Function and application of water reducing agent
1) Function of water reducing agent
It refers to the admixture which can reduce mixing water, improve concrete strength and save cement consumption under the condition of constant workability and cement consumption. Compared with the ordinary water reducing agent, the water reducing and strengthening effects are stronger.
2) Theory of electrostatic repulsion
After cement hydration, due to the van der Waals force between ions and the different charges of cement hydration minerals and main cement minerals in the process of hydration, the flocculation structure of concrete is produced. Most water reducing agents are anionic surfactants. When they are mixed into concrete, the anions - so -, - COO - in the water reducing agent will be adsorbed on the cement particles under the action of the positive charge Ca2 + ore of the cement particles, forming a diffusion double electric layer (zel). A potential), which forms on the surface
3) Steric hindrance effect
In the cement slurry with water reducing agent, the long chain of organic molecules of water reducing agent presents various adsorption states on the surface of cement particles. The different adsorption state is caused by the different molecular chain structure of superplasticizer, which directly affects the time-dependent change of slump of concrete mixed with the superplasticizer. Some studies have shown that the adsorption state of naphthalene series and melamine series water reducers is rod-shaped chain, so they are flat adsorption, and the electrostatic repulsion is weak. The result is that the zeta potential decreases rapidly, and the electrostatic balance is easily damaged with the development of cement hydration process, which makes van der Waals gravitation dominant and the slump changes greatly with time.
4) Lubrication
The polar hydrophilic group of water reducing agent is adsorbed on the surface of cement particles directionally, and it is associated with water molecules in the form of hydrogen bond. In addition, the hydrogen bond association between water molecules constitutes a stable water film on the surface of cement particles, which prevents the direct contact between cement particles, increases the sliding ability between cement particles, plays a lubricating role, and further improves the fluidity of slurry.
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