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Key points for supervision and control of ordinary highway asphalt mixing plants

The quality of asphalt mixture directly determines the quality of asphalt pavement engineering. This article discusses the key points of supervision of ordinary highway asphalt plants in order to better monitor the quality of asphalt mixture.

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The quality of asphalt mixture directly determines the quality of asphalt pavement engineering. This article discusses the key points of supervision of ordinary highway asphalt plants in order to better monitor the quality of asphalt mixture.
[1]. Basic requirements for asphalt mixer plants
Asphalt mixing plants must use intermittent mixers, and the number of cold silos must meet the mix ratio requirements. Before mixing production, the asphalt mixer weighing and measuring system should be calibrated and approved by relevant departments. The mixing site is hardened with cement concrete to ensure smooth drainage. A canopy is set up in the aggregate bin, and different material sources are stored in different grades. The signs are clear and partition walls are used to separate the materials to ensure that materials are not mixed.
The asphalt mixing plant has special qualifications for testing and testing, and its personnel, equipment, and regulations meet the requirements.
[2].Safe production
Safety production is the top priority in all production work. In addition to hanging safety production flags, safety production banners, job responsibility signs, safety operating procedures signs, etc., asphalt mixing plants should also conduct safety production inspections for every employee. Disclosure and safety education, and conscientiously implement safety production responsibilities.
In the early stage of construction, the asphalt mixing plant should carry out maintenance and adjustment of the mixing equipment, conduct inspections for key safety hazards such as boilers, and install lightning rods on the top of the storage tanks. Safety protection devices should be installed on work platforms, feed bins, asphalt tanks and other parts involving personal safety, and exposed parts of the transmission system should have protective devices and safety maintenance protection devices.
[3]. Quality control of raw materials
The quality of raw materials is the basis of the quality of asphalt mixture. Various raw materials should be strictly inspected before production. The main raw materials (asphalt) should have factory material sheets. The inspection frequency is as follows:
The first mix design is carried out before construction. The main testing items are: ① Penetration, ductility (elastic recovery), and softening point of modified asphalt; ② Grading test, sand equivalent, and apparent density of fine aggregate;
③ Gradation test of coarse aggregate, needle-like particle content, mud content, crushing value, apparent density, asphalt adhesion; ④ Appearance of mineral powder, gradation test, heating stability, hydrophilic coefficient, Liquid plastic limit, density.
The main testing items during construction include ① the penetration, ductility (elastic recovery), and softening point of modified asphalt. The inspection frequency is 1 time/car, and the random inspection frequency is 20%; ② The gradation test and sand equivalent of fine aggregate, the inspection frequency is 1 time/400m3, and the random inspection frequency is 20%; ③ The gradation test and needle inspection of coarse aggregate Flaky particle content, mud content, crushing value, apparent density, asphalt adhesion, the detection frequency is 1 time/400m3, and the sampling frequency is 20%; ④The appearance of the mineral powder, gradation test, heating stability, For hydrophilicity coefficient, liquid plastic limit, and density, the detection frequency is 1 time/400m3, and the sampling frequency is 20%.
[4]. Verification of asphalt mixture proportions
Verify the mix ratio of the asphalt mixture in a timely manner based on the asphalt mixture mix ratio reported by the asphalt mixing plant, and conduct a Marshall test according to the laboratory target mix ratio determined by the asphalt mixing plant to determine whether the mix ratio meets the requirements of the construction technical specifications. If necessary, a rutting test should be conducted to test the high-temperature performance of the asphalt mixture.
As an asphalt mixing plant supervisor, you should be completely familiar with the target mix ratio and production mix ratio, including asphalt content, mineral powder content and various mineral material ratios, as well as the primary cold material mixing of the asphalt mixer and the secondary screening of the hot material bin. Screen holes at all levels are used to prepare for adjusting the production mix ratio of asphalt mixture.
[5]. Supervision matters during production
5.1 Asphalt content, mineral gradation and Marshall test
Asphalt content, mineral gradation and Marshall test are important indicators of the quality of asphalt mixtures. Therefore, it is crucial to check the asphalt content, mineral gradation and Marshall test of asphalt mixture at the side plant frequently. The frequency of testing is 1-2 times per shift. Asphalt mixing plant test personnel are urged to affix the electronic strips printed by the combustion furnace and Marshall tester on the test report as a valid basis for the source of test data. The sampling frequency of supervision is 20% of the asphalt mixing plants, which are sent to the supervision center laboratory or a qualified testing and testing center for inspection, and provide data standards for road compaction testing.
