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Bitumen ROAD Construction process || in INDIA

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Bitumen ROAD Construction process  in INDIA.mp4

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LANDLOCK - Asphalt Reclamation & Sub-base Stabilization Process

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Depth layers of flexible pavement construction

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Depth layers of flexible pavement construction

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Description

The Flexible Pavements Program focuses on issues related to the design, construction, and maintenance of asphalt pavements.

Currently studies are underway that include design of long-life full-depth pavements, design of overlays that 🤬 reflection cracking, rubblization of existing concrete structures, full-depth reclamation, and use of new technologies to measure the quality of flexible pavements. The program conducts research into the optimal properties of each layer within flexible pavements. Soil stabilization and methods of mitigating sulfate heave problems continue to be a major focus area, together with quantifying the benefits of heavy-duty flexible-base materials. In the Flexible Pavements Program researchers make use of innovate nondestructive testing equipment and advanced laboratory testing equipment in order to understand and document pavement performance.

Researchers work closely with sponsoring agencies to ensure that the products of the research program are implemented. Developing and teaching training schools are ongoing activities.

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- FUNTION

Surface Course. Surface course or wearing course is the top most layer of flexible pavement which has direct contact with the vehicular loads. ... The main function of surface course is to provide skid-resistance surface, friction and drainage for the pavement. It should be water tight against surface water infiltration. The thickness of surface course generally provided is 25 to 50 mm.

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-DEPTH

MODULUS VARIATION WITH DEPTH Material  inhomogeneity  within  the  pavement  layer/sublayer  can  be  caused  by  the dependency  of  the  modulus  of  elasticity  on  the  temperature,  moisture,  and/or  other environmental  factors.  This  fact  imposes  limitations  on  the  current  analytical  elastic  solution which  does  not  take  into  consideration  the  variation  of  the  modulus  of  elasticity  with  depth within the same layer. However, our newly developed multilayered program MultiSmart3D can be  applied  to  any  variation  of  modulus  of  elasticity  in  the  pavement.  The  modulus  variation within the same layer can be modeled using several sublayers where the sublayer thickness and modulus are different for different sublayers.

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Functions of each layer are described as below:

·         Sub-Grade :

·         Functions: The load is transferred by the sub-grade effectively to the earth mass. However the locally available earth is used to construct the sub-grade but it becomes necessary that the sub-grade should be of required strength.

·         Testing: This makes it necessary to check the strength characteristics of the sub-grade by using the various methods. Here is the list of the tests that are employed to check the strength of the sub-grade:

a.  California bearing ratio test.

b.  California resistance value test.

c.  Tri-axial shear test.

d.  Plate load test.

California bearing ratio test is a kind of penetration test, in which we get the value of the California bearing ratio of the given soil sample. The test can also be performed in the field to take the in-situ measurements.

The value is used to design the thickness of the flexible pavements by using some empirical charts.This test is also used to calculate CBR value for the other layers too.

California resistance value is got by using the Hveem stabilometer. This test is used in empirical methods of the flexible design methods, based on the soil strength.

Tri-axial shear test: This test gives the value of the shear strength of the soil, but it is not done, because the values obtained from this test are used only in a very few theoritical methods of flexible pavement design.

Plate Load Test:    In this test we make use of the plates of some larger diameter. In this test we get the values of the elastic modulus of sub-grade. These values are used in the methods of flexible pavement designs like that in Mcleaod method and in method of layer system approach for analysis by Burmister.

The modulus of sub-grade reaction is also calculated for the rigid pavement analysis by the Westergaard's approach.

·         Sub-base and base course:

Base course and sub-base course is used in the flexible pavement to disperse the upcoming loads to large area through a finite thickness, so as to increase the load bearing capacity of the pavement. The material used is the broken stones, or gravels, or bound or unbound aggregates.

Sometimes the bricks can also be used as the sub-base and base materials. Generally the sub-base layers have the inferior quality of aggregates, than that used in the base course.

Generally smaller aggregates are used because the larger gravels or aggregates have the tendency to sink to the lose sub-grade soil under the heavy loading.

The function of the sub-base or the base layer in case of the rigid pavement is to -

1.  Check the pumping action.

2.   Protecting the sub-surface against the frost action.

The basic purpose of the sub-base and base layer is to transfer the load through a dispersed/larger area to the sub-grade. So it must of sufficient strength to do its job. These layers are evaluated using a suitable strength or stability tests like the plate load test, California bearing ratio test, and the Hveem stabilometer test, where each test has its own significance and importance.

