Before the sand gravel (wool) is mined, the soil layer covered by the useful layer is removed, and impurities such as covering soil and grass roots are not allowed to be mixed. The cover layer should be cleaned as much as possible once, and a margin is left to prevent the covering soil from slipping in the excavated wool. In view of the high groundwater level and the shallow depth of mudstone, before the mining, the drainage open channel is excavated to reduce the groundwater; during the excavation process, the stripping width is not less than 0.8m in the order from bottom to high; The excavation depth is controlled, and the thickness of the reserved layer is not less than 0.2 m.
The mechanical sand grading is poor, and the fineness modulus is large. The main reason is that the cumulative screening ratio of 2.36mm and the passing rate of 0.075mm are large. Therefore, the key to controlling the gradation and fineness modulus of the mechanical sand is to minimize The size of the vibrating screen and the adjustment of the dust removal (washing) strength.
The adjustment of the mesh size is reliably performed by replacing the vibrating screen, and the adjustment of the dust removal (washing sand) strength is reliably adjusted to complete the wind (water flow). Practice has proved that when the minimum vibrating screen mesh size is 3.5mm, the fineness modulus of the machined sand produced is generally within 3.4, and the grading meets the standard requirements.
In the production process, the mechanical sand is inevitably accompanied by a small amount of stone powder with a particle size of less than 0.075 mm. According to the quality standard of natural sand, particles smaller than 0.075 mm are defined as mud, and the content limit on mud is very strict. The stone powder in the machine sand is obviously different from the mud. A large number of experimental research and engineering application practice show that the mechanical sand containing a certain amount of stone powder has a great help to improve the working performance of the medium and low strength grade concrete, and has little effect on the concrete strength. However, when the content of stone powder is high, it has an adverse effect on the preparation of high-strength concrete. Therefore, how to remove and control the excess stone powder in the mechanism sand is one of the key technologies for the production of sand making machine.
The methods currently used mainly include dry dust collection and wet water washing. Dry dust collection is a dust collector with good dust collection effect, and the working condition parameters of the dust collector are determined according to the requirements of the stone powder content in the mechanism sand. However, this method is only applicable to the production of Class III mechanical sand. Mechanism sand washing powder is the key technology for producing high quality machine sand, but it needs to pay attention to water saving and environmental protection.
The mud in the machine sand is mainly caused by the entrainment of mud from the stone. To control the mud content in the sand, the following work must be done:
The crushing index of machine-made sand is used to measure the ability of mechanical sand to resist crushing under increasing load to evaluate its applicability in engineering. It is an important indicator for indirectly expressing the robustness of mechanical sand. The crushing index directly affects the strength of the prepared concrete, especially for high-strength concrete.
The mechanical crushing index value of the particle shape is generally in the range of 20% to 25%. The needle-like content in the mechanism sand is most sensitive to the crushing index value, and the non-professional mechanism sand field produces more granular needles. The value of the mechanism sand crushing index is generally above 30%, or even higher. For the mixing of ordinary concrete, the mechanical sand with the crushing index value below 30% should be used. The production control measures are mainly to select the rock with high compressive strength and good rock mass to make sand.
When the sand and gravel aggregates screened by the screening workshop are transported by the belt conveyor to the finished material storage yard, the separation wall should be set up and partitioned to prevent mixing in the material yard. The product signage is set in the stacking area of the finished material, and the spacing of the aggregates naturally stacked without the partition wall is >3m, and it must be neat and orderly. A blind ditch drainage system is built in the finished product yard to ensure that the washed aggregate can be quickly dehydrated after entering the pile to meet the moisture content requirements for concrete production.
As the country's investment in infrastructure increases, the amount of concrete and sand increases sharply, while 70% of concrete is gravel and sand. In addition to the depletion and prohibition of river sand resources, high-quality machine sand has become a construction sand. The primary choice is broad.