Emulsion In Road Construction

Emulsion In Road Construction

Bitumen has been traditionally used as the principal road construction material. There are different forms of bitumen used in specific applications. In recent years, however, the use of bitumen emulsion has gained considerable focus over other forms of bitumen due to its many desirable properties. 

Emulsion in road construction – what does it mean and why is it important?

An emulsion, as we know, is a mixture of two or more immiscible liquids that results in higher effectiveness, ease of usage, and more economical use of the active ingredient. Emulsion in road construction refers to bitumen emulsion, which is composed of bitumen water and an emulsifying agent.   

Bitumen emulsion is a liquid substance that combines bitumen and water. However, because bitumen is an oily product that does not mix with water, an emulsifier is added to the water before mixing. The emulsifier acts as a surface-active agent, helping to break down bitumen into tiny droplets that are suspended and disseminated.

Bitumen emulsions (also known as asphalt emulsions) are generally used for tack coats between hot mix asphalt layers, as prime coats for thin hot mix surface layers, or for seal coats for pavements.

Bitumen emulsions provide a wide range of qualities that are not available with other paving and maintenance materials. This makes them extremely adaptable and appropriate for a wide range of uses.

Unlike other forms of bitumen, the emulsions used in road construction don’t require the use of a petroleum solvent to become liquid, which saves energy. Moreover, they are not to be hot-mixed, which saves even more energy. 

All these signify the environmental benefits of bitumen emulsions. Their use produces minimal to no hydrocarbon emissions, making them an environmentally favorable solution for paving and maintenance work. Bitumen emulsions also have the advantage of being easier to clean up after use due to their water-based composition. Together, these benefits make bitumen emulsions a popular option for any project that involves new pavement or the maintenance of an existing one. 

All in all, bitumen emulsions are being widely used in road construction and maintenance because they are more efficient, sustainable, safe, and environment-friendly alternatives to pure bitumen, as well as providing superior performance at a reduced cost.

The chemistry of bitumen emulsion

Bitumen emulsion is a suspension of tiny bitumen globules (ranging in diameter from 1 to 10 μm) in water that includes an emulsifier. The emulsifier works by transferring an electrical charge to the surface of the bitumen globules, preventing them from coalescing.

By weight, the emulsions may comprise 40% to 80% bitumen. Because the emulsions are far less viscous than actual bitumen, they may be applied at lower temperatures. As a result, emulsion-based procedures require less energy and produce fewer emissions than processes that use hot mixing, cutback bitumen, etc.

Generally, bitumen emulsions look like a thick brown liquid when initially poured, but as they settle and bind the surrounding material (e.g., aggregates), the color changes from brown to black. As the water evaporates, the emulsion becomes increasingly similar to pure asphalt cement. The time required to break and set is determined by the type of emulsion, the application rate, the temperature of the surface to which it is applied, and the climatic circumstances.

Why using bitumen emulsion is more advantageous than regular bitumen

Bitumen emulsions are better substitutes for bitumen for the construction and maintenance of roads on several grounds, such as:  

  1. Easy application

Bitumen emulsion is more efficient and simpler to handle and apply than regular bitumen. Its reduced viscosity and ability to be used at lower temperatures help to avoid construction delays.

  1. Minimal environmental impact 

Bitumen emulsion is a more environmentally friendly option for road building because it is water-based and produces fewer toxic gasses and fumes when applied. Its production also uses less energy; therefore, its environmental impact is further minimized.

  1. Improved road performance 

Bitumen emulsion is a more dependable and adaptable material to ensure better road performance since it is more resistant to damage from water and can also be applied more readily in colder climates.

  1. Improved safety

The safety of workers is increased because bitumen emulsion application doesn’t require heating or other high-temperature procedures. This lowers the possibility of worker accidents and injuries.

  1. Lower total cost 

The use of bitumen emulsion results in lower total cost of road construction projects since it is less expensive to make, transport, and apply than regular bitumen.

What are the different types of bitumen emulsions used in road construction?

Bitumen emulsions are categorized into two main types:

  1. Based on the surface charge
  2. Based on setting time

Based on the surface charge 

The emulsifiers used in bitumen emulsion are ionic types that create a surface charge. As a result, bitumen emulsifiers can be categorized into two types depending on their surface charge:

  1. Anionic Bitumen Emulsion
  2. Cationic Bitumen Emulsion

Anionic bitumen emulsions include negatively charged bitumen particles, whereas cat-ionic bitumen emulsions contain positively charged bitumen particles. The cationic bitumen emulsion is the most often used today.

The mineral content of the construction aggregates influences whether an anionic or cationic bitumen emulsion should be utilized. For example, if silica-rich pebbles are applied, the surface will be electronegative, and the bitumen emulsion will need to be cationic. This will help bitumen spread and bind with aggregates.

Based on setting time

When bitumen emulsions are sprayed upon aggregates, water starts to evaporate. This causes bitumen to be released from the water and settle onto the aggregate bed, where it gradually hardens.

So, in terms of the rate at which water evaporates and bitumen particles separate from water, bitumen emulsion is classified into the following categories:

  1. Rapid Setting (RS)
  2. Medium Setting (MS)
  3. Slow Setting (SS)

How are bitumen emulsions applied?

Although bitumen emulsions are typically sprayed cold, they can be heated to 60ºC to increase fluidity. The fundamental advantage of using bitumen emulsion is its ability to be applied cold, although the product’s aqueous phase defines its slow or fast-breaking property. Followings are the main application areas of bitumen emulsion:

Tack coat 

A tack coat is a film of bitumen applied between the two bituminous layers in the road construction process. Applying one layer of bitumen emulsion as a tack coat between the two bituminous layers of surface courses aids in the bonding of the two layers and prevents them from slipping. This application requires a Cationic Rapid Set (CRS) or Cationic Slow Set (CSS) bitumen emulsion. A tack coat is also applied to the surface of an old, worn-out road before covering it with a new layer of asphalt. 

Prime coat 

 Bitumen emulsions are also used as prime coats due to their low viscous state to bind the granular aggregates of the base course. The good fluidity of bitumen emulsions helps them penetrate the base layer and create a light, protective bituminous layer on the base course, which helps in good bonding between the non-bituminous base course and the surface course made of asphalt concrete. The prime coat also prevents moisture ingress and ensures a stable, adherent surface layer. 

Seal coat  

Bitumen emulsions as seal coats are applied on the surface layer to protect against moisture and provide a long-lasting barrier. Seal coats also make the road more skid-resistant yet keep the surface smoother. 

Also, road emulsions are often used in conjunction with aggregator materials of varied sizes to maintain the proper rolling resistance. For example, in a double surface treatment, 3/8″ and 3/4″ crushed quarry materials with broken faces and less than 25% wear are commonly employed.