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· The load is transferred by the sub-grade effectively to the earth mass. However the locally available earth is used to construct the sub-grade but it becomes necessary that the sub-grade should be of required strength.

· This makes it necessary to check the strength characteristics of the sub-grade by using the various methods. Here is the list of the tests that are employed to check the strength of the sub-grade:

California bearing ratio test is a kind of penetration test, in which we get the value of the California bearing ratio of the given soil sample. The test can also be performed in the field to take the in-situ measurements.

is got by using the California resistance value Hveem stabilometer. This test is used in empirical methods of the flexible design methods, based on the soil strength.

Tri-axial shear test: This test gives the value of the shear strength of the soil, but it is not done, because the values obtained from this test are used only in a very few theoritical methods of flexible pavement design.

Plate Load Test: In this test we make use of the plates of some larger diameter. In this test we get the values of the elastic modulus of sub-grade. These values are used in the methods of flexible pavement designs like that in Mcleaod method and in method of layer system approach for analysis by Burmister.

The function of the sub-base or the base layer in case of therigid pavement is to -

Wearing course: Top most layer serves as the smooth riding surface for the traffic, and it wears all the abrading forces. The top most layer is constructed with the superior quality of aggregates because it has to wear the maximum intensity of loads.

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Functions and Testing of Various pavement components/layers(Overview)

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· The load is transferred by the sub-grade effectively to the earth mass. However the locally available earth is used to construct the sub-grade but it becomes necessary that the sub-grade should be of required strength. · This makes it necessary to check the strength characteristics of the sub-grade by using the various methods.

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Function layer of flexible pavement (TRESAGUET)

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Function layer of flexible pavement (TRESAGUET)

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Pavement Functions

The primary functions of a pavement are to:

PROVIDE A REASONABLY SMOOTH RIDING SURFACE: A smooth riding surface (Low Roughness) is essential for riding comfort, and over the years it has become the measure of how road users perceive a road. Roughness can arise from a number of causes, most often however it is from pavement distress due to structural deformation. Roughness is the distress parameter used by the vehicle operating cost sub-models of a pavement management system, to estimate the timing, type and cost of maintenance needs.

PROVIDE ADEQUATE SURFACE FRICTION (SKID RESISTANCE): In addition to a riding comfort, the other road user requirement is that of safety. Safety, especially during wet conditions can be linked to a loss of surface friction between the tyre and the pavement surface. A pavement must therefore provide sufficient surface friction and texture to ensure road user safety under all conditions.

PROTECT THE SUBGRADE: The supporting soil beneath the pavement is commonly referred to as the subgrade, should it be over-stressed by the applied axle loads it will deform and lose its ability to properly support these axle loads. Therefore, the pavement must have sufficient structural capacity (strength and thickness) to adequately reduce the actual stresses so that they do not exceed the strength of the subgrade. The strength and thickness requirements of a pavement can vary greatly depending on the combination of subgrade type and loading condition (magnitude and number of axle loads).

PROVIDE WATERPROOFING: The pavement surfacing acts as a waterproofing surface that prevent the underlaying support layers including the subgrade from becoming saturated through moisture ingress. When saturated, soil loses its ability to adequately support the applied axle loads, which will lead to premature failure of the pavement.

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1095_Pavement Layers and Their Functions1

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- MATERIAL

1 .Surface Course

Surface course or wearing course is the top most layer of flexible pavement which has direct contact with the vehicular loads. Since it is directly in contact with traffic, good quality aggregates and high dense bitumen or asphalt is recommended for the construction of surface course.

The main function of surface course is to provide skid-resistance surface, friction and drainage for the pavement. It should be water tight against surface water infiltration. The thickness of surface course generally provided is 25 to 50 mm.

2.Binder Course

Binder course is also constructed using aggregates and bitumen but with less quality than materials used for surface course. In general, its thickness is about 50 to 100 mm.

If economy is not a problem, binder course and surface course can be constructed monotonically using good quality materials with 100 to 150 mm thickness. The function of binder course is to transfer the loads coming from surface course to the base course.

3, Base Course

The base course is important layer of pavement structure and it distributes the loads from top layers to the underneath Subbase and sub-grade layers. It provides structural support for the pavement surface. It is constructed with hard and durable aggregates which may either stabilized or granular or both.

The thickness of base course must be great enough to reduce the load capacity on sub-grade and Subbase courses. The minimum base course thickness recommended is 100 mm. sub surface drainage system can be provided with in the base course.

4.Subbase Course

The Sub-base course is provided beneath the base course and it also functions as same as base course. If the sub-grade soil is strong and stiff, then there is no need to sub-base course.

