Construction of flexible pavement in short.

1. Construction of
Flexible Pavement
BY:
SHILPA KUMTHE FP15054
KIRAN D R FP15056
ARUN RAVINDRANATH FP15058
AJINKYA THAKRE FP15059
NATIONAL INSTITUTE OF CONSTRUCTION MANAGEMENT AND RESEARCH, PUNE.

2. INTRODUCTION
 PAVEMENT:-
“Pavement is load bearing and load distributary component of road”
 PURPOSE OF PAVEMENT:-
1. LOAD SUPPORT
2. SMOOTHNESS
3. DRAINAGE
4. ALL WEATHER OPERATION
5. DIRECTION AND GUIDANCE

3. TYPE OF PAVEMENT Type of
pavement
Flexible
pavement
Rigid
pavement
1 .FLEXIBLE PAVEMENT:
Those pavements which reflect the deformation of subgrade and the subsequent
layers to the surface.
2. RIGID PAVEMENT: The pavement are associated with rigidity or flexural strength
or slab action so the load is distributed over a wide area of subgrade soil. Rigid
pavement is laid in slabs with steel reinforcement.

4. FLEXIBLE PAVEMENT
 THE ADVANTAGES OF FLEXIBLE PAVEMENTS INCLUDE -
 Adaptability to stage construction
 Availability of low-cost types that can be easily built
 Ability to be easily opened and patched
 Easy to repair frost heave and settlement
 THE DISADVANTAGES INCLUDE -
 Higher maintenance costs
 Shorter life span under heavy use
 Damage by oils and certain chemicals
 Weak edges that may require curbs or edge devices

5. THICKNESS DESIGN
 Several Procedures are used.
 Based on volume and weight of traffic
 Load supporting capacity of soil is important.
 Heavy vehicle wheel load has greater impact.
 Traffic analysis in necessary.
 Designs are chosen based on
1) Designed traffic in terms of cumulative numbers of std. axels.
2) CBR value of subgrade.

6. Total thickness of pavement consists of :-
 Bituminous Surface (Wearing Course).
 Base Course.
 Subbase.
 Subgrade.

7. WEARING COURSE
 Three types of bituminous layers-
1. Bituminous Macadam.
2. Penetration Macadam.
3. Built up spray Grout.

8.  BITUMINOUS MACADAM
 It consist of crushed aggregate and bituminous binder heated and mixed
in a hot mix plant at specified temperature, transported to the
construction site, laid with a mechanical pawer and compacted by roller.
 Material used : Bitumen binder of grade VG -30,20 and Max size of
aggregate 50mm.

9.  BITUMINOUS PENETRASION MACADAM.
The coarse aggregate of specified size are first spread and compacted well in dry
state. Compacted thickness 50-75 mm. After compacting of dry aggregates, hot
bituminous binder of specified grade is spread in large quantity on the top of
this layer. Filling up a part of void and binding by key aggregate.
 BUILT UP SPRAY GROUT
It consist of a two layer composite construction of compacted crushed stone
aggregate with bituminous binder applied after each layer and key aggregate
placed on the top surface of the second layer.

10. BASE COURSE
 The base course is immediately beneath the surface course. It provides
additional load distribution and contributes to drainage and frost resistance.
Base courses are usually constructed out of
 AGGREGATES: Base courses are most typically constructed from durable
aggregates that will not be damaged by moisture and frost action.
Aggregates can be either stabilized or un-stabilized.

11. SUB-BASE COURSE
 Intermediate layer between subgrade and granular base
course
 Essentially a drainage layer
 Distributes the stresses imposed by traffic

12. FUNCTION OF SUB-BASE COURSE OF
FLEXIBLE PAVEMENT
It functions primarily as structural support but it can also help:
 Minimize the intrusion of fines from the sub-grade into the pavement
structure.
 Improve drainage.
 Minimize frost action damage.
 Provide a working platform for construction.
 The subbase generally consists of lower quality materials than the base course
but better than the sub-grade soils.

13. MATERIALS FOR SUB BASE
 LOCALLY AVAILABLE MATERIALS
 Natural sand
 Gravel or moorum
 Kankar
 Crushed stone
 Laterite
 INDUSTRIAL WASTE AND OTHER MATERIALS
 Steel slag
 Pond ash or Pond ash – Bottom ash mix
 Crushed concrete
 Brick bats

14. SUBGRADE
 It forms the foundation of the pavement system
 Subgrade soils are subjected to lower stresses than the surface, base, and
subbase courses.
 Since load stresses decrease with depth, the controlling subgrade stress
usually lies at the top of the subgrade.
 The combined thickness of subbase, base, and wearing surface must be
great enough to reduce the stresses occurring in the subgrade to values
that will not cause excessive distortion or displacement of the subgrade
soil layer.

15. FACTORS TO BE CONSIDERED
 General characteristics of the subgrade soils.
 Depth to bedrock.
 Depth to the water table.
 Compaction that can be attained in the subgrade.
 CBR values of uncompacted and compacted subgrades.
 Presence of weak or soft layers or organics in the subsoil.
 Susceptibility to detrimental frost action or excessive swell.

16. METHODS FOR SUBGRADE
PREPARATION
 COMPACTION
 In fill areas, subgrade below the top 150 mm (6 inches) is often considered
adequate if it is compacted to 90 percent relative density.
 In order to achieve these densities the subgrade must be at or near its
optimum moisture content (the moisture content at which maximum density
can be achieved).
 Usually compaction of in situ or fill subgrade will result in adequate
structural support.

17.  STABILIZATION
 The binding characteristics of these materials generally increase subgrade
load-bearing capacity.
 Typically, lime is used with highly plastic soils (plasticity index greater than
10), cement is used with less plastic soils (plasticity index less than 10) and
emulsified asphalt can be used with sandy soils.
 For flexible pavements, a primecoat is not effective on silty clay or clay
soils because the material cannot be absorbed into such a fine soil (TRB,
2000).

18.  OVER-EXCAVATION
 The general principle is to replace poor load-bearing in situ subgrade with
better load-bearing fill.
 Typically, 0.3 – 0.6 m (1 – 2 ft.) of poor soil may be excavated and replaced
with better load-bearing fill such as gravel borrow.

19. CONSTRUCTION STEPS
1. Preparation of Base
2. Provision of lateral confinement of aggregates
3. Preparation of Mix
4. for small quantity concrete mixer may be used
5. find OMC after replacing retained on 22.4 mm with material 4.75 to 22.4
mm
6. Spreading of Mix
 Spreading of mix to be done uniformly / evenly
 Should not be dumped in heaps

20.  Finishing by Paver /exceptional cases grader
 Due importance for segregation
7. Compaction
 8to 10 tonne static compactor up to 100 mm
 8-10 vibratory roller up to 200 mm
 Speed of compactor not to exceed 5 km/hour
 Displacement occurring due to roller operations are to be rectified
 Use small compactors near kerb/places not assessable to roller
 Rolling not be done when subgrade is soft/yielding/causes wave like
motion

21. 8. Any defections on the surface to be rectified
9. Setting and Drying
10. Opening to traffic after sealing

22. THANK YOU!