Date: Oct. 08, 2021
Mineral resources are an important material basis for economic and social development. As an important mineral resource in basic raw materials, sand and gravel aggregates have an annual production and consumption of about 40 billion tons in the world, of which my country accounts for about half. Under the current background of my country’s economic and social development, especially in the process of accelerating urbanization, the aggregate industry has a pivotal strategic position. For users of sand and gravel plants, how much do you know about the little knowledge of gravel aggregates? The following LZZG will give you a little knowledge of sand and gravel aggregates.
Coarse aggregate should mainly control its particle size, gradation, grain shape, stone powder content, mud content, and mud content. Each vehicle shall undergo a macro inspection, and the vehicle shall not be unloaded if it is unqualified. In addition, various indicators must be inspected in batches by the requirements of the specifications. Fine aggregate should be controlled fineness modulus, mud content, and mud content. Each vehicle shall undergo a macro inspection, and the unqualified vehicle shall not be unloaded; it shall also be inspected in batches by the requirements of the specification.
The particle size of the coarse aggregate is restricted by the diameter of the concrete pumping pipeline and the pumping height. Generally, the pumpable particle size decreases as the pumping height increases. For example, when the pumping height is less than 50m, the ratio of coarse aggregate particle size to delivery diameter is ≤1:3. When the pumping height is 100m, the ratio will be reduced to 1:5, otherwise, the pipe will be easily blocked.
When its content is high, the flexural strength of the needle-shaped coarse aggregate is relatively low, and the bonding strength between the coarse aggregates decreases, which causes the strength of the concrete to decrease. For ready-mixed concrete, the high content of needles and flakes will make the coarse aggregates poorly shaped, thereby reducing the fluidity of the concrete. At the same time, the needles and flake aggregates are easy to block at the pipeline, causing the pump to block or even burst pipes. . Therefore, the content of needles in pumped concrete is required to be controlled below the standard value, and the requirement for high-strength concrete is even higher.
Concrete needs to use medium sand. In addition to the standard requirements for sand gradation, mud content, and mud content, it is also important to note that the sand that passes through the 0.315mm sieve is not less than 15%. This has a great influence on the permeability of concrete. If the value is too low, it will easily block the pump and make the concrete have poor water retention and bleeding.
If the sand is too fine, the water demand for the concrete will increase. Moreover, the pumpability and plasticity retention of the concrete prepared with fine sand is extremely poor, the concrete strength will decrease, and the concrete will be easy to crack.
If there is a problem with the sand source, fine sand and some machine-made sand can be used to prepare pumped concrete. For example, fine sand with a fineness modulus of less than 2.0 can be mixed with machine-made sand with a fineness modulus of 3.0-3.2, and the ratio is about 6:4. Observe its fluidity and pumpability, and determine the ratio through experiments.
The sand content is large, the concrete water demand is large, the plasticity is poor, the shrinkage is increased, the concrete strength is reduced, and the structure is easy to crack. Therefore, the mud content of sand should be controlled ≤3% (C30-C50), and the mud content of high-strength concrete is more demanding. high.
In addition to the same impact as mud in sand and gravel, it can also seriously affect the strength of concrete. For example, mud blocks will weaken concrete sections. When pouring the ground, the mud blocks float up and will form pits and other defects on the surface after shrinking.
The amount of sand and gravel in the ready-mixed concrete is about 800-1100kg/m3, and every 1% of its water content will bring about 8-11kg of water in the concrete. In particular, sand is usually collected from the river, and the moisture content varies greatly. If the moisture content is not frequently detected and the mixing water consumption is adjusted in time, it will cause great fluctuations in the slump, pumpability, and strength of the concrete.
LZZG not only provides customers with corresponding mining machinery and equipment, our technical research and development team will also bring customers relevant knowledge about sand and gravel aggregates, sand and gravel aggregate material analysis, testing and testing machines, production line planning, equipment selection, etc. . All after-sales and cutting-edge technicians will regard users as friends and do their best to provide you with relevant technical guidance except for fine sand screening equipment.
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