Raw material quality cause analysis and preventive measures

Cause analysis and preventive measures for unstable mud content in sand

1.1 Cause analysis

As natural sand resources become less and less, the mud content of sand also fluctuates. This phenomenon sometimes occurs even in sand from the same sand source. When the mud content is large, more admixtures need to be added, because the mud adsorption reduces the components: when the mud content in the sand suddenly becomes small, if the amount of pumping agent is not reduced, the concrete mixture will segregate, because the admixture The amount has exceeded its saturation point.

1.2 Preventive measures

To maintain the stability of the mud content in the sand, when the sand is detected When there is a big difference in mud content (up to 0.5%), they should be stored separately and not mixed. Pay attention to the adjustment and use of the amount of admixtures in the mix ratio.

2 Analysis of causes and preventive measures of unstable fly ash quality

2.1 Analysis of causes

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The power plant must arrange maintenance every year, resulting in a reduction in fly ash production. At this time, if the grade or manufacturer of fly ash is frequently changed, and if the amount of pumping agent is not changed in time, the concrete mixture will segregate. Because fly ash of different grades and fineness are pumped into the same silo, it is difficult to predict when another type of ash will be used. When fly ash of the same grade from different manufacturers is put into the same silo, its properties such as loss on ignition may be different, which may also lead to segregation of the concrete mixture. Because fly ash with large loss on ignition generally contains high carbon content, it is easy to absorb pumping agents, affecting the slump loss and construction performance of concrete.

2.2 Preventive measures

Use the same manufacturer and the same grade of fly ash to prevent the merger of different manufacturers Different grades of fly ash are mixed into the same silo. If it is really necessary to replace the silo, wait until the fly ash in the silo is used up before adding new fly ash into it. Fly ash of different models or manufacturers must not be mixed.

3 Cause analysis and preventive measures for standard consistency water consumption in cement

3.1 Cause analysis

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When cement is mixed with poor mixing materials or clinker, the standard consistency water consumption will increase significantly. If this kind of cement is being used for production, The standard consistency of newly imported cement and the water consumption are significantly smaller, which can easily lead to segregation of the concrete mixture. The reason is that as the admixture in the cement becomes better, the adsorption of water-reducing components decreases. If the dosage of the pumping agent is not reduced in time, it will lead to overmixing of the pumping agent and segregation of the concrete mixture.

3.2 Preventive measures

When doing cement on-site inspection, the standard consistency of the cement must first be tested When the water consumption of the standard consistency changes significantly, the adaptability test of the water-reducing agent should be done to determine the appropriate dosage of the water-reducing agent. When the water consumption of the standard consistency becomes larger, more water-reducing admixture needs to be added to the concrete, and vice versa. To maintain the stability of the quality of the cement entering the site, communicate frequently with the cement manufacturers and require them to promptly notify the mixing station when there are changes in the mixing materials so that countermeasures can be taken.

4 Cause analysis and preventive measures of cementitious material temperature

4.1 Cause analysis

The temperature of the cementitious material is also an important factor affecting the segregation of the concrete mixture. In fact, the test temperature of the water-reducing agent is quite different from the temperature of the cementitious material used in production. The temperature difference range is about 25 to 30 degrees. The higher the temperature of the cementitious material, the more pumping agent is adsorbed. Therefore, the actual production will be higher than the dosage in the test. And if the production volume is discontinuous, segregation may occur if the amount of water-reducing agent is not reduced when work is restarted. Because the temperature of the cementitious material is relatively high when it is first unloaded into the silo, the temperature gradually decreases as time goes by. When the temperature of the cementitious material drops a lot before concrete is produced, overmixing will occur if the amount of pumping agent is not reduced.

4.2 Preventive measures

The first truck of concrete newly opened every day must be discharged to check the quality of the concrete. To check the workability, check whether there is segregation in the mixture. If there is slight segregation, it can be shipped from the factory. If there is serious segregation, gelling materials must be added for adjustment. Slight segregation means that the slurry flows out of the mixture pile within 3cm. If it is greater than 3cm, it should be serious segregation. The moisture content of the production materials should be measured regularly.

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