Granular aggregates are used to construct sub-base course. If sub-grade is weak minimum 100 mm thick sub-base course should be provided.

5. Subgrade

Subgrade is the bottom most layer which is nothing but natural soil layer compacted up to required depth generally about 150 to 300 mm to receive the loads coming from top layers. This layer is termed as foundation for the pavement system.

The sub-grade should be strong enough to take the stresses and also it is important to keep the stresses coming from top layers should be within the limit of sub-grade capacity. To reduce the amount of stress on soil sub-grade, provide thick layers of base course, Sub-base course and surface course.

Sub-grade
Fig 6: Compacting Sub-grade
Apart from the above layers, three types of coats or finishes are provided in flexible pavement system which are as follows

Seal Coat
Tack Coat
Prime Coat
a. Seal Coat

Seal coat is provided directly on the top of surface course to make it watertight and to provide skid resistance to the surface. Mixture of Emulsified asphalt, mineral fillers and water is used as seal coat material.

Seal Coat
Fig 7: Seal Coat
b. Tack Coat

Tack coat is provided on the top of binder course to develop strong bond between the binder course and surface course. Asphalt emulsion diluted with water is used as tack coat material.

c. Prime Coat

Prime coat is provided between base course and binder course to develop strong and water tight bong between them. Low viscous cutback bitumen is sprayed on the top of base course as prime coat material.

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FUNCTION THE LAYER OF FLEXIBLE PAVEMENT (McAdam

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FUNCTION THE LAYER OF FLEXIBLE PAVEMENT (McAdam

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INTRODUCTIO N OF FLEXIBLE PAVEMENT  ( METCALF )

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INTRODUCTIO N OF FLEXIBLE PAVEMENT  ( METCALF )

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Flexible pavement is composed of a bituminous material surface course and underlying base and subbase courses. The bituminous material is more often asphalt whose viscous nature allows significant plastic deformation. Most asphalt surfaces are built on a gravel base, although some 'full depth' asphalt surfaces are built directly on the subgrade. Depending on the temperature at which it is applied, asphalt is categorized as hot mix asphalt (HMA), warm mix asphalt, or cold mix asphalt. Flexible Pavement is so named as the pavement surface reflects the total deflection of all subsequent layers due to the traffic load acting upon it. The flexible pavement design is based on the load distributing characteristics of a layered system.

It transmits load to the subgrade through a combination of layers. Flexible pavement distributes load over a relatively smaller area of the subgrade beneath. The initial installation cost of a flexible pavement is quite low which is why this type of pavement is more commonly seen universally. However, the flexible pavement requires maintenance and routine repairs every few years. In addition flexible pavement deteriorates rapidly; cracks and potholes are likely to appear due to poor drainage and heavy vehicular traffic.

A valuable advantage of flexible pavement is that it can be opened for traffic within 24 hrs after completion. Also the repair and maintenance of flexible pavement is easy and cost effective.

Today 96% of all paved roads and streets in Pakistan are surfaced with asphalt. Almost all paving asphalt used today is obtained by processing crude oils. Man-made asphalt consists of compounds of hydrogen and carbon with minor proportions of nitrogen, sulfur and oxygen.

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Material layer of flexible pavement (tresaguet)

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Material layer of flexible pavement (tresaguet)

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1. Surface Course

Surface course or wearing course is the top most layer of flexible pavement which has direct contact with the vehicular loads. Since it is directly in contact with traffic, good quality aggregates and high dense bitumen or asphalt is recommended for the construction of surface course.

The main function of surface course is to provide skid-resistance surface, friction and drainage for the pavement. It should be water tight against surface water infiltration. The thickness of surface course generally provided is 25 to 50 mm.

2. Binder Course

Binder course is also constructed using aggregates and bitumen but with less quality than materials used for surface course. In general, its thickness is about 50 to 100 mm.

If economy is not a problem, binder course and surface course can be constructed monotonically using good quality materials with 100 to 150 mm thickness. The function of binder course is to transfer the loads coming from surface course to the base course.

3. Base Course

The base course is important layer of pavement structure and it distributes the loads from top layers to the underneath Subbase and sub-grade layers. It provides structural support for the pavement surface. It is constructed with hard and durable aggregates which may either stabilized or granular or both.

The thickness of base course must be great enough to reduce the load capacity on sub-grade and Subbase courses. The minimum base course thickness recommended is 100 mm. sub surface drainage system can be provided with in the base course.

4. Subbase Course

The Sub-base course is provided beneath the base course and it also functions as same as base course. If the sub-grade soil is strong and stiff, then there is no need to sub-base course.

