What is the action mechanism of polycarboxylic acid superplasticizer?

Water reduction is an important effect of surfactant on cement hydration. 

Water reducing agent does not affect the working condition of concrete, 

can reduce the unit water consumption; Or under the condition of not changing 

the unit water consumption, can improve the workability of concrete; 

Or admixtures that have both of the above effects and do not significantly change 

the gas content. At present, the concrete water reducing agents used are surfactants, 

belong to anionic surfactants. After mixing cement and water, hydration reaction, 

some flocculation-like structure, which is wrapped in a lot of mixing water, 

thus reducing the workability of fresh concrete (also known as workability, 

mainly refers to the fresh concrete in the construction, that is, in the mixing, 

transportation, watering and other processes can maintain uniform, 

dense without stratified segregation phenomenon performance). 

In order to maintain the required workability in the construction,

it is necessary to increase the amount of mixing water accordingly, 

because the increase of water will make the formation of excessive pores 

in the cement stone structure, thus seriously affecting the physical and mechanical 

properties of hardened concrete, if the water can be released, the water consumption 

of concrete can be greatly reduced. In the process of preparing concrete, 

adding a proper amount of water reducing agent can play such a role well. 

After adding water reducing agent to concrete, the hydrophobic group of 

water reducing agent is oriented adsorption on the surface of cement particles, 

and the hydrophilic group points to aqueous solution, forming a single molecular 

or multi-molecular layer adsorption film. Due to the directional adsorption of surfactants, 

the surface of cement colloidal particles with the same symbol of charge, 

so under the action of the same repulsion, not only can make the cement-water system 

in a relatively stable state of suspension, and can make the cement in the initial water adding

flocculating structure dispersion disintegration, so as to release the water in the flocculating structure, 

to achieve the purpose of water reduction. After the addition of water reducing agent, 

not only can improve the workability of new mixed concrete, but also because the water-cement 

ratio of concrete has decreased significantly, the internal pore volume of cement stone is significantly reduced, 

the cement stone is more dense, and the compressive strength of concrete is significantly increased. 

The addition of water reducing agent also has an effect on the hydration rate and setting time of cement. 

All of these properties are important for practical purposes.