Category: PAVEMENT DESIGN

Types of Road Pavement – Flexible and Rigid Pavement

Types of Road Pavements

Types of road pavement: The road pavements are mainly classified into two types:

Flexible Pavement
Rigid Pavement

Another two types of road pavement are becoming popular at present times, they are:

3. Semi-rigid Pavement
4. Interlocking Cement Concrete Block Pavement

1. Flexible pavements

Flexible pavement, as the name suggests they are flexible in nature under the action of loads. It has a low or negligible flexural strength.

The layer of flexible pavement may reflect both the non-recoverable and recoverable deformations of the lower layers including the subgrade onto the upper layers and also to the pavement surface.

When the lower layer of the pavement or soil subgrade is deformed or undulated, due to permanent deformation, the flexible pavement layers and pavement surface may get undulated to somewhat similar pattern.

In the case of flexible pavement, the vertical compressive stress is maximum on the pavement surface directly under the traffic load. The vertical compressive load of traffic is transmitted to a large area into the lower layers by grain-to-grain transfer.

Cross Section of Flexible Pavement

A typical flexible pavement consists of four components:

Sub-grade
Sub-base Course
Base Course
Surface Course

A typical Cross Section of flexible pavement is shown in the figure below:

Types of Road Pavement - Cross Section of flexible pavement

Read in Details Here: Component Parts Of Flexible and Rigid Road Pavements Structure and Their Function

2. Rigid Pavements

Rigid pavements, as the name suggests, they are rigid in nature under bending action. It has very high flexural strength or flexural rigidity.

In the case of rigid pavement, the concrete slab is constructed over the subgrade or a base course which is made up of some stabilizing materials. The rigid pavements or say cement concrete pavement is generally made of Portland cement concrete.

In rigid pavements, the stress is not transferred to the lower layers by grain-to-grain transfer as in the case of flexible pavement layers. It has the capability to transmit the traffic load stresses through a much wider area below the pavement.

Rigid pavement is usually built as plain concrete with dowel bars. Sometimes wire-mesh reinforcements are used to hold the cracked portion together.

Cross Section of Rigid Pavement

A typical Rigid pavement consists of three components:

Sub Grade
Base Course
Cement Concrete Slab

A typical cross Section of a rigid pavement is shown in the figure below:

Types of Road Pavement - cross Section of a rigid pavement

4. Interlocking Cement Concrete Block Pavement

Interlocking cement concrete block pavement is another type of road pavement that consists of a layer of cement concrete paver blocks. The shape, size, and strength of this block layer are specified.

Generally, these blocks are laid over the soil subgrade which is well-compacted. These blocks may be laid over the sub-base or base course or layer of sand bed.

The gap between two successive paver blocks is filled with joint filling sands and the vibration is implemented to provide a proper interlocking between the blocks. Adequate lateral confinement or support has to be assured by providing a suitable edge strip or beam or kerb at the end of the paved area.

Failure of Flexible Pavement

Failure of Rigid Pavement

How To Calculate Equivalent Single Wheel Load(ESWL)

Mathematical Problem: Example

The loaded weight on the rear dual wheels of a track is 5500 Kg. The centre-to-centre spacing and clear space in dual wheels are 30 cm and 10 cm respectively. Calculate the equivalent single wheel load or ESWL for pavement thickness 20 cm, 40 cm, and 70 cm.

How To Calculate Equivalent Single Wheel Load(ESWL)

Solution:

Formula for ESWL calculation is

[latex] \log_{10}ESWL = \log_{10}P + \frac{0.301\log_{10}(\frac{Z}{d/2})}{\log_{10}(\frac{2S}{d/2})} [/latex]

Where,

P is the wheel load (single wheel load) = 5500/2 = 2750 Kg.
S is the centre to centre distance between the two wheels = 30 cm.
d is the clear distance between two wheels = 10 cm
Z is the thickness of the pavement.