Granular aggregates are used to construct sub-base course. If sub-grade is weak minimum 100 mm thick sub-base course should be provided.

5. Frost Protection Layer

Frost protection layer is provided for the pavements in colder regions where temperatures are very low.  It is generally provided between Subbase and sub-grade soil.

The function of frost protection layer is to prevent damage of pavement from frost heaves, which are formed by freezing of groundwater. A good quality base course and Sub-base courses provided can also serves frost protection layer.

6. Subgrade

Subgrade is the bottom most layer which is nothing but natural soil layer compacted up to required depth generally about 150 to 300 mm to receive the loads coming from top layers. This layer is termed as foundation for the pavement system.

The sub-grade should be strong enough to take the stresses and also it is important to keep the stresses coming from top layers should be within the limit of sub-grade capacity. To reduce the amount of stress on soil sub-grade, provide thick layers of base course, Sub-base course and surface course.

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The composition and structure of flexible pavement consists of surface course, binder course, base course, subbase course, frost protection course, subgrade. Flexible pavements contain bitumen or asphalt layer as wearing course and supports loads through bearing. They have low flexural strength.

Composition and Structure of Flexible Pavement

1. Surface Course

Surface course or wearing course is the top most layer of flexible pavement which has direct contact with the vehicular loads. Since it is directly in contact with traffic, good quality aggregates and high dense bitumen or asphalt is recommended for the construction of surface course.

The main function of surface course is to provide skid-resistance surface, friction and drainage for the pavement. It should be water tight against surface water infiltration. The thickness of surface course generally provided is 25 to 50 mm.

2. Binder Course

Binder course is also constructed using aggregates and bitumen but with less quality than materials used for surface course. In general, its thickness is about 50 to 100 mm.

If economy is not a problem, binder course and surface course can be constructed monotonically using good quality materials with 100 to 150 mm thickness. The function of binder course is to transfer the loads coming from surface course to the base course.

3. Base Course

The base course is important layer of pavement structure and it distributes the loads from top layers to the underneath Subbase and sub-grade layers. It provides structural support for the pavement surface. It is constructed with hard and durable aggregates which may either stabilized or granular or both.

The thickness of base course must be great enough to reduce the load capacity on sub-grade and Subbase courses. The minimum base course thickness recommended is 100 mm. sub surface drainage system can be provided with in the base course.

4. Subbase Course

The Sub-base course is provided beneath the base course and it also functions as same as base course. If the sub-grade soil is strong and stiff, then there is no need to sub-base course.

Granular aggregates are used to construct sub-base course. If sub-grade is weak minimum 100 mm thick sub-base course should be provided.

5. Frost Protection Layer

Frost protection layer is provided for the pavements in colder regions where temperatures are very low. It is generally provided between Subbase and sub-grade soil.

The function of frost protection layer is to prevent damage of pavement from frost heaves, which are formed by freezing of groundwater. A good quality base course and Sub-base courses provided can also serves frost protection layer.

6. Subgrade

Subgrade is the bottom most layer which is nothing but natural soil layer compacted up to required depth generally about 150 to 300 mm to receive the loads coming from top layers. This layer is termed as foundation for the pavement system.

The sub-grade should be strong enough to take the stresses and also it is important to keep the stresses coming from top layers should be within the limit of sub-grade capacity. To reduce the amount of stress on soil sub-grade, provide thick layers of base course, Sub-base course and surface course.

Apart from the above layers, three types of coats or finishes are provided in flexible pavement system which are as follows

a. Seal Coat

Seal coat is provided directly on the top of surface course to make it watertight and to provide skid resistance to the surface. Mixture of Emulsified asphalt, mineral fillers and water is used as seal coat material.

b. Tack Coat

Tack coat is provided on the top of binder course to develop strong bond between the binder course and surface course. Asphalt emulsion diluted with water is used as tack coat material.

c. Prime Coat

Prime coat is provided between base course and binder course to develop strong and water tight bong between them. Low viscous cutback bitumen is sprayed on the top of base course as prime coat material.
Read More: Flexible Pavement Design by CBR Method Flexible Pavement Design by Semi Empirical Method Flexible Pavement Design by Group Index Method Types of Pavement - Flexible and Rigid Pavement

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Flexible Pavement Composition and Structure

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The composition and structure of flexible pavement consists of surface course, binder course, base course, subbase course, frost protection course, subgrade. Flexible pavements contain bitumen or asphalt layer as wearing course and supports loads through bearing. They have low flexural strength.

