What is Bitumen Emulsion?
Bitumen emulsion is a mixture of fine droplets of bitumen and water. But as the bitumen is a petroleum product it doesn’t mix with water and as it is sticky in nature, it doesn’t easily gets disintegrated into fine droplets. To overcome this problem an emulsifier is used.
Emulsifier can be defined as a surface-active agent. Emulsifier keeps the bitumen in its fine droplet state by disallowing it to mix with other droplets. As the droplets are very fine they suspend in water.
“Therefore, bitumen emulsion is a dispersed liquid consisting of three products, i.e. water, bitumen and emulsion”.
Manufacture of Bitumen Emulsion
The production of bitumen emulsion takes place in two simple steps:
Firstly, the water is mixed with the appropriate emulsifier and other chemical agents. The choice of emulsifier depends upon its ionic nature of the mix.
Now water emulsifier mix is added with bitumen in a colloidal mill. The amount of bituminous to be added depends upon the nature of use of bitumen emulsion. If it is used for important works then between percent can range up to 60 to 70%.
The average range of bitumen mixed is from 40 to 70%.
The colloidal mill breaks down the bitumen into very tiny droplets. Average size of bitumen droplet is about 2 Micron. But the droplets try to join them self with each other and make it settle down.
But the emulsifier added creates a coating of surface charge around every drop droplet of the bitumen that helps to keep away from each other on the other hand it is also it also keeps the droplet in dispersed and suspended form.
The mix received from the colloidal mill is stored in the storage tanks and used as per requirement.
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 bitumen 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
Based upon the type of surface charge, they are divided into 2 types,
- Anionic Bitumen Emulsion
- Cationic Bitumen Emulsion
In anionic bitumen emulsion, the tiny droplets of bitumen are electronegative recharged. In Cationic bitumen emulsion the tiny droplets of bitumen are electro positively charged.
The average and commonly used between 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 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.
Advantages and Limitations of Bitumen Emulsion
Advantages and Uses of Bitumen Emulsions are:
- Bitumen emulsion 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.
- Is ecofriendly as it is water based.
- Bitumen emulation is also 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 emulsion 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.
Limitations of Bitumen Emulsion
- Storage time of bitumen emulsion ranges from few days to 6 months depending upon the percentage of Bitumen added while production.
- Setting time may vary due to temperature, wind and type of emulsion.
- Not a single type of bitumen emulsion can be used for all works it depends upon the aggregate type setting time nature of work etc.