Study of design of the flexible pavements ppt

1. CEE 320
Steve Muench

2. Outline
1. Pavement Purpose
2. Types of pavements
3. Flexible pavement
4. Layers of Flexible pavement
5. Failures in Flexible pavement
6. Design procedure
7. Pavement composition
8. Testing of aggregates
9. Different forms of bitumen materials
10. Construction procedure of BT roads
11. Geometric standards of BT roads

3. 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 .

4. Types of pavement
 Flexible pavement
Loads transfer by grain to grain contact
through granular structure.
Less flexural strength and acts like a flexible
sheet.
Eg : Bituminous Roads.
 Rigid pavement
Wheel loads transfer to the sub-grade soil by
flexural strength.
Pavement acts like a rigid plate.
Eg : Cement concrete roads

6. Flexible pavement
 Flexible
pavements will
transfer the wheel
load stresses to the
lower layers by the
grain to grain
transfer through the
points of contact in
the granular
Structure.

7. The wheel load
acting on the
pavement will be
distributed to a
wider area, and
the stress
decreases with
the depth.

8. Layers of flexible
pavement
 Design of flexible pavements uses the
concept of layered system to distribute the
wheel load acting on it.
 Flexible pavements are constructed using
bituminous materials.
 Top layer should be of best quality to
sustain the maximum compressive stress.
 Low quality materials can be used for lower
layers.

10. Failures of flexible
pavement
 Types of failures
 Fatigue cracking
 Rutting
 Thermal cracking

11. Fatigue cracking : The
Fatigue cracking of
the flexible pavement
is due to the
horizontal tensile
strain at the bottom
of the asphaltic
concrete.

12. Rutting : Rutting
occurs only on
the flexible
pavement as
indicated by
pavement
deformation or
rut depth along
wheel load path

13. Thermal cracking :
Thermal cracking
includes both
temperature
cracking and
thermal fatigue
cracking

14.  Failure criteria : Critical locations in the
pavement

15. Design procedure
 DESIGN TRAFFIC:-
 Initial traffic
 Traffic growth rate
 Design life
 Vehicle damage factor (VDF)
 Vehicle distribution .

16. Testing of Aggregates
 Desirable properties of aggregates:
 Strength
 Hardness
 Toughness
 Shape of aggregates
 Adhesion with bitumen
 Durability
 Freedom from deleterious particles

17. AGGREGATE TESTS
 Crushing test
 Abrasion test
 Impact test
 Soundness test
 Shape test
 Specific gravity and water absorption
test
 Bitumen adhesion test

19. Bitumen
 Different forms of
Bitumen
 Cutback bitumen
 Bitumen emulsion
 Bituminous primers
 Modified bitumen

20.  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 naphtha, kerosene, diesel
oil, and furnace oil.

21.  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

22.  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

23.  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

24. Construction procedure of BT
Roads
 The existing surface is prepared by removing the pot
holes or rust if any. The irregularities are filled in with
premix chippings at least a week before laying surface
course.
 The premix is prepared in a hot mix plant of a required
capacity with the desired quality control.
 The hot mixed material is collected from the mixture by
the transporters, carried to the location, A mix after it
is placed on the base course is thoroughly compacted by
rolling at a speed not more than 5km per hour.
 The initial or break down rolling is done by 8 to 12 tonnes
roller and the intermediate rolling is done with a fixed
wheel pneumatic roller of 15 to 30 tonnes having a tyre
pressure of 7kg per sq.cm. the wheels of the roller are
kept damp with water.

25.  The final rolling or finishing is done by 8 to 10 tonnes
tandom roller.
 Periodical checks are made for ,
a) Aggregate grading
b) Grade of Bitumen
c) Temperature of aggregate
d) Temperature of paving mix during mixing and
compaction

26. Geometric standards of BT
Roads
 The carriageway or the black top portion of
the road is not really flat. There is a
transfer slope which is provided and that
transfer slope is known as camber.

27.  Basically the traveled way which is used
for movement of vehicles, it takes the
vehicular loading and predominant
vehicle loads is shared by this
component which is called ‘carriageway’.

28.  The black top of surface and on each side some extra width
or extra portion of the road called as ‘shoulder’
 Basically it gives support to carriageway and provides a
space for stop vehicle in case there is a necessity for a
vehicle to stop.
 If there is no shoulder then it will stop right on the
carriageway and it will block the entire carriageway.
 So, a shoulder is kept on each side of the carriage way
which can be used by vehicle for stopping the vehicle and
for parking.
 So it is basically one half the difference between the road
way width and the carriageway width.
 The carriageway including separator or median, in case it is
a divided road plus shoulders on both sides together is
known as roadway width .

30. Flexible Pavement – Construction
FYI – NOT TESTABLE

31. THANK YOU