Selection and use of concrete admixtures

Adding admixtures to concrete can significantly improve the technical properties of concrete and achieve significant technical and economic effects. Improper selection and use can cause accidents. Therefore, when selecting and using admixtures, you should pay attention to the following points:
1) Selection of admixture varieties There are many types and brands of admixtures with different effects, especially for different types of cement. When selecting admixtures, it should be determined through tests based on project needs, on-site material conditions, and with reference to relevant information.

2) Determination of the dosage of admixtures Concrete admixtures all have appropriate dosages. Too little dosage often fails to achieve the desired effect; too much dosage will affect the quality of concrete and even cause quality accidents. . Therefore, the optimal dosage should be determined through experiments.

3) Determine the method of adding admixtures. The amount of admixtures is very small and must be ensured to be evenly dispersed. Generally, they cannot be added directly to the concrete mixer. For water-soluble admixtures, it is advisable to prepare a solution of a certain concentration first and then add it to the mixer with water. For water-insoluble admixtures, it is advisable to mix them evenly with cement and sand before adding them to the mixer. In addition, the mixing time of admixtures also has a great impact on the effectiveness of the water-reducing agent. For example, in order to ensure the water-reducing effect of the water-reducing agent, the water-reducing agent has the same mixing method, post-mixing method, divided mixing, etc., which should be added according to the production Process and technology require appropriate dosing methods.

4) Matters needing attention when using admixtures

a) When the admixture is in colloidal, liquid or block solid form, it must first be made into a solution of a certain concentration. Shake or mix well before use, and deduct the water consumption of the admixture solution from the concrete mixing water; when the admixture is powder, it can also be mixed with cement and aggregate at the same time, but no agglomerates are allowed to be mixed in.

b) Appropriate admixtures should be selected according to the requirements of concrete, construction conditions, and construction techniques.

c) The adaptability of admixtures and cement should be tested. When two or more admixtures are used at the same time, the compatibility between admixtures and their impact on concrete properties should also be tested.

d) Admixtures should be tested and the optimal dosage should be determined.

e) The amount of admixture must be accurate, with a measurement error of 1%, otherwise it will affect the quality of the project, delay the construction period, and even cause accidents.

When using concrete with admixtures, attention should be paid to the operation of mixing, transportation, vibrator frequency selection and vibration; for post-mixed or dry-mixed concrete, the mixing time should be extended. During transportation, attention should be paid to maintaining the homogeneity of the concrete to avoid segregation. When adding air-entraining water-reducing agent, high-frequency vibration should be used to eliminate foam. </p