Sand is an important part of concrete aggregate, and its fineness modulus, particle size characteristics and other quality indicators have an important influence on the compactness, workability and physical and mechanical properties of concrete. The development of artificial mechanism technology is mainly due to the reduction of natural riverbed sand and gravel materials and the establishment of river channel protection laws; the increase in the scale of construction and the shortening of construction period, the sharp increase in the amount and strength of engineering sand is also the main reason for the development of mechanism sand technology. power. The maturity of machine-made sand technology has played a positive role in promoting the construction of water conservancy and hydropower projects.
1. The development status of machine-made sand technology
1.1 Machine-made sand processing technology
Machine-made sand processing is divided into wet sand making and dry sand making according to the process. In the past, due to the limitation of the feed size of the sand making equipment (also called superfine crusher), the sand making raw materials only had to undergo multi-stage crushing (generally 4 grades). ). Traditional sand making equipment such as ultra-fine crushing cone crusher and rod mill requires less than 25mm of sand making raw materials, and the process is quite complicated. With the development of crushing and screening technology and the emergence of high-performance crushing equipment, the maximum particle size of sand-making raw materials has reached 40-60mm. Summarizing domestic and foreign machine-made sand production technology experience, the general process flow is shown in Figure 1.
Whether the machine-made sand is produced by wet method or dry method, in addition to obtaining qualified fineness modulus and excellent particle size characteristics, excess stone powder and soil in the product must be removed to reduce and stabilize the moisture content of the finished sand.my country’s current sand and gravel standards require that the powder content of machine-made sand be controlled at 6%-12%, and the mud content
1.1.1 Wet sand making process
Rod mill is the most common wet sand making equipment. The feed size is 5-25mm, and the content of crushed stone larger than 5mm in the finished product is very small. The discharged product is divided into machine-made sand and waste sludge by a spiral classifier and a cyclone. The water and waste sludge water are finally sent to the rotary classifier or grit tank to recover the lost fine sand. In domestic and foreign hydropower projects, wet production uses special purification equipment to treat mud and sewage.
1.1.2 Dry sand making process
The typical production process is to use 5-40mm crushed stone (gravel) as the raw material to supply the sand making machine. The screening and grading equipment removes the crushed stone larger than 5mm and part of the 2.5-5mm fine crushed stone and returns to the sand making machine for reprocessing. It is classified into two levels of 0.6-2.5 and less than 0.6. The fine sand material less than 0.6 is passed through an air classifier to remove excess stone powder, and finally 2.5-5, 0.6-2.5mm and 3 materials less than 0.6 are uniformly mixed through the mixing equipment to meet the requirements. The quality requirements of machine-made sand. In some foreign projects, in order to reduce the stone powder content, reduce the wear of the sand making machine, and simplify the process flow, measures such as reducing the equipment crushing ratio and lowering the feed particle size are adopted to solve the problem.
1.2 Development of machine-made sand processing equipment
As my country increases investment in infrastructure construction and expands domestic demand, many domestic engineering projects will be started one after another in the “Twelfth Five-Year Plan”. Among the proposed engineering projects, general natural sand and gravel are relatively scarce, and artificial aggregates are likely to be used. Inevitably, further research on the processing technology of artificial aggregate will help improve the quality and efficiency of project construction.
(1) In large-scale engineering projects, the production of sand materials has always been paid attention to. Research on new sand making processes and the use of advanced sand making equipment can greatly improve the reliability of the machine-made sand production process, ensure product quality, and save engineering investment.
(2) For large-scale engineering projects, especially those with large concrete volume and high strength, the scale of concrete aggregate processing is huge. The production of machine-made sand should be separated from the production of coarse aggregate to facilitate the management of system production and operation and stabilize and balance the production of machine-made sand. Production.
(3) The machine-made sand is produced independently, which can realize automatic control, reduce the configuration of production management personnel, and realize real-time computer monitoring and automatic adjustment of product quality.
(4) When the production scale of machine-made sand does not exceed 200t/h and the quality of the quarried stone material is easy to control, it is recommended to consider dry production, which can not only save the total investment of the project, but also meet the environmental protection requirements more easily.
In short, the future of machine-made sand processing is aimed at quality control and cost saving. With the continuous emergence of new equipment and the continuous improvement and maturity of process technology, it will certainly play a huge role in promoting engineering construction.
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