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Water-Reducing Admixture Mechanism and Use Effect

2023-11-28 14:38

    First,Water-reducing admixture is a kind of surfactant, its molecule consists of hydrophilic group and hydrophobic group. When the cement is mixed with water, if there is no water-reducing admixture, due to the action of molecular cohesion between the cement particles, the cement paste will form a flocculating structure, and some of the mixing water will be wrapped in the flocculating structure of the cement particles, which will reduce the fluidity of the concrete mixture. After adding into concrete mix, it has dispersing effect on cement particles, which can improve its workability, reduce water consumption per unit and improve the fluidity of concrete mix; or reduce the amount of cement per unit and save cement.

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    Second, what are the types of water-reducing admixture

    1、According to the appearance and form

Divided into water and powder. The solid content of water agent is generally 20%, 40% (also known as mother liquor), 60%, and the solid content of powder is generally 98%.

    2、According to water reducing and enhancing ability

Divided into ordinary water-reducing admixture (also known as plasticizer, water reduction rate of not less than 8%, to lignosulfonate class as a representative), high-efficiency water-reducing admixture (also known as superplasticizer, water reduction rate of not less than 14%, including naphthalene, miamine, sulfamate, aliphatic, etc.) and high-performance water-reducing admixture (water reduction rate of not less than 25%, to the polycarboxylic acid system of water-reducing admixture as a representative), and were divided into the early-strength type, the standard and slow-setting type.

    3、According to the composition of materials

Lignin sulfonates, polycyclic aromatic salts, water-soluble resin sulfonates, naphthalene-based high-efficiency water reducers, aliphatic high-efficiency water reducers, amino high-efficiency water reducers, polycarboxylic acid high-performance water reducers and so on.

    4、According to chemical composition

Lignin sulfonate water-reducing admixture, naphthalene high efficient water reducing agent, melamine high efficient water-reducing admixture, amino sulfonate high efficient water-reducing admixture, fatty acid high water-reducing admixture, polycarboxylate high efficient water-reducing admixture.

    Third, what are the functions of water-reducing admixture

    1, in the case of not changing the proportion of various raw materials (except cement) and concrete strength, can reduce the amount of cement, mixing cement quality of 0.2% to 0.5% of the concrete water-reducing admixture, can save the amount of cement more than 15-30%.

    2, in the case of not changing the ratio of various raw materials (except water) and the slump of concrete, reduce the amount of water, can greatly improve the strength of concrete, early strength and late strength than the concrete without water-reducing admixture to improve the strength of concrete by 60% and more than 20%, through the reduction of water, can be realized by pouring the C100 grade of high-strength concrete.

    3, in the case of not changing the ratio of various raw materials, can greatly improve the rheology and plasticity of concrete, so that the concrete construction can be self-flow, pumping, no need for vibration and other ways of construction, improve construction speed, reduce construction energy consumption.

    4, mixed with high efficient water-reducing admixture for concrete, can improve the life of concrete more than double, even if the normal service life of the building is extended by more than double.

    5、Reduce the shrinkage rate of concrete solidification, to prevent cracks in concrete components; improve frost resistance, conducive to winter construction.

    Fourth, what is the role of water-reducing admixture mechanism

    1、Dispersion

After mixing cement with water, due to the hydration of cement particles, cement particles indicate the formation of double layer structure, so that the formation of solventized water film, and the surface of the cement particles with anisotropic charge so that the cement particles between the production of cohesion, so that the cement paste to form a flocculent structure, so that 10% to 30% of the mixing water is wrapped in cement particles, can not participate in the free flow and lubrication, thus affecting the concrete mix Mobility.

    When adding water-reducing admixture, due to the water-reducing admixture molecules can be directed adsorption on the surface of cement particles, so that the surface of the cement particles with the same kind of charge (usually negative charge), the formation of electrostatic repulsion, prompting the cement particles are dispersed each other, the flocculent structure disintegration, the release of part of the water wrapped up, participate in the flow, thus effectively increasing the fluidity of the concrete mix.

    2、Lubrication

The hydrophilic group in the water-reducing admixture has strong polarity, so the water-reducing admixture adsorption film on the surface of cement particles can form a layer of stable solvated water film with water molecules, which has good lubrication effect and can effectively reduce the sliding resistance between cement particles, so that the concrete fluidity is further improved.

    3、Space resistance

The hydrophilic branch chain in the structure of water-reducing admixture is stretched in the aqueous solution, thus forming a hydrophilic three-dimensional adsorption layer with a certain thickness on the surface of the adsorbed cement particles. When the cement particles are close, the adsorption layer starts to overlap, that is to say, it produces spatial resistance between the cement particles, the more overlap, the greater the spatial resistance repulsion, the greater the obstruction to the cohesion between the cement particles, so as to make the slump of the concrete keep good.

    4、Relaxation effect of graft copolymerization branch chain

New type of water-reducing admixture such as polycarboxylic acid water-reducing admixture in the preparation process, in the water-reducing admixture molecular grafting on some of the branch chain, the branch chain not only can provide spatial resistance effect, but also can be used in the preparation of water-reducing admixture.