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6.9 water reducing agent

Water-reducing agent is an important concrete admixture

which can minimize the water-cement ratio of concrete and improve the strength and durability of concrete. Water-reducing agents are divided into ordinary water-reducing agents and high-efficiency water-reducing agents.

Water-reducing agents with a water-reducing rate of more than 5% and less than 10% are called ordinary water-reducing agents, such as sodium rosin, sodium lignosulfonate and stearic acid soap Etc.; Water reducing agents with a water reduction rate greater than 10% are called high efficiency water reducing agents, such as melamine series, naphthalene series, sulfamic acid series, modified lignosulfonic acid series and polycarboxylic acid series. Among the many superplasticizers, the polycarboxylic acid superplasticizer with comb-shaped molecular structure has excellent properties such as high water reduction rate, good slump retention performance, low dosage, and no obvious retardation. The focus of research and development at home and abroad in recent years.

At the same time, the hydrophilic polyether side chain in the structure stretches in the aqueous solution, thereby forming a hydrophilic three-dimensional adsorption layer of a certain thickness on the surface of the adsorbed cement particles. When the cement particles approach, the adsorption layer starts to overlap, that is, The steric hindrance is generated between the cement particles. The more overlap, the greater the steric hindrance repulsion and the greater the hindrance to the cohesion between the cement particles, so that the slump of the concrete is maintained well.

Therefore, the polycarboxylic acid superplasticizer, which produces electrostatic force and steric hindrance repulsion on cement particles, has a significant dispersing effect on cement particles when the amount is small. At the same time, the hydrophilic polyether of the polymer The side chain can still be stretched in the cement mineral hydration product, so that the polycarboxylic acid type water reducer is less affected by the hydration reaction of the cement, can maintain the dispersion effect for a long time, and reduce the slump loss.

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