General Description of Bitumen Emulsion
Bitumen is the oldest known thermoplastic material in use today. Consequently, its usefulness and appeal derive from its simple thermoplastic property of being a thin liquid at high temperature and a virtual solid at ambient temperature.
Temperature and Viscosity
For most applications, bitumen is used in the temperature range of 140 to 230°C at a viscosity of around 200 cSt (20 Pa.s). Therefore, these conditions allow rapid throughput from hot bulk bitumen delivery through to final use without reheating.
Application Limitations
There are limitations to the coating film thickness achievable using hot-applied techniques. In some cases, it is necessary to apply bitumen at a lower temperature and/or viscosity. This is due to process requirements, application techniques, safety concerns, environmental factors, or final product properties.
Modification Methods
The two primary methods used to modify bitumen properties are:
- Emulsification with water
- Dilution with hydrocarbon solvents
As a result, these methods enable the bitumen to be applied cold, up to about 80°C for emulsions or up to about 150°C for cutbacks, depending on dilution and solvent used.
Bitumen Emulsion Structure
Bitumen emulsion is a heterogeneous, two-phase system consisting of two immiscible liquids: bitumen and water, stabilized by a third component, the emulsifier. Consequently, this structure enhances its applicability in various conditions.
Types of Bitumen Emulsions
- Cationic emulsions
- Anionic emulsions
- Nonionic emulsions
Each type behaves differently based on its charge and interaction with aggregates.
Production Method of Bitumen Emulsion
Bitumen emulsions have been developed and exponentially increased since their creation in 1900. In fact, currently, they account for approximately 20% of global bitumen use.
Manufacturing Process
Bitumen emulsions are an oil-in-water (O/W) dispersion, where bitumen particles are dispersed in water and stabilized with surfactants (surface-active agents). As a result, they are primarily used for tack coats between hot mix asphalt layers, prime coats for thin hot mix surfacing layers, or chip seal pavements.
Chemical Composition
Bitumen emulsions mainly consist of bitumen and water. They come in different grades, but typically, they contain between 55% and 75% bitumen. Additionally, emulsions contain 0.1%-2% of an emulsifier or “soap” that stabilizes the emulsion. Moreover, minor amounts of other additives may be included.
Classification of Bitumen Emulsions
- Rapid-Setting (RS)
- Medium-Setting (MS)
- Slow-Setting (SS)
- Quick-Setting (QS) & Micro-Surfacing
These classifications determine the speed at which emulsions break and interact with aggregates.
Stability Factors
- Type and quantity of emulsifier
- Water evaporation rate
- Bitumen content
- Bitumen globule size
- Mechanical forces
Due to these factors, the stability of emulsions varies significantly across applications.
Setting Time Categories
When bitumen emulsions are applied to aggregates, water starts to evaporate, causing the bitumen to separate and spread on the aggregate surface, acting as a binding material. Consequently, the setting speed classifies emulsions into:
- Rapid Setting (RS)
- Medium Setting (MS)
- Slow Setting (SS)
Naming and Modifications
- RS = Rapid Set
- SS = Slow Set
- QS = Quick Set
- MS = Medium Set
- HFRS = High Float Rapid Set
- C = Cationic
- AE = Anionic Emulsion
These names help classify emulsions based on their properties.
Polymer Modifications
- Polymers such as SBS & SBR improve flexibility and durability
- Enhance service life and early chip retention
Consequently, polymer modifications significantly enhance bitumen performance in various applications.
Classification of Bitumen Emulsions by Charge and Setting Time
| Slow |
Medium |
Rapid |
Time of Setting / Charge |
| CSS |
CMS |
CRS |
Positive Charge |
| ASS |
AMS |
ARS |
Negative Charge |