5.2 Heating temperature and mixing time of asphalt and mineral materials
There is no data directly showing the temperature of the finished asphalt mixture on the asphalt mixing machine, so you should pay close attention to the asphalt temperature and the heating temperature of the mineral material, including the drum temperature and the thermal extraction temperature of the mineral material, so as to infer the temperature of the finished asphalt mixture. The mixing time of the asphalt mixture is determined by trial mixing according to the specific situation. It is based on the asphalt evenly coating the aggregate. The production cycle of each plate of the intermittent mixer should not be less than 45s (the dry mixing time should not be less than 5-10s). , the mixing time of modified asphalt and SMA mixture should be appropriately extended.
5.3 Ore powder recycling rate
The recycling rate of mineral powder is required to be controlled within 25%. Changes in the utilization ratio of recycled powder include changes in the use of recycled powder caused by different dust removal effects. Even if recycled powder is not used, if the dust removal effect is weakened, In essence, it can still be regarded as part of the recovered dust being used, so asphalt mixing plants should be urged to carry out regular dust removal and bag cleaning. In addition to avoiding an increase in the recycling rate of mineral powder, it can also avoid asphalt mixing caused by excessive temperature at the secondary auger. Shut down failure, while meeting the requirements of environmental protection.
5.4 Loading and transportation
Transport trucks should be loaded with materials in three stages: front, rear and middle. The height should be consistent to prevent segregation. All trucks should be covered with insulation to prevent spillage when leaving the factory.
5.5 Factory temperature
Use a plug-in digital thermometer with a metal detector needle to insert into the finished asphalt mixture of the skip truck to a depth of 15cm to more accurately determine the factory temperature of the asphalt mixture. When the weather changes, transportation distance and isochronous adjustment, the temperature can be appropriately adjusted within the specified range to ensure that the asphalt mixture can reach the paving and rolling temperature when unloading and paving. Each shift is tested 10 times, and the temperatures are as follows:
Factory temperature of asphalt mixture (°C)
If the temperature of the asphalt mixture is too low, flowers will appear, and if the temperature is too high, the asphalt will burn. The primary mix of cold materials and the moisture content of the raw materials should be controlled to ensure the normal working condition of the burner, thereby ensuring the factory temperature of the asphalt mixture.
[6] things to note
6.1 Determination of combustion correction coefficient of combustion furnace
The accuracy of the combustion furnace directly affects the judgment of asphalt content. Before starting work, you should first ask a qualified measurement unit to perform regular calibration, and determine the combustion correction coefficient for mineral materials with different mix ratios from different origins.
The determination of the combustion correction coefficient plays a vital role in determining the asphalt content in the asphalt mixture. However, there is currently no clear operating procedure for determining the combustion correction coefficient. The usual methods are as follows: (1) Configure the selected asphalt through calculation Three groups of asphalt mixtures with a content and selected asphalt content ±0.3%; ⑵ Put them into a combustion furnace that has reached the set temperature and burn them to constant weight; ⑶ Calculate the loss rate of the asphalt mixture, using the loss rate and the preset The average value of the difference in asphalt dosage is used as the combustion coefficient.
Because there are many factors that affect the combustion correction coefficient, the combustion coefficient should be corrected frequently during construction. The combustion coefficient must be corrected when raw materials change, the mineral composition changes, and the proportion of recycled powder recovery changes.
6.2 Adjustment of production mix ratio
The primary allocation of cold materials is to calculate the speed of the batching motor of each cold material bin and the height of the material door based on the proportion of various materials in the target mix ratio to determine the transportation volume of various materials. If the primary mix of cold materials is inaccurate, there will be material waiting and overflow. The test personnel should adjust the primary mix of different raw materials based on the screening test data. The cylinder should be designed with a mix ratio that is consistent with the target mix ratio to ensure that the mix is ​​mixed properly. The stability and continuity of joint production. After the primary mix of cold material is stable, testers must screen the hot material bins to determine the proportion of materials with different particle sizes in each hot material bin. During the production and mixing process, asphalt mixing plant operators are not allowed to adjust the number of revolutions of the batching motor in the cold silo, change the production mix ratio data, and are not allowed to increase the productivity of the mixing plant by skipping materials, replenishing materials, etc.

