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Quality Control Method of the Mixture in Asphalt Mixing Plant

Thomas Huang posted this article in June 30, 2020

With the continuous increase of highway mileage, the rapid increase in vehicle load and the increasing traffic volume, serious road surface diseases such as flooding, loosening, potholes, etc. appear within one to two years after the asphalt pavement is completed and opened to traffic. Pavement construction quality puts forward new requirements. Although the causes of asphalt pavement diseases are multi-faceted, the quality of asphalt mixture also greatly affects the quality of pavement, so how to ensure the quality of asphalt mixture has become the focus of attention of a large number of asphalt concrete mixing plants. In this paper, the quality control method of asphalt mixture is put forward based on the common problems of asphalt mixture in the mixing process 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 different road grades, climatic conditions, pavement types, and traffic volume. High-temperature, high-speed, heavy-load, and long-slope pavement in summer should choose high-viscosity asphalt; on the contrary, if the climate is cold and the traffic volume is small, low viscosity can be used. asphalt. Each batch of asphalt should be sampled and inspected according to the technical specifications of highway asphalt pavement construction. Asphalt management should pay attention to the storage of asphalt from different sources, not to be mixed, to prevent pollution; its storage temperature is not higher than 170 ℃ during the construction period, not lower than 150℃; It should be carried out at low temperature during long-term storage.
1.1.2 Aggregate
Aggregate is the skeleton of asphalt concrete and the main factor affecting the strength of asphalt concrete. In the process of material selection, attention should be paid to reducing the variability of aggregate grading, and the key sieve that controls the aggregate grading should be set as the crusher’s Sieve holes are controlled to ensure the stability of aggregate gradation.
The shape of the aggregate must be close to a cube, and there are corners to make the mixed asphalt mixture have good mechanical properties and high temperature stability, so pay attention to not 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 muddy aggregate should be cleaned and the aggregates stacked in the stockyard 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 just filling. At the same amount of asphalt, the larger the surface area of the mineral material, the thinner the asphalt film formed and the greater the specific gravity of the structural asphalt. The stronger the cohesion of the material; therefore, the ore powder must be the ore powder after grinding the strong basic rock in limestone or magma rock. Before processing, the clay of the original stone must be removed, and water and moisture must be paid attention to when storing.
1.2 Control of mix ratio
The mix ratio design of the asphalt mixture should follow the three stages of the target mix ratio, production design mix ratio and production verification mix ratio in the technical specifications of highway asphalt pavement construction to determine the mineral gradation And the best amount of asphalt. Whether the mix design is reasonable will directly affect the engineering quality and service life of the asphalt pavement.
The gradation design of the mineral material should minimize the difference between the design gradation and the actual gradation, mainly by recording and researching the belt speed of the cold storage of the concrete mixing station and the flow of the cold material to determine the motor speed and feeding flow The frequency relationship between them can be better controlled within the gradation range when producing and mixing the mixture, improving the accuracy of the mixing ratio and reducing 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 high fluidity, so that the aggregate can be completely wrapped without the appearance of white materials. However, if the mixing temperature is too high, the aging of asphalt will be very serious. The lower the adhesion of asphalt and the adhesion of asphalt to aggregates, the more severe the segregation 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 difficult rolling. Generally, the mixing temperature of the hot asphalt mixture is 130~160℃, and the modified asphalt mixture temperature should be 10~20℃ higher than that of the ordinary asphalt mixture. The temperature of the modified asphalt mixture during storage The drop should be less than 10°C, the temperature of the aggregate should be 10 to 30°C higher than the temperature of the asphalt, and the storage time in the storage bin should not exceed 72 hours.
In addition, it is necessary to adjust the exit temperature of the mixture according to different climatic conditions and different construction conditions. To compensate for the absorption of heat by dump trucks and paver, generally the first pot storage material should be 10℃ higher than the normal temperature. When the temperature is higher at noon or summer, it can be 5-10℃ lower than the normal temperature.
1.4 Control of transportation and unloading
When unloading the material from the mixing station machine to the transport vehicle, the position of the vehicle should be moved for each bucket of unloaded mixture to reduce the segregation of thick and thin 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 ℃, the transport vehicle should be covered with tarpaulin to keep warm.
During the continuous paving process, the material transport vehicle should be stopped at 10-30cm in front of the paver, and it must not hit the paver. During the unloading process, the material transport vehicle should be placed in an empty position and driven by the paving.
Hard shells, lumps that have been segregated or condensed and cannot be crushed, and mixtures left on the vehicle when the transportation vehicle is unloaded, the mixture below the specified paving temperature or wetted by rain, should be discarded and must not be used Paving on the road.
2. Quality inspection during the mixing process
2.1 Appearance inspection
Mixing personnel can inspect the appearance of the mixture to check for abnormal conditions in the concrete mixing plant.
If the first few trays of asphalt concrete mixed every day are substandard waste, then it is necessary to check that the heating of the aggregate and asphalt has not reached the specified temperature; the staff can increase the amount of aggregate entering the drying cylinder to increase Flame temperature to solve the waste problem.
If white material appears, it indicates that the temperature of the aggregate is too low, the mixing time is short, or the quantity of fines 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 fines Material quantity.
If the color of the mixture is dark, it means 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 conducted 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 car. The depth must be at least 15cm. The mixture and the metal The temperature can be measured after the rod contacts. 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, 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 ; Extra coarse-grained asphalt mixture, the sampling quantity is not less than 16kg. Every time the hot-mix asphalt mixture is sampled, the temperature must be measured with a thermometer, accurate to 1 ℃.
Sampling of asphalt mixture should be random and fully representative. For the purpose of checking the mixing quality, such as oil-rock ratio and ore grading, samples should be taken from the bottom of the mixing machine or the lifting bucket, not multiple times. Use after sampling and mixing.
When taking a sample of asphalt mixture on a transport vehicle, it is advisable to drive to the car compartment after half of the car is loaded, take samples from three different heights in different directions with a shovel, and then mix together with a shovel to mix properly. Take out the specified quantity. When the car arrives at the construction site for sampling, the car should be driven out and sampled at three different heights in different directions after being unloaded halfway.
After the sampling, the results of the experiment should be found out of the substandard conditions and corrected.
3. Conclusion
As for the quality of the mixture of asphalt concrete mixing plant, it is affected by various factors such as construction conditions, raw materials, mixing ratio and mixing equipment, so it must have sufficient experimental strength and effective detection methods to guide and supervise the production process , Control the production of asphalt mixture within the ideal range, and lay high-quality asphalt concrete pavement.

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