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Surface course

Surface course is the layer directly in contact with traffic loads and generally contains superior quality materials. They are usually constructed with dense graded asphalt concrete(AC). The functions and requirements of this layer are:

It provides characteristics such as friction, smoothness, drainage, etc. Also it will prevent the entrance of excessive quantities of surface water into the underlying base, sub-base and sub-grade,

It must be tough to resist the distortion under traffic and provide a smooth and skid- resistant riding surface,

It must be water proof to protect the entire base and sub-grade from the weakening effect of water.

Binder course

This layer provides the bulk of the asphalt concrete structure. It's chief purpose is to distribute load to the base course The binder course generally consists of aggregates having less asphalt and doesn't require quality as high as the surface course, so replacing a part of the surface course by the binder course results in more economical design.

Base course

The base course is the layer of material immediately beneath the surface of binder course and it provides additional load distribution and contributes to the sub-surface drainage It may be composed of crushed stone, crushed slag, and other untreated or stabilized materials.

Sub-Base course

The sub-base course is the layer of material beneath the base course and the primary functions are to provide structural support, improve drainage, and reduce the intrusion of fines from the sub-grade in the pavement structure If the base course is open graded, then the sub-base course with more fines can serve as a filler between sub-grade and the base course A sub-base course is not always needed or used. For example, a pavement constructed over a high quality, stiff sub-grade may not need the additional features offered by a sub-base course. In such situations, sub-base course may not be provided.

Sub-grade

The top soil or sub-grade is a layer of natural soil prepared to receive the stresses from the layers above. It is essential that at no time soil sub-grade is overstressed. It should be compacted to the desirable density, near the optimum moisture content.

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DEPTH OF LAYERS FLEXIBLE PAVEMENT (TRESAGUET)

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DEPTH OF LAYERS FLEXIBLE PAVEMENT (TRESAGUET)

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The sub-base has already been designed on the foundation page, a link to which is at the bottom of this page.

The total thickness of the combined bituminous layer is then determined from
Figure 2.1 - Design Thickness for Flexible Pavements.

This is on a separate page so as to reduce the page download time. It may take a few seconds for the page to download but please be patient. It is essential that you look at the chart before progressing any further.

The final design of the pavement is then dependent on the material chosen for the wearing course. It is standard to use a wearing course consisting of either

45mm or 50mm of Hot Rolled Asphalt (HRA)

50mm of Porous Asphalt (PA).

If PA is used then it's contribution to the bituminous design thickness is 20mm. A 60mm base course of either HRA , Dense Bitumen Macadam (DBM), or High Density Macadam (HDM) is required below a PA wearing course.

If HRA is used then a base course is optional. If used it may be of any permitted material and should be at least 50mm thick.

Base courses over HDM should also be HDM

Example

Design traffic | 75 msa
Roadbase | HDM
Design Thickness | 320mm

Design Options given that HDM is the chosen material and thus from the design chart the total thickness is 320mm

1. 45mm HRA wearing course
55mm HDM base course
220mm HDM roadbaseChoosing a HRA wearing course with a standard thickness of 45mm. Assuming the use of a HDM roadbase and an optional base course, the base course should be at least 50mm thick and must be of the same material as the roadbase. The remainder is made up of the HDM roadbase.

2. 45mm HRA w/c
275mm HDM r/b

3. Choosing a HRA wearing course with a standard thickness of 45mm. Assuming the use of a HDM roadbase and no optional base course, the remainder is made up of the HDM roadbase.

1. 50mm Porous asphalt w/c
60mm HDM b/c
240mm HDM roadbase

2. Choosing a PA wearing course with a standard thickness of 50mm. Assuming the use of a HDM roadbase then a 60mm base course is required. The contribution of the PA wearing course is 20mm and the remainder is made up of the HDM roadbase.

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DEPTH LAYER OF FLEXIBLE PAVEMENT

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The top layers of pavement which is in direct contact with the wheel of the vehicle. Usually constructed of material in which bitumen is used as binder materials.

a. Bituminous Pavement: (Flexible Pavement)

Consists of combination of mineral aggregate with bituminous binder ranging from inexpensive surface treatment ¼ in or less thick to asphaltic concrete. For good service throughout the full life, bituminous pavement must retain the following qualities:

Freedom from cracking or raveling.

Resistance to weather including the effect of surface water heat and cold.

Resistance to internal moisture, particularly to water vapors.

Tight impermeable surface or porous surface (if either is needed for contained stability of underlying base or subgrade).

