Things to note and how to use concrete admixtures

As the current mainstream concrete admixture and high-efficiency water-reducing agent in my country, the action mechanism is anionic surfactant. It is directionally adsorbed on the surface of cement particles through the hydrophobic group, and the hydrophilic group points to the solution, forming a single surfactant on the surface of the cement particles. The molecular or multi-molecule adsorption film releases the free water wrapped in the cement flocculation structure under the action of homogeneous charge repulsion to achieve the purpose of water reduction. Therefore, all types of this generation of water reducing agents have ionic electrostatic repulsion as a common feature. However, because different precursors are synthesized using different raw materials and processes, there will be certain differences in performance, which leads to Different parent superplasticizers have different effects on cement.

Because concrete admixtures can effectively improve the properties of concrete and have good economic benefits, they have been widely used in many countries and have become an indispensable material in concrete. Especially with the use of high-efficiency reducing agents, the cement particles can be fully dispersed, the water consumption is greatly reduced, and the cement potential is fully utilized. As a result, the cement stone is denser, the pore structure and the microstructure of the interface zone are well improved, thus making the concrete The physical and mechanical properties of concrete have been greatly improved. Whether it is impermeability, chloride ion diffusion, carbonization, resistance to sulfate erosion, impact resistance, wear resistance and other aspects, it is better than concrete without additives. Not only Increased strength, improved workability. It can also improve the durability of concrete. Only by adding high-efficiency water-reducing admixtures, it is possible to prepare high-performance concrete with high workability, high strength and high durability.

1. When using porous aggregate, it is advisable to add water and stir first, then add water-reducing agent.

2. When the slump is large, attention should be paid not to vibrating for too long to prevent bleeding and delamination.

Naphthalene-based high-efficiency water reducing agents can be divided into high-concentration products (Na2SO4 content 10%). Most naphthalene-based high-efficiency superplasticizer synthesis plants have the ability to control the Na2SO4 content below 3%, and some advanced companies can even control it below 0.4%. Naphthalene-based water-reducing admixture is the most widely produced and widely used high-efficiency water-reducing agent in my country (accounting for more than 70% of the water-reducing agent dosage). It is characterized by a high water-reducing rate (15% to 25%) and does not cause any problems. It has little impact on the setting time, has relatively good adaptability to cement, can be used in combination with various other admixtures, and is relatively cheap. Naphthalene-based superplasticizers are often used to prepare high-fluidity, high-strength, and high-performance concrete. The slump loss of concrete simply mixed with naphthalene-based superplasticizer is faster. In addition, the adaptability of naphthalene-based water reducing agents to certain cements needs to be improved.

The aliphatic superplasticizer of concrete admixture is carbonyl pyroaldehyde synthesized by the sulfonation of acetone. The hydrophobic main chain is aliphatic hydrocarbons, which is a green and high-efficiency water-reducing agent. Does not pollute the environment and does not harm human health. It has wide applicability to cement, obvious reinforcement effect on concrete, small slump loss, and no sodium sulfate crystallization phenomenon at low temperatures. It is widely used in the preparation of pumping agents, retarder, early strength, antifreeze, air entrainment and other types of personalized water reduction. agent, it can also be used in combination with naphthalene-based water-reducing agent, amino water-reducing agent, and polycarboxylate water-reducing agent. Aliphatic high-efficiency water-reducing agent: main technical indicators

　1. Appearance: brown-red liquid; 2. Solid content >35%; 3. Specific gravity 1.15-1.2 Performance characteristics 1. High water reduction rate. With a dosage of 1-2%, the water reduction rate can reach 15-25%. Under the condition of the same strength and slump, adding aliphatic high-efficiency superplasticizer can save 25-30% of cement consumption;

　2. Early strength and enhancement effect are obvious. Concrete mixed with aliphatic high-efficiency water-reducing agent can reach 60-70% of the design strength in three days, 100% in seven days, and the strength is 30-40% higher than that of blank concrete in 28 days; 3. High plastic retention. The slump loss of concrete over time is small, with basically no loss in 60 minutes and 10-20% loss in 90 minutes; 4. It has wide applicability to cement, good workability and cohesiveness. Good compatibility with other types of admixtures;

5. It can significantly improve the freeze-thaw resistance, impermeability, and sulfate corrosion resistance of concrete, and comprehensively improve other physical properties of concrete; 6. It is especially suitable for the following concrete : Fluid plasticized concrete, natural curing, steam curing concrete, impermeable and waterproof concrete, durable freeze-thaw resistant concrete, sulfate corrosion resistant marine concrete, as well as steel bars and prestressed concrete;

7. The aliphatic superplasticizer is non-toxic, non-flammable, does not corrode steel bars, and does not crystallize sodium sulfate in winter.

How to use concrete admixtures:

1. Find the optimal dosage through experiments, the recommended dosage is 1.5-2%;

2. Fat The aliphatic superplasticizer and the mixing water can be added to the concrete at the same time, or post-addition can be used. When adding the aliphatic superplasticizer, the mixing of the concrete should be extended for 30 seconds;

3. Due to the The water reduction rate is large, and before the concrete initially sets, a layer of yellow slurry will secrete on the surface, which is normal. The color will disappear after the concrete is pounded and grouted, or the color will disappear naturally after the concrete is strengthened. The color will disappear faster through watering and curing without affecting the internal and surface properties of the concrete.

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