flexible pavement

1. FLEXIBLE
PAVEMENTS`

2. Pavement Purpose
› Carries traffic smoothly and safely with minimum cost.
› Distribute the applied vehicle loads to the sub-grade.
› Acceptable riding quality, adequate skid resistance, favorable light
reflecting characteristics, and low noise pollution.

3. FLEXIBLE PAVEMENTS
 Flexible pavement
 Loads Transfer by grain to grain contact through granular structure.
 Less flexural strength and acts like a flexible sheet.
Eg. Bituminous roads.

4.  Rigid pavement
 Wheel loads transfer to the sub-grade soil by flexural
strength.
 Pavement acts like a rigid plate.
Eg. Cement concrete Roads.

5. Load transfer
› Load is transferred to the lower layer by grain to grain
distributions as shown in the figure given below

6. Load Transfer
› The wheel load acting on the pavement will be distributed
to a wider area, and the stress decreases with the depth.
Flexible pavement layers reflect the deformation of the
lower layers on to the surface layer.

7. › Typical layer of a conventional flexible pavement include
seal coat, surface course, sub-base course,
compacted sub-grade, and natural sub-grade.
Typical Layers of a Flexible Pavement

8. Typical layers of a Flexible pavement
› Seal coat is a thin surface treatment used to water-proof
the surface and to provide skid resistance.
› Tack coat is a very light application of asphalt emulsion
diluted with water. And it provides bonding between two
layer of binder course.
› Prime coat is an application of low viscous cutback
bitumen to an absorbent surface like granular bases on
which binder layer is placed and provides bonding
between two layers.

9. › Surface course is the layer directly in contact with
traffic loads and are constructed with dense graded
asphalt concrete.
› Binder course purpose is to distribute load to the
base course. Binder course requires lesser quality of
mix as compared to course above it.
› Base course provides additional load distribution and
contributes to the sub-surface drainage

10. › Sub-base course the primary functions are to provide
structural support, improve drainage, and reduce the
intrusion of fines from the sub-grade in the pavement
structure
› Sub-grade The top soil or sub-grade is a layer of natural
soil prepared to receive the stresses from the layers above

11. Failures of flexible pavement
 Types of failures
 Fatigue cracking
 Rutting
 Thermal cracking

12. Fatigue cracking
Fatigue cracking is an asphalt pavement distress most
often instigated by failure of the surface due to traffic
loading. However, fatigue cracking can be greatly
influenced by environmental and other effects while traffic
loading remains the direct cause.

13. Rutting
Rutting occurs only on the flexible pavement a indicated
b pavement deformation or rut depth along wheel load path

14. Thermal cracking
Thermal cracking is a process in which hydrocarbons
present in crude oil are subject to high heat and temperature
to break the molecular bonds and breaking down long-
chained, higher-boiling hydrocarbons into shorter-chained,
lower-boiling hydrocarbons.

15. Different forms of Bitumen
 Cutback bitumen
 Bitumen emulsion
 Bituminous primers
 Modified bitumen

16.  Cutback bitumen
Solvent used lowers the viscosity of bitumen.
The solvent from the bituminous material will
evaporate and the bitumen will bind the aggregate.
The distillates used are oil, and furnace oil.

17.  Bitumen emulsion
This type of bitumen is a liquid with aqueous medium
containing 50 to 60% bitumen in a finely divided form.
It is used for making and repairing roads.

18.  Bituminous primers
The distillate is absorbed by the road surface on which it is
spread.
These are prepared in road sites by mixing penetration
bitumen with petroleum distillate

19.  Modified bitumen
Certain additives or blend of additives called as bitumen
modifiers can improve properties of Bitumen and bituminous
mixes.
Bitumen treated with these modifiers is known as modified
bitumen

20. Advantages
Adjusts to limited differential settlement
 Easily repaired Additional thickness added any time
 Non-skid properties do not deteriorate
 Quieter and smoother
 Tolerates a greater range of temperatures

21. Disadvantages
Shorter lifespan than rigid pavement.
 Frequent maintenance required, which drives up the cost.
 Susceptible to oil stains and damage from other chemicals.
 Edges are weak and therefore require curb structures or
edging.