How to choose the appropriate admixture?

Additives used well in mixing station A are not necessarily used well in mixing station B. For the application of additives, only when the products satisfying the performance requirements and stable quality are selected, can the additives play their due role. The source and performance of concrete are different, and the amount of concrete admixture determined is not the same as that recommended by the supplier. It is necessary to adjust the mix ratio of concrete and the formula of admixture when necessary. Therefore, the choice of admixtures should be based on concrete performance requirements and concrete composition materials. Xinyang Lingshi Technology Co., Ltd. is a manufacturer of cement, mortar, concrete and other additives. Now let's see how to choose the appropriate additives.

Generally, the selection of additives should be considered from the aspects of technical performance and sensitivity, quality stability, compatibility with cement cementitious materials, credibility of additives manufacturers, technical support ability, logistical support ability and cost.

Selection of additives should first determine the performance requirements of concrete according to the type of concrete structure, concrete strength grade, concrete construction method and construction conditions, durability and other special requirements. Such as strength, workability and workability maintenance time, setting time and so on. According to concrete performance requirements and concrete cementitious materials and sand and gravel materials available, the initial mix ratio of concrete is determined, such as water-cement ratio, amount of cementitious materials, water consumption, sand ratio, and technical performance requirements of additives, such as water reduction, workability retention, retarding or accelerating setting, etc.

It should be pointed out that the content of water reducer should not be near the saturation point. Most water reducers are very sensitive near the saturation point. Small fluctuations in concrete production towel may cause great changes in concrete performance. If the determined admixture content is very close to the saturation point, the product is not suitable. Therefore, besides the performance test of concrete, the sensitivity test of admixture and mix ratio is also needed to determine the working range of admixture and the allowable fluctuation range of concrete mix ratio.

Additives of different varieties or different manufacturers of the same variety may have different dosage ranges. In this range, the relationship between performance (such as water reduction rate, setting time, air content, etc.) and admixture content should be close to linear relationship, that is to say, the change of concrete performance with admixture content is predictable. Beyond this range, the performance of concrete is very sensitive to the dosage of admixtures. Various problems may occur at any time, such as segregation, bleeding, or excessive setting time, or excessive air content, etc. The smaller the scope of work, the more difficult the operation and management of concrete production is.

For additives with retarding effect, besides determining the relationship between dosage and setting time, the sensitivity of setting time to temperature should also be determined. The application range of additives to seasonal temperature can be determined by temperature sensitivity.

Another important factor is the sensitivity to concrete mix ratio, especially high slump or high flow concrete. In actual production, there are always some normal fluctuations in the composition and ingredients, especially the fluctuation of water content in sand and gravel, which results in the fluctuation of concrete actual water consumption of 5 kgm3 and 10 kgm3. After determining the admixture content and concrete proportion through performance test, it is necessary to carry out sensitivity test of water catfish. That is to say, adding or subtracting 5 kgm3-10 kgm3 water on the basis of the determined concrete mix proportion and admixture content to check whether there are other phenomena such as segregation and bleeding in the workability of concrete besides the appropriate change of slump or fluidity.

As a concrete mixing station, it is necessary to test the compatibility of the admixture with other possible cement in advance at the stage of admixture selection. In most cases, it can be solved by adjusting the admixture dosage appropriately. If there is a real incompatibility, another formulation or variety of additives need to be determined to solve it.

The selection of additives should also determine the technical plans when possible but uncontrollable events occur, such as traffic jams, the reduction of workability of concrete caused by long waiting time at the construction site, etc. Adding additives on site can be considered to restore the pumping pouring performance. Prepare test data in advance to determine the relationship between site addition and slump increase, and additional additives should not have a significant impact on concrete setting time and early strength development. Therefore, the additives added on site should be non-retarding water reducers, and these plans should be submitted to the design and supervision units before the start of the project.