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At present, it is rare to use a single type of admixture for compounding concrete admixtures, and it has gradually developed towards high efficiency and multifunctionality. The purpose of compounding concrete admixtures is to meet the needs of concrete for various properties simultaneously, as well as to produce a “superposition effect” through the joint action of various compounding components.
Composite additives are usually composed of multiple surfactants or inorganic electrolytes, such as composite early strength agents, composite antifreeze agents, pumping agents, composite retarding and air-entraining water-reducing agents, etc. Generally, compound additives are formulated with at least two components to form binary or multicomponent composites. Each additive in the composite admixture works at different stages of cement hydration or works together at the same time.
1.The water-reducing components include lignin, naphthalene-based high-efficiency water-reducing agent, sulfonated melamine high-efficiency water-reducing agent, aminosulfonate high-efficiency water-reducing agent, aliphatic high-efficiency water-reducing agent, polycarboxylate high-performance water-reducing agent, etc. Ensure that the workability of concrete meets the construction process requirements under a certain water-cement ratio. Suitable water-reducing components should be used for different types of cement and admixtures, and the dosage should be sufficient.
2.The retarding components include organic and inorganic compounds such as lignin, sugars, phosphates, tartrate, gluconate, citric acid and its salts, cellulose and its derivatives.
Control slump loss and concrete setting time to ensure normal transportation and pumping. When using different raw materials and mix proportions, appropriate retarding components should be used, and the amount used should be appropriate to avoid problems with cement adaptability and setting time abnormalities. When used together with water-reducing components, the water reduction rate increases.
3.The water-retaining components include various water-reducing agents, cellulose and its derivatives, etc.
Adjust the variety and dosage of water-retaining components according to the concrete trial mixing situation to ensure that the concrete and workability meet the requirements.
4.The air-entraining components include Wensha resin, rosin soap, alkyl sulfonate, alkylbenzene sulfonate, lignin, etc.
Proper air entrainment can improve the pumping performance and workability of concrete and has great benefits for the durability of concrete.
There is a certain water reduction rate. It is generally advisable to keep the air content of concrete around 2-3% (except for special products), which not only does not affect the strength of concrete, but also significantly improves various properties of concrete.
When preparing additives, full consideration should be given to their adaptability to various raw materials, while also paying attention to the interaction between different components and the order of solid dissolution.
Different types of cement, admixtures, and other components in additives still have a significant impact on the performance of water reducers. For example, when naphthalene-based water reducers and sodium gluconate are used together, the water reduction rate is significantly improved. Organic and inorganic types should be reasonably matched.
Different types of cement and admixtures, as well as different mix proportions, can cause changes in the retarding effect.
The air-entraining effect of air-entraining agents is influenced by many factors, such as cement fineness, stone particle size, sand-to-mud content, temperature, mix proportion, etc. When adding fly ash, with a large amount of fine materials, small particle size of stones, high slump, and low temperature, the air content of concrete will be high.
In short, the adjustment of additives should be based on the actual situation and the test results.
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