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The water-reducing agent should be used with concrete admixture, which will reflect the water-reducing effect. Cement quality is therefore a direct factor of the effect of water-reducing agent.
If you encounter different “problem” types of cement, different strategies should be used according to the different types:
High alkali cement
High-alkali is a cement type with a large amount of alkali. Alkali in high-alkali is usually higher than that of conventional cement.
The high-alkali cements have a high degree of alkalinity. This can impact the performance. High-alkali Cement can encourage the setting reaction, which is beneficial to the early development of strength in concrete. High-alkali Cement can also increase the fluidity of cement, making it more workable and easier to pump.
But there are also some issues with high-alkali clinkers. As an example, high alkali cements can reduce the efficiency of water-reducing agents and cause concrete to lose its slump faster. High-alkali cement may also lead to corrosion and carbonation problems in the reinforcement of concrete.
High-alkali Cement can benefit from water-reducing agents that contain a higher content of sodium sulfate. High-alkali cement contains a high amount of alkali, which accelerates C3A’s dissolution. Sodium sulfate reacts with C3A, forming AFt crystals. This can improve the fluidity in cement mortar.
Low-alkali sulfur-deficient cement
Low alkali-sulfur cement is a cement with a lower sulfate level than normal cement. Ordinary cement is high in sulfate. It reacts with water and the sulfate forms crystals that cause cracking.
Reduced sulfate cements reduce the effect of alkali-aggregate reactions (alkali-silica reactions) in concrete. The alkali silica reaction is a reaction between the cement and the aggregate that causes expansion and cracking. The use of low-alkali cements that are sulfur-deficient can help reduce this reaction, and increase the durability and life of the concrete.
Due to the lower sulfate contents, water reducers work less well with low alkali-sulfur cement. Water-reducing agents can cause concrete to lose slump quickly if they are used in excess. In this case, the conventional method of using water-reducing agents may not work. Instead, it is best to choose a water reducing agent that contains sulfate.
High C3A cement content
Cement with a high C3A-content is one that contains a large amount of C3A. C3A is a mineral found in cement which reacts with the water to produce an expansive substance when it hydrates. Cements with high C3A contents have a faster setting time and higher early strength. They are ideal for projects that need rapid setting.
Cement with a high C3A percentage can cause some problems. C3A and sulfate react to form sulphoaluminate. This can cause concrete to expand or crack. In humid environments, cements high in C3A are susceptible to producing corrosive calcium-sulfate precipitates, which can have a negative impact on the durability of concrete and steel structures.
Cement with high C3A will have a greater ability to bind water-reducing agents. This will result in a reduction of the fluidity of concrete and its slump. If you are using a water-reducing chemical, choose a water-reducing agent that has a high sulfate content or a retarder which contains hydroxycarboxylate. These will help reduce C3A adsorption and improve concrete fluidity.
There are two types of products that reduce water: one is the naphthalene-based water-reducing product, and another is polycarboxylic-based water-reducing product. The main difference in water reduction is the naphthalene. It is high-efficiency, and polycarboxylic is high-performance. For general foam concrete, the naphthalene cubic addition is between a few hundred to a kilogram.