In general, there are two types of pavement, namely rigid pavement and flexible pavement. Flexible pavements, particularly asphalt concrete pavement are abundantly seen in and around urban areas and developed cities. However, flexible pavement is more durable and lasts longer. They are emerging to replace flexible pavement in developed countries.
In this article, rigid pavement is discussed in detail, reasons for rigid pavement and their types. Also, a comparison between rigid pavement and flexible pavement is made here. In the FAQs section, advantages and disadvantages are put as a priority question and answer.
What is Rigid Pavement?
Rigid pavement is a type of road construction that consists of a series of uniformly thick slabs made from Portland Cement Concrete, forming a solid road surface. It is characterized by its high flexural strength and the concrete layer allows rigid pavement to distribute the load from vehicles more efficiently, reducing stress on the underlying layers and increasing the road’s lifespan. This type of pavement is also called concrete pavement or heavy-duty pavement.
The rigid pavement includes macadam, reinforced concrete and a few other options. The pavement is featured with joints to accommodate thermal expansion and contraction. Concrete pavement is commonly used in highways, airports, and other areas with heavy traffic loads.
Also, read: What is Cement Concrete?: Comprehensive Guide and 2 Types (PCC and RCC)
Composition of Rigid Pavement
Rigid pavement also known as concrete pavement is composed of multiple following:
- Surface Course
- Granular Base Course
- Granular Sub-base course
- Subgrade
Surface Course
This is the topmost layer in the structure of rigid pavement which withstands wheel load directly. It is constructed from reinforced (R.C.C.) or plain cement concrete (P.C.C.) with a certain design thickness. Typically, the thickness of the surface course is between 150 to 300 mm thick. The concrete grade of M40 is advised by IRC for heavy traffic to extremely severe traffic loads.
As the surface course is a layer of concrete slab, it is resistant to water and petroleum products which makes them durable and rigid. However, a smooth surface is not encouraged and staging of water may make the surface slippery reducing the traction between the wheel and the surface. Thus, proper camber must be maintained to expel the water on the surface and a roadside drain must be built to prevent surface erosion of the adjacent shoulder.
Granular Base Course
This is the second layer from the top in the hierarchy of the rigid pavement structure. It is also known as dry lean concrete (DLC) composed of cement concrete constituting crushed aggregate. The surface course should be laid on the granular base course layers. This thickness of the granular base course is 100 mm thick.
Granular Sub-Base Course (GSB)
The Granular Sub-base course, also known as the lower base course is the third layer from the top resting on the subgrade. This layer acts as a drainage for pavement materials and IRC recommends permeability coefficient be at least 30 m/day.
The material to be used for the work shall be natural sand, moorum, crushed gravel/stone, or a combination thereof depending upon the grading required. The material shall be free from organic or other deleterious constituents and shall conform to the quality standards as prescribed in the specifications.
Subgrade
This layer is the natural earth layer which is excavated out or filled with proper compaction. If the excavation is done for the subgrade, the depth of the cut from the ground level should be the combination of granular sub-base to the surface course. The width of the subgrade is equal to the width of the surface course plus 150 mm on both sides.
The subgrade should be well compacted and consolidated with a power road roller of 8 to 12 tonnes. The procedure is continued till the soil becomes evenly and densely consolidated and behaves as an elastic mass.
Reasons for Rigid Pavement
There are several reasons for rigid pavement to be chosen from other types of pavement methods as such asphalt pavement and WBM (Water Bound Macadam) pavement. The reason for using rigid pavement stems from its hardness. Since the surface is harder, it is also more durable over time. This keeps the road in good working order for longer than softer surfaces asphalt pavement and WBM. The other advantage of concrete roads is their shaping. Since the surface can withstand a lot of weight without deformation, it is possible to create groves and channels in the road to provide extra traction and move water off the road’s surface.
Also, read: WBM Road: Specifications, Construction, Typical and Cross Section
Types of Rigid Pavement
Basically, rigid pavements are made of concrete and reinforcement bars. They are classified into the following types: –
- Jointed plain concrete pavements (JRC)
- Jointed reinforced concrete pavements
- Continuously reinforced concrete pavements (CRCP)
- Pre-stressed Concrete Pavements
1. Joint Plain Concrete Pavements
Jointed plain concrete pavements are primarily characterized by their unreinforced slab properties. They are also known simply as jointed concrete pavements constructed with closely spaced contraction joints. Dowel bars and aggregate interlocks are generally used for load transfer across joints. They normally have a joint spacing of 8 to 15 meters.
