How can we produce high-quality sand and gravel aggregates for railways?

1. First of all, we must choose a qualified parent rock

The requirements for the raw materials of the parent rock for railway ballasts and sand and gravel for railway concrete are higher than those of other industries, and the quality of the parent rock determines the quality of the sand and gravel aggregate.

The raw materials of the parent rock must first meet the requirements of the alkali aggregate test, and the radioactivity should meet the requirements of GB6566.

Indicators such as the dry density, saturation compressive strength, crushing value index, robustness, moisture content, and dry water absorption rate of the saturated surface of the parent rock are qualified.

Hazardous substances such as sulfides, sulfates, organic matter, light substances, chloride ions and mica content are qualified for testing.

The mother rock of processed sand and gravel aggregates should generally not be less than 90MPa for igneous rocks, less than 80MPa for metamorphic rocks, and less than 60MPa for hydrogenic rocks (sedimentary rocks).For the preparation of mechanical sand for concrete of C50 and above, the ratio of the compressive strength of the parent rock to the strength grade of the concrete should not be less than 1.5.When processing railway ballasts, try to choose volcanic rocks with high compressive strength and toughness such as basalt, tuff, granite, etc.

When using cave slag raw materials, try to choose second- and third-level surrounding rocks with low impurity content such as soil and light matter as the parent rock.

Dry sand must first ensure that the quality of the parent rock meets the basic requirements of soil, moisture, etc.; The raw materials of the hole slag must also be tested for changes in the raw materials in a timely manner, sorted, pre-sieved, and stored in the shed to reduce the moisture content of the raw materials of the parent rock.

2. Reasonable selection of sand and gravel aggregate processing technology and equipment

According to the characteristics of the local climate and the characteristics of the parent rock, try to choose dry processing technology and crushing equipment with good performance.

For the processing of medium-soft materials of limestone, a counterattack crusher can be used instead of a hammer crusher. This is because the aggregate processed by the hammer crusher has a high content of needle flakes, many dark cracks inside the aggregate, low crushing value, and large loss of robustness. The highway industry clearly adopts the recommended use of counterattack to break the processed aggregate.

Processing railway ballasts or using high-hard materials such as basalt, granite, tuff, etc., medium crushing equipment generally uses single-cylinder hydraulic cone crushers or multi-cylinder hydraulic cone crushers, and fine crushing equipment generally uses multi-cylinder hydraulic cone crushers with laminated crushing function to minimize the needle-like content of sand and gravel aggregates.

The shaping sand-making machine should adopt an impact breaking with a “stone-to-stone” crushing cavity type, with a linear speed of 60-70 m/s at the edge of the rotor, good aggregate shaping effect, moderate sand-forming rate, and less stone powder production; after shaping the sand, it produces sand, 4.75-10mm, 10-20 mm three-stage configuration or sand, 4.75-10mm, 10-16mm, 16-25 mm four-stage configuration.