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    The asphalt mixing equipment mentioned here may also refer to an asphalt concrete mixing plant. At present, asphalt mixing equipment generally uses a complete set of equipment for mixing. So what are the benefits of using a complete set of equipment?
    1. More effective.
    In today’s industrial production, a complete set of asphalt mixing equipment can help improve production efficiency and ensure product quality. This is why even in a mixing plant, the equipment used is a complete set of equipment.
    2. Ensure quality.
    When mixing asphalt, a certain ratio is set. For this type of asphalt liquid used in different occasions, its ratio control has strict requirements. It is necessary to determine its mixing method and mixing time to ensure that the asphalt liquid is consistent with the production site. One of the advantages of a mixing plant is that the quality can be effectively controlled.
    3. It can be sampled.
    After mixing at the mixing plant, the quality inspector can sample and inspect to ensure that the mixed asphalt liquid meets the use requirements.
    In short, asphalt mixing equipment will use a complete set of equipment, mainly to facilitate the later asphalt to meet production needs. Through the mixing plant, the mixing time and feeding sequence can be better controlled, so that the mixed product can meet different use requirements. And after using the archiving equipment, effective spot checks can be carried out, which can better ensure that the quality meets the construction requirements.

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    1. Pay attention to daily inspection. Before the asphalt mixing plant officially works, the drying drum needs to be tested and inspected to see whether each pipeline is reliably connected, whether the lubrication of the whole machine is feasible, whether the motor can be started, whether the functions of each pressure valve are stable, whether the instrument is normal, etc.
    2. Correct operation of the mixing station. At the beginning of the asphalt mixing plant, manual operation can only switch to automatic control after reaching the specified production capacity and discharge temperature. The aggregate should be dry and have a standard mode so that it can maintain a constant temperature when flowing through the drying drum. When the entire aggregate is sent to dry, the moisture content will change. At this time, the burner should be used frequently to compensate for the change in moisture. During the rolling stone processing, the amount of water directly formed is basically unchanged, the amount of combustion accumulation increases, and the amount of water in the deposited accumulation material may change.
    3. Reasonable maintenance of the asphalt mixing plant. Aggregates should be deactivated when the asphalt mixing plant is not in operation. After work every day, the equipment should be operated to discharge the aggregate into the dryer. When the material in the hopper leaves the combustion chamber, the combustion chamber should be closed and allowed to idle for about 30 minutes to cool down, so as to reduce its impact or make the machine run in a straight line. Install the drying cylinder fixing ring on all rollers synchronously.

    Now on the construction site, including in some engineering construction, one of the equipment used is asphalt mixing plant. It can be said that it can be used in many ranges and fields, and it can provide certain help for my country’s infrastructure construction. Of course, in the process of use, it is necessary to do a good job in many aspects, so that the use of mixing plant can be safer and more worry-free.
    1. Maintain standardized operating procedures
    In fact, it is not only in the use of asphalt mixing plant, but also in the use of other equipment. It should be done well. It can be said that this mixing plant will also have certain dangers. If there is any carelessness, it may also cause great losses. Therefore, at this time, it is still necessary to pay attention to the correct specifications and follow the process step by step. Only in this way can it be used safely and other use problems can be effectively avoided.
    2. Adjust the reasonable mixing ratio
    In the application of asphalt mixing plant, the most important and core step is the mixing. The mixing ratio of raw materials should be within a reasonable range and completed according to actual needs. Do not add or reduce raw materials at will according to your own wishes. Such operation is not standardized. In addition, after making a good ratio, you should also pay attention to safety protection measures during operation.
    Asphalt mixing plant still plays an important role. If you want to make the use of the mixing plant safer and more worry-free, you should pay more attention when using it and have a certain understanding of these precautions. Only in this way can you ensure that there will be no other problems in use and ensure the safety of the mixing plant.

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    1. During the operation of the mixing equipment, in addition to ensuring that the equipment is in good condition, it should also be equipped with a mineral moisture content detector and a finished material tester, and the relevant data should be frequently tested for the operator to adjust the operation in time to keep the equipment in good condition.
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    3. Before operation, all working parts and devices of the mixing equipment should be fully checked to see if they are intact and normal. If there are any problems, they must be properly handled before operation, and it is forbidden to operate with illness.
    4. The operation must be carried out strictly in accordance with the procedures and precautions specified in the instruction manual. After normal ignition, the dust collector should be monitored to ensure that the drying drum burns under negative pressure; after production starts, the hot material elevator and agitator should be monitored to see if they are working normally to coordinate the operation of other parts.