There are currently dozens of varieties of water reducing agents produced in China. According to its chemical composition, it can be divided into six categories: lignin series, naphthalene sulfonate series, resin series, molasses series, humic acid series and composite series; according to the plasticizing effect, it can be divided into ordinary water-reducing agent and high-efficiency water-reducing agent. Water-reducing agent refers to an admixture that has water-reducing and strengthening effects without affecting the workability of concrete. When used, the water consumption of the concrete mixture can be significantly reduced under the condition that the concrete slump is basically the same. , hence the name.
1. The pH value, density (or fineness), and water reduction rate of ordinary water-reducing agents and high-efficiency water-reducing agents should be tested before construction and application. They can only be used after meeting the requirements. The optimal dosage is It is determined that the performance requirements such as design strength, workability, durability and economy must be met under the engineering environmental conditions. According to the recommended dosage provided by the supplier, a reasonable dosage can be obtained through trial preparation. Excessive dosage of high-efficiency water reducing agent will cause severe bleeding of cement concrete and massive loss of cement slurry, resulting in insufficient compactness and thus affecting the strength.
2. The water-reducing agent should be prepared into a uniform solution. The harmful effect of admixture precipitation is the same as that of excessive admixture dosage. Undissolved solid precipitates in the solution should be removed every day. According to the needs of the project, ordinary water-reducing agents and high-efficiency water-reducing agents can be used in combination with other miscible admixtures.
3. Adding retarder, high-temperature retarder, plastic retaining agent or retarding water-reducing agent that is compatible with cement into the high-efficiency water-reducing agent can reduce the slump loss in hot weather. When transporting cement concrete by mixer truck or tanker, high-efficiency water-reducing admixture can be added twice at the pouring site, and the material can be discharged after rapid stirring and uniformity. Do not add more water, and quickly complete pouring, vibrating, finishing, etc.; use retarding type Highly efficient water reducing agent.
4. The health maintenance link is a key link to ensure that the cement concrete structure does not crack and micro-cracks. Therefore, the cement concrete structure of highway projects mixed with ordinary water-reducing agents and high-efficiency water-reducing agents should be strengthened and repaired as soon as possible. Keep warm, moisturize and maintain health. Cement concrete components mixed with ordinary water-reducing admixtures are not suitable for steam curing; cement concrete components mixed with retarding water-reducing admixtures must be allowed to stand still for a period of time to allow the cement concrete to form a certain structural strength before they can be steam-cured. Cement concrete mixed with superplasticizer can be cured by steam curing.
Mechanism of action of water reducing agent
1. The workability of the concrete mixture is reduced. The cement minerals in the concrete mixture have different charges during the hydration process, resulting in opposite charges. The suction force, or the angular collision, adsorption and gravitational force between particles caused by the thermal movement of cement particles in the solution cause a flocculated structure, which contains a lot of mixing water, thus reducing the workability of the concrete mixture.
2 Adsorption-dispersion If an appropriate amount of water-reducing agent is added to concrete, this surfactant will be directionally adsorbed on the surface of cement particles, making the hydrophilic groups point toward the aqueous solution. Due to the ionization of the hydrophilic groups, the cement particles are charged with the same sign. Under the action of electrostatic repulsion, the cement particles are dispersed, resulting in the disintegration of the flocculated structure, thereby releasing the moisture contained in the cement flocs. Water reduction purpose and effectively increase the fluidity of concrete mixture.
3. The lubrication and wetting effects of water-reducing agents. Anionic surface-active water-reducing agents have very strong polarity in their hydrophilic groups and are easily combined with water molecules in the form of hydrogen bonds. A stable solvated water film is formed on the surface, which prevents direct contact between cement particles, lubricates between particles, improves the fluidity of concrete, and improves the workability of concrete mixtures.
4. The lubrication effect of polar bubbles. The incorporation of water-reducing agent will introduce a certain amount of fine polar bubbles. These polar bubbles are surrounded by the adsorption film formed by the water-reducing agent and adsorb to the cement particles. The signs of the membrane charges are the same, so the electrical repulsion between bubbles and bubbles and cement particles also causes the cement particles to disperse, thereby increasing the sliding ability between cement particles (such as ball bearings).
5 Improve the strength of concrete. Due to the dispersion effect of the water-reducing agent on the cement, the surface of the cement particles in contact with water increases, which increases the hydration area of the cement particles, making the hydration more complete and different. It changes the pore structure of cement stone after hardening to a certain extent, reducing macropores and increasing micropores, thus improving the strength and durability of concrete.
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