High-quality Aggregate Processing Process2020-04-24

Summary´╝ÜFive technological processes for processing high-quality aggregatesAfter resuming work, various provinces have successively released investment plans for key pr

High-quality Aggregate Processing Process

Five technological processes for processing high-quality aggregates

After resuming work, various provinces have successively released investment plans for key projects in 2020. The scale of infrastructure investment is still relatively large, and the market demand for gravel aggregates is huge. For a long time, construction sand mainly comes from river channel sand mining and machine-made sand. River channel sand mining causes the depletion of sand and gravel resources, water pollution, and easily causes various problems such as river bank safety.

The development of high-quality machine-made sand with stable output and quality instead of river sand can solve the contradiction between the imbalance between supply and demand of gravel aggregates during construction, and can also absorb solid waste residues such as tunnel slag. It is a green environmental protection industry. Sustainable development is of great significance.

In order to solve the problem of shortage of natural river sand resources and the inferior quality of machine-made sand on the market that cannot meet the demand for high-performance concrete sand for infrastructure projects, this article shares the research case of high-quality machine-made sand production technology in a railway construction project in Guizhou, and promotes the use of high-quality machine-made sand in railways. Engineering especially the application in prestressed components.

1. Main quality problems of machine-made sand

crusher

At present, the mechanized sand on the Guizhou market is affected by the rock material and production process. There are generally quality problems such as poor gradation, excessive stone powder content, and many particles and corners, which have a great impact on the performance of concrete.

Firstly, the gradation of machine-made sand is characterized by "more than two ends and less in the middle", in which the remaining size of the particle sieve with a particle size greater than 2.360mm is as high as 40%, and the remaining size of the particle sieve with a particle size of less than 0.075mm is as high as 15% or more. The void ratio is large, and the concrete strength and working performance are poor.

The second is that the content of stone powder is too high, which leads to quality problems such as reduced concrete strength and increased shrinkage deformation.

The third is that there are many particles and corners. Under the same amount of slurry, the machined sand concrete has poorer workability, fluidity and density than the rounded river sand concrete.

Focusing on the main quality problems of machine-made sand, the focus is on the construction of high-quality machine-made sand production and quality environmental protection control systems from the aspects of optimizing mines, improving production processes, and environmental protection.

2. High-quality machine-made sand production process and quality control

2.1 Preferred mine

The quality of the parent rock determines the quality of the machine-made sand from the source. In the selection of sand field mines, survey work should be done, and mines with thin soil layers, less interbedded mud, high parent rock strength and good rock integrity should be selected.

The parent rock should not have potential alkali-aggregate reactivity, and limestone, dolomite, granite, basalt, etc. that are clean, hard in texture, free of weak particles and weathered fossils should be used.

The lithology of the strata exposed in the surface of Guizhou is mainly limestone, with certain basalts distributed in the west and shallow metamorphic rocks distributed in the southeast.

In the selection of railway sand and gravel mines, the principles of high quality, environmental protection and economy should be followed, and a quality inspection team should be set up to explore, test and analyze the sand and gravel sources. A certain one with shallow overburden and recoverable reserves greater than 1.5 times the design requirement mine. The mine is dominated by sandy limestone with reserves of 5 million tons.

2.2 "5S" high-quality aggregate processing technology

Most of the machine-made sand on the Guizhou market uses the "two crushing + sieving" production process, which lacks adjustment of aggregate gradation, control of stone powder content and particle shape. In response to the above problems, by improving the process, the "double desilting, double counterattack, double impact, double circulation, double separation powder" 5S high-quality aggregate aggregate processing technology is adopted to ensure the product quality is qualified and the performance is stable; The semi-finished products and finished product silos are closed and waste recycling measures are taken to solve the problems of traditional process dust, water pollution and waste disposal.

1) 5 levels of crushing, 2 times of shaping

  1. First, the jaw crusher is used to squeeze the first pre-crushing (coarse crushing) of the parent rock to reduce the diameter of the parent rock and reduce the production pressure of the impact crusher;
  2. Then use the impact crusher to crush the masterbatch for the second time (medium crushing) by means of stone throwing, so that the micro-cracks of the aggregate generated by the jaw breaking further develop, and finally the aggregate is broken again from the micro-cracks to complete the aggregate 2nd crushing and 1st shaping;
  3. Finally, the vertical shaft impact crusher was used for the third crushing (fine crushing) and the second shaping of the aggregate in the "stone hitting stone" or "stone hitting iron" manner.

2) Secondary desilting

Before coarse crushing, use a bar feeder and a desilting screen to perform the first desilting treatment of the mother rock and soil with a particle size of less than 30mm, and perform the second desilting of aggregates with a particle size of less than 10mm before medium crushing Treat and remove the soil and stone chips in the aggregate to ensure that the value of the aggregate is less than 0.5.

3) Grading adjustment

In both the middle and fine crushing stages, there is a circulation screening system, which can adjust the silo through GSP to make part of the aggregate return through the circulation system to be crushed again into smaller particle size. Adjust the production ratio of different particle size aggregates according to the needs The air separation and control powder adjusts the content of small particles to solve the problem of grading "more at the two ends and less at the middle".

4) Air selection powder

The finely crushed aggregate is first subjected to gravity air separation control powder to control the stone powder content to about 10%. Before the finished sand enters the silo, adjust the wind pressure of the stone powder extracted by the air separator as needed to adjust the stone powder content again to meet different The requirements of the strength concrete for the content of machine-made sand powder.

5) Automatic humidification

After the air separation process is completed, the finished sand is automatically humidified, and the water content of the finished sand is controlled at 2.5% to 3.5%. The stable water content is convenient for concrete production and quality control, which can effectively avoid dust during production and transportation, and prevent the segregation of aggregate during loading, unloading and transportation.

3. Environmental protection

In terms of mining, in accordance with the construction requirements of green mines, environmental protection, restoration and treatment, green restoration, energy conservation and emission reduction, soil and water conservation, and prevention of geological disasters are well done.

During the blasting process, dust control is carried out by spraying or water bag covering.

In terms of production equipment selection, choose crushing and screening equipment with superior noise reduction performance and less dust generation.

In terms of dust removal process design and layout, a dust suction device is set at each dust-generating location, and then box-type and V-type dust collectors are used for centralized dust removal, and semi-finished products and finished product silos are fully enclosed and isolated by color steel tiles.

In terms of waste reuse, the debris from the second extraction is separated again, and the stone is used for secondary processing as raw materials for roadbed fillers and concrete bricks. The mud is stacked separately for later vegetation restoration to improve material utilization and increase economic benefits. , To reduce the land occupied by waste residue storage and reduce hidden safety hazards of waste residue storage.

Faced with the depletion of natural river sand resources, the outstanding quality of low-quality machine-made sand on the market cannot meet the requirements of high-performance concrete sand for railway engineering. You can choose mines along the railway or use tunnel waste to produce high-quality machine-made sand in place to replace the shortage. River sand is used for project construction, which can not only greatly reduce the construction cost, but also reduce the environmental impact of waste residue, which has great economic value and environmental protection significance.

Next : Vertical Shaft Impact Crusher Equipment

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