Superplasticizer effect and principle

2020-03-20 16:01:34

The high-efficiency water reducing agent can significantly improve the fluidity of the stirring slurry, so that the foaming mud can reach self-leveling in the mold, reducing or even no bread. It can dramatically reduce water consumption while keeping the slump of the concrete, and the water reducing agent is also called dispersant or plasticizer. It is the most commonly used admixture.

The role of water-reducing agent:

  1. Reduce the solid-liquid interface energy of cement particles

  2.Static repulsion

  3.Spatial repulsive force

  4. Lubrication effect of hydration film

Water reducing agent principle:

The specific surface area of cement is generally 350-400m2 / kg, and the particle size of more than 90% of cement particles is in the range of 7-80 microns, which belongs to the category of fine powder particles. For the cement-water system, the surface of cement particles and hydrated cement particles has a slightly polar surface and has strong hydrophilicity. Fine cement particles have sizeable specific surface energy (solid-liquid interface energy). To reduce the total heat on the surface  solid-liquid, fine cement particles tend to spontaneously condense into floc to minimize the interface energy of the system and make the system thermodynamic. Maintain stability. At the same time, in the early stage of cement hydration, the surface of C3A particles is positively charged, while the surfaces of C3S and C2S particles are negatively charged. The electrostatic attraction of positive and negative charges also promotes the formation of the flocculation structure of cement particles.

There are three ways of water in concrete: free water-bound water and adsorbed water. In the early stage of mixing cement, there is less chemically bound water and adsorbed water, and the mixed water mainly exists in the form of free water. However, due to the flocculation structure of the cement particles, 10% -30% of open water will be wrapped in it, thereby severely reducing the fluidity of the concrete mixture. The primary role is to destroy the flocculation structure of the cement particles, keep it in a dispersed state, and release the free water in the package and the floc, thereby improving the fluidity of the fresh concrete.

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