Bitumen Road Construction : Materials, Design, Construction Techniques
Bitumen roads are the most commonly found in India. Rural, urban, mountains, or deserts, the black or blue ribbons connect every nook and corner of the country. In this blog, we’ll look at the features and construction of bitumen roads in detail.
What is bitumen road?
Bitumen is a black, sticky, and very viscous liquid that is a semi-solid form of petroleum. When combined with other aggregates such as sand, gravel, or crushed stone, it forms a robust and flexible surface suited for road construction.
Bituminous road, often known as asphalt road, is a type of road construction that uses bitumen as a binding agent to hold aggregates together.
Bituminous roads provide various advantages, including excellent water and weather resistance, and smooth riding surfaces, and can be constructed or repaired quickly. They do, however, require periodic maintenance and resurfacing to remain in good shape as a result of traffic and weather.
Bitumen road construction
The construction techniques for bituminous roads vary depending on factors such as traffic volume and climate conditions. However, the general process of constructing a new bitumen road involves preparing the subgrade and the road layers. The subgrade is the foundation of the road structure, and road layers consist of main layers and sublayers.
The main layers are the surface course, base course, and sub-base course. The sub-layers that are placed between the main layers to stick them together are tack coat, binder course, and prime coat. In addition, protective asphalts are used to protect the surface course from damage. Let’s look at their preparation.
Subgrade preparation:
The subgrade which is the foundation of a bitumen road, ensures proper drainage and stability. It is made of either natural dirt or a constructed base. The subgrade, which supports all subsequent layers, must be correctly compacted. This layer must be properly compacted to avoid settling and distortion due to vehicle and road weight.
Sub-base preparation:
The sub-base is the layer that comes after subgrade and before the base course, serves as a transition between the two. It is usually made from recyclable resources such as gravel or crushed stone. The sub-base increases load capacity and helps to evenly distribute loads. Proper compaction and thickness are required to maintain stability and prevent subgrade dirt from combining with the top layers.
Base course preparation:
The base course, also known as the base layer, rests above the sub-base. This layer is intended to improve the road’s load-carrying performance and offer additional structural support. It is typically made from stronger materials such as crushed stone, densely graded aggregate, or stabilised materials. The base course is critical for distributing traffic loads, preventing rutting, and promoting even weight distribution.
Binder course preparation:
As implied by its name, a binder course binds the layers above and below. It is made of a bitumen mixture with coarser particles than the surface course. Also uses bitumen emulsion or hot mix asphalt binder. The binder course improves the road’s strength, flexibility, and ability to withstand heavy traffic loads. It also works as a moisture barrier, preventing water from harming the sublayers.
Surface layer preparation:
The uppermost layer of the bitumen road, known as the surface course, comes into close contact with moving cars. This layer is designed to offer a durable, smooth, and skid-resistant driving surface. It is composed of a premium bituminous mixture combined with smaller particles. The surface course is responsible for ensuring that driving is aesthetically pleasing and comfortable, as well as providing weather protection.
What are the different types of bitumen used for road construction?
Following are the four different types of bitumen used for road construction:
Cutback bitumen:
Cutback bitumen is a type of binder made by blending (mixing) penetration grade bitumen with a hydrocarbon solvent, such as paraffin or mineral turpentine. When the solvent evaporates, the binder returns to its original penetration grade, binding the particles together.
Bitumen Emulsion:
Bitumen emulsion is a liquid form of bitumen with C. Ordinary bitumen becomes a low viscosity liquid that can be used in a range of applications, including road repair and maintenance, waterproofing, spraying, and so on, after being dispersed in water and treated with an emulsifier.
Emulsions make bitumen easier to handle, store, transport, and apply at low temperatures. This form of bitumen does not require heating before application because it is liquid.
Bituminous Primers:
In bituminous primer, the distillate is absorbed by the road surface where it is applied. As a result, the absorption rate is determined by the surface porosity. Bitumen primers are effective on stabilised surfaces and water-bound macadam base courses. Bituminous primers are typically created at road locations by combining penetrating bitumen with petroleum distillate.
Bitumen Modifier:
Certain additives, or combinations of additives known as bitumen modifiers, can improve the qualities of bitumen and bituminous blends. Bitumen treated with these modifiers is known as modified bitumen. Polymer modified bitumen (PMB)/crumb rubber modified bitumen (CRMB) should only be used in wearing courses due to harsh weather conditions.
FAQ
Why is bitumen used in road construction?
Bitumen’s particular qualities make it an excellent binding agent for aggregates used in road building, guaranteeing that the road is resilient and long-lasting, capable of withstanding heavy traffic and adverse weather conditions.
Which road is better, concrete or bitumen?
The initial cost of a bituminous road is much less than concrete road, but the running cost is higher due to the frequency of maintenance and repair compared to a concrete road. Other than the cost, each type has their merits and demerits.
How to calculate bitumen quantity for road?
For a given length of road, the amount of bitumen required depends on its thickness. For a 3.75-metre-wide road, 10 metric tonnes of bitumen are required every kilometre with a carpeting thickness of 20 millimetres. This consists of a surface coat, a wearing coat, and a seal coat.
How to lay a bitumen road?
The bitumen road laying steps are as follows:
- Surface Preparation
- Application of a tuck coat
- Placing of aggregates mixed with bitumen
- Compaction by roller
- Quality check
- Finishing of the surface
How long do bitumen roads last?
The longevity of a bitumen road is determined by a variety of factors, including the quality of the materials used, the road’s design, traffic volume, and climate. In general, a well-built and maintained bitumen road can last for 20 years or more.