There are nearly 100 kinds of polycarboxylic acid superplasticizers with different chemical components on the market, which can be roughly divided into four types: the first type is methacrylic acid / enoic acid methyl ester copolymer, also known as polyester type polycarboxylic acid superplasticizer; the second type is allyl ether copolymer, also known as polyether type polycarboxylic acid superplasticizer. The third category is amide / imide polycarboxylic acid polymer. The fourth category is amphoteric polycarboxylic acid superplasticizer, also known as polyamide / polyethylene glycol branched chain superplasticizer.
Water reducing mechanism of PCE powder
Polycarboxylic acid superplasticizer is a kind of anionic surfactant, which can be adsorbed with cement particles. Polycarboxylic acid molecules are adsorbed together by negatively charged carboxyl groups and positively charged calcium ions on the surface of cement particles by static electricity. Polycarboxylic acid molecules can use the steric hindrance effect of straight-chain molecules on the side chain to prevent cement flocculation. From the point of view of the molecular structure of polycarboxylic acid, the polyoxyethylene side chain and sulfonic group and other side groups form carding molecules, and the carboxyl group and sulfonic group on the main chain produce repulsive force by adsorbing the double electric layer on the surface of cement clinker. prevent cement clinker molecules from approaching, and have a good lubrication effect, so that the cement paste system is in a relatively stable state, and the dispersion effect of the cement paste system is more obvious. The side chain groups of mass molecules with strong negative groups can be well combined with cement clinker and then form hydrogen bond with water molecules to form a stable dispersion system.
According to the above analysis, after adding polycarboxylic acid superplasticizer to concrete, the dispersed polycarboxylic acid interacts with hydrolyzed cement clinker molecules through side chain functional groups. in the cement slurry system, the cement concrete paste forms a complex and stable colloid through the comprehensive action of electrostatic repulsion and steric resistance, adsorption, calcium complexation and sulfonic group complexation.
Problems existing in the use of polycarboxylic acid superplasticizer
Polycarboxylate superplasticizer has many advantages in use, but it has some problems in engineering application, including:
The water reducing effect of polycarboxylate superplasticizer is highly dependent on the raw materials and mix ratio of concrete, the water reducing effect is very sensitive to the amount of superplasticizer, the performance of the prepared concrete mixture is very sensitive to water consumption, and the prepared high fluidity concrete is easy to separate layer by layer. Poor compatibility of polycarboxylate superplasticizer with other superplasticizers and admixtures. No superposition effect, slightly acidity of polycarboxylate superplasticizer and its possible problems, technical depth and product performance stability are worthy of attention.
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