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A brief discussion on close gradation, open gradation and semi-open gradation

Release time:Apr.20.2024 Views:0

The particle gradation of sand and gravel aggregate refers to the proportion of particles of different particle sizes. (stone crusher)Good gradation means that the gaps between coarse particles are filled by medium particles, and the gaps between medium particles are filled by fine particles. Such step-by-step filling makes the sand form. In the densest packing state, the void ratio reaches the minimum value and the packing density reaches the maximum value. This can achieve the purpose of saving cement and improving the comprehensive performance of concrete. Therefore, the particle gradation of sand and gravel aggregate can reflect the size of the void ratio.

Dense gradation, open gradation and semi-open gradation are mainly divided according to the classification standard of void ratio. The void ratio here is affected by the gradation composition of the mineral material. A relatively large void ratio is an open gradation. If it is relatively dense, In fact, the void ratio is relatively small, which means dense gradation.

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Dense grading

Dense gradation is a concrete mixture with continuous particle gradation of various particle sizes, dense mineral materials embedded in each other, and mixed with asphalt binder. Dense gradation, which is similar to the concept of continuous gradation, refers to the filling situation. Therefore, even if the aggregate transition curve is not smooth, as long as the porosity is relatively low and the mixture is densely filled, it is called dense gradation. The mix ratio is designed according to the principle of maximum density, and the void ratio is 3% to 6% for dense gradation.

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Open grading

Open gradation is an open asphalt mixture that is mainly composed of coarse aggregates embedded, with less fine aggregates and fillers, the minerals are pulled apart from each other, and the void rate after compaction is not less than 12%.


Half open gradation

Semi-open gradation is a semi-open asphalt with an appropriate proportion of coarse aggregate, fine aggregate and a small amount of filler (or no filler) mixed with asphalt binder. The residual void rate after compaction is between 6% and 12%. The mixture, also known as asphalt gravel mixture, is generally used as a flexible base.

The difference between open gradation and semi-open gradation is the different extrusion composition of the mixture. In addition, there is continuous open gradation. The entire mineral particle distribution range is narrow. From the maximum particle size to the minimum particle size, there are only a few particle sizes. The mixture appears in a continuous form. This graded mixture has more coarse aggregates and less fine aggregates, has a higher internal friction angle but lower cohesion.

The assessment of particle gradation can be carried out by particle size analysis. This method performs particle size analysis on sand and gravel samples to obtain the percentage of particles in different particle size ranges, thereby determining the particle gradation. Commonly used equipment for particle size analysis include wet screening method, dry screening method and laser particle size analyzer. Through particle size analysis, the cumulative percentage curve or particle distribution curve of sand and gravel can be obtained, from which the proportion and distribution of various particle sizes in sand and gravel can be understood.

Better sand and gravel gradation can effectively reduce the void ratio of aggregates in concrete and improve the working performance of concrete. At the same time, it can reduce the amount of glue and admixtures and save costs without reducing the workability and strength of concrete.

As a leader in green and environmentally friendly solution providers in the construction crushing industry, Xingao Heavy Industry has worked in the crushing industry for decades and accumulated rich experience. The sand and gravel aggregate production line can be customized according to the actual production needs of users. Specification of production equipment, with rational and scientific configuration, excellent particle size of finished products and reasonable gradation, can reduce costs and increase efficiency within an effective range. The case sites cover mining, cement, construction waste and other fields, and the service outlets are more It is spread across every province in the country.