The domestic consumption of polycarboxylate superplasticizers has been gradually increasing in recent years, and its raw material, sodium hypophosphite, is showing a trend of gradually replacing mercaptopropionic acid and sodium formaldehyde sulfoxylate (SPF). The performance of polycarboxylate superplasticizer polymers depends on the average molecular weight and molecular weight distribution of the polymer, as well as the hydrophilic functional groups attached to the main chain, such as carboxyl groups (-COOH), hydroxyl groups (-OH), sulfonic acid groups (-SO3H), and oxyalkyl polyoxyalkylene groups (-(CH,CH,O)_R). The mechanism of action of polycarboxylate superplasticizers can be understood from the following aspects:

Comb-shaped polycarboxylate superplasticizers mainly disperse and maintain the dispersion of cement particles by adsorbing onto cement particles or cement hydration products, generating a steric hindrance effect. Because the dispersion mechanism of polycarboxylate superplasticizers differs from the electrostatic repulsion of naphthalene-based superplasticizers, they are not sensitive to the type and concentration of ions in the cement paste solution, and have better adaptability to cement quality. The longer side chains are not easily covered by cement hydration products, allowing them to exert their dispersion effect for a longer period of time, and exhibiting excellent fluidity retention.

The mechanism by which water-soluble active polymers control the slump loss of concrete is that the hydrolysis of ester groups or acid anhydrides produces strong anionic groups, which make the surface of cement particles negatively charged. The enhanced electrostatic repulsion improves the dispersibility of cement particles, thus controlling the slump loss of concrete. The slump loss of concrete can also be better controlled through the local cross-linking of water-reducing agent molecules. The mechanism is that the cross-linked parts in the structure of water-reducing agent molecules are easy to break, and the adsorption on the surface of cement particles forms a comb-like structure, which also has better dispersion and retention performance. The longer the molecular side chain of polyoxyethylene, the more favorable it is for the dispersion of cement particles, because the stereorepulsive force between cement particles adsorbing water-reducing agents is enhanced. In the future, modern testing methods such as atomic force microscopy, electrodynamic acoustic amplification (ESA) method, and determination of the Zeta potential of cement paste with actual water-cement ratio can be used to conduct in-depth research on the dispersion mechanism and action model of polycarboxylate-based high-performance water-reducing agents and other chemical admixtures. Combined with Auger electron spectroscopy, X-ray diffraction spectroscopy, and scanning electron microscopy, the structure and evolution law of fresh cement paste, and the change law of hardened concrete structure and performance can be analyzed to guide the molecular structure design and performance optimization of polycarboxylate-based water-reducing agents.