【Sand aggregate】Exploration of the use of machine-made sand in concrete

        Writer:市场部Source:米科思 Date:2020-11-25 12:37
        Due to the composition of the raw materials used and the stone quality, production equipment, technology and other factors, machine-made sand will have great differences in particle shape, gradation, firmness, and stone powder content.  Due to the particle gradation, needle flake content, stone powder content, and mud content of machine-made sand, these indicators can be adjusted and controlled by changing the equipment and process parameters during the production process.  Reasonable crushing and shaping equipment and supporting technology ensure good grain shape and gradation.
         At present, there are two main forms of domestic machine-made sand production. One is specially produced machine-made sand. Its gradation and fineness modulus can be better than natural sand, and its grain shape can also be similar to natural sand.  The other is the use of various tailings to produce or produce, which is the main body of the current machine-made sand, most of the stone chips after the production of crushed stone are simply processed and screened or directly used.  There are many machine-made sands made from stone chips. Some stone chips with unqualified gradation or grain shape are used as fine aggregates. The result is poor workability and low strength. Therefore, some people think that machine-made sand is not good or comparable.  Not on natural sand, this is a misunderstanding.  The essential difference between machine-made sand and natural sand is that many of its indicators are to be controlled and controllable, so as long as the production process is advanced and reasonable, and the control is strict, high-quality machine-made sand can be produced.
        1-Pay attention to the content of stone powder in machine-made sand. Stone powder has a different composition, particle size distribution, shape, and role in concrete from the mud in natural sand.  Stone powder is inevitable in the production of machine-made sand, and the effect of proper amount of stone powder in machine-made sand is beneficial.  A proper amount of stone powder in the concrete can play a filling role, which is conducive to the improvement of the strength of machine-made sand concrete, but the best stone powder content of machine-made sand concrete with different strength grades is different.  The complete micro-gradation and rough surface of the stone powder play a good filling effect, nucleation effect, activity effect, water retention effect and lubrication effect at the interface of concrete.  It makes the paste compact, reduces the porosity, reduces the size of hydrate crystal particles, reduces the degree of orientation, reduces the actual water-cement ratio of the paste around the aggregate, and improves the workability of concrete.  In addition, as the content of machine-made sand and gravel powder increases, the permeability coefficient of machine-made sand concrete gradually decreases, increasing the compactness of cement stone.  Of course, if the parent rock is siliceous rock or sandstone and other materials with poor water requirements, the high content of stone powder may increase the water consumption of concrete.  The powder content of machine-made sand should be appropriately controlled.  From the production practice point of view, the stone powder content is controlled at 8%~10%, which can play a good role in concrete with various strength requirements. It is not necessary to reduce the amount of stone powder if the concrete strength level is high. The key is to control the methylene blue MB value.  , Use stone powder with methylene blue MB value less than 0.5, the effect is best.  But too high content of stone powder will increase water consumption, affect the strength of concrete, and cause plastic cracks in concrete.
        2-Adjust the design idea of ​​concrete mix ratio
         The characteristics of machine-made sand determine that the mix ratio design of machine-made sand concrete should be different from the design of natural sand concrete mix ratio. The technical personnel of concrete production enterprises using machine-made sand must change their concepts and systematically understand the technical indicators of the machine-made sand used, and  The impact on the performance of concrete must be aware of its differences, so as to adjust the design ideas of concrete mix ratio.
         01Sufficient amount of cementing material
         Under the influence of stone chips and stone powder, sufficient amount of cementitious material must be ensured to meet the workability of concrete. If the amount of cementitious material is too small and the sand rate is low, the concrete mixture will have poor viscosity, poor fluidity, and easy  Segregation can easily cause mixing difficulties, pipe blockage, and difficulty in pouring and construction.
         02Reasonable sand rate
         Reasonable sand ratio refers to the sand ratio value at which the concrete mixture obtains the maximum fluidity and maintains good cohesiveness and water retention when the water consumption and the amount of cementitious materials are constant.  The sand ratio of machine-made sand concrete is related to the porosity of concrete stones and the fineness modulus of machine-made sand.
         03 suitable slump
         Because the machine-made sand concrete mixture has good viscosity, poor fluidity, fast setting, easy segregation and high pumping resistance, the slump of concrete should be strictly controlled.
         04Added air-entraining composite admixture
         For machine-made sand with lack of fine particles and poor gradation, a certain air-entraining agent or thickener can be added, which can not only improve the durability of concrete, reduce the segregation and bleeding of concrete mixture, but also introduce it  The air bubbles, such as "balls", can increase the workability of concrete and make it easier to pour and compact.  In this way, the viscosity and plasticity of concrete can be increased, and the pumping performance of concrete can be improved.
        3- Pay attention to the maintenance measures taken
         When the concrete produced with machine-made sand is used in the construction of cast-in-place slabs, it is covered with a plastic film for moisture maintenance immediately after the concrete is poured.  As long as the maintenance measures are proper, the cracks of the cast-in-place slab can be effectively solved.

        TypeInfo: Company News

        Keywords for the information:Sand aggregate 

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