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The main function of high efficiency water reducing agent

Release time:

2022-06-21

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高效减水剂的主要作用

　　SuperplasticizerThe main role:

(I) Increased mobility. Under the condition of constant water consumption and water cement ratio, the slump of concrete can be increased by 100~200mm without affecting the strength of concrete.

(2) improve the strength of concrete. Under the condition of keeping the fluidity and cement dosage unchanged, the mixing water consumption can be reduced by 10% ~ 40%, thus reducing the water cement ratio and improving the concrete strength.

(3) Save cement. In the case of fluidity and water cement ratio unchanged, can reduce the mixing water, reduce the amount of cement.

(4) improve the durability of concrete.

At present, it is generally believed thatSuperplasticizerThe water-reducing effect is mainly due to the adsorption, dispersion, wetting and lubrication of the superplasticizer. In the process of mixing cement and water, because the cement minerals contain different charge components, the mutual attraction of positive and negative charges will make the concrete form a flocculated structure. Flocculated structures may also be caused by thermal motion of cement particles in solution. These corners collide and attract each other. Because the flocculation structure wraps a part of the mixed water and reduces the fluidity, the effect of the superplasticizer is reflected in the following three aspects.

　　(1)SuperplasticizerIt is a kind of surface active substance, its molecule is composed of two parts: hydrophilic group and hydrophobic group. The hydrophobic group is directionally adsorbed on the surface of the cement particles, and the hydrophilic group points to the aqueous solution, so that the surface of the cement particles has the same charge, and the repulsion force separates the cement particles, releasing the flocculation structure of the free ions, and increasing the fluidity.

(2) The hydrophilic group adsorbs a large number of water molecules, increases the thickness of the solvated water film on the surface of the cement particles, plays a lubricating role, and improves the workability.

　　(3)SuperplasticizerThe surface tension is reduced, the cement particles are more easily wetted and hydrated more fully, thereby increasing the strength of the concrete.

Now it is generally believed that there are three theories of the mechanism of high-efficiency water reducing agent: electrostatic repulsion theory, steric hindrance theory and reactive polymer slow release theory.

Electrostatic repulsion theory: most of the superplasticizers are anionic surfactants. Since the surface of cement particles is positively charged (Ca2 +) at the initial stage of hydration, the negative ions SO3-and COO-in the molecule of the superplasticizer are adsorbed on the cement particles. The adsorption electric double layer is formed on the surface, and the cement particles close to each other will be affected by the electrostatic repulsion and van der Waals attraction between the particles at the same time. As the potential value increases, the repulsive force between particles gradually dominates, thus preventing the cohesion between particles. At the same time, the electrostatic repulsion can also release the moisture wrapped in the cement particles, so that the system is in a good and stable dispersion state. With the progress of hydration, the amount of superplasticizer adsorbed on the surface of cement particles decreases, the potential value decreases, the system becomes unstable and agglomerates. The theory is mainly applicable to naphthalene series, melamine series, modified wood calcium series and other commonly used high efficiency water reducing agent.

Key words:

Superplasticizer

Synthesis and compound method of high efficiency water reducing agent

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