This type of bitumen forms a two-phase system with two immiscible liquids.
One of them is dispersed as fine globules within the other liquid. When discrete globules of bitumen are dispersed in a continuous form of water, bitumen emulsion is formed.
The emulsion consists of bitumen globules held in suspension in water by the electrostatic charge provided by emulsifying agents. The emulsion doesn’t require heating before application, so it is energy-saving.
An emulsifier having a long hydrocarbon chain with either a cationic or anionic ending is used for dispersing the bitumen globules. This emulsifier provides an electrochemical environment. The ionic part of the chain has an affinity towards water and the bitumen is attracted by the hydrocarbon part.
The emulsions can be cationic (positive charge) or anionic (negatively charged). The globules of the same charge hence repel each other, making the whole system stable. To facilitate adhesion with the aggregates (that are negatively charged), cationic emulsions are more preferred.
Slow Setting Emulsion
Bitumen emulsion, a special type of emulsifier, is used to slow the process of water evaporation. These types of emulsifier are relatively stable.
SS-1 : Slow Setting Emulsion – 1
SS-2 : Slow Setting Emulsion – 2
Medium Setting Emulsion
Bitumen emulsion doesn’t break as when applied on aggregate. The process of evaporation starts when the fine dust of minerals are mixed with the aggregate emulsion mix.
MS : Medium Setting
Rapid Setting Emulsion
Bitumen emulsion breaks down rapidly as it comes with contact with aggregate helping in fast setting and rapid curing.
RS-1 : Rapid Setting Emulsion – 1
RS-2 : Rapid Setting Emulsion – 2
Types of bitumen emulsifiers and their quantity
Water evaporation rate
Bitumen globules size
The emulsions are applied by using sprays. For this viscosity is a primary concern. With the increase of bitumen content, the mixture becomes more viscous. This is found to be sensitive when the amount exceeds 60%.