Bitumen emulsion is a binding material, consisting of water and bitumen. Emulsion is a disperse system, with particles of bitumen dispersed in water. The main task is to keep bitumen microparticles from coalescing, which maintains physicochemical properties of the emulsion and its quality. This stability is achieved with special emulsifiers.
Bitumen emulsions are transportable, easily stored materials. They are kept in the storage warehouses in cylindrical containers at plus temperatures for up to several months, without losing their properties.
All stabilizers/emulsifiers are supplied at exact doses, since they strongly affect characteristics of the finished product. Latex polymers are ideal modifiers and are added to bitumen emulsion to improve properties. Solvents increase the viscosity and emulsifying properties.
Bitumen from different manufacturers may differ in their physico-chemical properties. This also needs to be taken into consideration when preparing bitumen emulsions.
Anionic and cationic bitumen emulsion
There are two main types of bitumen emulsions: cationic and anionic.
The main difference between them is that the former, anionic emulsions are less sensitive to the presence of minerals or other materials in water; and actively interact with them.
According to the type of setting, and the process of mixing with mineral materials, bitumen emulsions are divided into 3 classes.
- rapid settling RS type (RS-1 , RS-2 anionic, CRS-1, CRS-2 cationic)
- medium settling MS type (MS-2 anionic, CMS-2 cationic)
- slow settling SS type(SS-1, SS-1h anionic, CSS-1, CSS-1h cationic)
Rapid setting emulsions that are used for the surface treatment of freshly laid asphalt concrete act as primers. Medium setting emulsions are used for binding loose building materials together (crushed stone, gravel). of a Slow setting emulsions are stable and are used for mixing mineral materials and processing before setting.
Bitumen binding characteristics are improved with the help of various additives.
One of the additives is acetic acid. Recently, it has been replaced by phosphoric acid as acetic acid promotes the formation of corrosion on metal parts of colloidal mills.
Potassium chloride serves as a catalyst. This salt increases the viscosity, improves the emulsifiers properties and can also minimize emulsion shrinkage.
Latex often acts as a polymer additive, which improves the performance of bitumen emulsions. For best results, it is added into a liquid phase.
A long-term storage, transportation and freezing can reduce the qualitative characteristics of emulsions, due to chemical processes occurring: shrinking, flocculation and coalescence.
Shrinking occurs when bitumen loses properties it acquired during emulsification. Flocculation is manifested in the accumulation of bitumen particles in conglomerates. Such emulsion is enough to mix before using in production. Coalescence means the formation of large compounds from fine bituminous particles, and usually occurs during the breakdown of emulsions.
Bitumen Emulsion Preparation and Applications
Bitumen is a binding material commonly used in road repairs and construction. At room temperature bitumen is highly viscous and cannot be used. To make the material usable, there are several methods:
- Heating to 100-200 ⁰С;
- Mixing with a solvent;
- Using it as part of an emulsion.
Bitumen emulsion is a construction material, which consists of bitumen particles in water. In other words, it is bitumen dispersed in water. Emulsion may be prepared using bitumen of varying viscosities and using various additives (polymers, surfactants and solvents).
Depending on the surfactant used, bitumen emulsions can be anionic or cationic.
In terms of stability when mixed with mineral materials, bitumen can be fast, medium or slow breaking.
Mixing of cationic and anionic bitumen emulsion leads to charge neutralization, breaking the emulsion. Therefore, before switching to the other emulsion type, storage tanks are emptied and cleaned from the remaining material.
Physical and chemical properties of bitumen emulsions depend on the amounts of bitumen, emulsifier and acid (or base) used. The main role in production of emulsion with the desired properties is played by correct selection of the emulsifier. There are many chemicals in the market now, but only several are commonly used to to econmical and process limitations.
Cationic emulsion are most widely used: they are more versatile and ensure good adhesion of the binder to the various mineral surfaces.
Compared with straight bitumen, emulsion have the following advantages:
- Bitumen economy (up to 30-50%);
- Reduction of energy costs (by 25-40%);
- Capability for application on wet solid surfaces;
- Complete adhesion to the road base;
- Flexibility of road construction planning and operations;
- Fire safety;
- Environmental safety.