Smooth riding and non skidding surface.

b. Concrete Pavement (Rigid pavement):

Rigid pavement is the technical term for any road surface made of concrete. Concrete roads are called rigid while asphalt-covered roads are flexible. These terms refer to the amount of deformation created in the road surface itself when in use and over time.)

There are four types of concrete pavement:

Plain pavements with dowels that use dowels to provide load transfer and prevent faulting,

Plain pavements without dowels, in which aggregate interlock transfers loads across joints and prevents faulting,

Conventionally reinforced pavements that contain steel reinforcement and use dowels in contraction joints, and

Continuously reinforced pavements that have no contraction joints and are reinforced with continuous longitudinal steel.

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CONSTRUCTION OF FLEXIBLE PAVEMENT

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th main function of surface course is to provide skid-resistance surface, friction and drainage for the pavement. It should be water tight against surface water infiltration. The thickness of surface course generally provided is 25 to 50 mm.

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A true flexible pavement yields “elastically” to traffic loading. It is constructed with a bituminous surface treatment or a relatively thin surface of hot-mix asphalt (HMA) over one or more unbound base courses resting on a subgrade. Its strength is derived from the load-distributing characteristics of a layered system designed to ultimately protect each underlying layer including the subgrade from compressive shear failure.

Progressively better materials are used in the upper structure to resist higher near-surface stress conditions caused by traffic wheel loads. These materials include an all-weather surface that is resistant to erosion by the environment and traffic action. The bituminous/ HMA surface layer must also be resistant to fatigue damage and remain stable under traffic loads when pavement surface temperatures are in excess of 150ºF.

In this manual, the term “flexible pavements” is used in a more generalized way to describe any “black-topped” structure (other than HMA-overlaid concrete). These pavements range in composition from true flexible pavement to semi-rigid systems (including the full-depth or perpetual design). This chapter is applicable to the design of these types of structures.

The fundamental difference between a flexible, semi-rigid, and rigid pavement is the load distribution over the subgrade. The semi-rigid pavement has a higher composite modulus than a true flexible pavement and begins to resemble the rigid structure in terms of how the traffic loads are distributed over the subgrade. The elements contributing to the higher modulus may be:

1. increased thickness in asphalt concrete pavement,

1. chemical stabilization of the base, subbase, and/or subgrade layers,

1. asphalt stabilization of the base course.

The higher modulus adds to the structural capacity of the pavement layers. As a result, the load is distributed over a wider area of the subgrade.

These pavements may fall into one of the following categories:

surface-treatment on a granular base,

thin hot-mix asphalt (< 2 in.) on a granular base,

intermediate hot-mix asphalt (2 - 4 in.) on a granular base,

thick hot-mix asphalt (> 4 in.) (semi-rigid),

thin hot-mix asphalt on a chemically stabilized base or subbase (semi-rigid),

thin hot-mix asphalt on an asphaltic bound base (semi-rigid).

Stabilization of the subgrade layer can be used with any of the above pavement types. Typical stabilizers include asphalt cement (for base only), lime, cement, fly ash, or lime-fly ash combinations.

There are two types of pavements based on design considerations i.e. flexible pavement and rigid pavement. Difference between flexible and rigid pavements is based on the manner in which the loads are distributed to the subgrade.

Before we differentiate between flexible pavements and rigid pavements, it is better to first know about them. Details of these two are presented below:

Flexible Pavements

Flexible pavement can be defined as the one consisting of a mixture of asphaltic or bituminous material and aggregates placed on a bed of compacted granular material of appropriate quality in layers over the subgrade. Water bound macadam roads and stabilized soil roads with or without asphaltic toppings are examples of flexible pavements.

The design of flexible pavement is based on the principle that for a load of any magnitude, the intensity of a load diminishes as the load is transmitted downwards from the surface by virtue of spreading over an increasingly larger area, by carrying it deep enough into the ground through successive layers of granular material.

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It is the layer immediately under the wearing surface (Applied whether the wearing surface is bituminous or cement concrete and whether its a thick or thin bituminous layer).

As base course lies close under the pavement surface it is subjected to severe loading. The material in a base course must be of extremely high quality and its construction must be done carefully. The LA Abrasion test can determine the quality of the aggregate for this purpose.

Types of Base Course

1. Granular Base Course:

It is a mixture of soil particles ranging in size from coarse to fine. Processing involves crushing oversized particles and screening where it is necessary to secure the desired grading. The requirements of a satisfactory soil aggregate surface are;

Stability

Resistance to abrasion

Resistance to penetration of water

Capillary properties to replace moisture lost by surface evaporation upon the addition of wearing course requirement change.

