How asphalt made? It is a relative complex process. Asphalt mixture, as an important material in the field of roads and construction, whose production process incorporates the scientific ratio and efficient mixing of asphalt and aggregate. From the quality control of the raw materials to the precise calculation of mixing ratio, each step reflects the ultimate pursuit of performance and durability. This article will briefly introduce how asphalt mixture is produced under a series of strict processes, and how each batch of asphalt mixture is ensured at the best state by modern equipment and technical methods to ensure.
Production Process Of Asphalt Mixture
Asphalt mix can be divided into two kinds, hot mix asphalt and cold mix asphalt. As we can see from the name, these two asphalt mixtures are produced by different methods, cold mix and hot mix.
Cold Asphalt Mixing Process
The production process of cold mix asphalt is relatively simple and environmentally friendly.
- First of all, all kinds of aggregates are put into the mixer according to the batching ratio preset, and all kinds of materials are mixed evenly after a certain time of mixing.
- Next, the prepared asphalt emulsion(the asphalt raw materials is dispersed in water) and the additives (if any) are added to the blender in accordance with the ratio, and continue to stir until the asphalt emulsion is fully mixed with the mineral aggregate. The specific mixing time needs to be determined according to the equipment model, raw material characteristics and design requirements. The mixing speed and mixing time can be adjusted according to the requirements during the mixing process to achieve the best mixing effect.
- Finally, discharge the finished mixture.
Hot Mixing Asphalt Production Process
The production process of hot mix asphalt is relatively complex. Heating and melting in the process of mixing are the key links in the production of hot mix asphalt.
- First of all, all kinds of cold sand and stone after the initial allocation into the drying cylinder for drying and heating.
Then, the hot aggregate is screened in multiple stages. Then a second accurate weighing is performed. - Next, according to the ratio of various aggregates, powders, additives, etc. Into the blender, and add hot liquid asphalt to mixing. In the mixing process, it is necessary to strictly control the time and speed of heating and mixing to ensure the uniformity and stability of the asphalt mixture.
- The mixed asphalt should be transported to the site within the specified time and used as soon as possible, or stored in the finished product warehouse to maintain normal storage temperature and maintain stable product performance.
Precautions During Each Step Of Asphalt Mading Process
Material Preparation
- Preparation Of Aggregates
Coarse aggregate and fine aggregate should be clean, dry, non-weathering, no impurities, meeting the related standards and technology requirement. Coarse aggregates should have good performance in particle shape and adhesion, meanwhile, fine aggregates should have nice characteristics of sufficient strength and wear resistance.
- Preparation Of Bitumen
Commonly used asphalts include pavement petroleum asphalt, soft coal asphalt, liquid petroleum asphalt, emulsified petroleum asphalt, etc.
Road Petroleum Asphalt
This kind of asphalt is the most commonly used raw material. It is a black or brown semi-solid substance extracted form petrol, with good fluidity at high temperatures and adhesion. Road petroleum asphalt is the main component of asphalt mixture, which is the important factor to effect the performance of the finished mixture.
Soft Coal Asphalt
Although less commonly used than road petroleum asphalt, soft coal is also an asphalt material that be used in the production of asphalt mixture. It is usually derived from the dry distillation process of coal, with unique physical and chemical properties.
Liquid Petroleum Asphalt
This is also a kind of common asphalt material, similar to road petroleum asphalt, but with lower viscosity and higher fluidity, suitable for some specific asphalt mix production needs.
Emulsified Petroleum Asphalt
Emulsified petroleum asphalt is a mixture of asphalt and water, liquid at room temperature, easy to construction. The application of emulsified petroleum asphalt is also increasingly extensive, especially in some occasions where the construction temperature needs to be reduced or the construction efficiency needs to be improved.
When raw asphalt or bitumen material enter the site, it needs to be strictly sampled and stored in a special storage tank. At the same time, mixing equipment is added to ensure the uniformity of asphalt use.
- Mineral Powder Preparation
Mineral powder as a filler, should be dry, clean, fineness to meet the requirement. Usually, the mineral powder obtained by grinding hydrophobic stone such as strong basic rock in limestone or lime paste is used.
Heating Treatment
- Asphalt Heating
The asphalt is heated to the specified mixing temperature, usually 140โ-160โ๏ผ specific temperature needs to be adjusted according to the type of asphalt and modifier.
- Aggregate Preheating
The aggregate is preheated to a certain temperature in the oven, usually about 150โ, to enhance the adhesion of the aggregate to the asphalt.
Mixing Process
- Dry Mixing
The preheated aggregate( including coarse aggregate and fine aggregate) is put into the mixer for dry mixing to remove moisture and impurities on the surface of the aggregate, and the initial mixing is uniform. Dry mixing time is usually 10-15s.
- Wet Mixing
Add heated asphalt to the aggregate after dry mixing, and wet mix. In the wet mixing process, the mixing time should be strictly controlled to ensure that the asphalt and aggregate are fully mixed evenly. Batch mixing equipment each pot mixing time is generally controlled in 30-50s ( dry mixing shall not be less than 5s). For the warm mixing asphalt mixture, it is also necessary to add warm mixing additives in the asphalt, and slowly pour in the stirring state, stirring for about 10min to complete the preparation of warm mixing asphalt.
- Adding Mineral Powder
After the asphalt and aggregate are evenly mixed, a certain amount of mineral powder is add for the final mixing. The mineral powder should be heated to a certain temperature in a separate heating device before being added to ensure a good combination with asphalt and aggregate.
Quality Control
- Temperature Control
In the whole mixing process, it is necessary to strictly control the temperature of the asphalt and aggregate to ensure that the mix has good workability and uniformity during the spreading operation.
- Uniformity Control
Check the storage condition of the silo regularly to ensure the balance of the storage material in each bucket to prevent full silo or cross-silo storage. At the same time, the number of components in each batch of materials is set strictly according to the production mix ratio, accurate weighing, and strict control of mixing time.
- Mixing Design
According to the engineering requirements and the performance characteristics of asphalt mixture, the mix design is carried out to ensure that the physical properties and road performance of asphalt mixture meet the requirements.
Inspection And Storage Of Finished Products
- Finished Product Inspection
Quality inspection of the mixed asphalt mixture, including appearance inspection, temperature detection, sampling test, etc., to ensure the quality of the finished product.
- Storage And Transportation
The qualified asphalt mixture is transported to the construction site in a timely manner for paving operations. Measures should be taken to prevent mixture segregation and temperature drop during storage and transportation.
Through the above steps, the asphalt mixture can be made to meet the requirements and provide high-quality raw materials for road construction.
