Flexible Pavements: Objective, Advantage, Disadvantage, Components, and Affecting Factors

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Flexible Pavements

Flexible Pavements are those which on the whole have low or negligible flexural strength and are rather flexible in their structural action under the loads. Means, Flexible pavements are designed to pass the load immediately from the point where it occurs. Thus, if the lower layer of the pavement or soil subgrade gets deformed or undulated due to permanent deformation, the flexible pavement layers and also the pavement surface may get undulated to a somewhat similar pattern.

Objective of Flexible Pavements

Flexible pavements are generally designed to fulfill two main requirements:
1. To limit the recoverable or elastic deformation of the pavement within the permissible limits so that the pavement can sustain a large number of repeated load applications during the design life, without resulting in structural damages due to fatigue failure of the pavement layers.
2. To restrict the verticle strains on the subgrade and the other pavement layers within the desired limits so that the accumulated non-recoverable deformation in the form of rutting of the pavement surface along the wheel paths is within permissible limits during the design life of the pavement.

GEOMETRIC DESIGN AND GENERAL FEATURES

Advantages of Flexible Pavements

  1. Flexible pavements are generally designed and constructed for a design life of 15 years.
  2. The functional evaluation studies can be carried out at desired intervals and the deteriorated functional condition of the road surface can be restored with a thin bituminous re-surfacing layer.
  3. It is possible to resort to “milling and recycling” techniques and thus utilize a substantial portion of damaged bituminous pavement layers.
  4. The curing period for the bituminous surface course is less and hence the surface can be opened to the traffic within 24 hours.
  5. Flexible pavements are of low-cost maintenance as it can be restored at the point of distortion by filling it with appropriate material.

Disadvantages of Flexible Pavements

  1. The bituminous pavement layers get deteriorated when exposed to stagnant water due to poor drainage of surface and subsurface water.
  2. It is essential to carry out routine and periodic maintenance of the drainage system, shoulders, and the pavement surface.
  3. It is difficult to carry out repairs of deteriorated bituminous pavements or patching of pot-holes during the rains or under wet weather conditions.
  4. The total thickness of the flexible pavement and the quantity of hard aggregates required is higher than CC pavements, particularly for the construction of highways where subgrade soil is weak and carrying the load is higher.
  5. Night visibility of the bituminous surface is very poor, particularly under wet weather conditions.

Components of Flexible Pavements

  1. Prepared soil subgrade
  2. Granular sub-base cum drainage layer
  3. Granular base course
  4. Bituminous binder and/or surface course
Flexible Pavements: Objective, Advantage, Disadvantage, Components, and Affecting Factors

Factors that Affect the Design of Flexible Pavements

  1. Wheel loads of heavy vehicles or the traffic loads
  2. Subgrade Soil
  3. Climate Factors
  4. Pavement Component materials in different layers
  5. Drainage and environmental factors

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