Generally speaking, asphalt production including asphalt concrete is a labor intensive process. But the costs for production, transportation and paving do not worry new businessmen. This fact has been further confirmed by the regular annual increases of the number of asphalt production plants being produced and sold.
It must be admitted that this peculiarity is more clearly observed in the countries that have an unsatisfactory general condition of their roadway systems.
So, what is asphalt actually made of?
Asphalt concrete consists of crushed stone, sand, mineral fillers and bitumen. Each of these components performs a separate function. Sand is necessary to fill in the small holes where the larger crushed stone can not penetrate. Mineral fillers are used for better coating and the bitumen serves as the “glue” of the final product. Some formulations however, also contain gravel.
What are the different kinds of asphalt?
Depending on the composition, there are (1) sand (sand, bitumen); (2) rubble (gravel, sand, bitumen, mineral powder); and (3) gravel (gravel, crushed stone, bitumen, mineral powder) asphalt concrete. The production of asphalt requires a strict following the dosage and recipe requirements for all components.
Only the implementation of this condition can contribute to the production of a high quality pavement. The process of asphalt laying is divided into cold and hot procedures. But in fact, the actual difference in temperature is not very great.
The temperature of hot asphalt laying ranges from 130 to 170?С and that of cold laying is usually no higher than 80?С. Cold laying is usually used when repairing potholes as opposed to hot laying that is used during original road or highway construction.
Asphalt production plants:
There are two types of asphalt production plants: cyclic and continuous. The main difference consists in the blending process, metering, amount of mixture production, storage method and mobility. Cyclic asphalt production plants are equipped with a column and a coarse sieve. The base material is separated into factions, after which it is divided into batches and only then is supplied to the drum for drying individual parts. The application of such a technology allows for easy changes of the mixture formulation.
It has been estimated that a manufacturer can influence the formulation up to fifty times during the production process. The disadvantages of cyclic asphalt concrete plants include their stationarity and relatively small amount of asphalt they are able to produce. The construction of these plants is justified in large metropolises where asphalt is delivered to different parts of the city that utilize different asphalt compositions and different production procedures.
Continuous asphalt plants are characterized by the ease of handling. They are not equipped with a column so they are easily transported from one place to another and quickly mounted. Mobility with the continuos plant is always comfortable, but there are also some disadvantages such as the absence of the coarse sieve. In most cases, the crushed stone delivered does not meet the required standards. The absence of stone sorting leads to a formulation failure and, as a result, influences the quality of the final asphalt concrete mixture.
The production facilities may be equipped with additional equipment to separate fractions that require great investments. One of the undeniable advantages of continuous asphalt concrete plants is a constant supply of fractions into a heating bunker that allows the equipment owners to produce much more asphalt.
The production facilities should be equipped with a special silo to store the asphalt mixture.
Asphalt Production Technique
There are several stages of asphalt production. At the very beginning, the quality of the source material is checked and then the aggregates are processed. At the next stage, sand is sieved and crushed stone is fractionated. Then the crushed stones are supplied to a special cylinder to be dried. It is necessary to maintain a high temperature in the cylinder and necessary to remove water from the initial components since water deteriorates the strength of asphalt concrete mixtures.
The GlobeCore colloid mills, designated as the GlobeCore KLM line of equipment, allows for preparation of bitumen and its heating in containers up to 160?С. The next stage is the blending of components such as sand, crushed stone, mineral components and bitumen which is performed by special blades in a bunker.
The blending process is necessary to provide good encapsulation and proper adhesion of bitumen with grains of crushed stone and sand. Some production facilities tend to pass the asphalt mixture through a wide range of sieves to obtain the necessary amount of portions with an even distribution of components.
Once blended thoroughly, the mixture is supplied to a bunker for storage. A rather high temperature is maintained in the bunker to preserve the high quality characteristics of the finished product.
On average, about three tons of asphalt is produced in one shift. Once loaded, a dump truck delivers the asphalt concrete mixture to the construction site. It is very important to deliver the material hot to meet all the requirements.
In Europe, rubber crumbs are added to the asphalt as well as caoutchouc, latex and other materials. Colorful asphalt concrete is also produced with this technique.
What is Road Bitumen Emulsion? Its Advantages and Disadvantages
Road bitumen emulsion is a construction material that will save up to 30% of bitumen when performing road construction projects in comparison with the traditional hot technologies. Additionally, bitumen emulsions possess a wide range of other undeniable advantages such as follows:
- saving of energy resources up to 40%;
- production cost reduction; and
- extension of the road construction season from early spring to late autumn.
The technical characteristics of bitumen emulsion depend on its composition and production technology. This construction material has enjoyed a wide acceptance when constructing and tack coating of pavement layers. Tack coating requires a special machine to spray material called a tar sprayer. It sprays an even distribution of bitumen emulsion along the entire treated area consuming only 0.3 l/m2 of material.
When the paving process is completed, the material dries and water evaporates. Bitumen emulsion is harmless to the environment and has low flammability and greatly improves road pavement quality and service life.
The use of a tar sprayer provides an even bitumen film that ensures an optimal adhesion of several pavement layers at one time. Roads are paved with bitumen emulsion possess better crack resistance and experience a longer service life.
If it is necessary to improve the treatment of a loose surface road, bitumen emulsion is heated up to 40?С predominantly in a rainy or cold weather. The preparation of bitumen emulsion with the necessary technical characteristics is a very difficult process.
It is realized by special equipment and corresponding conditions for its operation. As a rule, a unit for bitumen emulsion production includes:
- production block with a colloid mill;
- metering lines for bitumen and water phases;
- electronic and production process control systems;
- storage container for bitumen emulsion;
- containers for temporary storage of bitumen; and
- small containers for oth