What is Pavement? (Road Pavement)
“A pavement is one type of hard surface made from durable surface material lay down on an area which is intended to carry vehicular or foot traffic”.
its main function is to distribute the applied vehicle loads to the sub-grade through different layers. The road Pavement should provide sufficient skid resistance, proper riding quality, favorable light reflecting characteristics, and low noise pollution.
Its goal to reduce the vehicle transmitted load, so that they will not exceed the bearing capacity of the sub-grade. The Road Pavements are playing a crucial role in the development of any construction. There are mainly two types of road pavement used namely flexible and rigid pavements road.
Ideal Road Pavement Requirement
A good pavement should possess the following requirement,
- it should have required thickness to distribute the wheel load stresses to a safe value on the sub-grade soil,
- It should be structurally strong to resist all types of stresses imposed upon it.
- To prevent the skidding of vehicles, it should have a sufficient coefficient of friction.
- It should have a smooth level surface that offers comfort to road users even at high speed.
- Ensure less noise when the vehicle moving on it.
- It should be dustproof so that there is no danger of traffic safety.
- It must provide an impervious surface, so that sub-grade soil is well protected, and
- It should offer low maintenance with long life.
Types of Pavements (Road Pavement)
There are major two types of pavement based on their structure,
1. Flexible pavement.
2. Rigid Pavement.
Flexible pavements, vehicular stress is transferred to subgrade through gain to gain contact of the aggregate through the granular structure. These types of road have less flexural strength, acts like a flexible sheet (e.g. bituminous road).
In the case of rigid pavement, vehicle loads are transferred to sub-grade soil by flexural strength of the pavement and the pavement acts as a rigid plate (e.g. cement concrete roads).
A combined pavement also used which is known as semi-rigid pavement. In this, a rigid pavement is provided with a thin layer of flexible pavement over it and is an ideal pavement with most desirable characteristics. However, these types of combinations of pavements are rarely used in new construction because of the high cost and complex analysis required.
1. Flexible Pavements
In Flexible Pavement, wheel loads are transferred to subgrade by grain-to-grain transfer through the points of contact in the granular structure. The wheel load stresses acting on the pavement are distributed to a larger area and the stress decreases with the depth. Considering this load distribution characteristic of flexible pavements, it has many layers.
Hence, a flexible pavement design system uses the concept of a layered system. By considering this the flexible pavement should have better quality to sustain maximum compressive stress, in addition, to wear and tear. Below layers are accepted to experience the magnitude of stress and low-quality material can be used.
In the construction of flexible roads mainly bituminous materials are used. Defects in the flexible road can be seen on the surface if there is a settlement of the lower layer. The design of flexible pavement is done by considering the overall performance of the road, and the stresses produced should be kept well below the allowable stresses of each road layer.
Types of Flexible Pavements
The following are major types of flexible pavement,
- Conventional layered flexible pavement,
- Full-depth asphalt pavement, and
- Contained rock asphalt mat (CRAM).
1. Conventional Flexible Pavements
Conventional flexible pavement uses the layered system. In which high-quality materials are placed at the top of the pavement layer to resist maximum stress and low-quality cheap materials are placed in lower layers.
2. Full-depth Asphalt Pavements
It is constructed by placing bituminous layers directly on the soil sub-grade. These types of pavement most suitable when there is high traffic and local materials are not available.
3. Contained Rock Asphalt Mats
It is constructed by placing dense/open-graded aggregate layers in between two asphalt layers. Properly designed asphalt concrete is placed above the sub-grade. This asphalt concrete will reduce the vertical compressive strain on soil sub-grade and protect from surface water.
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Road Pavement Layers or Road Construction Layers (What is Pavement Made of)
Following are pavement layers road construction or Road construction layers included,
- Compacted subgrade (150 – 300mm).
- Sub-base Course (100 – 300 mm)
- Base Course (100 – 300 mm)
- Prime Coat
- Binder Coat (50 -100 mm)
- Tack Coat
- Surface Course (25 – 50 mm)
- Seal Coat.
1. Compacted Sub-grade (150 – 300 mm)
The compacted subgrade is a base of all pavement layers. All the above pavement layers transfer the stress to this layer. So, it is essential to ensure that soil sub-grade is not overstressed. Therefore, it should be properly compacted to the desired density, near the optimum moisture content.
2. Sub-base Course (100 – 300 mm)
It is a layer of material below the base course. It is a major role to provide structural support, improve drainage, and reduce the intrusion of fines from the sub-grade in the pavement structure. In the case of the base, the course is open graded then the sub-base course with more fine material can be utilized as filler between sub-grade and the base course.
