Bitumen emulsion (emulsified liquid bitumen) is an artificial building material obtained by mixing in special facilities an aqueous solution of emulsifier and petroleum bitumen. It is a homogenous fluid (consistency of milk) liquid of brown or dark-brown color.
The emulsion is the dispersion (i.e., uniform distribution) of tiny droplets of one liquid in another. Dispersed liquid droplets usually have a diameter of 1 to 100 µm (0.001-0.01 mm).
The peculiarity is that under normal conditions such liquids do not mix with each other (e.g., oil and water). Immediately during mixing these substances can form an emulsion. Still, once the mixing stops, the emulsion quickly loses stability and separates (small drops of one liquid attract each other and eventually form a solid film).
To prevent the process of separation of one substance from another (to give the emulsion stability), emulsifiers (substances that slow down the separation of bitumen and water) are used.
The use of bitumen emulsions in road works
High requirements are imposed on modern materials used in road construction, according to which they must be produced at a lower cost, and at the same time they must have all the necessary list of technical and operational properties to ensure the proper quality and durability of road surfaces. The most common binder used in road construction is petroleum bitumen, which is processed to ensure the necessary characteristics.
Purpose of bitumen emulsions in road construction
The primary purpose of bitumen binders is to reliably bind all the components of mineral mixtures together to ensure the integrity, high strength, and reliability of road surfaces.
In addition, emulsions can be protective when applied over an already completed road surface as part of the surface treatment. Applied in a thin layer, the emulsion protects the asphalt, seals small cracks, and waterproofs the pavement.
Disadvantages of petroleum bitumen for road works
Despite a large number of advantages, bituminous emulsions also have some disadvantages.
One of the most notable is that in the initial stages of decomposition, the material cannot withstand external influences, such as operating loads or adverse climatic factors.
The necessary resistance of coatings to external factors is achieved after a certain period of time, the duration of which depends on the rate of decomposition and emulsion formation.
In addition, the disadvantages of petroleum bitumen include its high viscosity, which complicates the process of applying the material, reduces the quality of the road surface, and leads to unreasonably high consumption of binder. To solve this problem, bitumen is subjected to additional processing.
The following techniques are used:
- Heating. This type of exposure is aimed at obtaining a hot asphalt concrete mixture.
- Mixing with special solvents to liquefy the bituminous binder.
- Emulsification. This involves dispersing bitumen in water through the use of emulsifiers.
The emulsification, in which petroleum bitumen is mixed with a solution of an emulsifier on a water base, results in compositions with the lowest viscosity. The use of such technology makes it possible to create so-called liquid bitumen or bituminous emulsion.
Advantages of bituminous emulsions
The advantages of bitumens produced by emulsification are expressed in a number of unique properties of such materials, including the following:
Low viscosity
Due to sufficiently liquid consistency, bituminous emulsions penetrate even after disintegration into the smallest cracks and pores, effectively filling the voids. This property makes them an ideal choice when carrying out road repairs, pouring crushed stone, and performing a whole range of other tasks
Stability
Less dependent on weathering factors. If necessary, bituminous emulsions can be used at low temperatures and at high viscosity levels, as the properties of such materials allow for high-quality of work even in the presence of adverse climatic influences.
High adhesion
Emulsions provide high-quality adhesion to various types of materials and surfaces. They interact well with acidic and alkaline minerals, asphalt, concrete, and metal surfaces. Versatility allows the proper quality of coatings.
Accurate dosing
High dosing accuracy. Due to the low viscosity structure and the use of special equipment (pounder), bituminous emulsions can be distributed as thin and uniformly layer as possible, thus minimizing the total consumption of binder in the performance of works and ensuring greater economics.
Efficiency and cost-effectiveness
Reduction of energy costs for the production of material and the process of its preparation before work. Energy savings due to the absence of a material heating cycle before use.
Environmental friendliness
A minimal amount of harmful emissions into the environment, thus contributing to maintaining a favorable environmental situation. Emulsions belong to the category of low-hazard materials that are not harmful to human health.
What types of road works are performed with the use of bituminous emulsions?
Their performance characteristics and advantages determine the use of bituminous emulsions in the performance of road works. The low viscosity of such compositions allows using them to provide the following tasks:
- Surface treatment of the roadbed
- Priming of the road base
- Production of cold asphalt concrete
- Waterproofing of road construction
- Patching repair
Surface treatment of road surfaces
Bitumen emulsions are the most demanded for this category of road works because they may be applied in the thinnest possible layer. Roadbed treatment with liquid bitumen solves several tasks at once, such as effective roadbed waterproofing, dedusting, and filling small cracks with binding compounds. Such protective properties provide greater durability of road surfaces by increasing their durability.
Priming of road bases
One of the essential conditions for the durability and long service life of road surfaces is a reliable bond between the base and the top layers.
