flexible pavement road construction process step by step
Flexible Pavements
In a flexible pavement, wheel loads are transferred to the subgrade through grain-to-grain contact points within the granular structure. The stresses caused by the wheel loads are spread over a larger area, resulting in a decrease in stress with depth. Due to this load distribution characteristic, flexible pavements are constructed with multiple layers.
Road Construction Layers (Road Pavement Layers)
Following are pavement layers in road construction,
1.Compacted subgrade.
2. Sub-base Course or Granular sub-base (G.S.B)
3. Base Course or wet mix macadam (W.M.M)
4. Prime Coat
5. Binder Coat or Dance bituminous macadam (D.B.M)
6. Tack Coat
7. Surface Course or Bituminous Concrete (B.C)
8. Seal Coat
1. Compacted Sub-grade
The compacted subgrade serves as the foundation for all pavement layers. The stress exerted by the layers above is transferred to this subgrade layer. Hence, it is crucial to ensure that the soil subgrade does not experience excessive stress. To achieve this, the subgrade should be adequately compacted to achieve the desired density, preferably at or near the optimum moisture content.
Thickness varies between (150 – 300 mm)
Tolerance ± 20mm
Comparison 97%
CBR =above 5%
2. Sub-base Course or (G.S.B)
It is a layer of material below the base course.The compacted subgrade serves as the foundation for all pavement layers. The stress exerted by the layers above is transferred to this subgrade layer. Hence, it is crucial to ensure that the soil subgrade does not experience excessive stress. To achieve this, the subgrade should be adequately compacted to achieve the desired density, preferably at or near the optimum moisture content.
Thickness varies between (100 – 300 mm)
Size – max: 75mm
Tolerance ± 6mm
3. Base Course or (W.M.M)
The base course is a layer of material located just beneath the surface of the binder course in a pavement structure. It serves two main purposes: providing additional load distribution and contributing to sub-surface drainage. Various materials can be used for base courses, including crushed stone, crushed slag, and other untreated or stabilized materials.
Thickness varies between (100 – 300 mm)
Size – max: 53mm
4. Prime Coat
A prime coat is applied by evenly spreading low-viscosity cutback bitumen onto an absorbent surface, such as granular bases, before placing the binder layer. Its primary purpose is to establish a strong bond between two layers of the pavement structure.
5. Binder Coat or (D.B.M)
The binder coat is a significant component of the asphalt concrete structure. Its primary role is to evenly distribute the load to the base course, providing structural integrity. The binder course primarily consists of aggregate mixed with a lower proportion of asphalt, and it does not require the same level of quality as the surface course.
Thickness varies between (50 – 100 mm)
6. Tack Coat:
In the tack coat, a little amount of asphalt is applied to the surface.It is typically an asphalt emulsion that is diluted with water. Its primary purpose is to ensure proper bonding between two layers of the binder course. It should be applied thinly and uniformly to cover the entire surface, and it should set quickly.
7. Surface Course (B.C)
The surface course is the primary layer responsible for bearing the direct traffic load and is typically composed of high-quality materials. Graded asphalt concrete (AC) is commonly used for constructing the surface course. It is important to ensure that the surface course has a durable and rigid surface to resist deformation caused by traffic and provide a smooth and skid-resistant riding surface.
Thickness varies between (25 – 50 mm)
8. Seal Coat
The seal coat is a thin layer with a water-proof surface and provides skid resistance.