Don’t say you don’t know the principles for selecting concrete admixtures!

Concrete admixtures are one of the important measures and methods to ensure the high performance of concrete. As an important component of concrete, the adaptability of cement and admixtures affects the overall performance of concrete. The adaptability of the two involves knowledge of cement chemistry, surface physics, polymer materials science and electrochemistry. An extremely complex puzzle. When choosing concrete admixtures, you should choose appropriate admixtures based on project needs, construction conditions and construction techniques. Let me introduce to you the principles of selecting concrete admixtures:

For general Concrete mainly uses ordinary water-reducing admixtures. When mixed with early-strength and high-strength concrete, high-efficiency water-reducing admixtures are used. When the temperature is high, a water-reducing agent with high air-entraining properties or a retarding water-reducing agent is used. When the temperature is low, Generally, a single air-entraining water-reducing agent is not used, but a composite early-strength water-reducing agent is often used; in order to improve the workability of concrete, air-entraining water-reducing agents are generally added; non-air-entraining high-efficiency water-reducing admixtures are often used for moist heat curing concrete. Antifreeze should be used for concrete constructed at low temperatures in the north. Waterproofing and impermeability agents should be used when waterproofing is required. Pumping agents should be used when pumping concrete in high-rise buildings and large-volume structures. The types of admixtures should be selected according to different concrete construction and performance requirements. Each admixture has its own characteristics and should not be substituted for each other. For example, a high-efficiency water-reducing agent can be used as an ordinary water-reducing agent, and an ordinary water-reducing agent should be used as a strong water-reducing agent. All are inappropriate and uneconomical.

Most of the concrete admixtures used in commercial concrete mixing stations are compounded water-agent products. Some are water-agent products directly produced by admixture manufacturers, and some are powder products provided by manufacturers far away. The mixing station is remixed in the station itself. Since the self-mixing of mixing stations is limited by site, equipment, and technical strength, specialization and multi-variety mixing are often difficult to achieve. It may seem that cost savings may actually outweigh the gains. The harm and economic losses caused by improper use of admixtures are far greater than their own value. Therefore, it is particularly important to choose one or several suppliers that have stable production and have aqueous agent production plants or compounding stations nearby. It is uneconomical to supply aqueous agents that are too far away. It is convenient and economical to choose a nearby aqua agent factory.

How to purchase and use admixtures correctly

Proper purchase and use of admixtures can produce huge economic and technical value. It can not only improve the strength of concrete, but also reduce the cost of concrete mix ratio. The specific methods are as follows:

Testing link

Testing and testing of various technical indicators of admixtures is an important link before procurement negotiations. Through the test, the qualification standards of various technical indicators of the admixture should be determined. Including technical indicators such as the solid content of admixtures, water reduction rate, density, slurry fluidity, concrete water reduction rate, etc. It is recommended that concrete water reduction rate be used as a key indicator to measure the quality level of admixtures.

Procurement link

After clarifying the qualification standards for admixtures, purchase negotiations can begin. It is recommended to invite bids for admixture manufacturers according to the qualification standards determined by the test. On the premise that the quality level of the supply of additives is not lower than the bidding requirements, the supplier will be determined based on the principle of winning the bid at a low price.

At the same time, the selection of admixture manufacturers should comprehensively consider the manufacturer’s production scale, transportation distance, transportation capacity, large-scale mixing station or large-scale engineering project supply experience and supply quality level, and after-sales service capabilities. and level, it is not appropriate to use price as the only indicator for manufacturer screening.

Acceptance process

The admixtures in the mixing station should be tested before they are put into storage. The test results can only be put into storage after they pass the contract signing standards. It is recommended to distinguish between key indicators and reference indicators. Through long-term practice, the author believes that the key indicators of admixtures are water reduction rate (mortar) and concrete water reduction rate; the reference indicators are density (specific gravity), solid content and cement slurry fluidity. Due to the testing time, the technical indicators generally tested during the acceptance process are density, cement slurry fluidity and water reduction rate (mortar).

Concrete admixtures also have problems with compatibility and adaptability with cement. Different types of cement have different mineral compositions, setting agents, mixing materials and fineness. If the admixtures and dosage are the same, the application results (water reduction rate, slump, bleeding rate, etc.) segregation, etc.) will make a difference. After initially selecting the brand of admixture, it is necessary to conduct a cement and admixture adaptability test.

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