2. Macadam Base:

Successive layers of crushed rock mechanically locked by rolling and bonded by stone screening (rock duct, stone chips etc).

3. In-water bound Macadam:

The crushed stones are laid, shaped and compacted and then finer materials are added and washed into surface to provide a dense material.

4. Treated Bases:

Compose of mineral aggregate and additive to make them strong or more resistant to moisture. Among the treating agents is bitumen.

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(TRESAGUET)

The design of flexible pavement relies heavily on the entire structural section, meaning the subgrade, subbase, base and surface course. Under loading, the flexible pavement transfers and spreads the loading downward and outward. For this reason, the base course and subbase course (if used) and subgrade must be well compacted and have the ability to handle the additional loading. The strength of flexible pavement relies on all layers, especially the subgrade.

Rigid pavements, such as concrete pavement, do not rely as heavily on the lower base material because it can bridge the material. The strength of rigid pavement is in the concrete itself.

Flexible pavements are not heavily stressed by temperature variations. It is designed to be flexible and move. Rigid pavement does not do as well under temperature variations.

Flexible pavement can be “self-healing” to some extend under heavy loads and stresses. Rigid pavement will fail if the load or stress is too much.

Flexible pavement can be patched. Rigid pavement generally cannot be patched, but must be repaired. For this reason, where there are numerous underground utilities, it is much better to have flexible pavement that can be replaced quickly.

Fexible pavement tends to cost less in the short term, but may not last as long as ridid pavement if it is not well maintained.

Now, in your question, you talk about flexible pavement consisting of 6 things.

Embankment is generally what we refer to when we need to use borrow to build up the roadway or slopes.

Subgrade can actually be embankment material, or native material. Subgrade plays a major role in the support structure of flexible pavement. As I previously mentioned, the loading is transferred through each layer down to subgrade. The flexible pavement gets quite a bit of its strength from subgrade, subbase, and base materials. If they are not compacted properly, it weakens the flexible pavement.

Subbase is often a mechanically stabilized material. Subbase is not always used.

Base material is typically something like a 3/4″ aggregate, or a material that is free draining and can be well compacted.

I don’t necessarily agree with your 2nd and 1st components. While the top 2 lifts can be made of these materials, it is not always the case.

There are various types of flexible asphalt pavement that are used for various purposes.

stone matrix

open graded

dense graded

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It is layer of granular material provided above sub-grade generally natural gravel. It is usually not provided on sub-grade of good quality.

The materials used may be either unbound granular, or cement-bound. The quality of sub-base is very important for the useful life of the road and can outlive the life of the surface, which can be scrapped off and after checking that the sub-base is still in good condition, a new layer can be applied. (Unbound granular materials are usually crushed stone, crushed slag or concrete, or slate.)

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1) Definition and explanation Flexible Pavement (TRESAGUET)

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1) Definition and explanation Flexible Pavement (TRESAGUET)

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Definition

Flexible pavements are those pavements which reflect the deformation of subgrade and the subsequent layers to the surface. Flexible, usually asphalt, is laid with no reinforcement or with a specialized fabric reinforcement that permits limited flow or repositioning of the roadbed under ground changes.

The design of flexible pavement is based on load distributing characteristic of the component layers. The black top pavement including water & gravel bound macadam fall in this category.

Flexible pavement on the whole has low or negligible flexible strength flexible in their structural action). The flexible pavement layers transmit the vertical or compressive stresses to the lower layers by grain transfer through contact points of granular structure.

The vertical compressive stress is maximum on the pavement surface directly under the wheel load and is equal to contact pressure under the wheels. Due to the ability to distribute the stress to large area in the shape of truncated cone the stresses get decreased in the lower layer.

As such the flexible pavement may be constructed in a number of layers and the top layer has to be strongest as the highest compressive stresses.

To be sustained by this layer, in addition to wear and tear, the lower layer have to take up only lesser magnitude of stress as there is no direct wearing action due to traffic loads. Therefore, inferior material with lower cast can be used in the lower layers.

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You can never look at roads ever the same again after you discover the difference.

Any ground surface that you can step on which carries a considerable amount of weight or load is called a pavement. Pavements are primarily constructed for use by vehicles and pedestrians, transferring the load from the upper surface to the natural soil. The earliest record of the first constructed pavements is from the 4000 BC. They consist of stone paved streets or timber roads, with roads of the earlier times dependent on stone, gravel and sand for construction. Road and pavement construction has evolved.

There are two broad categories that pavements can fall into: flexible pavement and rigid pavement. How is the one different from the other?

