Pavement in Roads

 What is pavement?

Roads and driveways are both examples of pavements, which are built with concrete or asphalt.

• TYPES OF PAVEMENTS :

From the point of view of structural performance, pavements can be classified as:

1. Flexible pavement

2. Rigid pavement

3. Semi-rigid

4. Composite

• RIGID AND FLEXIBLE PAVEMENT:

1. FLEXIBLE PAVEMENT : 

In simple terms, a flexible pavement can be defined as a pavement layer comprising a mixture of aggregate sand bitumen, heated and mixed properly and then laid and compacted on a bed of granular layers. A typical flexible pavement consists of a bituminous surface course over the base course and a sub-base course. The surface course may consist of one or more bituminous or Hot Mix Asphalt (HMA) layers. 

These pavements have eligible flexure strength and hence undergo deformation under the action of loads. 

The structural capacity of flexible pavements is attained by the combined action of the different layers of the pavement. The load from trucks is directly applied on the wearing course, and it gets dispersed (in the form of a truncated cone)with depth in the base, sub-base, and subgrade courses, and then ultimately to the ground.

Types of Flexible Pavement

Flexible pavement can be classified as one of the following types:

1. Conventional layered flexible pavement,
2. Full-depth asphalt pavement, and
3. Contained rock asphalt mat (CRAM).

1. Conventional Flexible Pavements

The layered system is used in conventional flexible pavements. The top layer of asphalt is constructed with high-quality materials to withstand maximum stress while the lower layers are constructed with cheap, low-quality materials.

2. Full-depth Asphalt Pavements

In this method, bituminous layers are placed directly on top of the soil subgrade. High traffic and the absence of local materials make these types of pavements the best choice.

3. Contained Rock Asphalt Mats

An aggregate layer is layered between two asphalt layers and is dense and open-graded. It is necessary to place properly designed asphalt concrete above the subgrade. Surface water will be protected from surface runoff by this asphalt concrete by reducing vertical compressive strain.

2. RIGID PAVEMENT : 

Rigid pavements have sufficient flexural strength to transmit the wheel load stresses to a wider area below. A typical cross-section of the rigid pavement is shown in Figure. Compared to the flexible pavement, rigid pavements are placed either directly on the prepared subgrade or on a single layer of granular or stabilized material. 

Since there is only one layer of material between the concrete and the subgrade, this layer can be called a base or sub-base course. In rigid pavement, the load is distributed by the slab action, and the pavement behaves like an elastic plate resting on a viscous medium. Rigid pavements are constructed by Portland cement concrete (PCC) and should be analyzed by plate theory instead of layer theory, assuming an elastic plate resting on a viscous foundation.

Types of Rigid Pavements

Rigid pavements can be classified into four types,

1. Jointed plain concrete pavement (JPCP),
2. Jointed reinforced concrete pavement (JRCP),
3. Continuous reinforced concrete pavement (CRCP), and
4. Pre-stressed concrete pavement (PCP).

1. Jointed Plain Concrete Pavement

Concrete contraction joints are closely spaced in rigid pavements constructed with plain cement concrete. As part of this dowel, steel bars are generally used to transfer load across joints. Approximately five to ten meters are between each joint.

2. Jointed Reinforced Concrete Road

Adding reinforcement to rigid pavement does not improve its structural stability, but it can drastically increase the joints' spacing by 10 to 30m. In the slab, reinforcement is used to keep the pavement together even after cracks have occurred. The main purpose of the dowel bar is to transfer loads.

3. Continuous Reinforced Concrete Road

By providing reinforcement, this type of structure does not have joints.

 3. SEMI-RIGID PAVEMENT  : 

Pavements that are semi-inflexible enjoy a middle ground between flexible pavements and inflexible pavements. There is less flexural electricity in the pavement than in a concrete slab. In flexible pavements, lateral loads are distributed through the pavement intensity, but with some assistance. Semi-rigid pavements consist of the intermediate class of semi-rigid materials like soil cement and lean cement concrete, which are used at the sub-base or base of layers of pavements. A composite pavement consists of a flexible pavement layer and one or more semi-rigid pavement layers. Interlocking concrete block pavement (ICBP) is the last member.

4. COMPOSITE PAVEMENT :

Pavements made from asphalt and concrete are known as composite pavements. Asphalt surface layers serve as a wearing surface course and provide structural capacity. A roller-compacted concrete (RCC) pavement can also be used with this asphalt pavement type to provide the structural capacity that would be provided by a conventional concrete pavement base.