Pumping agents have also been vigorously promoted in China due to their good adaptability to most cements, excellent slump retention performance, rapid strength growth, low alkali content, green and environmental protection, etc., and can give fresh concrete good and easy It has good strength development and excellent durability (low shrinkage, excellent frost resistance, etc.), slump retention, workability, etc. However, some problems often occur in actual production.
1. The pumping agent still has the problem of adaptability to cement. For some cements, the water reduction rate will be low and the slump loss will be large. Therefore, when the pumping agent has poor adaptability to cement The pumping agent formula should be trial-mixed and its components adjusted to achieve the best results. In addition, the fineness, temperature and storage time of the cement will also affect the effectiveness of the pumping agent.
2. The pumping agent is more sensitive to changes in raw materials. When the quality of sand, stone materials and admixtures such as fly ash, mineral powder and other raw materials changes significantly, the pumping agent will be mixed. The performance of the concrete will be significantly affected, and the trial mix test should be carried out again with the changed raw materials to adjust the dosage to achieve the best effect.
3. Due to the high water reduction rate of the pumping agent, the concrete slump is particularly sensitive to water consumption. Therefore, the dosage of pumping agent and the water consumption of concrete must be strictly controlled during use. Once the amount is exceeded, the concrete will suffer from undesirable phenomena such as segregation, slurry, hardening, and excessive air content.
4. The pumping agent cannot be mixed with the naphthalene-based water-reducing agent. When using the pumping agent, the mixer and mixer truck that has used the naphthalene-based water-reducing agent must be flushed, otherwise the pumping agent may be damaged. Reduce the water-reducing effect and significantly reduce the strength of concrete. The compatibility of the pumping agent with other series of pumping agents should be determined through tests.
5. The pumping agent should avoid long-term contact with iron materials. Since pumping agent products are often acidic, long-term contact with iron products will cause a slow reaction, which may even darken or blacken the color, resulting in a decline in product performance. It is recommended to use polyethylene plastic barrels or stainless steel barrels for storage to ensure performance stability.
6 For concrete above C45, high-efficiency special pumping agents should be prepared. If ordinary pumping agents are also used, the concrete mixture will be too sticky and difficult to pump. When doing mix proportion tests for concrete of C50 and above, the backflow time of the test mixture in the slump cylinder can be increased (that is, place the slump cylinder with the big mouth facing up on the iron plate, fill it with concrete and tamp and scrape it flat) , start the stopwatch when lifting the slump cylinder); the backflow time should not be greater than 20 seconds. Otherwise, pumping difficulties will occur.
7 The pumping agent is particularly sensitive to the mud content of the aggregate. Excessive mud content will reduce the performance of the pumping agent (the soil will absorb part of the pumping agent, resulting in a significant water reduction rate of the pumping agent) reduce). Therefore, the quality of aggregates should be strictly controlled when using pumping agents. When the mud content of the aggregate increases, the dosage of pumping agent should be increased. When inspecting the surface of the incoming sand and gravel, carefully observe whether there is any obvious difference in mud content. When a significant difference is seen, samples should be taken for testing immediately. If the mud content is higher than the mud content of the previously imported sand and gravel, When the amount exceeds 1%, the newly brought sand and gravel must be stored separately and the mix ratio must be adjusted before use. Otherwise, the factory slump of the concrete will vary from time to time, and sometimes the concrete mixture arriving at the construction site will collapse too quickly; sometimes the concrete will segregate severely, and even cause the pump pipe to be blocked; causing great damage to the buyer. Trouble.
8. The pumping agents are not from the same batch. Due to the different water-reducing effects of the raw materials, the water-reducing rate (at the same dosage) increases or decreases. In actual production, if other raw materials have not changed significantly and the water consumption has not changed, the produced concrete mixture becomes dry: this means that the water reduction rate of the pumping agent has become smaller, and pumping should be increased immediately. The dosage of the agent. If the produced concrete mixture becomes thinner, it means that the water reduction rate of the pumping agent becomes larger, and the dosage of the pumping agent should be reduced immediately. The specific amount of increase or decrease should be determined based on the difference between the slump of the concrete mixture and the required extrusion slump. The amount can be increased or decreased by 0.1% for each 20mm difference in slump.
9. The setting time of concrete pumping agent changes with the change of atmospheric temperature. The setting time of admixtures added to concrete is formulated based on the recent average atmospheric temperature. When the atmospheric temperature suddenly changes, if the amount of pumping agent is not adjusted in time, concrete retardation accidents may occur. Especially in late autumn and early spring, windy and cooling weather often occurs. When it is known from the forecast that there will be strong winds and cooling, the concrete production mix ratio should be adjusted 12 hours in advance, that is, the concrete mix ratio should be increased by one level, the pumping agent dosage should be reduced by 1/4 (based on the original dosage), and increased by 15 ~20 kg of water usage. This will prevent the concrete from retarding.
10 There is a big gap between the on-site inspection data of pumping agent and the actual production. When the dosage of pumping agent is the same, the water consumption required to produce concrete is 20 more than that during on-site inspection. About kilograms. Moreover, the collapse loss of the concrete mixture is also significantly accelerated. The reasons are mainly due to the large volume of production and the high temperature of the gelling material in the powder silo (which can reach more than 80°C in summer). The high temperature of the material will absorb the pumping agent, resulting in a reduced water reduction effect. ; Also because the exit temperature of concrete is high, the collapse loss of the mixture will be significantly increased.��. Therefore, when conducting on-site inspection of the pumping agent, the water consumption can be controlled at 150-155 kg/m3, and the slump of the outgoing concrete can reach 210mm or above.
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