With the widespread use of commercial concrete, the use of concrete admixtures has also become a popular trend, which greatly improves the flow properties of concrete and reduces the amount of cementitious materials in concrete. Therefore, concrete admixtures are widely used. In experiments and practices, people have found that adding admixtures to concrete can improve the technical properties of concrete and achieve significant technical and economic effects. Mastering the correct use of admixtures can improve the strength of concrete and reduce costs. Improper use of admixtures can also cause insufficient concrete strength, poor workability, and increased costs. It may also cause an accident. Therefore, when using admixtures, you should pay attention to the following points:
(1) Selection of concrete admixture varieties
There are many varieties of admixtures with different effects, especially for different types of concrete admixtures. Different types of cement have different effects. When selecting admixtures, it should be determined through tests based on project needs, on-site material conditions, reference to relevant information.
(2) Determination of the dosage of admixtures
Concrete admixtures all have appropriate dosages. If the dosage is too small, the expected effect will often not be achieved; if the dosage is too large, It will cause waste, sometimes affect the quality of concrete, and even cause quality accidents. Therefore, the optimal dosage should be determined through experiments.
(3) Methods of adding admixtures
Different methods of adding concrete admixtures into concrete mixtures have different effects. For example, the post-mixing method of water-reducing agent is more effective than the first-mixing method and the simultaneous-mixing method, and the dosage is only half of that of the first-mixing method and the simultaneous-mixing method. The so-called first-mixing method is to mix the water-reducing agent with cement first and then stir it with aggregate and water; the co-mixing method is to dissolve the water-reducing agent in water to form a solution and then add it to the mixture and stir together; the post-mixing method It means that after the concrete mixture is delivered to the pouring site, the water-reducing agent is added and stirred evenly again for pouring. Therefore, the use of concrete admixtures must be determined through experiments based on project characteristics, material conditions and construction conditions.
To make good use of various concrete admixtures, you must at least do the following points to ensure the quality of the project.
(1) The dosage should be accurate. During construction, admixtures should be added accurately according to the designed dosage. If it is a liquid, the liquid concentration must be measured accurately; if it is a powder, it should be added evenly and accurately so that the error is controlled within ±2%.
(2) Mix evenly, and be sure to try to make the admixture evenly distributed throughout the mixture so that it can fully play its role and avoid adverse consequences caused by excessive local concentration. If the powder is added together with cement, it should be spread out and the mixing time should be appropriately extended; the liquid should also be spread evenly to prevent concentration.
(3) The mixing process cannot be messed up. For concrete mixed with several admixtures, attention should be paid to the order in which they are added. Some are allowed to be added after being transported to the site.
(4) Admixtures should be replaced in time as the seasons change. Different admixtures have different characteristics. When construction turns from autumn to winter, the types of concrete admixtures should be replaced in advance and should be used in winter. Anti-freeze early-strength admixture to prepare for winter construction.
(5) Designate a dedicated person to take charge. In order to ensure the quality of mixing, when using concrete admixtures, a dedicated person is assigned to take charge every time. Before operation, these workers are first specially trained and the mixing method is carefully explained to ensure the accuracy of the mixing amount.
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