Asphalt emulsions are liquid binders that are well-distributed over the base course and penetrate the base course.
Making cold asphalt pavements
Bitumen emulsions are one of the basic materials in cold asphalt concrete mixtures. To produce them, the bituminous binder is mixed with various mineral aggregates, and auxiliary components are added to produce the final mix. The use of cold asphalt mixtures for road construction is in demand due to the greater efficiency of such technology compared to asphalting with hot bituminous mixtures.
Waterproofing of road structures
In addition to roadbed maintenance, bitumen emulsions are also in demand for waterproofing of various road constructions and corrosion protection coating. Such structures include bridge supports, foundations, fire tanks, etc.
Pothole repair
This repair involves the targeted elimination of certain defects (cracks, potholes, etc.) on certain road parts. Bitumen emulsions in patching are used for the preparation of cold asphalt-concrete mixtures as well as for works by jet-injection technology. In the latter case, they perform the functions of impregnation and binder for fractional materials used to fill the pothole.
It should be noted that such pothole repair technology is characterized by ease of performance and high work speed, which is why it is applicable in case of necessity in promptly eliminating defects.
Equipment for applying bituminous emulsions
Feed and uniform distribution of bituminous emulsions to provide the necessary performance in the performance of processing is carried out by using special equipment – asphalt emulsion pumps.
Such devices can have different configurations:
TRAILER-MOUNTED ASPHALT PADS.
Such machines have a solid size and can hold large volumes of bituminous emulsions. It is appropriate to use them in the case of large-scale works, for example, if it is necessary to carry out the surface treatment of the road surface on a site of considerable length.
MOBILE ASPHALT DISTRIBUTORS
These convenient and compact units are easy to use and can be designed as either a completely manual tar-bearing machine or a mobile unit placed on a wheeled cart with a tank for binding agents.
Purpose and application of bitumen emulsion
The purpose of bitumen emulsion is due to its properties. It is easy to apply on various surfaces (including vertical) due to low viscosity penetrating into the pores of materials, it is also well mixed with mineral materials (crushed stone, gravel, sand, mineral powder) firmly linking them together.
Thus emulsified petroleum bitumen has two main functions:
- Binding function – is to use emulsion to bind mineral materials (crushed stone, gravel, sand, mineral powder) and their particles between each other, which is a prerequisite for the production of asphalt mixtures (emulsion-mineral, black-brick, cold, etc.). Protective function – is to protect materials and surfaces from the effects of aggressive environments (water and water-salt solutions).
- There are many areas of industry that can use bituminous emulsion, but its main consumers are civil engineering (waterproofing of foundations, walls, and floors), hydraulic (waterproofing of hydraulic and underground structures), and road-building industry.
For the road-building industry, the use of bitumen emulsion became an integral part as it is used in many technologies of road patching, surface treatment of asphalt pavements and the creation of wearing courses, membrane technology, as well as in the preparation of asphalt-concrete mixtures.
The main areas in which emulsified bitumen is used are as follows:
- Preparation of road construction mixtures for asphalting, repair and rehabilitation of roads
- Emulsion mineral mixtures for surface treatment of asphalt pavements and creating protective wear layers
- Cold stockpiled organic-mineral mixtures for road patching
- Cold recycled asphalt concrete mixtures for cold recycling
- Surface treatment of road base and road pavement
- Priming of roadbeds and pavements prior to subsequent asphalting
- Surface waterproofing of road surfaces
- Dusting of roads
- Consolidation of shifting sands
- Consolidation of soils of the upper part of the roadbed
- Arrangement of a protective membrane
- Repair of asphalt and preventive maintenance of roads
- Filling of small cracks in asphalt concrete pavement
- Waterproofing of porous and obsolete asphalt concrete pavement
- Asphalt patching by jet-injection method (pneumatic spraying)
Bitumen emulsion can be used not only in the construction of asphalt concrete pavements but also in the creation of cement concrete roads. The introduction of bitumen emulsion into the cement concrete mixer is one of the ways to increase the physical and mechanical properties of cement concrete (water resistance, frost, and cracking resistance).
The typical composition of bituminous emulsion and its production technology
Bitumen emulsions used in the road building industry are usually of direct type (“oil in water” – M / W), in which bitumen (30 to 70%) is in the form of tiny particles evenly distributed in the water. In emulsions of inverse type (“water in oil” – B / M), the water is dispersed in bitumen (mass fraction of which is from 70 to 80%).
Component composition of emulsified bitumen
The typical composition of bituminous road emulsion includes 5 main components:
- Bitumen
- Water
- Emulsifier
- Stabiliser
- Acid
1. Bitumen (mass fraction in emulsion 30 to 70 %). In most cases for the preparation of emulsified bitumen used viscous oil road bitumen of different grades (BND 90/130, BND 130/200, etc.). In order to improve the physical and mechanical properties of bitumen emulsion instead of conventional petroleum bitumen can be used polymer-bitumen binder (PBB), which has higher performance and physical-mechanical properties compared to conventional bitumen.
