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.
What is Pavement?
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.
Key Functions of Road Pavement:
- Transmit the vehicle load from base coarse to sub base to the underlying ground surface.
- Robust enough to bear Heavy Vehicle load for the entire design life duration with minimum maintenance or intermittent pavement treatment.
- Provide adequate skid resistance either by directly applying high PSV (Polished Stone Value) surface course or by applying HFS (High Friction Surface) Treatment.
- Provide low noise level (generated by tyre and pavement surface friction) in the urban road by applying TSCS or a similar surface course.
- Allow comparatively a high noise level on rural motorways/ national road but minimise the construction and maintenance cost in long run.
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/ limitation, etc.
Broadly Road Pavements are classified into three distinct categories based on the pavement material types
Types of Pavements
There are three key types of pavements depending upon the materials used as shown below:
- Flexible Pavement
- Semi-Rigid Pavement
- Rigid Pavement
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 categorised into two materials named Thin Surface course System (TSCS) and Hot Tolled Asphalt (HRA).
- Surface Course
- Base Course
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 aggregate 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)
- Hot Rolled Asphalt
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 tyre 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:
- Type-A: 12mm to 18mm
- Type-B: 18mm to 25mm
- Type-C: 26mm to 50mm
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 high skid resistance ability. A high PSV (polished stone value) value chipping makes the HRA more skid resistance.
As a result, it generates a high level of noise due to vehicle tyre friction and so, its 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 Surface Course:
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.
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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 a 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 minimises the damage of the sub-base from excessive vehicular loading.
The capping layer provides additional strength to the Sub-Base and also shield the underlying soil from heavy construction vehicle and machine loading during the construction stage.
Geogrid is predominantly a Geosynthetics and made like an open mesh grid structure. It enhances the tensile strength of the underlying soil and minimises the undercutting soil. It holds soil particles but permits the movement of fluids, so greatly enhance the performance of the Pavement Sub-Base.
The pavements 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.
Hope this blog helps you understand the key functions of Road Pavement and also various type of Pavement Layers. Please feel free to comment and share.
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