Different layers of flexible pavement

Detail about layers of flexible pavement.

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

13. 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.

14. Granular sub-base (GSB) It plays two major roles – 1. I t works as  drainage layer. 2. I t 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.

15. 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.