Most substances used in households and industry are dispersed systems (solid particles or droplets suspended throughout another substance) or solutions, where mixing takes place at the molecular level. Examples of suspensions are mortar mixture, paint, white glue or bitumen emulsion used for waterproofing works.
What is bitumen emulsion?
Bitumen is a hydrocarbon resin (derived from petroleum) which solidifies in the air at normal temperatures, forming a watertight flexible film. The mixture of bitumen with sand and gravel is used for roadworks (known as asphalt). Aqueous bitumen emulsion is widely used for waterproofing foundations, roofs and sealing joints between concrete blocks in construction.
Types of bitumen emulsion and production formulas
Emulsions are divided by two parameters
- Settling rate (water separation, forming of bituminous film):
– rapid setting: immediately within 5 minutes of application;
– middle setting: within 5-10 minutes when applied on rubble, concrete, etc;
– slow setting: more than 10 minutes, also known as “ultra stable”;
- type of emulsifier added to stabilize the emulsion: anionic (alkali salt) and cationic (acid soap). Emulsifier solution for bitumen emulsions are prepared directly before heating and mixing water with bitumen.
Preparation and dispensing of bitumen emulsion
The primary methods used for production of disperse systems are mechanical and acoustic. In the mechanical process the emulsion is formed by mixing bitumen and water solution by a rotor rotating 0.2-0.6 mm from a stator. These machines are known as colloid mills and are divided into two types:
- batch mixers, where bitumen and emulsifier are fed into a dispensing mechanism first, then heated and mixed;
- continuous mixers (dispersers), rotary or plunger. Water and emulsifier components connect in a flow line, where they chemically react with acid. The colloid mill processes the solution and heated bitumen that are mixed into the finished product. After cooling down, the bitumen emulsion is dispensed into containers.
Advantages of dispersers:
- continuous operation (until the flow of raw materials stops);
- high productivity without dispensing devices and additional pumps for them;
- ability to quickly switch from one emulsion to another.