Also, read: Dowel Bars: A Key Element for Durability and Load Transfer
2. Jointed Reinforced Concrete Pavements
Joined reinforced concrete pavements contain a steel mesh that reinforces the structure of the concrete slab. The concrete slabs used in this style are often larger than those used in Joint Plain Concrete designs with a joint spacing of 10 to 30 meters. Reinforcement helps to keep the slab together even after the development of cracks on the surface of the concrete slab. Dowel bars are provided at the joints between the concrete slab in order to transfer the load.
Also, read: Joints in Concrete Pavements: Transverse Joints & longitudinal joints
3. Continuously reinforced concrete pavements (CRCP)
Continuous Reinforced Concrete Pavement (CRCP) is a form of rigid pavement distinguished by its lack of transverse joints, featuring uninterrupted steel reinforcement across the entire pavement section. The absence of transverse joints eliminates the necessity for joint maintenance and minimizes the risk of faulting and pumping. This type of pavement is frequently employed for highways and roads experiencing substantial traffic loads.
4. Pre-stressed Concrete Pavements
Pre-stressed concrete types of road pavement are designed and produced to be pre-stressed to bear tensile forces caused by external loads by various live objects such as vehicles on the roads or aircraft in the airports.
As compared to asphalt pavements, pre-stressed concrete pavements are more resistant to aeroplanes’ or vehicle’s wheel thrust and also it causes less wear and tear to themselves. These types of road pavement are also useful to minimize maintenance costs.
Also, read: Understanding Road Camber: Effects on Vehicle Handling and Road Safety
Difference Between Flexible Pavement and Rigid Pavement
| SL.No. | Flexible Pavement | Rigid Pavement |
|---|---|---|
| 1. | It consists of a series of layers with the highest quality materials at or near the surface of the pavement. | It consists of one layer of Portland cement concrete slab or relatively high flexural strength. |
| 2. | It reflects the deformations of the subgrade and subsequent layers on the surface. | It can bridge over localized failures and areas of inadequate support. |
| 3. | Its stability depends upon the aggregate interlock, particle friction and cohesion. | Its structural strength is provided by the pavement slab itself by its beam action. |
| 4. | Pavement design is greatly influenced by the subgrade strength. | The flexural strength of concrete is a major factor in design. |
| 5. | It functions by a way of load distribution through the component layers | It distributes the load over a wide area of subgrade because of its rigidity and high modulus of elasticity. |
| 6. | Temperature variations due to changes in atmospheric conditions do not produce stresses in flexible pavements. | Temperature changes induce heavy stresses in rigid pavements. |
| 7. | It functions by way of load distribution through the component layers | Any excessive deformations occurring due to heavier wheel loads are not recoverable, i.e. settlements are permanent. |
Also, read: 12 Types of cracks in asphalt pavement | Symptoms | Causes | Treatment of defects
FAQs:
Q: What are the advantages of rigid pavements?
Answer: The advantages of rigid pavements are as follows: –
1. They are more durable and have a longer life than flexible pavements.
2. Low maintenance and operation costs.
4. Are environment-friendly compared to flexible pavement.
5. Rigid pavements are known for resisting petroleum products, oils, and chemicals.
Q: What are the disadvantages of rigid pavements?
Answer: The disadvantages of rigid pavement are: –
1. The construction cost of the rigid pavement is very high due to the high cost of installation and materials.
2. Maintenance is more difficult than flexible pavement.
3. Requires at least 28 days for the concrete to gain its complete strength (i.e. 99%) before opening to traffic.
Q: What are the joints provided to cement concrete pavement?
Answer: Generally cement concrete pavement is provided with two types of joint namely transverse joint and longitudinal joint. The transverse joints are further classified into four types as follows:
1. Contraction joint
2. Expansion joint
3. Warping joint
4. Construction joint
Q: Why are joints provided to concrete pavement?
Answer: Concrete paverment also known as rigid pavements are provided with joinst such as Transferse joint and Longitudinal joint to Control Cracking and Relieve Stress.
References:
- Nikolaides, A. (2015).Pavements, Materials and Control of Quality. Highway Engineering. Taylor & Francis Group. Boca Raton. London. New York
- Rogers, M. (2003). Highway Engineering. Blackwell Publishing.
- IRC:15-2011 (4th revision). Standard Specifications and Code of Practice for Construction of Concrete Roads. Indian Road Congress. Kama Koti Marg. New Delhi-110022
- IRC:58-2015. Guidelines for the Design of Plain Jointed Rigid Pavement for Highways. Indian Road Congress. Kama Koti Marg. New Delhi-110022