Source: About Civil

Flexible pavements are those consisting of a mixture of asphaltic or bituminous material and aggregates placed on a bed of compacted granular material of appropriate quality in layers over the subgrade. Its design is based on the principle that a load of any magnitude diminishes as the load is transmitted downwards from the surface. The load spreads over an increasingly larger area, which carries it deep enough into the ground through successive layers of granular material. This is why materials with high degree of strength are used at or near the surface without the need for steel reinforcement.

Source: Flexible Pavements
On the other hand, rigid pavements are associated with rigidity or flexural strength or slab action so the load is distributed over a wide area of subgrade soil. They are usually laid in slabs with steel reinforcement, with design based on providing a structural cement concrete slab of sufficient strength to resist the loads from traffic. Rigid pavements require high modulus of elasticity.

Rigid pavement. Source: RRJ

The main difference between the flexible and rigid pavements is based on the manner in which the loads are distributed to the subgrade. The pavement design is also one major factor, with flexible pavements reliant on subgrade strength and rigid pavement dependent on the flexural strength of concrete.

Source: ACPA

Moreover, temperature variations are sensitive in rigid pavements inducing heavy stresses; whereas such do not produce stress in flexible pavements. Deformations pose permanent settlements in rigid pavements; while in flexible pavements, they have self-healing properties that can recover from heavier wheel loads.

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What is the Difference Between Flexible and Rigid Pavement?

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You can never look at roads ever the same again after you discover the difference. Any ground surface that you can step on which carries a considerable amount of weight or load is called a pavement. Pavements are primarily constructed for use by vehicles and pedestrians, transferring the load from the upper surface to the natural soil.

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Flexible pavement is composed of a bituminous material surface course and underlying base and subbase courses. The bituminous material is more often asphalt whose viscous nature allows significant plastic deformation. Most asphalt surfaces are built on a gravel base, although some 'full depth' asphalt surfaces are built directly on the subgrade. Depending on the temperature at which it is applied, asphalt is categorized as hot mix asphalt (HMA), warm mix asphalt, or cold mix asphalt. Flexible Pavement is so named as the pavement surface reflects the total deflection of all subsequent layers due to the traffic load acting upon it. The flexible pavement design is based on the load distributing characteristics of a layered system.

It transmits load to the subgrade through a combination of layers. Flexible pavement distributes load over a relatively smaller area of the subgrade beneath. The initial installation cost of a flexible pavement is quite low which is why this type of pavement is more commonly seen universally. However, the flexible pavement requires maintenance and routine repairs every few years. In addition flexible pavement deteriorates rapidly; cracks and potholes are likely to appear due to poor drainage and heavy vehicular traffic.

A valuable advantage of flexible pavement is that it can be opened for traffic within 24 hrs after completion. Also the repair and maintenance of flexible pavement is easy and cost effective.

Today 96% of all paved roads and streets in Pakistan are surfaced with asphalt. Almost all paving asphalt used today is obtained by processing crude oils. Man-made asphalt consists of compounds of hydrogen and carbon with minor proportions of nitrogen, sulfur and oxygen.

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CONSTRUCTION OF FLEXIBLE PAVEMENT ( McAdam )

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CONSTRUCTION OF FLEXIBLE PAVEMENT ( McAdam )

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SUB BASE STABILIZATION .

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i)MATERIAL

The sub-grade material should be clean and free from organic matter and should be able to be compacted by roller, to form stable sub-base. The material should have the following characteristics:

Well graded, uniformity coefficient (D60/D10) should not be less than 3.

Fraction passing sieve #200 shall not be greater than 2/3rd of the fraction passing sieve #40.

Should have a L.L not greater than 25%.

P.I not greater than 6

CBR should not be less than 25.

In coarse grain, aggregate retained by #10 sieve, %age of wear shall not be greater than 5%.

The maximum dia of any particle shall not be greater than 2/3rd of the layer thickness of sub-base

ii) DEPTH

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Flexible pavement is composed of a bituminous material surface course and underlying base and subbase courses. The bituminous material is more often asphalt whose viscous nature allows significant plastic deformation. Most asphalt surfaces are built on a gravel base, although some 'full depth' asphalt surfaces are built directly on the subgrade. Depending on the temperature at which it is applied, asphalt is categorized as hot mix asphalt (HMA), warm mix asphalt, or cold mix asphalt. Flexible Pavement is so named as the pavement surface reflects the total deflection of all subsequent layers due to the traffic load acting upon it. The flexible pavement design is based on the load distributing characteristics of a layered system.