2. Water (mass fraction in the emulsion of 15 to 70%).
3. Emulsifier (mass fraction in emulsion of 0,15 to 3 %). Emulsifiers – substances which have the ability to make bituminous emulsion stable (prevent its breakdown). Surfactants (surfactants) that are soluble in both phases of emulsion (water and bitumen) or in one of them (only water or only bitumen) are used as emulsifiers. Most often used in the production of emulsified bitumen are water-soluble emulsifiers, which include the so-called anion-active and cation-active surfactants. Depending on which of these two types of surfactants was used in the preparation of the bitumen emulsion, it will be called anionic (EBA – bitumen emulsion anionic) or cationic (EBC – bitumen emulsion cationic). In rare cases, instead of surfactants may be used solid highly dispersed mineral powders (clays, oxides, carbonates, sulfates, cement, carbon black, etc.).
4. Stabilizer (mass fraction in the emulsion of 0,05 to 0,5 %). An aqueous solution of calcium chloride or other soluble salts is used as a stabilizer (only used in cationic emulsions).
5. Acid (mass fraction in emulsion from 0.5 to 3 %). This component is required to increase the stability of the emulsion. In most cases, hydrochloric acid (less often acetic or orthophosphoric acid) is used.
As additional components in the bituminous emulsion may include various solvents, thinners, polymers, and modifying additives.
Modified bitumen emulsion is a bitumen emulsion prepared on modified bitumen or contains modifying additives (latex, polyethylene, epoxy, synthetic rubber, synthetic resin, etc.).
Modification of bituminous emulsion can be carried out in two ways:
- By introducing a modifying additive into the aqueous phase of the emulsion or directly into the emulsion during its preparation.
- By emulsifying the modified bitumen.
Technology for producing emulsified bitumen
The production of bitumen emulsion is usually carried out on an emulsion plant, although there are other dispersing devices. Emulsion units can be of periodic (batch) or continuous operation. A batch system allows a certain amount of control and management of the emulsion production process by the operator. In the continuous unit, all processes (water heating, dosing of materials…) are carried out in semi-automatic or automatic mode.
The main working body of the emulsion unit is the colloidal mill. The dispersion of bitumen into the water and the subsequent mixing of all components of the emulsion takes place with the help of this mill. Before dispersion, bitumen is heated to 100-160 ° C, the water phase is heated to 30-70 ° C (to dissolve the emulsifier and to achieve the desired emulsification temperature after mixing with bitumen).
The storage period of ready emulsion is from 1 to 2 months (depending on the type and brand of bitumen emulsion). It is stored in vertical cylindrical vessels at an air temperature of at least 5 ° C. Transportation of finished bitumen emulsion can be carried out using truck asphalt pumps, bitumen trucks, railway tanks or tanker trucks, as well as in metal drums.
Classification of bitumen emulsions
Bitumen emulsion must either be mixed with a mineral material (for asphalt mixtures) or applied to a surface (for undercoating and surface dressing) before it can be made into a continuous bitumen film in order to perform its function as a binding agent or as a protective coating. This transformation process is called decomposition.
Bitumen emulsion decomposition is the separation of bitumen from water to form a continuous bitumen film. It may result from the evaporation of water (in the case of an anion emulsion) or through chemical interaction with the mineral material (in the case of a cationic emulsion).
The bitumen emulsion decomposition rate is the time during which the bitumen is separated from the water and forms a continuous film. The rate of decomposition depends on the composition of the emulsion, the size of bitumen particles, the reactivity of the emulsion, air temperature, and humidity, as well as other parameters.
Depending on the rate at which the emulsion disintegrates when mixed with mineral materials, the emulsions are divided into 3 classes:
- Rapidly decomposing
- Medium-decaying
- Slowly decomposing
Bitumen road emulsions are divided into 2 kinds according to the chemical nature of the emulsifier:
- Anionic (EBA – anionic bitumen emulsion). Anionic surfactant (surfactant) is used as an emulsifier
- Cationic (EBC – bituminous cationic emulsion). Cationic surfactant is used as an emulsifier.
To increase the performance of bitumen emulsion, it can be prepared not with conventional petroleum bitumen, but with a polymer-bitumen binder.
Anionic bituminous emulsions decompose during the evaporation of water, and this process depends largely on weather conditions (temperature and humidity), which complicates its use in road construction.
For this reason, in the vast majority of cases in the road construction industry preference is given to cationic bituminous emulsions (EBC), the decomposition of which is determined by the characteristics of the mineral material (crushed stone, gravel, sand, mineral powder) with which the emulsion interacts.
The cationic emulsion allows a more accurate prediction of the rate of disintegration, which is an important factor in the production of works.
