Main points of supervision and control of ordinary highway asphalt mixing station

23 Aug 2019 09:01

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The quality of asphalt mixture directly determines the quality of asphalt pavement engineering. This paper discusses the main points of supervision work of ordinary highway asphalt mixing station in order to better monitor the quality of asphalt mixture.

Basic requirements for asphalt mixing plants
The asphalt mixing station must use a batch mixing machine. The quantity of the cold storage bins meets the mixing ratio requirements. Before the mixing production, the asphalt mixing machine weighing and measuring system should be calibrated and passed the acceptance of the relevant departments.

The mixing site is hardened with cement concrete to ensure smooth drainage.

The collection bin is equipped with a canopy, and the different materials are stored in different grades. The nameplate is clear, and the partition is separated by the partition to ensure that the materials are not mixed.

The asphalt mixing station has special qualification for testing and testing, and its personnel, equipment and regulations meet the requirements.

Safe Production
Safety production is the middle of all production work. In addition to the safety production banner, safety production banner, post responsibility card, safety operation code, etc., the asphalt mixing station should, more importantly, safety production for each employee. Pay close attention to safety education and earnestly implement safety production responsibilities.

In the pre-construction asphalt mixing station, the mixing equipment should be inspected and adjusted, and the key safety hazards such as boilers should be checked, and the lightning rod should be installed on the top of the highest storage tank.

Safety protection devices shall be provided for the parts of the work platform, feed bins, asphalt tanks, etc. that involve personal safety. The exposed parts of the transmission system shall have protective devices and safety inspection and protection devices.

Quality control of raw materials
The quality of raw materials is the basis of the quality of asphalt mixture. Before the production, various raw materials are strictly inspected. The main raw materials (asphalt) should have a factory material list. The detection frequency is as follows:
The mix design is first carried out before construction. The main test items are: 1 penetration degree, ductility (elastic recovery) and softening point of modified asphalt; 2 gradation test of fine aggregate, sand equivalent, apparent density;
3 grading test of coarse aggregate, needle-like particle content, mud content, crush value, apparent density, asphalt adhesion; 4 appearance, grading test, heating stability, hydrophilic coefficient, Liquid plastic limit, density.

The main testing items in the construction have the penetration degree, ductility (elastic recovery) and softening point of the modified asphalt.

The detection frequency is 1 time/car, and the sampling frequency is 20%; 2 the gradation test of the fine aggregate, the sand equivalent, the detection frequency is 1 time/400m3, the sampling frequency is 20%; 3 the grading test of the coarse aggregate, the needle Flaky particle content, sludge content, crushing value, apparent density, asphalt adhesion, detection frequency is 1 time / 400m3, sampling frequency is 20%; 4 appearance, grading test, heating stability of mineral powder, Hydrophilic coefficient, liquid plastic limit, density, detection frequency is 1 time / 400m3, sampling frequency is 20%.

Verification of asphalt mixture ratio
According to the asphalt mixture ratio reported by the asphalt mixing station, the mixing ratio of the asphalt mixture is verified in time, and the Marshall test is carried out according to the target mixing ratio determined by the asphalt mixing station to determine whether the mixing 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 station supervisor, you should be fully familiar with the target mix ratio and production mix ratio, including asphalt content, mineral powder content and various mineral ratios, as well as the primary mix of the cold mix of the asphalt mixer and the secondary screening of the hot bin. Screening holes at all levels to prepare for adjusting the mix ratio of asphalt mixture production.

Supervision matters in production
1 Asphalt content, mineral gradation and Marshall test
Asphalt content, mineral grading and Marshall test are important indicators of the quality of asphalt mixture. Therefore, it is crucial to side by side and check the bitumen content of the asphalt mixture, mineral grading and Marshall test.

The detection frequency is 1-2 times per shift, and the tester of the asphalt mixing station is urged to attach the electronic strip printed by the burning furnace and the Marshall tester to the test report as an effective basis for the test data source.

The sampling frequency of the supervision is 20% of the asphalt mixing station, sent to the laboratory of the supervision center or a qualified test and inspection center for inspection, and provides data standards for road surface compaction inspection.

