BITUMEN EMULSION – WHAT, WHY & HOW?
What is Bitumen Emulsion?
Bitumen Emulsion
Bitumen emulsion is a mixture of water & bitumen. You might have this question in mind that oil and water cannot mix. The answer is that; this is possible by adding an emulsifier (a surface-active agent) with water before bitumen is added to it. Adding emulsifier with water facilitates the breaking of bitumen into minute particles and sustains it dispersed in suspension.
Due to what was mentioned earlier it is correct to say that bitumen emulsion falls in the category of liquid and is constituted of three things, (i.e., water + Emulsion + Bitumen) this is where droplets of bitumen suspend in water.
How is it Manufactured?
The production of bitumen emulsion involves two significant steps.
As the 1st step, they mix the water with the proper emulsifying agent and other chemicals. The ionic nature of the mix is what determines the type of emulsifier to be used.
As the 2nd step, they add bitumen to the water-emulsifier mix. This process takes place in a colloidal mill. Based on the type of use, the amount of bitumen mixed with water may differ from 40 to 70%. Then they introduce the water-emulsifier mix and bitumen to a colloidal mill.
The colloidal mill forces the bitumen in breaking into tiny droplets. The diameter for these tiny droplets is averagely around 2 microns. This is the explanation of how the emulsifier functions in this process. It coats the surface charge surrounding the bitumen droplets that cause these tiny droplets to be kept away from each other. It also always keep them separated.
After the 2nd step is completed, the bitumen emulsion will be introduced into the storage tanks.
Classification – How to Classify Bitumen Emulsion?
There are only two different types of emulsion bitumen, and they classify as follows.
- According to the surface charge
- According to the setting time
BASED ON SURFACE CHARGE
With different types of surface charges, different types are formed, but they primarily are categorized into two groups.
- Anionic Bitumen Emulsion
- Cationic Bitumen Emulsion
If it is anionic bitumen emulsion, then the bitumen particles are charged electro-negatively, cat-ionic emulsions, bitumen particles are charged electro-positively. Nowadays, what is being used mostly is cationic bitumen emulsion.
The choice of bitumen emulsion (both anionic or cationic) is depending upon the mineral composition of aggregate that is used in construction. When silica-rich aggregates, the surface of the aggregates are charged electro-negatively. Based on that, a cationic emulsion should be used. That can assist with better spreading and binding of bitumen with aggregates.
BASED ON SETTING TIME
When we apply bitumen emulsions on aggregates, water starts to vaporize, causing bitumen to separate from water. Also, then bitumen starts to expand on the surface of the aggregate and reacts as a binding material and slowly achieves its strength.
Now based on the level in which water vaporizes and bitumen particles separate from the water, there is another categorization for bitumen; as in the following 3 types.
- Rapid Setting Emulsion (RS)
- Medium Setting Emulsion (MS)
- Slow Setting Emulsion (SS)
Note: what we mean here by saying “setting” doesn’t mean attaining the strength. Instead, it means that it took the bitumen to separate from the water.
In (RS), bitumen tends to break rapidly. So this type of emulsion is appropriate for situations in which it is required to set and cure rapidly.
(MS) Do not break spontaneously when we apply them on aggregates.
However, when the fine dust in the mineral is mixed with the aggregate-emulsion mix, this process of breaking starts.
(SS) Are produced by utilizing a particular type of emulsifier, that can also make the process of setting very slow. Compare to other types These types of emulsion are considered relatively stable.
Factors Affecting Setting of Emulsions
These following factors have an effect on the setting & curing of the bitumen emulsion mixes.
- Water absorption of aggregate
- Surface inclusion of aggregate
- the volume of mineral dust in aggregate
- Aggregate progression
- Mineral composition of aggregate
- The intensity of charge on aggregate surface
- Type of emulsifier used & its quantity
- Atmospheric condition, climatic conditions
- Wind velocity & altitude
- Drainage conditions at the construction site
What are the Uses of Bitumen Emulsions?
- They mostly use them in bituminous road construction work because of being helpful for maintenance and patch repair works.
- Emulsions are easy to use in an unfortunate situation, such as when it is raining.
- Stabilization of the dust is the other Important use of emulsion bitumens, particularly for stabilization of the sands in desert areas.
- A rapid setting type emulsion is very useful for dressing the surface and penetration macadam type of construction.
- Medium setting type is used for premixing with coarse aggregates.
- Whenever fine aggregates, meaning the surface area of aggregate is more and as a result, more time is required to mix the emulsion. Therefore slow-setting emulsion is the primary choice which gives sufficient time for uniform blending of the mix.