The document describes the different layers of a flexible pavement, including the surface course, binder course, base course, subbase course, and subgrade. The surface course is the top layer and provides skid resistance, with a thickness of 25-50mm. The binder course is below this and is constructed of aggregates and bitumen. The base course distributes loads and is a minimum of 100mm thick. Below this is the subbase course, which provides drainage and a base for the base course. The bottom layer is the subgrade, which is the compacted natural soil acting as the pavement foundation.

1. Different layers of flexible pavement.
Submitted to: Submitted
by:
Dr. Tanuj Chopra Rohan
Kumar
(802023014)

2. Composition and Structure of Flexible
Pavement.
 The composition and structure of
flexible pavement consists of
surface course, binder course,
base course, subbase course,
subgrade.

3. SURFACE COURSE.
 Surface course or wearing
course is the top most layer
of flexible pavement which
has direct contact with the
vehicular loads.
 The main function of
surface course is to provide
skid-resistance surface,
friction and drainage for
the pavement.
• The thickness of surface course generally
provided is 25 to 50 mm.

4. Bituminous concrete(BC)
 Bituminous concrete( BC) is used for wearing course and profile corrective courses.
BC is generally laid in single layer on a previously prepared bituminous
bound surface.
The thickness of single layer of BC shall be 30mm,40mm and 50mm.

5. Grades of BC -

6. BINDER COURSE.
 Binder course is also constructed using aggregates
and bitumen but with less quality than materials
used for surface course. Generally, its thickness is
about 50 to 100 mm.

7. BITUMINOUS MACADAM (BM):
 BM shall consist of mineral aggregate and appropriate binder, mixed in a hot mix
plant and laid with a mechanized paver.
 It is laid in a single course or in a multiple layers on a previously prepared base.
Thickness of the single layer shall be 50 mm to 100 mm.
• The bitumen shall be viscosity graded paving bitumen complying with Indian
Standard Specification for paving bitumen, IS:73.
• The grade of bitumen to be used would depend upon the climatic conditions and
the traffic.

8. Viscosity Graded (VG) bitumen and their
Applications.
Viscosity Grade (VG) General Applications
VG-40 (40-60 penetration) Use in highly stressed areas such as those
in intersections, near toll booths, and
truck parking toll in lieu of old 30-40
penetration grade.
VG-30 (50-60 penetration) Use of paving in most of India in lieu of
old 60/70 penetration grade.
VG-30 (50-60 penetration) Use of paving in most of India in lieu of
old 60/70 penetration grade
VG-20 (60-80 penetration) Use in cold climatic, high altitude regions
of North India.
VG-10 (80-100 penetration) Use in spraying applications such as
surface dressing and paving in very cold
climatic region in lieu of old 80/10
penetration grade.

9. Dense Bituminous Macadam (DBM):
 A continuously graded material of a relatively low binder content.
 DBM acts as a bituminous base course and thickness of a single
compacted layer shall be 50 mm to 100 mm.
• Selection for viscosity grade bitumen based on highest and lowest daily mean
temperatures at a particular site -

10. Grades of DBM

11. BASE COURSE.
 The base course is important layer of pavement structure and it distributes the
loads from top layers to the underneath Subbase and sub-grade layers.
 The minimum base course thickness recommended is 100 mm. sub surface
drainage system can be provided with in the base course.

12. Wet Mix Macadam (WMM) base course:
 Wet Mix Macadam laying method contains of laying spreading and compacting of clean,
crushed, well-graded granular materials on a prepared and Granular sub-Base.
 Wet Mixed Macadam (WMM) Base thickness of single compacted should not be less than
75 mm. WMM shall be laid in layers of 75mm or 100mm as per thickness.
Material-
• Aggregate for Wet Mix Macadam Construction.
• Coarse aggregate shall be crushed stone or
crusher run as per IRC 109 or clause 406.2.1 of
MORT&H specification

14. Sub-base Course.
 The Sub-base course is provided beneath the base course and it also functions
as same as base course. If the sub-grade soil is strong and stiff, then there is no
need to sub-base course.
 If sub-grade is weak minimum 100 mm thick sub-base course should be
provided.

15. Granular sub-base (GSB)
 It plays two major roles –
1. It works as drainage layer.
2. It provides a good sub base to laid base layer on it.
Grading :
Grading III and IV shall be used in lower sub base. Grading V and VI shall be used as sub-base-cum-
drainage layer.

16. Subgrade.
 Subgrade is the bottom most layer which is nothing but natural soil layer
compacted up to required depth generally about 150 to 300 mm to receive the
loads coming from top layers. This layer is termed as foundation for the
pavement system.