Concrete admixtures are added during the concrete mixing process to improve the properties of concrete. However, there are many types of concrete admixtures on the market. What basic principles should we pay attention to when selecting and using them?
1. Selection of admixtures
1. The variety of admixtures should be based on the engineering design and The selection of construction requirements is determined through experiments and technical and economic comparisons.
2. It is strictly prohibited to use additives that are harmful to the human body or pollute the environment.
3. The cement used in concrete mixed with admixtures should be Portland cement, ordinary Portland cement, slag Portland cement, pozzolanic Portland cement, fly ash Portland cement and composite silicic acid. Salt cement, and the adaptability of the admixture and cement should be tested and used only if it meets the requirements.
4. The materials used in concrete mixed with admixtures, such as cement, sand, stone, admixtures and admixtures, should comply with the relevant national standards. When trial mixing concrete mixed with admixtures, the raw materials used in the project should be used. The testing items should be determined according to the design and construction requirements. The testing conditions should be the same as the construction conditions. When the raw materials used in the project or the performance requirements of the concrete change, the test should be carried out again. With test.
5. When using different types of admixtures in combination, attention should be paid to their compatibility and impact on concrete properties. Tests should be conducted before use to ensure that the requirements are met before use.
2. Additive dosage
1. The dosage of admixture should be based on gelling Expressed as a percentage of the total amount of material, or expressed in mL/kg cementitious material.
2. The dosage of admixture should be determined through testing according to the dosage recommended by the supplier, usage requirements, construction conditions, concrete raw materials and other factors.
3. Admixtures containing chloride ions, sulfate ions and other ions should comply with the provisions of this specification and relevant standards.
4. For concrete that is in contact with water or in a humid environment, when alkali-active aggregates are used, the alkali content (calculated as the equivalent of sodium oxide) brought by the admixture should not exceed 1kg/m3 of concrete. The total amount of concrete Alkali content should still comply with relevant standards.
3. Quality control of admixtures
1. Selected admixtures The agent should have the following technical documents provided by the supplier:
(1) Product instructions, and the main ingredients of the product should be indicated.
(2) Factory inspection report and certificate of conformity.
(3) Performance inspection report of concrete mixed with admixtures.
2. When the admixture is transported to the concrete mixing station, representative samples should be taken immediately for inspection. The incoming goods must be consistent with the trial mix of the project before they can be stored and used. If any inconsistency is found, use should be stopped.
3. Admixtures should be stored separately according to different supplier units, different varieties, and different brands, and the labels should be clear.
should be prevented from agglomerating due to moisture. If there are agglomerations, they should be crushed until all pass the 0.63mm sieve before use after passing the performance test. Liquid admixtures should be placed in a cool and dry place to prevent sunlight, freezing, pollution, water ingress or evaporation. If there is precipitation, etc., they can only be used after passing the performance test.
5. The labeling of the admixture batching control system should be clear, the measurement should be accurate, and the measurement error should not be greater than 2% of the admixture dosage.
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