicular load and transmit that to the Capping and underlying soil.
The thickness of the Sub-Base Course is dependent on the CBR of the existing adjacent ground. The lower the CBR value, the higher the thickness of the sub-Base.
The sub-base course is an unbound layer and made of material such as crushed stone or crumpled concrete or slag.
Capping Layer is also considered as a part of the Pavement Foundation and termed as an unbound layer. The aggregate used in Capping is generally of inferior quality than the sub-base course. It supports the Sub-base and minimizes the damage of the sub-base from excessive vehicular loading.
The capping layer provides additional strength to the Sub-Base and also shields the underlying soil from heavy construction vehicles and machine loading during the construction stage.
Geogrid is predominantly a Geosynthetics and is made like an open mesh grid structure. It enhances the tensile strength of the underlying soil and minimizes the undercutting soil. It holds soil particles but permits the movement of fluids, so greatly enhances the performance of the Pavement Sub-Base.
The pavement sub-base is commonly constructed from the traditional aggregate. Semi-Rigid Pavement is made of waste materials such as steel industry wastes such as granulated slag, BF slag, Flyash, SMS, etc.
These steel industrial wastes are very useful to use as Sub-Base material and it improves the performance of the Sub-Base significantly.
Rigid pavements are made of a mix of aggregate and Portland cement in the form of a concrete slab. The slab is laid over the sub-base material which is made of granulated material or placed directly over the capping layer.
Our Highway Engineering Course has covered a detailed module on Pavement Design.
Please see the Freeview of the course on our Youtube channel.
Hope this blog helps you understand the key functions of Road Pavement and also various types of Pavement Layers.
Please feel free to comment and share.
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