ASPHALT PRODUCTION PROCESS19.05.2022 16:05
Asphalt (bitumen); It is obtained by precipitation of crude oil in nature in natural processes or by human distillation. This substance has a hydrocarbon composition and a color ranging from dark brown to black. Sometimes bitumen is modified with polymers to improve performance.
Asphalt, which is used as a superstructure material especially in road construction works; It is an adhesive bituminous binder mixture produced by including minerals and aggregates. Aggregates in asphalt mixtures to be used in asphalt road construction are hard minerals selected according to the characteristics of the superstructure to be produced. These are materials such as crushed stone, gravel and sand.
The most produced asphalt road types are divided into three as hot mix asphalt, cold asphalt and surface coating.
1-Hot mix asphalt: Aggregate at 145-160°C and bitumen liquefied by heating at almost the same temperature are mixed at the desired rates. Aggregate and bitumen ratios in the mixture vary according to the characteristics of the product to be produced. However, almost 95 % of the mixture is aggregate and 5 % is bitumen.
In hot mix asphalt production facilities, aggregates in 3 different sizes are generally used. The aggregates are dried in a dryer at a temperature of 145-160°C and then mixed with the bitumen heated at 155-160°C in a mixer. Additives such as fillers and stone mastic can also be added to the mixture. Each batch mixing time is approximately 45 seconds. Bitumen and aggregate must be completely homogenized with each other. Fine mineral fillers are also added to the mix and help bind the bitumen onto the aggregate. Asphalt production facilities produce asphalt at approximately 160°C. Two types of asphalt plants are used, fixed and mobile.
2-Cold asphalt: It is a mixture created with fine aggregate, asphalt emulsion, mineral fillers and water. It is used in the maintenance and repair of the asphalt pavement surface. Its cost is lower than hot asphalt and other coating applications.
Cold asphalt is very effective in eliminating ruts, bumps and potholes on the road that affect driving performance for those who drive in traffic, and in cases where surface smoothness is aimed. It is also economical and easier to manufacture.
The bitumen mixture is generally applied to the road surface with the paving machines mounted on the truck and designed accordingly. Additional additives can be added to the mixture mortar if desired.
3-Surface coating: It is the application where the binder and aggregate are laid on the surface one after the other. With the asphalt distributor, asphalt emulsions are sprayed on the road surface, then gravel is laid on top of it and the material is compacted with a roller. Surface coating can also be applied as one or more layers. It is easy to lay and the cost is low. However, since it is affected by changing climatic conditions, maintenance and repair costs are high.
The shorter the distance from the asphalt production facilities to the work area, the faster the production can be made and the completion of the work.
There are three types of asphalt plants, namely Batch plants, Drum mix (continuous mixing) plants and Integrated asphalt plants. All three types can be produced as fixed and mobile.
1-Batch Type Asphalt Plent: It is the most used facilities in the world. High quality production can be made in this type of plant. After all components are individually weighed according to the desired specifications in a production process, they are included in the production process and each production period is completed in approximately 40-50 seconds. The production amount in such plants is lower than drum mix plants.
2-Drum mix (continuous mix) asphalt plant: In this type of facilities, unlike batch plants, bitumen and other additives are added to the aggregate when leaving the dryer. Since there is no mixer, waiting times (mixing, opening and closing the mixer cover, material discharge, etc.) do not occur as in batch type plants. Therefore, production amounts are higher than batch type plants.
3-Integrated asphalt plant: They are compact plants with crushing-screening systems on them. While aggregates that are crushed and separated according to their size are used in classical facilities, the crushing-screening process is carried out on an asphalt plant in compact facilities.
Modules in Asphalt Plant and Asphalt Production Stages
asphalt plants; It consists of feeding silos, conveyor belts, dryer, automatic scale, mixer and loader modules.
Feeding silos: These are silos where aggregate is stored.
Conveyor Belts: It is the system that enables the aggregate stored in the silos to be transported to the dryer called a rotary kiln.
Dryer: It is a rotary kiln where the material coming from the feeding band is dried. Material enters from one end of the rotary kiln, and there is a burner at the other end. The burners heat and dry the aggregate in the rotary kiln to a predetermined temperature.
Sieve and hot aggregate hopper: The hot aggregate coming from the dryer is separated according to their size in the sieves and comes to the hot aggregate hopper. The material on the sieve is sent back to the crusher. The materials coming to the hot aggregate bunkers are taken to the mixer in the desired amount with the automatic weighing system according to the production recipe.
Mixer: It is the part where the aggregates coming from the hot aggregate bunkers and the hot bitumen material meet and are mixed. The hot mixture coming out of the mixer, which combines the aggregate and the binding bitumen in a homogenized manner, is transferred directly to the trucks or silos.
Dust control system: There is a dust control system in all asphalt plants since there will be a high amount of dust emission during the operations in the asphalt plants. Generally, a dry type, replaceable bag filter system is used.
Bitumen system: It consists of bitumen storage tanks and a heating system. Bituminous materials brought to the plant from the refinery by heat-insulated vehicles are stored in bitumen tanks. There is a heating system in the tanks to prevent the bituminous material from freezing. Generally, liquid or gas fueled hot oil boilers are used.