Bitumen emulsion is a mixture of water & bitumen. 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 bitumen into minute particles and keeps it dispersed in suspension.
Therefore we can say that a bitumen emulsion is a liquid product consisting of three things, (i.e. water + Emulsion + Bitumen) where droplets of bitumen are suspended in water.
Production – How is it Manufactured?
The production of bitumen emulsion consists of two primary steps.
In the 1st step water is mixed with appropriate emulsifying agent and other chemicals. The type of emulsifier to be used depends upon the ionic nature of the mix.
The 2nd step is the addition of bitumen with the water-emulsifier mix. This is done in a colloidal mill. Depending upon the use, the amount of bitumen to be added with water may range from 40 to 70%. Water-emulsifier mix and bitumen is pumped to a colloidal mill. The colloidal mill breaks the bitumen into tiny droplets. The average diameter of these tiny droplets of bitumen is about 2 micron. Here comes the role of emulsifier. Emulsifier creates a coating of surface charge around the bitumen droplets that helps to keep these tiny particles away from each other. It also helps to keep these particles in a dispersed form.
After completion of the 2nd step, the bitumen emulsion is pumped into storage tank.
Classification – How to Classify Bitumen Emulsion?
There are two different ways to classify bitumen emulsion, as given below.
Based on surface charge
Based on setting time
BASED ON SURFACE CHARGE
Depending upon the type of surface charge, bitumen emulsions are primarily classified into the following two types.
Anionic Bitumen Emulsion
Cationic Bitumen Emulsion
In case of an anionic bitumen emulsion, bitumen particles are electro-negatively charged, where as for cat-ionic emulsions, bitumen particles are electro-positively charged. Now days cationic bitumen emulsion are most commonly used.
The choice of bitumen emulsion (i.e. whether anionic or cationic) to be used depends upon the mineral composition of aggregate used for construction. In case of silica rich aggregates, the surface of the aggregates are electro-negatively charged. Therefore a cationic emulsion should be used. This will help better spreading and binding of bitumen with aggregates.
BASED ON SETTING TIME
When bitumen emulsions are applied on aggregates, water starts to evaporate causing separation of bitumen from water. And then bitumen spreads on the surface of the aggregate and acts as a binding material and slowly attains its strength.
Depending upon the speed at which water evaporates and bitumen particles separate from water, it is classified into following 3 types.
Rapid Setting Emulsion (RS)
Medium Setting Emulsion (MS)
Slow Setting Emulsion (SS)
Note: Here the word “setting” should not mean attainment of strength; rather it means the time taken by the bitumen to separate from water.
In case of rapid setting emulsion, bitumen is intended to break rapidly. Therefore this type of emulsion sets and cures rapidly.
Medium setting emulsions do not break spontaneously when applied on aggregates. But the process of breaking starts when fine dusts of minerals are mixed with aggregate-emulsion mix.
Slow setting emulsions are manufactured by using special type of emulsifier, which makes the setting process very slow. These types of emulsion are relatively stable.
Factors Affecting Setting of Emulsions
The following factors affect the setting & curing of bitumen emulsion mixes.
Water absorption of aggregate
Surface texture of aggregate
Amount of mineral dust in aggregate
Mineral composition of aggregate
Intensity of charge on aggregate surface
Type of emulsifier used & its quantity
Atmospheric condition, climatic conditions
Wind velocity & altitude
Drainage conditions at construction site
Applications – What are the Uses of Bitumen Emulsions?
Emulsions are used in bituminous road construction work. They are especially helpful for maintenance and patch repair works.
Emulsion can be used in wet weather even when it is raining.
Also emulsions have been used in soil stabilization, particularly for stabilization of sands in desert areas.
A rapid setting type emulsion is suitable for surface dressing and penetration macadam type of construction.
Medium setting type is used for premixing with coarse aggregates.
In case of fine aggregates, the surface area of aggregate is more and as a result long duration of time is required to mix the emulsion. Therefore slow setting emulsion is preferred which gives sufficient time for uniform blending of the mix.
What are the Advantages & Limitations of Bitumen Emulsion?
ADVANTAGES – WHY TO USE BITUMEN EMULSIONS?
The strength properties of bitumen are preserved in emulsion mixes since emulsions do not need hot mixing. Generally cold mixing or just slightly warming the ingredients of the emulsion mix are done for construction of pavements.
Emulsion can be used in wet weather even when it is raining.
Emulsions possess anti-stripping properties.
Emulsions with lower viscosity or thinner consistency improve spreadability and allows better coating of the bitumen on the surface of aggregate.
There is no wastage during laying and storage.
Since emulsions are water based, there is less effect on the environment.
It is the least energy intensive of all construction material: there is no need to heat.
No one type of emulsion is suitable for every work. it depends upon whether the aggregate is acidic or basic in nature..
The setting time may vary depending on the air temperature, wind velocity and type of emulsion.
There is a wide range of curing time; a suitable emulsion mix needs to be designed for a particular need, i.e. we need to determine for each case, the optimum quantity of emulsion based on zone, type of emulsion, mix grade and desired mechanical properties
It has limited storage time (ranging from few days to six months)