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Quality Control Method of Asphalt Concrete Mixing Plant

Thomas Huang posted this article in August 25, 2020

With the continuous increase in the mileage of highways in China, the surge in vehicle load and the increasing traffic volume, the asphalt pavement has serious road diseases such as oil flooding, looseness, potholes, etc. within one to two years after it is opened to traffic. The quality of asphalt pavement construction puts forward new requirements. Although the causes of asphalt pavement diseases are multifaceted, the quality of the asphalt mixture also greatly affects the quality of the pavement. Therefore, how to ensure the quality of the asphalt mixture has become the focus of attention of a large number of asphalt concrete mixing plants. In this article, the common problems of asphalt mixture in the mixing process are mainly combined, and the quality control method of asphalt mixture is proposed to improve the quality of asphalt mixture.
1. Quality control method of asphalt mixture
1.1 Quality control of raw materials
1.1.1 Asphalt

It should be selected according to the road grade, climatic conditions, pavement type, and traffic volume. High-viscosity asphalt should be selected for high-temperature, high-speed, heavy-duty, and long-slope roads in summer; on the contrary, if the weather is cold and the traffic volume is small, low viscosity should be selected. asphalt. Each batch of asphalt should be sampled and inspected in accordance with the construction technical specifications. Asphalt management should pay attention to the separate storage of asphalt from different sources, not to be mixed, to prevent pollution; its storage temperature during the construction period is not higher than 170℃ and not lower than 150℃; Long-term storage should be carried out at low temperatures.
1.1.2 Aggregate
Aggregate is the skeleton of asphalt concrete and is the main factor affecting the strength of asphalt concrete. In the process of selecting materials, attention should be paid to reducing the variability of aggregate gradation, and the key sieve for controlling aggregate gradation is set as the crusher's receiving The sieve holes are controlled to ensure the stability of the aggregate gradation.
The shape of the aggregate must be close to a cube, with edges and corners to enable the blended asphalt mixture to have good mechanical properties and high temperature stability, so be careful not to use needle-shaped aggregates. The mud content of the aggregate will also affect the adhesion performance of the aggregate and asphalt and the stability of the mixture. Therefore, before mixing the mixture, the mud-containing aggregate should be cleaned and the aggregate stacked in the stock yard should be covered. Prevent dust pollution.
1.1.3 Mineral powder
Mineral powder plays an important role in the aggregate cementation of asphalt mixture, not a simple filling function. Under the same asphalt dosage, the larger the surface area of the mineral aggregate, the thinner the asphalt membrane formed, and the greater the specific gravity of the structural asphalt. The stronger the cohesion of the material; therefore, the mineral powder must be ground mineral powder from limestone or magmatic rock with strong basic rocks. Before processing, ensure that the clay of the raw material is removed, and pay attention to waterproof and moisture-proof storage.
1.2 Control of mix ratio
The mix ratio design of asphalt mixture should follow the three stages of target mix ratio, production design mix ratio and production verification mix ratio in the technical specifications for highway asphalt pavement construction on hot mix asphalt mix ratio design to determine the mineral aggregate gradation And the optimal amount of asphalt. Whether the mix design is reasonable or not directly affects the engineering quality and service life of the asphalt pavement.
The grading design of the mineral material should minimize the difference between the design gradation and the actual gradation, mainly by recording the speed of the belt of the cold material warehouse of the concrete mixing plant and the flow of the cold material to determine the motor speed and the feeding flow. The frequency relationship between them can be better controlled within the gradation range when producing and mixing the mixture, which improves the accuracy of the mix ratio and reduces the deviation.
1.3 Control of mixing temperature
The mixing temperature of the asphalt mixture determines the viscosity of the asphalt. At high temperatures, the asphalt has a higher fluidity to completely cover the aggregate and no white material will appear. However, if the mixing temperature is too high, the aging of the asphalt will be very serious. The lower the cohesive force of the asphalt, the cohesive force of the asphalt and the aggregate, the more serious the segregation phenomenon after paving. However, if the temperature of the mixture is too low, it will affect the quality of paving and rolling, resulting in uneven mixing and difficulty in rolling. Generally, the mixing temperature of hot-mix asphalt mixture should be 130~160℃, and the mixing temperature of modified asphalt should be 10~20℃ higher than that of ordinary asphalt mixture. The temperature of modified asphalt mixture should be increased during storage. The drop should be less than 10°C, the temperature of the aggregate should be 10-30°C higher than that of the asphalt, and the storage time in the storage bin should not exceed 72 hours.
In addition, it is also necessary to adjust the exit temperature of the mixture according to different climatic conditions and different construction conditions. In order to compensate for the heat absorption of dump trucks and pavers, the storage temperature of the first pot should be 10°C higher than the normal temperature. When the temperature is higher at noon or summer, the temperature can be 5-10°C lower than the normal temperature.
1.4 Control of transportation and unloading
When discharging from the mixing station machine to the material transporter, the position of the car should be moved every time a bucket of mixed material is unloaded to reduce the segregation of coarse and fine aggregates and minimize the falling distance of the storage bin.
When the transportation time is more than half an hour or the temperature is lower than 10°C, the material carrier should be covered with tarpaulin for insulation.
During the continuous paving process, the material carrier should be parked 10-30cm in front of the paver, and shall not hit the paver. During the unloading process, the material carrier should be placed in a neutral gear and driven forward by the paving.
Hard shells and agglomerates that have been segregated or condensed and cannot be crushed, as well as the mixture left on the vehicle when unloaded by the transport vehicle, and the mixture that is lower than the specified paving temperature or wet by rain, should be discarded and not used Pave on the road.
2. Quality inspection of the mixing process
2.1 Appearance inspection