2 Heating temperature and mixing time of asphalt and mineral materials
There is no data directly on the asphalt mixer that directly shows the temperature of the finished asphalt mixture. Therefore, the temperature of the asphalt and the heating temperature of the ore should be closely monitored, including the temperature of the drum and the hot extraction temperature of the mineral, to infer the temperature of the finished asphalt mixture.

The mixing time of asphalt mixture is determined according to the specific conditions, and the aggregate is uniformly coated with asphalt. The production cycle of each batch of batch mixer should not be less than 45s (the dry mixing time should not be less than 5-10s) The mixing time of the modified asphalt and SMA mixture should be extended appropriately.

3 mine powder recycling rate
The recovery and utilization rate of the ore powder is required to be controlled within 25%, and the change in the proportion of recycled powder is used, including the change in the use of the recycled powder due to the difference in the dust removal effect, even if the dust removal effect is weakened without using the recycled powder. In fact, it can still be regarded as part of the recycled dust being used. Therefore, the asphalt mixing station should be urged to carry out regular dust cleaning and cleaning bags. In addition to avoiding the recovery of the mineral powder, it can also avoid the excessive temperature of the secondary auger. The machine fails and meets the requirements of environmental protection.

4 loading and transportation
The transporter should be loaded three times before, after, and three times, with the same height to prevent segregation. All trucks should be covered with heat preservation and anti-spray when leaving the factory.

5 factory temperature
Insert the digital thermometer with metal detector needle into the asphalt mixture of the finished vehicle, the depth is 15cm, to judge the ex-factory temperature of the asphalt mixture more accurately.

When the weather changes, the distance and the isochronous adjustment, the temperature can be appropriately adjusted within the specified range to ensure that the asphalt mixture can reach the optimal paving and rolling temperature during the unloading.

Each shift is tested 10 times and the temperature is as follows:
Asphalt mixture factory temperature (°C)
If the temperature of the asphalt mixture is too low, the flower will appear. If the temperature is too high, the asphalt will be burnt. The primary distribution of the cold material and the water content of the raw material should be controlled to ensure the normal working state of the burner, thus ensuring the factory temperature of the asphalt mixture. .

6 notes
1 combustion furnace correction coefficient determination
The accuracy of the furnace directly affects the judgment of the asphalt content. Before starting the construction, the qualified units should be regularly calibrated, and the correction factors for the different proportions of the different materials should be determined.

The determination of the combustion correction coefficient plays a crucial role in determining the asphalt content in the asphalt mixture. However, the current combustion correction coefficient determination method does not specify the operating procedures. The usual practices are as follows: (1) Accurately configure the selected Asphalt content and selected asphalt dosage ±0.
3% of the three groups of asphalt mixture; (2) placed in the furnace that has reached the set temperature for combustion to constant weight; (3) Calculate the loss rate of the asphalt mixture, using the average of the difference between the loss rate and the preset amount of asphalt Combustion coefficient.

Since there are many factors affecting the combustion correction coefficient, the combustion coefficient should be corrected frequently during construction. The combustion coefficient must be corrected in the case of changes in raw materials, changes in the composition of the mineral material, and changes in the recovery ratio of the recovered powder.

2 production mix adjustment
The primary material of the cold material is calculated according to the proportion of various materials in the target mix ratio, and the rotational speed of the batching motor of each cold silo and the height of the material door are calculated to determine the conveying amount of various materials.

If the primary material of the cold material is not accurate, the phenomenon of material waiting and flashing will occur. The tester should adjust the primary material of different raw materials according to the screening test data. The cylinder design has a matching ratio with the target mix ratio to ensure the mixing. Production stability and continuity.

After the primary cooling of the cold material is stabilized, the tester must perform a hot silo screening to determine the proportion of the different particle size materials in each hot silo.

During the production mixing process, the operator of the asphalt mixing station shall not adjust the number of revolutions of the batching motor of the cold silo, change the production mix ratio data, and cannot increase the productivity of the mixing station by means of skipping or feeding.

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