The mixing of asphalt mixture is directly related to the quality of asphalt concrete. Whether the finished material can meet the quality requirements is a necessary condition to ensure the quality of asphalt concrete pavement construction. The following introduces how to control the quality of asphalt concrete from several aspects: stability of equipment system and material condition, temperature control, segregation control, gradation control, mixing time control, quality inspection of finished asphalt mixture, mixing station quality management system.
Stability of equipment system and material condition
Whether it is a large asphalt plant or a mini type asphalt plant, the stable operation must be guaranteed, and daily maintenance, inspection and repair must be done every day. At the same time, do a good job in the maintenance of key components.
The material condition in production is stable and needs to be adjusted in due course based on experience. The released hot material can be put back to the material yard for reuse, remember not to put it directly into the cold material bin to avoid the temperature fluctuation. This can effectively avoid the occurrence of low temperature and overheating materials. Wet materials should be avoided as much as possible, especially fine aggregates should not have wet materials. Over-wet aggregates will cause low aggregate temperature and high residual water content, which will affect the mixing quality of asphalt mixture.
Temperature control
The ex-factory temperature of the finished asphalt concrete has a large range of variation according to the specification requirements to ensure the paving temperature. The temperature sensor temperature measurement should be accurate. On the mixing equipment, there are generally two temperature sensors, the drum temperature sensor and the thermal bin sensor. These two sensors should show a good correlation between temperature (a difference of 3-5°C is normal), otherwise the cause should be found out.
Segregation control
Aggregates of various specifications in the stockyard should be stacked in layers, and the thickness of each layer should not exceed 1 m, which can reduce the segregation phenomenon caused by the difference in particle size. Do not overfill each cold silo to prevent the silos from being strung together. Hot silo should be checked to prevent stringing of silos due to wear and tear of the aggregate.
Grading control
Due to the large specific surface area of fine aggregate, under the same amount of asphalt, the amount of fine aggregate will seriously affect the quality of asphalt mixture, so it must be strictly controlled. The fine aggregate is mainly in the hot silo, basically composed of machine-made sand and medium sand. In order to prevent the pressure chamber, it can be artificially controlled not to add too much cold material, and the weighing number can be accurately controlled by adjusting the drop, and the real temperature of the aggregate can be accurately displayed at the same time.
During the production process, the feed specifications of the stock yard will change, which is specifically manifested in the overflow or waiting materials of a certain hot silo. At this time, it is necessary to adjust the ratio on site according to the actual situation, that is, to adjust the flow rate of the cold silo appropriately to match the feed ratio of the hot silo and meet the requirements of the standard grading.
Mixing time control
Generally speaking, if there are more fine aggregates, the mixing time will be longer; if the asphalt content and temperature are higher, the mixing time will be shorter. The longer the mixing time, the better the mixing uniformity; but it should not be too long, too long time will have a negative impact on the quality of the mixture. Because the mixing process of the mixture in the mixer is the process of fully contacting the asphalt film with oxygen at high temperature, that is, the aging process, which reduces the penetration of asphalt. Usually the longest mixing time should not exceed 90 s.
Quality inspection of finished asphalt mixture
The quality standards of asphalt mixture includes appearance inspection, laboratory testing and factory testing.
In appearance, the asphalt mixture should be uniform, free of white material, agglomerates and serious separation of coarse and fine materials.
The testing data of the laboratory should be able to reflect the quality status of the finished material well, so as to guide the production accurately and timely.
Base on the Factory inspection of asphalt mixture, a thermometer with a dial should be used for temperature detection. The measuring points should be representative, and the average value should be taken from multi-point detection.
Quality management system
The asphalt plant manufacturer installs a management system on the asphalt mixing plant, which is used for real-time monitoring of production, early warning, data analysis and statistics, etc. Through real-time monitoring and collection of data, it is transmitted to the background of the mixing plant management system through the Internet. After system processing and analysis, the production chart is intuitively displayed in the background, and the staff can log in to view the detailed information of the concrete.
The information management of the asphalt mixing plant can control the quality of the concrete from the source, avoiding the production of unqualified products and the waste of raw materials. Improve work efficiency, reduce management costs, strengthen construction quality, and ensure construction progress.