1. For Z = 20 cm

[latex] \log_{10}ESWL = \log_{10}2750 + \frac{0.301\log_{10}(\frac{20}{10/2})}{\log_{10}(\frac{2 \times 30}{10/2})} [/latex]

[latex] \log_{10}ESWL = \log_{10}2750 + \frac{0.301\log_{10}(\frac{20}{5})}{\log_{10}(\frac{60}{5})} [/latex]

[latex] \log_{10}ESWL = \log_{10}2750 + \frac{0.301\log_{10}4}{\log_{10}12}[/latex]

[latex] \log_{10}ESWL = 3.43933 + 0.16792 [/latex]

[latex] \log_{10}ESWL = 3.60725 [/latex]

[latex] ESWL = 10^{3.60725} [/latex]

ESWL = 4048 Kg

2. For Z = 40 cm

[latex] \log_{10}ESWL = \log_{10}2750 + \frac{0.301\log_{10}(\frac{40}{5})}{\log_{10}(\frac{60}{5})} [/latex]

[latex] ESWL = 10^{3.69123} [/latex]

ESWL = 4912 Kg

3. For Z = 70 cm

[latex] \log_{10}ESWL = \log_{10}2750 + \frac{0.301\log_{10}(\frac{70}{5})}{\log_{10}(\frac{60}{5})} [/latex]

[latex] ESWL = 10^{3.7590} [/latex]

ESWL = 5741 Kg

4 Component Parts Of Flexible and Rigid Road Pavements Structure and Their Function

Component Parts Of Flexible & Rigid Road Pavements Structure

The following are the 4 component parts of road pavement:

Subgrade or formation.
Subbase course.
Base course.
Surface course or wearing course.

4 Component Parts Of Flexible and Rigid Road Pavements Structure and Their Function

1) Subgrade or Formation

The finished and compacted surface of earthwork on which a road pavement rests is called subgrade or formation.

Functions of Subgrade

The Functions of subgrade are as follows:

To provide adequate and uniform support to the road pavements.
To bear ultimately the entire load of pavement including the traffic load transmitted through the pavement.

2) Sub-base course

The layer of granular material such as burnt clinker, gravel, or slag provided in between the subgrade and base course in a road pavement is called a sub-base course. In some places, boulder stones or bricks are also used as a sub-base course.

Function of Sub-base Course

The functions of sub-base course are:

To improve the bearing capacity of the subgrade.
To provide additional help to the base and surface course in distributing the load.
To prevent the undesirable entry of fine-grained soils from subgrade to base course.
To minimize the damaging effect of frost action.
To improve the drainage.

3) Base Course

The layer of broken stones or brick provided over the subbase course or immediately over the subgrade in the absence of subbase, in a road pavement is called base course.

Function of Base Course

The Functions of the base course are as follows:

To act as the foundation of the road pavement and to transfer the traffic load safely to the subbase and subgrade.
To withstand high shearing stresses due to the impact of traffic.
To prevent the undesirable entry of subgrade soil in the pavement when the base course is constructed directly over the subgrade.

4) Surface Course or Wearing Course

The topmost layer of the road pavement directly exposed to the traffic is called the surface course or wearing course. In flexible pavement, normally a bituminous surface is used as a wearing course. In Rigid Pavement, the cement concrete layer acts as a base course as well as a wearing course.

Functions of Surface or Wearing Course

The Functions of the surface or wearing course are as follows:

To provide a smooth and uniform rigid surface.
To resist the abrasive forces of traffic.
To prevent dust nuisance.
To act as a structural part of the pavement.

10 Difference Between Flexible & Rigid Pavements

6 Causes of Rigid Pavement Failures

Necessity of Providing Joints in Cement Concrete Road

Joints are provided in cement concrete road (pavement) to achieve the following objectives (Read more- what is joint in cement concrete road)

1. To allow for expansion of the slab due to the rise in slab temperature.

2. To permit the contraction of the slab due to the fall in slab temperature.

3. To relieve stresses included due to warping.

4. To prevent longitudinal cracking in the pavement as a result of differential shrinkage and swelling due to rapid change in subgrade moisture under the edges than the center of the road.

5. Construction joints are provided to close the day’s job and for the commencement of the same in the next day.

Read more:

Types Of Joints In Cement Concrete Road

The joints provided in cement concrete road are classified into the following two categories:

1. Longitudinal Joints.
2. Transverse Joints.

1. Longitudinal Joints

These joints are provided longitudinally in cement concrete roads which have a width more than 4.5 m. Such joints are provided to prevent longitudinal cracking in the pavement.

