what is flexible pavement? Flexible pavement layers, Types of flexible pavement.

 

LITERATURE REVIEW 

 

  Introduction to Pavement Analysis:

A pavement is a structure of road consisting of superimposed layers of processed materials above the natural soil sub-grade, to complete and whose primary function is to distribute the applied vehicle loads to the sub-grade provide top surface. The pavement structure should be able to provide a surface of satisfactory riding quality, adequate skid struggle, favorable light reflecting characteristics, and low noise pollution. The definitive aim is to ensure that the transmitted stresses due to wheel load are adequately reduced, so that they will not surpass bearing capacity of the sub-grade. Two types of pavements are generally accepted as serving this purpose, specifically flexible pavements and rigid pavements. This topic gives us overview of pavement types, layers of pavement, and their functions, and pavement failures results. Improper analysis of pavements leads to early failure of pavements affecting the riding quality. The analysis of pavement is the process in which we set up the best possible way to calculate the results of different factors effect on the pavement.

Flexible Pavement

Types of Flexible Pavements

The various types of construction is used in flexible pavement:

1.         conservative layered flexible pavement

2.         Full - depth asphalt pavement

3.         Enclosed rock asphalt mat

Conventional flexible pavements are layered systems with high quality costly materials are placed in the top where stresses are high, and low quality economical materials are positioned in inferior layers.

Full - depth asphalt pavements are constructed by insertion of asphaltic layers straight on the soil sub-grade. This is more appropriate when there is high traffic and local materials are not available.

Contained rock asphalt mats are constructed by placing thick/open graded aggregate layers in between two asphalt layers. Personalized dense graded asphalt concrete is placed above the sub-grade will significantly reduce the vertical compressive strain on soil sub-grade and guard from surface water.

Asphalt Working

 Usual layers of a flexible pavement

usual layers of a straight flexible pavement includes seal coat, surface course, tack coat, binder course, prime coat, base course, sub-base course, compacted sub-grade, and natural sub-grade.

Sub-grade

The layer of natural soil which is at the bottom of the pavement layer. It receives loads from the above layers and distributes it equally. It is compacted to make it dense.

 

Sub-Base course

It is the layer between the base course and sub grade. Its main function is to give structural hold up and to provide drainage. In some cases sub base course is not provided.

                                                                       

 Base course    

                                                                                                                                                                 it gives extra load division and contributes to the sub-surface drainage It may be made up of crushed stone, crushed slag, and other raw or steady materials                                                                                        

Binder course

This layer provides the volume of the asphalt concrete structure. Its main function is to distribute load to the different part of road base course the binder course usually consists of aggregates with less down asphalt and doesn't the need feature as high as the surface course, so replacing a part of the surface course by the binder course outcomes in more cheap design. 

Surface course

Surface course is the layer straight in effect under traffic loads and usually consist high quality materials. They are typically constructed with thick graded asphalt concrete (AC). The functions and necessities of this layer are

•           It provides features such as friction, softness, drainage, etc. Also it will avert the entrance of unnecessary quantities of surface water into the primary base, sub-base and sub-grade,

•           It must be defend to the load of  heavy traffic oppose the deformation under traffic and give a smooth and plane surface skid- resistant riding surface for load,

•           It must be water resistant to protect the whole base and sub-grade from the deteriorating effect of water.

 

 

2The cross slope which is recommended is 0.02 feet per foot. Also it should not be less than 0.015 feet per foot or greater than 0.04 feet per foot. In case of a horizontal curve the road is lifted upward on the outer bank to provide stability to the moving vehicle, and this design technique is known as super elevation. This gradient change is very necessary and it is provided in all types of roads and the increase efficiency and safety.

Road Top

 Fatigue Life.

            The fatigue life of a pavement is described as time required or the number of major axles carried by a pavement before requiring any type of maintenance and rehabilitation work.

            It generally depends upon the traffic type for which the pavement is going to be used and the fatigue life generally ranges from 10 to 15 years before requiring any major work.

            Fatigue life is affected by many factors like temperature, thicknesses of layers, kinematic viscosity, modulus and air voids etc.

            In this project we will check those effects of above mentioned variable on fatigue life will try to develop an idea for the effects of all the variables and will make a graphical representation of the project. Figure 2.6 shows the pavement before and after the ending of fatigue life.