Precautions for quality control of machine-made sand

Poor grading of machine-made sand and instability of stone powder control are the main problems in the use process. The shape of machine-made sand is sharp, which is unfavorable to the workability of concrete, and an appropriate amount of stone powder can make up for this defect. Appropriate stone powder can improve the workability of concrete, increase the amount of concrete and the viscosity of the slurry, reduce bleeding and segregation; it can also be used as an admixture to reduce the amount of cement. The range of these two indicators is the focus of quality control. It is recommended that the gradation range be controlled at level II, the fineness modulus should be controlled between 2.6 and 3.0, and the stone powder content should be controlled between 6% and 9%.

To control the poor gradation of machine-made sand and the unstable stone powder content, the following two aspects should be considered:

(1) Grasp equipment investment. The production of machine-made sand should use an impact crusher, which can better control its gradation and angularity; the dust removal method in the production process should use a dry dust removal system for dust removal and adjustment of the stone powder content, so as to effectively and stably control the stone powder content.

(2) Strengthen sample sampling. The production line needs to conduct self-inspection and self-school once a week. The finished machine-made sand must be sampled every working day for particle gradation, stone powder content, and mud block content; the apparent density, bulk density, and porosity must be tested every 7 working days; methylene blue value, organic matter content, light matter content detection, so as to ensure the stable quality of the machine-made sand production line. After the machine-made sand enters the field, the particle gradation, stone powder content, and mud block content are tested every working day; the crushing index, apparent density, and porosity index are tested every 7 working days. The chloride ion and alkali aggregate reaction test should be carried out when selecting the stockyard in the early stage, and the adaptability test of cement, admixtures and machine-made sand should also be carried out when the mix ratio is designed.

Control of moisture content during use

Due to the high content of stone powder, the internal water content of machine-made sand will vary greatly with the external environment. It is easy to make the state of the concrete after mixing unstable due to the uneven water content of the machine-made sand stored in the silo, and the slump changes more rapidly. If it is large, it will bring difficulties to concrete control. Aiming at this problem, the moisture content control process can be correspondingly added in the silo management in the front and rear fields of production. Such as dry sand making, it is necessary to add a water spray device when the finished product is out of the machine, so that the machine-made sand has a stable moisture content, and the moisture content is 3% to 5%. Ensure that the water content of the machine-made sand is uniform. For sand production by water washing, attention should be paid to the control of the stone powder content, and after water washing, the water content of the machine-made sand should be within the control range before it can be transported out of the field. When the machine-made sand is stored in the backyard, the stacking height of the silo shall not be higher than 5m, which can not only reduce the internal change of the water content, but also prevent the machine-made sand from rolling off and segregating.

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