Bitumen Emulsion Description
Bitumen emulsion is a mixture of water & asphaltum. Hey wait, we know that bitumen is a oil product and it cannot be mixed with water. That is why we add an emulsifier (a surface active agent) with water before adding bitumen. Addition of emulsifier with water facilitates breaking of asphaltum into minute particles and keeps it dispersed in suspension.Therefore we can say that bitumen emulsions are a liquid product consisting of three things, (i.e. water + Emulsion + Asphaltum) where droplets of Asphaltum are suspended in water.
Bitumen emulsions are usually dispersions of minute droplets of bitumen in water and are examples of oil-in-water emulsions.
The bitumen content can be varied to suit different requirements and is typically between 30% and 70%. The primary objective of emulsifying bitumen is to obtain a product that can be used without the heating normally required when using cutbacks and paving grade bitumen. In the manufacture of bitumen emulsions, hot bitumen is sheared rapidly in water containing an emulsifying chemical (emulsifier). This produces very small particles of bitumen (the dispersed phase) dispersed in water (the continuous phase). The bitumen particles are stabilised in suspension and do not readily coalesce due to the presence of the emulsifier, which is concentrated on the surface of the bitumen particles. During application, the water in a bitumen emulsion is either lost by evaporation, or it may separate from the asphalt because of the chemical nature of the surface to which the emulsion is applied. This process is referred to as breaking. Because Asphaltum has a density only slightly higher than water, sedimentation of the Asphaltum droplets in an emulsion during storage is very slow. Emulsions can usually be regenerated after long storage times by gentle stirring to redisperse the bitumen droplets.
Composition and Different Types of Bitumen Emulsion
The bitumen emulsion is classified into two types:
1- Based on Setting Time
When the bitumen emulsion is applied on the aggregate for the road works the water evaporates leaving behind the asphalt droplets. These droplets spread on the aggregate and bind with each other and gains strength eventually.
Based upon the time taken by the vitamin emulsion to evaporate the water and between particles to separate from water, bitumen emulsion is further classified into 3 types based on setting time:
a) Slow setting emulsion
In this type of emulsion, a special type of emulsifier is used to slow the process of water evaporation. This type of emulsifier are relatively stable.
b) Medium setting emulsion
This type of bitumen emulsion doesn’t break as when applied on aggregate. The process of evaporation starts when the fine dust of mineral are mixed with the aggregate emulsion mix.
c) Rapid setting emulsion
This type of bitumen emulsion breaks down rapidly as it comes with contact with aggregate helping in fast setting and rapid curing.
2- Based on Surface Charge
Bitumen emulsion is a combination of water and asphalt. As the mixture of water and oily products quickly separate, a third component is normally added to the mixture, in order to make it more stable.
Known as an emulsifier, this third component is used for making a mixture of water and oil dispersed in each other. In addition to their ability to reduce the tension between oil and water molecules, emulsifiers have an electronic charge that affects the molecules of emulsion and lead to the categorization of it into Cationic and Anionic.
– Anionic Bitumen Emulsion
– Cationic Bitumen Emulsion
In anionic bitumen emulsion, the tiny droplets of bitumen are electronegatively recharged. In Cationic bitumen emulsion, the tiny droplets of bitumen are electro positively charged.
The average and commonly used emulsions is cationic between emulsions. Selection of positive or negative recharge between emulsions depends upon the mineral composition of aggregate on which it is used
Ex: In the case of silica-rich aggregates the surface of silica is aggregate is positively charged therefore cationic bitumen emulsion is used which helps in better spreading and binding of bitumen with aggregates.
The electronic charge of BE decides on what kind of surface it should be used. Some aggregates (such as marble aggregates) mix better with anionic bitumen emulsion and some others are a better solution to cationic bitumen emulsion (such as granite aggregates).
Both cationic and anionic bitumen emulsions are categorized according to the setting time. Look at the table below to find the various categories of bitumen emulsion and their globally standard names.
Bitumen Emulsion Applications
Emulsion Bitumens primarily used for tack coats for use in between hot mix asphalt layers and prime coats for thin hot mix surfacing layers or a chip seal pavements. Each application places particular demands on the emulsion. There is a considerable amount of variation between countries on the choice of emulsion for each application, but the table summarizes the most common practice. Anionic emulsions are hardly used outside North America for road construction but may be used for some industrial coatings.
– It can be used in damp environment on wet aggregates
– Road repair work can be carried out in minimum time
– Provides better tack coat with better workable conditions
– It can be used in any season
– Since heating is not required it can’t pollute air
– Long storage stability in clean containers/Tanks
Advantages and Uses of Bitumen Emulsions are:
- used extensively in bituminous road construction. Other than this they are used for maintenance and repair work.
- Emulsions can be used in wet weather even if it is raining.
- it Is ecofriendly as it is water based.
- used in soil stabilization in desert areas.
- It doesn’t need extra heat while placing.
- There is no wastage in placing and laying of bitumen.
- They possess anti-stripping properties.
- Rapid setting type of emulsion are used in surface of roads.
- Medium setting type of emulsion are used in premixing of bitumen and coarse aggregate.
- Slow setting type of emulsion are used with fine aggregates as the surface area is large and requires time for uniform mixing.