Mixing personnel can check the abnormal conditions of the concrete mixing station by observing the appearance of the mixture.
If the first few batches of asphalt concrete mixed every day are all substandard waste materials, then pay attention to check that the aggregate and asphalt heating have not reached the specified temperature; the staff can reduce the amount of aggregate entering the drying cylinder to improve Flame temperature to solve the waste problem.
If white material appears, it means that the aggregate temperature is too low, the mixing time is short, or the amount of fine material is too large; the corresponding solution is to increase the heating temperature of the aggregate, increase the mixing time of the mixture, or reduce the fine material. Material quantity.
If the color of the mixture is dark, it indicates that the heating temperature is too high and the asphalt is aging; for this, the heating temperature of the asphalt should be strictly controlled.
2.2 Temperature test
The temperature test of the asphalt mixture should be carried out every half an hour. Generally, it is measured with a plug-in thermometer on the material truck. The metal rod is used to insert the mixture from the reserved hole on the side of the carriage. The depth must be at least 15cm. The mixture and metal The temperature can be measured after the rod touches. If the temperature is too high or too low, the mixing process must be adjusted in time.
2.3 Sampling experiment
According to the nominal maximum particle size of the asphalt mixture aggregate, the sampling quantity of fine-grained asphalt mixture is not less than 4kg; the sampling quantity of medium-grained asphalt mixture is not less than 8kg; the sampling quantity of coarse-grained asphalt mixture is not less than 12kg ; For special coarse-grained asphalt mixture, the sampling quantity is not less than 16kg. Every time you sample the hot-mix asphalt mixture, you must use a thermometer to measure the temperature to an accuracy of 1°C.
The sampling of the asphalt mixture should be random and sufficiently representative. For the purpose of checking the mixing quality, such as the oil-stone ratio and mineral material grading, the sampling should be taken from under one discharge of the mixer or in the lifting bucket. Use after sampling and mixing.
When taking samples of asphalt mixture from a transportation vehicle, it is advisable to drive halfway to the vehicle compartment and use a shovel to take samples from 3 different heights in different directions, and then mix them together with a hand shovel to mix evenly. Take out the specified amount. When taking samples after the car arrives at the construction site, the car should be driven out to take samples from 3 different heights in different directions after half unloading.
After sampling, the experimental results should find out the specific reasons and correct the non-compliance.
3. Conclusion
Regarding the quality of the mixture of the asphalt concrete mixing plant, it is affected by various factors such as construction conditions, raw materials, mixing ratio and mixing equipment. Therefore, it is necessary to have sufficient experimental power and effective testing methods to guide and supervise the production process. , Control the production of asphalt mixture within the ideal range, and pave high-quality asphalt concrete pavement.

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