Bitumen emulsion production units can be batch or continuously operated. Comparing the two types, the latter allows to:
- Quickly switch from one type of emulsion to another;
- Reduce labor and operation costs;
- Improve efficiency by using portioning devices.
Colloid mill is the one most important part of bitumen emulsion machines. Some of the characteristics of the mills, which influence the quality of the emulsion, are:
- The gap between the rotor and the stator of the mill (can be fixed or adjustable);
- Rotor rpm;
Production of Bitumen Emulsion
Bitumen emulsions are produced on bitumen mills. Generally they produce 5 – 40 tons/hour of the finished product. A smaller laboratory colloid mill is used in developing new emulsion recipes, and capable of producing up to 300 liters per hour of finished emulsions.
An emulsion is made in several steps:
- bitumen is heated, if necessary, dehydrated and is fed into the mill ;
- water is mixed with additional components (emulsifier, hydrochloric acid, stabilizer, etc.), heated and fed into the mill;
- bitumen is mixed with water/emulsifier solution;
- emulsions transportation to storage places.
The emulsions at the outcome have different viscosities. They depend on the choice of raw materials and the correct dosage of ingredients. An excessive or insufficient amount of bitumen also significantly affects the quality of the final emulsion. A mill breaks bitumen into tiny particles. Here an emulsifier coats bitumen particles keeping them away from each other making the emulsion stable. The final emulsions are all stored separately in storage tanks.
Summarizing the importance of emulsifiers/stabilizers in emulsion preparation, it is important add their precise doses for correct distribution of molecules in dispersed medium.
The lower is the viscosity of bitumen, the better is the emulsion. In the vast majority of applications bitumen emulsion is heated, but not exceeding 80-90 C, otherwise it is destroyed as higher temperatures evaporate water out of emulsion. Boiling in such cases is unacceptable!
Emulsion can not be overheated and cannot be frozen. In this case, heaters are used for heating and storage.
Equipment for Production of Bitumen Emulsions
A colloid mill is specifically designed for production of bitumen emulsions. It can be set for a continuous or cyclic operation. In the first case, emulsifiers are mixed with water and bitumen is continuously supplied into the water phase. In the second case, water and bitumen are mixed first, and the additives are added later in the process .
The mode of emulsion production is determined, taking into account that a continuous operation is automatic and a cyclic production is done by an operator of a colloid mill.
Advantages of Bitumen Emulsions
Economically, technologically and environmentally bitumen emulsion proved to be a great solution. In addition to saving money on power consumption by one and a half time, production of emulsion requires 30-40% less bitumen than in hot bitumen application.
Also the emulsions produced on GlobeCore equipment are environmentally friendly and do not need high temperature for production or application. As it is a well-known fact that the environment suffers from carcinogenic emissions formed as a result of petroleum products the breakdown.
Technology of Use
In a percentage comparison, the bitumen content in asphalt concrete is 5% and 95% aggregates. The amount of bitumen directly affects the quality of asphalt surface, as it improves the binding between aggregates.
Bitumen emulsions (dispersed bitumen molecules in aqueous medium), are viscous substances of dark brown color. They are used as binders in the repair and construction of roads.
Depending on the class and type, road emulsions can be used for different aggregate, different setting time and different nature of work.
Properties of road emulsions
Bitumen emulsions are obtained through:
The 1st method s used more often as it is more efficient and less expensive. Dispersing is the process of grinding a solid or liquid material in liquid medium. The condensation method is used with two aqueous solutions by lowering the temperature to a critical value and lower. The technology is chosen according to type of emulsifier used in production and the class of emulsion in the outcome.
Bitumen emulsions are produced using three methods: mechanical, hydrodynamic and chemical. The first is the most popular among road workers.
Four main properties of bitumen emulsion:
- viscosity, measured at 20 C. Viscosity of bitumen affects its processing.
- stability to decomposition during transportation and long-term storage. A good stability is ensured by a proper quality of components, that were designed for specific properties.
- compliance with industry standards
- structural integrity of the finished product during operation, preventing water losses and re-emulsification. This phenomenon is typical for substances that are saturated with emulsifiers.
The properties above determine the quality of bitumen emulsion.