A sub base is not strictly needed or used. For example, road pavement made on high quality, hard sub-grade may not need the additional features offered by a sub-base course. In such situations, the sub-base course can be avoided.
3. Base Course (100 – 300 mm)
It is a layer of materials just below the surface of the binder course and it provides additional load distribution and contributes to the sub-surface drainage. The different materials are used for base courses such as crushed stone, crushed slag, and other untreated or stabilized materials.
4. Prime Coat
A prime coat is applied by spreading low viscous cutback bitumen to an absorbent surface like granular bases on which the binder layer is placed. It is primly used to provide a bond between two layers. A prime coat is able to penetrate into the below layers, plugs the voids, and forms a watertight surface.
5. Binder Coat (50 -100 mm)
The Binder coat has the bulk of the asphalt concrete structure. Its main function is to distribute the load to the base course. The binder course primly consists of aggregate mixed with low asphalt and doesn’t require quality as high as the surface course. Replacement of some part of the surface course by the binder course results in a more economical design.
6. Tack Coat:
In tack coat, a little amount of asphalt is applied to the surface. It is generally asphalt emulsion diluted with water. Its main function is to provide proper bonding between two layers of binder course and must be thin, uniformly cover the entire surface, and set very fast.
7. Surface Course (25 – 50 mm)
It is the main layer that bears the direct traffic load and generally contains superior quality materials. The surface course is generally constructed with graded asphalt concrete (AC). The functions and requirements of this layer are:
- This course offers major characteristics like friction, smoothness, drainage, etc. Also, it prevents the entry of excess water into the underlying base, sub-base, and sub-grade,
- It should be provided with a hard surface to resist the distortion under traffic and provide a smooth and skid-resistant riding surface,
8. Seal Coat
The seal coat is a thin layer with water-proof the surface and to provide skid resistance.
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2. Rigid Pavements
This type of pavement is cable to transfer wheel load to a wider area as it has good flexural strength. In rigid pavement, there are not many layers of materials as in the case of flexible pavement. In rigid directly placed on a well-compacted subgrade or on a single layer of granular or stabilized material. As there is only a single layer between the concrete and the sub-grade, this layer can be called a base or sub-base course.
In rigid, the vehicular traffic load is transferred through slab action, and the road behaves like an elastic plate resting on a viscous medium. It is constructed by using plain cement concrete. Generally, its design is analyzed by plate theory instead of layer theory, assuming an elastic plate resting on a viscous foundation.
The plate theory assumes that the road pavement slab a medium-thick plate that is plane before loading and to remain plane after loading. Pavement slab experiences the bending due to wheel load and temperature variation and the resulting tensile and flexural stress.
Types of Rigid Pavements
Rigid pavements can be classified into four types:
- Jointed plain concrete pavement (JPCP),
- Jointed reinforced concrete pavement (JRCP),
- Continuous reinforced concrete pavement (CRCP), and
- Pre-stressed concrete pavement (PCP).
1. Jointed Plain Concrete Pavement
This type of rigid pavement is constructed using plain cement concrete with closely spaced contraction joints. In this dowel, steel bars are generally used for load transfer across joints. It has joint spacing around 5 to 10m.
2. Jointed Reinforced Concrete Road
It is clear in the rigid pavement that placing reinforcement does not increase its structural stability, but they can drastically increase the joint spacing to 10 to 30m. The main function of the dowel bar is transfer load only and reinforcement used in the slab to keep the pavement together even after cracks.
3. Continuous Reinforced Concrete Road
In this type, there is no joints are provided between and it is achieved by providing reinforcement.
Q.1 What are the Types of Pavements?
TYPES OF PAVEMENTS (ROAD PAVEMENTS)
Two Major Types of Pavements are:
1. Rigid Pavement
2. Flexible Pavements
Henceforth, which are further classified as,
1. Rigid Pavements:
JPCP, JRCP, CRCP, and PCP.
2. Flexible Pavement:
Conventional layered flexible pavement, Full-depth asphalt pavement, and contained rock asphalt mat (CRAM)
Q.2 What is the function of Road Pavement?
FUNCTION OF ROAD PAVEMENT:
The main function of Pavement is to distribute the applied vehicle loads to the sub-grade through different layers. The road Pavement should provide sufficient skid resistance, proper riding quality, favorable light reflecting characteristics, and low noise pollution.
Q.3 What are the requirements of Ideal Road Pavement?
REQUIREMENTS OF IDEAL ROAD PAVEMENT:
1.It should be structurally strong to resist all types of stresses imposed upon it.
2.To prevent the skidding of vehicles, it should have a sufficient coefficient of friction.
3.Ensure less noise when the vehicle moving on it.
4.It should be dust-proof so that there is no danger of traffic safety.
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