The longitudinal cracking in the pavement is formed as a result of differential shrinkage and swelling due to rapid changes in subgrade moisture under the edge than the center of the road. In longitudinal joints tie bars are provided to hold the adjacent slabs.

2. Transverse Joints

Transverse joints in cement concrete roads are further classified into the following categories:

i) Expansion Joints
ii) Contraction Joints
iii) Warping Joints
iv) Construction Joints

i) Expansion Joints

Expansion joints are provided in cement concrete roads to allow for expansion of the slab due to rising in the slab temperature.

These joints are provided at an interval of 50 m to 60 m if the slab is laid in winter and 90 m to 120 m if the slab is laid in summer.

The approximate gap width for this type of joint is 20 mm to 25 mm. These joints also permit the contraction of the slab.

ii) Contraction Joints

Contraction joints are provided in cement concrete roads to allow for contraction of the slab due to falling in the slab temperature.

These joints are spaced closer than expansion joints. As per I.R.C, the maximum spacing of these joints is 4.5m in plain cement concrete slabs and 14 in reinforced cement concrete slab of thickness 20cm.

iii) Warping Joints

Warping joints in cement concrete roads are provided to relieve the stresses included due to warping.

During the mid-day, the top of the pavement slab has a higher temperature than the bottom. This causes the top fibers of the slab to expand more than the bottom fibers and the slab curls at the edge. This phenomenon is known as the warping down of the slab.

Similarly, the slab warps up during midnight due to the higher temperature of the bottom slab as compared to the top. Warping joints are provided to minimize the stresses induced due to warping. These joints are also known as hinged joints. Longitudinal joints with tie bars fall in this class of joints.

iv) Construction Joints

Construction joints are provided in cement concrete road to close the day’s job and for the commencement of the same in the next day.

How to Prevent Concrete Deterioration

Causes of Deterioration of Concrete

Joints in Cement Concrete Roads

Joints are provided in cement concrete roads to allow expansion, contraction and warping of the slabs due to the variation in the temperature of the slabs.

An increase in temperature causes the expansion of the slab horizontally. Similarly, a decrease in temperature causes contraction of the slab horizontally.

The slab movements also take place, in the vertical direction due to the difference in temperature between the top and bottom of the pavement slab.

During the mid-day, the top of the pavement slab has a higher temperature than the bottom. This causes the top fibers of the slab to expand more than the bottom fibers and the slab curls at the edge. This phenomenon is known as the warping down of the slab.

Similarly, the slab warps up at midnight due to the higher temperature of the bottom slab as compared to the top. To minimize the temperature stresses in the pavement slab, expansion, contraction and warping joints are provided transversely across the full width of the pavement.

Longitudinal joints are provided to allow differential shrinkage and swelling due to the rapid change in subgrade moisture at the edge and centre

Read more

Causes of Rigid Pavement Failures

Types Of Joints In Cement Concrete Road

Failure of Flexible Pavement

Flexible pavement failure is defined by the formation of potholes, ruts, cracks, localized depressions and settlement. The failure of any one or more components of the pavement structure such as subgrade, base course, wearing course is liable for pavement failure.

Following are some of the typical flexible pavement failures:

1. Alligator (map) cracking.
2. Consolidation of pavement layers.
3. Shear failure.
4. Longitudinal cracking.
5. Frost heaving.
6. Lack of binding to the lower course.
7. Reflection cracking.
8. Formation of waves and corrugations.

Read more:

Causes of Rigid Pavement Failures

Types of Road

6 Causes of Rigid Pavement Failures

Rigid pavement failure is observed by the development of structural crack resulting in progressive subsidence of some portions of pavement. Following 6 general causes of pavement failures are described below:

1. Defects in the quality of material used.

2. Defects in the construction method and quality control during construction.

3. Inadequate surface drainage or subsurface drainage in the locality.

4. Increase in the magnitude of wheel loads and the number of load repetitions due to the increase in traffic volume.

5. Settlement of foundation of the embankment.

6. Environment factors including heavy rainfall, soil erosion, high water table, snowfall, frost action etc.

Read more:

Failure of Flexible Pavement

Types of Road in India