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The adaptability of concrete admixture? Seven-step solution! (2)

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The adaptability of concrete admixture? Seven-step solution! (2)

Issue Time:2020-04-23
The third step of the adaptability test is to find out the saturation blending value of the superplasticizer used for this cement. If two or more superplasticizers are mixed, the cement paste is passed through the total amount of the mixture. Test to find the saturation dosage point. The closer the amount of superplasticizer is to the saturated content of the cement, the easier it is to obtain good adaptability. However, the saturation blending point of early strength cement is generally high, making traditional high-efficiency water-reducing agent more than 1% or 0.8% (calculated based on active ingredients), which is generally achieved for pumping agents with a blending amount not exceeding 2.5% Saturation dosage is not realistic, even "close" is impossible, mainly depends on the compounding of different high-efficiency water-reducing agents, and compounding with a variety of retarders to achieve the purpose of adjusting adaptability. According to experience, the amount of water-reducing agent is less than 70% of the saturated dosage, even if a variety of retarders are used to adjust the adaptability at the same time, satisfactory results cannot be obtained. (Grouting)

The cement paste test can be done with pure cement, or the total amount of 300g of cementitious material can be distributed according to the proportion of cementitious material in the concrete mix ratio. It is often easier to find the correct result by using the previous plan and then the latter plan.

4 Clinker plasticity
The fourth step is to try to adjust the degree of alkali sulfate in the cement, that is, the degree of clinker plasticization to a suitable range. The calculation formula of the SD value of the clinker plasticity is:

SD = SO3 / (1.292Na2O + 0.85K2O)

The content of each component is listed in the clinker analysis. The SD value ranges from 40% to 200%. If it is low, it means that there is less sulfur trioxide. If a small amount of sulfur-containing salt such as sodium sulfate is added to the admixture, if it is too high, it means that the molecule is too large, that is, sulfur trioxide. The pH of the admixture should be adjusted slightly with alkali, for example with sodium carbonate. (Sichuan admixture)
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5 suitable coagulant
The fifth step is to test compound admixtures and find out the suitable coagulant varieties and the proper blending amount through the pure pulp test. To refer to the results of the second step of investigation, select a possible effective coagulant.

Cement with a lot of tricalcium silicate minerals should use sodium gluconate and other hydroxy carboxylates, and use polyphosphates, especially sodium hexametaphosphate and sodium tripolyphosphate, but the interaction between sodium gluconate and hexameta is easy. It is not recommended to use at the same time. In addition to choosing sodium gluconate, cement with a large amount of aluminate minerals must also be compounded with appropriate additives-partners, such as sodium tripolyphosphate, modified starch and dextrin, etc. Monosaccharides have a synergistic effect on sodium gluconate Can be used when the temperature is high. So the good quality liquid sodium gluconate is sometimes better for this reason. However, when the total amount of retarder exceeds 0.07% of the amount of gelling material, retarder becomes the main effect. There is a view that the polycarboxylic acid water-reducing agent should be used at this time, because aluminate minerals seriously adsorb sulfonic acid-based superplasticizers such as naphthalene sulfonate but do not adsorb polycarboxylic acid-based superplasticizers.

The sand content of a commercial concrete company's sand is average, but the slump loss of the concrete has always been very large. After the test, all the polycarboxylic acid water-reducing agents were used, so that the problem of large slump expansion and small expansion was satisfactorily solved. If you cannot know the chemical and mineral composition of cement clinker or the type of cement mixture, the admixture can only be explored with any of sodium gluconate, sodium citrate or sodium hexametaphosphate. Addition of sulphate must also be tested in turns. (Waterproof repair agent)

When the quality of the sand is poor, such as a lot of mud, or full use of artificial sand or ultra-fine sand mixed concrete, after satisfactory results are obtained in the slurry test, it is appropriate to continue the mortar test and further adjust the adaptability to the admixture. Due to the poor sensitivity of the mortar test, when the material is insufficient, the concrete test is directly conducted after the slurry test.

6 Concrete test
The sixth step of the adaptability test is the concrete test. At least less than 10 liters. Due to the addition of sand, stone, water and other materials, the amount of cementitious material is also more than 10 times larger than that of the cleansing test, and there are different factors such as the different operating methods of the test personnel, the results of the cleansing and concrete tests are often contrary. Although it may be necessary to make major adjustments, it is not necessary to reinvent the wheel. Most of the admixture ingredients used in the previous test can continue to be used, but the dosage will be different. Some components need to be added or deleted. It is sometimes necessary to increase the dosage of high efficiency water reducer. In short, if the paste is adjusted, it may still not work in the concrete. If the paste is not adjusted, the concrete will not work.

The increasingly poor quality of local building materials is a common phenomenon at present. The high mud content of sand has become "normal" in many areas, which makes adaptive adjustment difficult. Due to the high mud content in the aggregate, the mixture becomes too viscous, and the effect of using the viscosity reducer is not obvious at this time. The sulfamate superplasticizer and the naphthalene superplasticizer are often combined and mixed appropriately Retarders that are prone to bleeding may get better results.

After a small amount of test is successful, sometimes it is necessary to repeat the magnification, such as 25-45 liters, because the results may be different. (Professional intelligent manufacturer of special materials)

7 Properly modify the mix ratio

Only when a certain number of concrete tests are successful can the adaptive adjustment be completed. However, in many cases, the method of adjusting the admixture alone can not always achieve satisfactory results, even if the adaptability can be passed, sometimes the product cost is too high, and it is not acceptable to users. Therefore, the seventh step of the adaptive adjustment test is to appropriately modify the concrete mix ratio: depending on the different performance of the adaptation, the number of mineral admixtures can be appropriately increased or decreased, and the single admixture is changed to double admixture, that is, both There is no doubt about the superiority of double blending than single blending of different materials; increasing or reducing the amount of cement can solve the problems of concrete stickiness, rapid collapse and concrete bleeding, especially surface sand leakage; slightly increase or reduce water use Quantity; increase or decrease the sand rate, and even partly exchange the sand varieties, such as the combination of coarse and fine sand, natural sand and artificial sand. The cost of these small modifications will be basically unchanged, and the operation is simple, but the effect is sometimes obvious. Of course, changing the cement of a production plant when necessary will also solve long-standing problems.
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