Concrete vs Asphalt Road Which Material is Best for Roads
What is Concrete Road?
Concrete roads are made of 5 layers stacked on top of each other. The top surface is called the surface course where the concrete slab is provided and under this layer is provided the Stabilised base course, Stabilised sub-base or granular sub-base is beneath it, then comes the frost protection layer and subgrade soil.
- Surface Course: It is the top layer and is made up of concrete and its thickness is generally between 150-300mm. It is made to be water resistant so water could not infiltrate through this layer. As Concrete slab is a top layer and is directly in contact with the vehicles so it is made skid resistant by ingrooving it to offer friction.
- Stabilised Base Course: It is the second layer from the top and helps to bear the additional loads which make it further stabilizes the course. It is made up of crushed aggregates and the minimum thickness provided is 100mm.
- Stabilised Sub-base Course: It is also known as Granular Sub-base. It is provided when the loading exceeds 100000 pounds and it is made up of aggregates but it’s aggregate quality is kept in between the quality of base course and subgrade aggregates.
- Frost Protection Later: It is provided in the areas of low-temperature and high water table because the water from the water table will freeze itself in low temperature thus the volume of the road will increase making the road rough and non-uniform.
- Subgrade Soil: It is the last layer of Road Pavement of Concrete type which is nothing but just the already existing soil compacted with tools and machines to make it stable and transfer the load underground.
Talking about the concrete, it is the mixture of Cement(generally Portland cement), coarse aggregate, fine aggregate and water. The long term use of concrete road comes out as economical than other pavement materials. It is highly durable and less prone to wear and tear. It is grooved to make it skid resistant so the concrete road becomes safer. The requirement of maintenance is very minimal and the age of concrete pavements is considered 40 years. In the year 1865 in Inverness, Scotland the first concrete pavement was built.
How Concrete Roads are Constructed?
The Materials required for constructing Concrete Roads are:
- Cement
- Admixtures
- Coarse Aggregates
- Fine Aggregate
- Water
- Steel
There are a total of 3 methods of constructing the Concrete Roads:
Alternate Bay Method
In Alternate Bay Method the construction is done by converting the pavement in alternate bays and moving to another bay after the previous one has been hardened.
Continuous Bay Method
As the name suggests the bays are laid out continuously leaving a joint after the day is over.
Expansion Joint and Strip Method
The step-by-step method for constructing the Concrete Road is as follows:
Sub-grade Preparation:
We prepare Subgrade by cleaning and levelling. It is further uniformly compacted and saturated with water.
Sub-base Provisioning:
It is provided when the sub-base is not stable. The factors to be considered when providing the sub-base are type of soil, design load, funds, traffic intensity.
Forms Placement:
The permissible deviation in 3m depth of the form is 5mm in horizontal plane and 3mm in vertical plane. They’re made up of Timber & mild steel and are fixed and braced properly.
Watering the subgrade:
The subgrade is properly saturated 12 hours in advance.
Mixing and Batching of Materials:
All the materials required are proportioned by weight batching and mixed properly in the dry state.
Transportation and Placing:
At this stage the materials mixed are transported to the site and deposited on the sub-grade quickly at 50-80 mm thickness.
Compaction of Concrete:
After the placement of concrete the compaction is very important so that the concrete has no holes and air in it. Tampering, vibration, and heavy machines are used to compact the Concrete Road.
Floating:
This is done by wooden floats to even the uneven surface.
Belting:
Belting is done to make the surface skid resistant by making it rough(non-slippery).
- Brooming
- Edging:
Edges of the concrete road are finished.
Curing:
Curing is the process of wetting the concrete by water after 24 hours of placing concrete till 28 days.
Filling of joints
After all these steps the Road is ready to have traffic on it.
Advantages & Disadvantages of Concrete Roads
| Advantages | Disadvantages |
|---|---|
| Concrete roads are durable and can last upto 40-50 years. | The initial cost is 15-20% high comparatively. |
| Load distribution in Concrete Roads is designed more flexibly and accurately. | If proper hydration of concrete is not achieved then it develops cracks, warping & twisting. |
| These roads are unaffected by weathering and temperature. | It takes a long time to be ready to open as the curing is done. |
| They have better visibility in the dark. | Less resilient compared to bituminous roads and Water Bound Macadam. |
| Concrete roads are impervious. | Difficult to locate pipe lines or sewers under the pavement. |
Concrete Road Vs Asphalt Road
The binding material in Concrete road is Cement which binds the aggregates together. Whereas, in Asphalt road bitumen which is a sticky and dark crude oil substance that holds fine aggregates together.
- Concrete road’s durability and life span is greater than the Asphalt Road.
- The initial cost of a concrete road is higher than the Asphalt road.
- The maintenance of concrete roads is less but Asphalt Road is much more easily repaired or maintained.
- Oil leaks are damaging to Asphalt roads and not for the Concrete Roads.
- Asphalt roads are more prone to damage compared to Concrete Roads.
- Asphalt roads are said to be more skid resistant.
- Long term evaluation of concrete roads in terms of finance comes out cheaper than Asphalt Roads.
Conclusion
Concrete roads have numerous advantages in terms durability, life span and more. The only drawback is high initial cost but the long term cost is cheaper as it requires less maintenance and the life-span is also way more than other types of roads. If the concrete is properly batched, mixed, placed and proper curing is done then it will be free from any cracking and warping issues. Seeing it’s advantages and disadvantages and comparing it to Asphalt roads, concrete roads can be a good choice to consider.
